Keywords : ray diffraction

Growth, Linear and Nonlinear Optical Studies of D-Tartaric Acid Crystal

M. Esthaku Peter; Getahun Leliso; Seblewongel Getachew; Betelhem Alemu; Tirngo Abay; Eleni Binalfeus

Advanced Materials Letters, 2019, Volume 10, Issue 9, Pages 651-655
DOI: 10.5185/amlett.2019.0028

A single crystal of D-Tartaric acid, a stereoisomer of tartaric acid, has been grown by a slow solvent evaporation technique. Good crystals to be used for optical testing were harvested after multiple recrystallizations, whose maximum size is 30x20x4mm 3 . In view of finding second harmonic generation efficiency and properties supporting for a nonlinear optical device, the grown crystals were subjected to various characterizations. Firstly, the compound was confirmed by single crystal and powder X-ray diffraction analysis and thereafter further studies were undertaken. Various possible functional groups available in the grown crystalline compound were identified using Fourier transform infrared analysis and reported. The second harmonic generation, a nonlinear optical property of a crystal, was studied and compared with standard KDP crystal. The percentage of linear optical transmittance in the ultraviolet, visible and infrared radiation of wavelength ranging from 200 to 1100 nm was studied and explained in detail. Thermal studies such as Thermogravimetric and Differential thermal analysis were carried out to find the thermal stability of the crystalline material. Vicker’s microhardness testing was made on the as-grown crystalline surface to find the surface hardness, yield strength and other related mechanical properties of the crystal. Copyright © VBRI Press.

Improved electrical and photoluminescence properties in Nd substitution of 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 lead free multi-functional ceramics 

Kumara Raja Kandula; Sai Santosh Kumar Raavi; Saket Asthana

Advanced Materials Letters, 2018, Volume 9, Issue 9, Pages 656-659
DOI: 10.5185/amlett.2018.2038

Nd 3+ -substituted lead free 0.94(Na0.5Bi0.5-XNdXTiO3)-0.06BaTiO3 (x=0, 0.01) ceramics were synthesized by using conventional solid state route. The XRD studies revealed the phase purity and existence of the monoclinic (Cc), cubic (Pm3m) along with the minor tetragonal phases confirmed with help of structural refinement. The electrical poling field induces the structural modification to rhombhohedral (R3c), cubic (Pm3m) along with the minor tetragonal phase (P4mm). The dielectric measurements revealed the relaxor behavior. The coercive field drops remarkable and there is slight improvement in the polarization with the substitution of Nd as compared to the pure 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3. The luminescence occurred from the optically active element Nd 3+ under the influence of the average crystal symmetry of 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3. The luminescence quenching observed without any shift in position upon the poling supports the observation of higher symmetric structure.

Structural And Optical Properties Of Bulk MoS2 For 2D Layer Growth

Akhilesh Pandey; Shankar Dutta; Anand Kumar; R. Raman; Ashok K. Kapoor; R Muralidhran

Advanced Materials Letters, 2016, Volume 7, Issue 10, Pages 777-782
DOI: 10.5185/amlett.2016.6364

Molybdenum-di-sulfide (MoS2) is being considered as an alternative 2-D material to graphene. Deposition of ultrathin MoS2 layer from bulk MoS2 sample is an important criterion in determining the viability of its application.  This paper discusses about growth and characterization of bulk MoS2 pellet from MoS2 powder and exfoliation of MoS2 layer from it. The MoS2 pellets were sintered at different temperatures (500 - 850 ° in nitrogen atmosphere. The sintered samples were found to be polycrystalline in nature with hexagonal flakes of 100 nm – 1.0 µm sizes. In addition to MoS2 phase, surface of the bulk samples also has also some MoO3 phase content, which was found to decrease with the increase in sintering temperature, confirmed by XRD. The optical absorption study showed MoS2 absorptions around 1.82 eV, 2.01 eV due to spin orbit and direct band to band absorption from ?k-k valley. The sintered MoS2 samples were found to have characteristic Raman peaks of A1g and E2g with a separation of 26.5 cm -1 . Ultrathin MoS2 layers, exfoliated from the sintered sample, showed the reduced separation between Raman peaks A1g and E2g of 24.5 cm -1 few layer MoS2.

Tunable Structural, Optical And Electrical Properties Of Annealed ZnO-SnO2 Composite Thin Films deposited By Pulsed Laser Deposition

Sudip. K. Sinha

Advanced Materials Letters, 2016, Volume 7, Issue 4, Pages 319-324
DOI: 10.5185/amlett.2016.6155

We report the thermal annealing effect of ZnO-SnO2 composite thin films deposited by pulsed laser deposition on its structural, electrical, and optical properties. The results present a consistent portrayal of the evolution of ZnO-SnO2 composite oxide films phase formation in post-annealed condition and its subsequent effect on various physical properties. X-ray diffraction confirms that the films transform from nearly amorphous to fully crystalline state on thermal annealing at 600 °C. X-ray photoelectron spectroscopy reveals a small shift in Sn-3d peak towards lower energy and O-1s and Zn-2p < /em> peaks towards higher binding energy with increasing ZnO concentration and confirms the formation of combined oxides of ZnO and SnO2. The average optical transmission is greater than 80 % in the visible region of the annealed ZnO-SnO2 composite films. The lowest electrical resistivity of 9.8 × 10 -4 Ωcm has been obtained in the film containing 25 wt % ZnO. Our results suggest that annealed ZnO-SnO2 composite films with improved electrical and optical properties could find potential use in thin film solar cells or touch pad control panels. 

Structural, Growth and Characterizations of NLO Crystal: Triglycinium Calcium Nitrate

M. Esthaku Peter; P. Ramasamy

Advanced Materials Letters, 2016, Volume 7, Issue 1, Pages 83-88
DOI: 10.5185/amlett.2016.5944

Single crystals of triglycinium calcium nitrate, a semiorganic nonlinear optical (NLO) material, have been grown by slow solvent evaporation technique at room temperature. The size of the grown crystal is up to the dimension of 29×19×5 mm 3 . The structure of the crystal was analyzed by single crystal X-ray diffraction and the functional groups present in the sample were identified by FTIR spectral analysis in the range 4000-450 cm -1 . The UV-vis-NIR studies was undertaken to find the transmittance in the ultraviolet and visible region. The efficiency of second harmonic generation was analyzed by Kurtz-Perry powder technique and compared with standard KDP crystal. Thermogravimetric and differential thermal analysis have been performed to determine the thermal stability of the crystal. Dielectric properties such as dielectric constant and dielectric loss were studied at various temperatures and frequencies. Vickers microhardness testing was carried out on the as-grown crystal surface to reveal the mechanical properties of the crystal. Etching studies were made on the as grown crystal to analyze the structural imperfection of the crystal. 

Study The Influence Of Different Mol% BLTMNZ Doping On KNLN Ceramics By Using The XRD And Impedance spectroscopy

Shweta Thakur; Seema Sharma;Ashutosh Tiwari; Radheshyam Rai

Advanced Materials Letters, 2016, Volume 7, Issue 1, Pages 29-35
DOI: 10.5185/amlett.2016.6001

Polycrystalline samples of (K0.45Na0.45Li0.1NbO3)1-x-(Ba0.96La0.04Ti0.815Mn0.0025 Nb0.0025Zr0.18 O3)x ceramics (where x = 0.1, 0.3, 0.5, 0.7 and 0.9) were prepared by using a high temperature solid state reaction technique. The XRD patterns of the BLTMNZ doped KNLN at room temperature with x = 0.7 have pure pervoskite phase with tetragonal structure at room temperature and have maximum value of dielectric constant at x = 0.9. Detailed studies of dielectric and impedance properties of the materials in a wide range of frequency (100Hz–1MHz) and temperatures (30 – 500 o C) showed that properties are strongly temperature and frequency dependent. The plots of Zʹʹ and Mʹʹ versus frequency at various temperatures show peaks in the higher temperature range (>300 o C). The compounds show dielectric relaxation, which is found to be of non-Debye type and the relaxation frequency shifted to higher side with increase in temperature. The Nyquist plot and conductivity studies showed the NTCR character of samples.

Influence Of Gd On Structural And Impedance Properties Of Multiferroic Composites: BiFeO3-PbTiO3

Nilaya K. Mohanty; Ajay K. Behera; Santosh K. Satpathy; Banarji Behera; Pratibindhya Nayak

Advanced Materials Letters, 2015, Volume 6, Issue 11, Pages 947-953
DOI: 10.5185/amlett.2015.5839

The Gd-modified BiFeO3-PbTiO3 composites i.e. 0.5BiGdxFe1-xO3-0.5PbTiO3 (BGxF1-x-PT) with x=0.00, 0.05, 0.10, 0.15, 0.20, were prepared by mixed oxide method at high temperature. The structural study reveals that the composites showed tetragonal crystal structure at room temperature and tetragonality (c/a ratio) of composites decrease with increase in Gd concentration. The average crystallite size of the composites was found to be in the range of 30-89 nm. Surface morphology of the composites was studied by scanning electron microscopy (SEM). The Goldschmidt tolerance factors of the composites were found to be in the range of 0.989-0.976. The nature of Nyquist plot confirmed the presence of both bulk and grain boundary effects, and non-Debye type of relaxation process occur in the composites. The activation energy of the composites was found to be in the range 0.13-1.38eV. The analyses of ac conductivity data obey the universal agreement with Jonscher’s power law. Further, the explanation of conduction mechanism through correlated barrier hopping (CBH) model was discussed.

Silver Ion Conducting Characteristics Of A Polyethylene Oxide-based Composite Polymer Electrolyte And Application In Solid State Batteries

S. Amudha; S. Austin Suthanthiraraj

Advanced Materials Letters, 2015, Volume 6, Issue 10, Pages 874-882
DOI: 10.5185/amlett.2015.5831

The matrix embracing a combination of polyethylene oxide [PEO] as the host polymer component and silver trifluoromethane sulfonate [AgCF3SO3] (also known as silver triflate) as the dopant salt yielding a composite polymer electrolyte [CPE] with varying compositions based on rich contents of Oxygen/Metal [O/M] ratio has been prepared in the form of thin film specimens using solution casting technique and examined for its application in a solid state battery configuration as a test cell. Such composite polymeric films optimized using electrical conductivity studies have provided realization of a maximum electrical conductivity value of 2.9 ×10 -5 Scm -1 at room temperature (298 K) whereas their temperature-dependent electrical conductivity is found to obey the Arrhenius behavior. Silver ionic transference number (tAg + ) data for these polymeric composites were indomitable using ac/dc polarization technique whereas the occurrence of a transition of phase in accordance with structural and thermal parameters could be investigated by means of X-ray diffraction (XRD) and differential scanning calorimetric (DSC) analyses. The morphological and compositional analyses were carried out by employing scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) as analytical tools. Electrochemical cells have been fabricated with the common cell configuration Ag|CPE|(I2+G+CPE) and relevant cell parameters evaluated in terms of their discharge characteristics under a constant load of 1 M at room temperature.

Correlation Between Oxygen Partial Pressure And Properties Of Pulsed Laser Deposited SnO2/Fe2O3 Composite Films

M. Chowdhury; S.K. Sharma; R.J. Chaudhary

Advanced Materials Letters, 2015, Volume 6, Issue 10, Pages 930-934
DOI: 10.5185/amlett.2015.6017

SnO2/Fe2O3 composite thin films were deposited on quartz substrates at various oxygen partial pressures with a substrate temperature of 750 °C by pulsed laser deposition. The structural and optical properties of the deposited films were studied by X-ray diffraction (XRD), Atomic force microscopy (AFM), UV–visible spectroscopy and Photoluminescence. X-ray diffraction analysis revealed the formation of mixed phases (tetragonal SnO2 and hexagonal α-Fe2O3) at lower oxygen partial pressure (0.1 mTorr) and only tetragonal phase at higher oxygen partial pressures (50-250 mTorr). Atomic force microscopy studies show the dense and uniform distribution of composite films. The average RMS roughness of the films increases with increasing oxygen partial pressure. The bandgap was found varying between 3.55 and 3.85 eV for different oxygen pressures. A strong broad blue emission band was observed for all the oxygen partial pressures. The origin of the blue emission in the composite film is discussed with the help of vacancy creation. A correlation between oxygen partial pressure and the properties of SnO2/Fe2O3 .

Effect Of Diffusion Parameters On The Efficiency Of C-Si Solar Cell

Vineet Kumar Singh; Jampana Nagaraju

Advanced Materials Letters, 2015, Volume 6, Issue 7, Pages 600-606
DOI: 10.5185/amlett.2015.5616

This paper presents the effect of emitter thickness and post-annealing process on the conversion efficiency of crystalline silicon (c-Si) solar cells. Diffusion parameters like pre-deposition temperature, drive-in temperature, and process duration assist to control the emitter thickness and inturn improves the conversion efficiency of the solar cells. It is observed that shallower emitter cells have higher conversion efficiency of 10.81% than deeper emitter cells of 7.62%. Post-annealing process at 700 °C for 60 minutes boosts the efficiency of shallower emitter cell from 10.81% to 12.06%. Dark current-voltage characteristics authenticate the formation of p-n junction and also elucidate the presence of recombination saturation current along with diffusion saturation current. Illuminated and dark current-voltage characteristics further provide the evidence that post-annealing process during phosphorus diffusion reduces the trap density and thus the recombination saturation current, which helps to improve the efficiency. The combination of a shallower emitter with post-annealing process provides an excellent approach to enhance the solar cell efficiency.

Structural Analysis By Rietveld Method And Its Correlation With Optical Propertis Of Nanocrystalline Zinc Oxide

Vikash Kumar; Swati Kumari; Pawan Kumar; Manoranjan Kar; Lawrence Kumar

Advanced Materials Letters, 2015, Volume 6, Issue 2, Pages 139-147
DOI: 10.5185/amlett.2015.5632

The correlation between structural and optical properties of nanocrystalline ZnO synthesized by the citrate precursor method has been investigated. The Rietveld refinement of X-ray diffraction pattern confirms the P63mc space group and formation of single phase hexagonal wurtzite structure with presence of tensile strain at the lattice site. The presence of Raman active optical phonon mode at 436 cm -1 which is a significant character of ZnO with hexagonal wurtzite structure supports the XRD result. FE-SEM result shows that the size of the particle is about 20 nm with nearly spherical shapes. The optical band gap energy at room temperature has been calculated as 3.28 eV using the Tauc plot technique. The UV-Vis sub-gap absorption curve supports the presence of strain inside the crystal. The photoluminescence spectrum indicates the dominancy of the defect related deep level or trap state emissions over the near band edge UV emissions using an excitation wavelength of 320 nm.

Structural and Hydrogen Storage Properties Of Mg-x Wt% ZrCrMn Composites

Ankur Jain; Pragya Jain; Shivani Agarwal; Paola Gislon; Pier Paolo Prosini; I.P. Jain

Advanced Materials Letters, 2014, Volume 5, Issue 12, Pages 692-698
DOI: 10.5185/amlett.2014.7588

Magnesium hydride is a promising material for hydrogen storage due to its high storage capacity i.e.7.6wt%. But its high stability i.e. high desorption temperature (~350? o C) limits its practical application towards hydrogen economy. Moreover the kinetics is also too slow even at high temperatures. Composite formation with Zr based laves phase alloys, especially ZrCr2 family, is an effective method to improve the hydriding properties of MgH2. This work presents the synthesis, structural, morphological, and hydrogenation properties of Mg-x wt% ZrCrMn composites. Both phases i.e. Mg & ZrCrMn remain their presence after milling and several hydriding cycles as well. SEM results suggest the homogeneous distribution of alloy particles on Mg matrix. Pressure composition temperature (PCT) analysis shows a reduction in desorption temperature down to 250 o C for these composites. TG experiments suggest a total hydrogen capacity of 5.9% and 4.35% for x =25, 50 in Mg-x wt% ZrCrMn composites respectively. The enthalpy of hydride formation is also calculated using Van’t Hoff plots, which is found similar to the parent material i.e. MgH2. A remarkable enhancement in the kinetics of hydrogen absorption / desorption is reported here by forming these composites.

Structural And Dielectric Properties Of Nb And Fe Co-doped PZT Ceramic Prepared By A Semi-wet Route

Arvind Kumar; S. K. Mishra

Advanced Materials Letters, 2014, Volume 5, Issue 8, Pages 479-484
DOI: 10.5185/amlett.2014.564

In the present work, detailed investigation of dielectric, piezoelectric and ferroelectric properties of Nb and Fe co-doped PZT ceramic near the MPB composition has been carried out. Pb1-3x/2 Fex(Zr0.52Ti0.48)1-5y/4 NbyO3 (PFZTN) ceramics for x = 1- 6 mol% and y = 5.50 mol% have been prepared by a semi-wet route. X-ray diffraction studies confirm the formation of single phase perovskite structure. It is shown that Fe doping in PZNT improves the dielectric, ferroelectric and piezoelectric properties of ceramics. It has been found that at room temperature, dielectric constant and d33 start to increase up to the composition x = 0.05 and thereafter decrease. The maximum value of dielectric constant and d33 has been found for the composition x = 0.05. It has been shown that doping of Fe does not affect over the transition temperature uptown x = 0.04. The value of remnant polarization is of the order of 11.62 µC/cm 2 at x= 0.04. The investigated material seems to be promising candidate for multilayer capacitor applications.

Structural And Electrical Properties Of Li2Pb2Sm2W2Ti4Ta4O30 Ceramics 

S. Behera; Piyush R. Das; B. N. Parida; P. Nayak; R. N. P Choudhary

Advanced Materials Letters, 2014, Volume 5, Issue 3, Pages 143-147
DOI: 10.5185/amlett.2013.fdm.60

The polycrystalline sample of complex tungsten-bronze compound Li2Pb2Sm2W2Ti4Ta4O30 was prepared by a high-temperature solid-state reaction technique. Room temperature X-ray diffraction (XRD) study suggests the formation of a single-phase compound. Microstructure of the pellet sample was studied by scanning electron microscope. The temperature variation of dielectric constant shows dielectric anomaly in the sample. Study of electrical properties (impedance, conductivity, etc.,) of the material exhibits a strong correlation between its micro-structure (i.e., bulk, grain boundary, etc) and electrical parameters. A typical Arrhenius behavior was observed in the temperature dependence of dc conductivity.

Synthesis, Electrical And Thermal Properties Of  Bi4V2-xCuxO11 (x=0.0 And 0.02) Ceramics 

M. Roy; S. Sahu; S. K. Barbar; S. Jangid

Advanced Materials Letters, 2014, Volume 5, Issue 3, Pages 122-126
DOI: 10.5185/amlett.2013.fdm.30

Polycrystalline ceramic samples of pure and Cu +2 doped Bi4V2-xCuxO11(x=0.0 and 0.02) have been synthesized by standard solid state reaction method using high purity oxides. The dielectric constant and dielectric loss and hence ac conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy and hence its ac conductivity increases with the increase of temperature. The dc conductivity of material has been measured as a function of temperature from room temperature to 653 K and its activation energy was calculated using the relation σ = σo exp (- Ea/kT). The dc conductivity increases with the substitution of Cu on the vanadium site. The Modulated Differential Scanning Calorimetry (MDSC) has been used to investigate the effect of substitution on the phase transition of the compounds. The results are discussed in detail.

Synthesis And Electrical Properties Of Sr(Bi0.5V0.5)O3 Electroceramic 

B. C. Sutar; Piyush R. Das; R. N. P. Choudhary

Advanced Materials Letters, 2014, Volume 5, Issue 3, Pages 131-137
DOI: 10.5185/amlett.2013.fdm.51

Lead-free polycrystalline material Sr(Bi0.5V0.5)O3 was prepared using a high- temperature solid state reaction technique (calcinations and sintering temperature =850 and 950 o C, respectively) using high-purity ingredients. The formation of the material in the monoclinic crystal structure was confirmed by preliminary X-ray structural analysis with room temperature data.The nature of microstructure obtained by scanning electron microscopy (SEM) shows that the compound has well defined grains which are uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material carried out in the frequency range of 1 kHz –1MHz at different temperatures (30 0 C to 455 0 C) have provided many interesting properties. Detailed studies of dielectric properties of the compound showed an existence of diffus e phase transition around 258 0 C. The temperature dependence of electrical parameters (impedance, modulus etc.) of the material exhibits a strong correlation of its microstructure with the electrical parameters. The negative temperature coefficient of resistance (NTCR) behavior also was observed in the material. The complex electric modulus analysis indicates the presence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.

Dielectric Behavior Of Mixed Cadmium Magnesium Hydrogen Phosphate Crystal 

K. K. Bamzai; Rashmi Gupta; Shivani Suri; Vishal Singh

Advanced Materials Letters, 2014, Volume 5, Issue 2, Pages 89-95
DOI: 10.5185/amlett.2013.fdm.41

Magnesium hydrogen phosphate (MHP) and transition metal doped cadmium magnesium hydrogen phosphate (CdMHP) was synthesized in the form of crystalline material by room temperature solution technique known as gel encapsulation technique. The synthesized crystals were then characterized for their structural, mechanical and electrical investigations using various chemical and physical methods. X - ray diffraction analysis (XRD) establishes magnesium hydrogen phosphate and cadmium magnesium hydrogen phosphate belonging to orthorhombic crystal system with space group Pbca. The mechanical behaviour of these crystals was studied by calculating Vicker’s hardness number. The behaviour of microhardness with applied load was observed to be complex. The electrical behaviour was carried out by calculating dielectric constant at different temperatures and for different frequencies. The dielectric constant (ε/) was found to be strongly dependent on temperature and frequency. The transition metal doping of cadmium in magnesium hydrogen phosphate remarkably decrease the value of dielectric constant from 68 to 23. The transition temperature also decreases from 330ËšC in case of magnesium hydrogen phosphate to 310ËšC in case of cadmium magnesium hydrogen phosphate.

A Comparative Study Of Electrical Properties Of Some Rare Earth Based Tungsten Bronze Ceramics

P. S. Sahoo; B. B. Mohanty; R. N. P. Choudhary

Advanced Materials Letters, 2014, Volume 5, Issue 2, Pages 96-99
DOI: 10.5185/amlett.2013.fdm.47

The advent of nanoscience & technology have completely changed the orientation/direction of studies of eco-friendly (lead-free) materials bringing them at the forefront of scientific developments with considerably enhanced physical properties suitable for a wide variety of challenging applications. Barium based ferroelectric materials have gained much importance due to their vast applications as they possess high dielectric constant, non-linear spontaneous polarization, negative temperature coefficient of resistance behavior etc.. All these characteristics stimulated the researchers to replace toxic and hazardous lead based materials by barium based TB materials from industry. Our present research work deals with the synthesis of polycrystalline samples of Ba2Sr3RTi3V7O30 (R = Gd, Sm) by a high temperature solid state reaction technique and a comparative study of the electrical properties of the samples. Preliminary structural (XRD) analyses of these compounds show the formation of single-phase orthorhombic structures at room temperature having average crystallite size of the order of some nanometer for both the compounds. The electrical properties for both the samples are studied in a wide range of temperature (30–500 o C) and frequency (100Hz-1MHz). The dielectric properties suggest that both the compounds have undergone ferroelectric-paraelectric phase transition well above the room temperatures (i.e., 230 and 313 0 C for R= Sm and Gd respectively at frequency 100 kHz).The bulk resistance of the materials exhibits negative temperature coefficient of resistance behavior as observed in semiconductors.

Effect Of La And Pb Substitution On Structural And Electrical Properties Of Parent And La/Pb Co Doped BiFeO3 multiferroic

Poorva Sharma; Dinesh Varshney

Advanced Materials Letters, 2014, Volume 5, Issue 2, Pages 71-74
DOI: 10.5185/amlett.2013.fdm.10

La/Pb co-doped BiFeO3 compounds were prepared by a solid-state reaction. X-ray diffraction of BiFeO3 (BFO), Bi0.725La0.1Pb0.175FeO3 [BLPFO] showed single phase in nature. BFO crystallize in the rhombohedral distorted perovskite structure (space group-R3c) while to that BLPFO crystallize in distorted pseudocubic (Pm-3m) symmetry which has been confirmed by the Rietveld refinement of the room temperature X-ray powder diffraction data. The effect of La/Pb substitution on dielectric constant, and loss tangent, of the samples was studied at room temperature in a wide range of frequency 10 Hz – 1 MHz. The room temperature dielectric constant of BFO (BLPFO) was 120 (200). Ferroelectric measurement reveals remnants polarization of BLPFO is about 0.24 μC/cm 2 at an applied field of 15 kV/cm. Weak ferroelectric effect is observed for co-doped BiFeO3 compound.

Characterization Of Nano-structured Magnesiumchromium ferrites Synthesized By Citrate-gel auto Combustion Method

M. Raghasudha; D. Ravinder; P. Veerasomaiah

Advanced Materials Letters, 2013, Volume 4, Issue 12, Pages 910-916
DOI: 10.5185/amlett.2013.5479

Nano-ferrites of the composition Mg Crx Fe2-xO4 (where x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were synthesized at a very low temperature (180°C) by Citrate-gel auto combustion method. The as synthesized powders were sintered at 500 0 C for four hours in an air and were characterized by X-ray diffraction (XRD) which confirmed the formation of cubic spinel structure of ferrites. The crystallite size was in the range of 7 to 23nm for different compositions with the significant decrease of ~16nm in response to the increase in Cr substitution. Such low nano sized ferrites are desirable for variety of applications like, in magnetic data storage and in targeted drug delivery, etc. Morphological studies by Scanning Electron Microscopy (SEM) revealed formation of largely agglomerated, well defined nano particles of the sample. Elemental composition characterizations of the prepared samples were performed by Energy Dispersive Spectroscopy (EDS) which shows the presence of Mg, Cr, Fe and O without precipitating cations. The FTIR spectral studies at room temperature in the range of 400 to 800cm-1 showed two strong absorption bands. The high frequency band (ν1) around 600 cm -1 is attributed to the intrinsic vibrations of tetrahedral complexes and the low frequency band (ν2) around 400 cm -1 is due to octahedral complexes. The spectra showed the characteristic peaks of ferrite sample. The observed results can be explained on the basis of composition and crystal size.

Local Electronic Structure Of Heavy-ion Irradiated Nano-crystalline Stoichiometric La0.8Sr0.2Mn0.8Fe0.2O3 Particles Using Highresolution Mössbauer Spectroscopy

Usha Chandra; K. Asokan; V. Ganesan

Advanced Materials Letters, 2013, Volume 4, Issue 11, Pages 862-868
DOI: 10.5185/amlett.2013.4455

Nanocrystalline stoichiometric La0.8Sr0.2Mn0.8Fe0.2O3 manganites synthesized by sol gel technique were irradiated by 200 MeV Ag +16 ion beam at various fluences and investigated by X-ray diffraction (XRD), magnetization and high resolution Mössbauer spectroscopic techniques. The analysis of Mössbauer patterns were done using Kopcewicz et al. (2004) proposition considering Double exchange mechanism. Both XRD and Mössbauer spectroscopic analysis indicated isostructural vacancy formation at Mn site at the fluence 5x10 12 ions/cm 2 . The system showed amorphous phase at the higher fluence of 1x10 13  ions/cm 2 . The local electronic environments seen through high resolution Mössbauer spectroscopic technique on the irradiated systems were understood in terms of ferromagnetic coupling between different Mn environment surrounding Fe ions. This proposition is supported by enhanced magnetization observed in the irradiated samples (Kopcewicz et al., 2004). The similarity to the hydrostatic applied pressure (at low value) is seen through the transformation from Fe 4+ to Fe 3+ at low fluence.

Magnetic Study Of Nano-crystalline Cobalt Substituted Mg-Mn Ferrites Processed Via Solution Combustion Technique

Gagan Kumar; Ritu Rani; Vijayender Singh; Sucheta Sharma; Khalid M. Batoo; M. Singh

Advanced Materials Letters, 2013, Volume 4, Issue 9, Pages 682-687
DOI: 10.5185/amlett.2013.1409

Co 2+ substituted Mg-Mn nanoferrites having formulae Mg0.9Mn0.1CoxFe2-xO4, where x = 0.0, 0.1, 0.2 & 0.3, have been prepared for the first time by solution combustion technique. The magnetic properties of nanoferrites such as M-H, initial permeability (μi) and magnetic loss tangent (tan δ) have been investigated as a function of frequency in the range 700 Hz to 30 MHz. X-ray diffraction patterns confirmed the formation of single phase spinel structure of all the nanoferrites. The surface morphology of the samples is studied by using scanning electron microscopy (SEM), while elemental compositions of samples are studied by energy dispersive X-ray analysis (EDAX). Saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) are found to be increasing with an increase in cobalt content while initial permeability and magnetic loss tangent are found to be decreasing with an increase in frequency as well as with the increasing concentration of Co 2+ ions. The very low values of magnetic loss tangent even at high frequencies are the prime achievements of the present work.

Thermal Analysis And Luminescent Properties Of Sr2CeO4 blue phosphor

Pradip Z. Zambare; K. V. R. Murthy;O. H. Mahajan; K. D. Girase

Advanced Materials Letters, 2013, Volume 4, Issue 7, Pages 577-581
DOI: 10.5185/amlett.2012.11457

In this paper we report Strontium Cerium Oxide (Sr2CeO4) blue phosphor was synthesized via solid state reaction method using strontium carbonate SrCO3 and cerium oxide CeO2 as raw materials. The samples were characterized by Thermo analytical techniques (TG, DTA, DTG and DSC) in nitrogen atmosphere, Fourier transformation infrared (FTIR) spectroscopy, and Photoluminescence at room temperature. Thermal analysis indicates that Sr2CeO4 phosphor can be prepared at temperature higher than 1100 °C. In excitation spectra two excitation peaks were located at 262 and 399 nm respectively. The emission spectrum was a broad band peaking at 470 nm, which was suitable for the doping of rare earth ions. The color co-ordinates for the pure Sr2CeO4 were x = 0.1918 and y = 0.2483. This material has potential for applications in the field of emission devices.

A Convenient Route To Synthesize Hexagonal Pillar Shaped ZnO nanoneedles Via CTAB Surfactant

K. Kaviyarasu; Prem Anand Devarajan

Advanced Materials Letters, 2013, Volume 4, Issue 7, Pages 582-585
DOI: 10.5185/amlett.2012.10443

In this work we report the successful formation of hexagonal pillar shaped ZnO nanoneedles with high yield and by using simple cheap method with CTAB as the surfactant. SEM and TEM microscopic observation revealed that the ZnO nanorods were smooth and uniform throughout their length and the functional groups in the molecule were identified by FTIR analysis. PL properties of ZnO nannorods were found to be dependent on the growth condition and the resultant morphology revealed that ZnO nanorods were highly transparent in the visible region.

Characterization and Photoluminescence Of Sr2CeO4: Eu+3, La+3

Ch. Atchyutha Rao; Poornachandra Rao V. Nannapaneni; K. V. R. Murthy

Advanced Materials Letters, 2013, Volume 4, Issue 3, Pages 207-212
DOI: 10.5185/amlett.2012.7395

In this paper we report the synthesis and luminescence of strontium cerium oxide (Sr2CeO4:Eu 3+ (0.5mol%),La 3+ (0.5mol%) prepared by solid state reaction method in air at 12000C.These samples were characterized by X-ray diffraction, scanning electron microscope (SEM) and photoluminescence (PL) techniques, particle size analysis. The photo luminescence (PL) spectra of pure and Eu 3+ , La 3+ codoped Sr2CeO4 were recorded at room temperature. Sr2CeO4 phosphor was effectively excited around 250 nm and observed a broad emission band peak around 467 nm. XRD data revealed that the structure of Sr2CeO4 is orthorhombic, and the mean crystallite size of Sr 2CeO4 and Sr2CeO4: Eu 3+ , La 3+ were 9 nm and 11nm respectively. The colour co-ordinates of Sr2CeO4 were x = 0.16 and y = 0.18 and CIE co-ordinates revealed that the present phosphors may be used in white light applications.

Impedance Properties Of 0.7(BiFeO3)-0.3 (PbTiO3) Composite

Ajay Kumar Behera; Nilaya K. Mohanty; Banarji Behera; Pratibindhya Nayak

Advanced Materials Letters, 2013, Volume 4, Issue 2, Pages 141-145
DOI: 10.5185/amlett.2012.6359

The polycrystalline sample of 0.7(BiFeO3)-0.3(PbTiO3) [0.7(BFO)-0.3(PT)] was prepared by a high temperature solid state reaction technique. Studies of structural analysis confirm the formation of the compound with rhombohedral structure at room temperature. The electrical properties (impedance, modulus and conductivity) of the material were analyzed using a complex impedance spectroscopy technique in a wide temperature (225-300 o C) and frequency (10 2 -10 6 Hz) range. The studied material exhibits a significant contribution of grain (bulk) effect and non-Debye of relaxation process. The bulk resistance decreases with rise in temperature which exhibits negative temperature coefficient of resistance (NTCR) behavior. Electrical modulus study confirms the presence of bulk effect in the material. This compound also exhibits the temperature dependence of relaxation phenomena. The ac and dc conductivity of the materials were found to be increase with increase in temperature. The activation energy of the compound is found to be less than 1eV and suggests the conduction process is of mixed type (ionic-polaronic and singly-ionized oxygen ion vacancies).

The Influence Of Substrate Temperature On The Structure, Morphology, And Optical Properties Of ZrO2 thin Films Prepared By E-beam Evaporation

K. J. Patel; M. S. Desai; C. J. Panchal

Advanced Materials Letters, 2012, Volume 3, Issue 5, Pages 410-414
DOI: 10.5185/amlett.2012.5364

Zirconium dioxide thin films were prepared by e-beam evaporation method to study the effect of substrate temperature on the structural, surface morphology, compositional, and optical properties. X-ray diffraction measurement shows that the films grown at 400 ℃ substrate temperature have monoclinic crystal structure. The root mean square surface roughness of the film increases with increase in the substrate temperature. The optical transmittance spectra indicate an average 80% transmittance in the visible region of light. The optical energy band gap of ZrO2 thin film decreases from 5.68 to 5.63 eV as the substrate temperature increases from room temperature to 400 ℃, respectively.

Structural, Dielectric And Conductivity Properties Of Ba2+ doped (Bi0.5Na0.5)TiO3 ceramic 

Meera Rawat; K. L. Yadav; Amit Kumar; Piyush Kumar Patel; Nidhi Adhlakha; Jyoti Rani

Advanced Materials Letters, 2012, Volume 3, Issue 4, Pages 286-292
DOI: 10.5185/amlett.2012.2322

Polycrystalline (Bi0.5Na0.5)1-xBaxTiO3 [here after BNBT], x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1 ceramics have been synthesized by conventional solid state reaction process and were characterized by X-ray diffraction technique, which indicates that on substitution of Ba 2+ in Bi0.5Na0.5TiO3 (BNT) ceramic there is splitting of the (2 0 0) peak for x ≥ 0.06. This splitting in the peak position reveals that the composition BNBT-0.06 is well in Morphotropic Phase Boundary (MPB) region where rhombohedral and tetragonal phase co-exist. Scanning electron micrograph shows decrease in grain size from 0.66 to 0.53 μm with increasing concentration of Ba 2+ ; and the dielectric constant of Ba 2+ doped BNT ceramics increased with decreasing grain sizes and a maximum value was attained at size of 0.54 ~ 0.56 μm. Doped BNT ceramic also exhibit diffuse phase transition and are characterised by a strong temperature and frequency dispersion of the permittivity which would be connected with the cation disorder in A-site of perovskite unit cell. Complex impedance spectroscopy is used to analyze the electrical behaviour of BNBT, which indicates the presence of grain effect and the composition exhibits Negative Temperature coefficient of resistance (NTCR) behaviour. The compounds exhibit Arrhenius type of electrical conductivity and the presence of non-Debye type of relaxation has been confirmed from impedance analysis.

Synthesis Of CdSe Nanoparticles By Solvothermal Route: Structural, Optical And Spectroscopic Properties

Punita Srivastava;Kedar Singh

Advanced Materials Letters, 2012, Volume 3, Issue 4, Pages 340-344
DOI: 10.5185/amlett.2012.5341

We have developed successfully the synthesis of highly yielded CdSe nanoparticles (NPs) at 60 0C by solvothermal route in which the cadmium and selenium precursors have been dissolved in deionized water, ethylene glycol and hydrazine hydrate. This route is very facile, inexpensive and less hazardous and ensures almost complete yield of the precursors. The powder product was well characterized by powder X- ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), UV-Vis spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) .It is investigated that as synthesized powder has a hexagonal (Wurtzite) structure of CdSe with diameters of the particles are in the range of 10-15 nm. The formation mechanism is also discussed.

Structural And Impedance Spectroscopy Analysis Of Ba(Fe0.5Nb0.5)O3-BaTiO3 ceramic System 

N. K. Singh; Radheshyam Rai;Andrei L. Kholkin; Pritam Kumar

Advanced Materials Letters, 2012, Volume 3, Issue 4, Pages 315-320
DOI: 10.5185/amlett.2012.5345

Polycrystalline samples of BaFe0.5Nb0.5O3 and (1-x)Ba(Fe0.5Nb0.5)O3-xBaTiO3, [referred as BFN and BFN-BT respectively] (x = 0.00, 0.15 and 0.20) have been synthesized by a high-temperature solid-state reaction technique. The formation of the compound was checked by an X-ray diffraction (XRD) technique. The microstructure analysis was done by scanning electron micrograph. The spectroscopic data presented in impedance plane show the grain and grain boundary contributions towards electrical processes in the form of semi-circular arcs. Detailed studies of dielectric and impedance properties of the materials in a wide range of frequency (100Hz–5MHz) and temperatures (30-282°C) showed that these properties are strongly temperature and frequency dependent.

A Study Of Structural, Dielectric And Electrical properties of Ba(Nd0.5Nb0.5)O3 Ceramics

Advanced Materials Letters, 2012, Volume 3, Issue 2, Pages 143-148
DOI: 10.5185/amlett.2011.8298

Dielectric spectroscopy is applied to investigate the electrical properties of a barium neodymium niobate, Ba(Nd0.5Nb0.5)O3 (BNN) in a temperature range from 323 K to 453 K and in the frequency range from 50 Hz to 1 MHz. The X-ray diffraction of the sample at room temperature shows a tetragonal phase. The scanning electron micrograph of the sample shows the average grain size of BNN ~ 1.92 mm. An analysis of the dielectric constant (e ¢) and loss tangent (tand) with frequency is performed assuming a distribution of relaxation times. The low frequency dielectric dispersion corresponds to DC conductivity. The logarithmic angular frequency dependence of loss peak is found to obey an Arrhenius law with activation energy of 0.55 eV. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behavior of tangent loss (tanδ) suggests that the distribution of relaxation times is temperature independent in BNN. 

Photoelectrochemical Cell Performance Of Chemically Deposited MoBi2Te5 Thin Films

Manauti M. Salunkhe; S. M. Patil; R. M. Mane; S. V. Patil; P. N. Bhosale

Advanced Materials Letters, 2012, Volume 3, Issue 2, Pages 71-76
DOI: 10.5185/amlett.2012.1304

Molybdenum bismuth telluride thin films have been prepared on clean glass substrate using Arrested Precipitation Technique (APT) which is based on self organized growth process. As deposited MoBi2Te5 thin films were dried in constant temperature oven at 110 o C and further characterized for their optical, structural, morphological, compositional and electrical analysis. Optical absorption spectra recorded in the wavelength range 300-800 nm showed band gap (Eg) 1.44 eV. X-ray diffraction pattern and scanning electron microscopic images showed that MoBi2Te5 thin films were nanocrystalline having rhombohedral structure. The energy dispersive spectroscopic analysis of as deposited thin films showed close agreements in theoretical and experimental atomic percentages of Mo 4+ , Bi 3+ and Te 2- and suggest that the chemical formula MoBi2Te5 assigned to molybdenum bismuth telluride thin film material is confirm. The resistivity and thermoelectric power measurement studies showed that the films were semiconducting with n-type conduction. The fill factor and conversion efficiency (η) are determined by fabricating PEC cell using MoBi2Te5 thin film electrode. In this article we report the optostructural, morphological, compositional and thermoelectric characteristics of nanocrystalline MoBi2Te5 thin films to check its suitability as photoelectrode in PEC Cell.

AC impedance spectroscopy and conductivity studies of Ba0.8Sr0.2TiO3 ceramics

Subrat K. Barik; R.N.P. Choudhary; A.K. Singh

Advanced Materials Letters, 2011, Volume 2, Issue 6, Pages 419-424
DOI: 10.5185/amlett.2011.2228

The AC impedance and conductivity properties of Ba0.8Sr0.2TiO3 ceramics in a wide frequency range at different temperatures have been studied. The compound was prepared by a high-temperature solid-state reaction technique. A preliminary structural analysis of the compound by X-ray diffraction technique confirmed its single phase. An ac impedance spectroscopic technique was used to correlate between the microstructure and electrical properties of the compound. The presence of both grain (bulk) and grain boundary effect in the compound was observed. The frequency-dependent electrical data were used to study the conductivity mechanism. An analysis of the electric impedance and modulus with frequency at different temperatures has provided some information to support suggested conduction mechanism.

Structural properties of Fe doped TiO2 films on LaAlO3 and Si substrates

Komal Bapna; R.J. Choudhary; D.M. Phase

Advanced Materials Letters, 2011, Volume 2, Issue 4, Pages 281-284
DOI: 10.5185/amlett.indias.205

We have prepared 4 at.% Fe doped TiO2 thin films on LAO (001) and Si (111) substrates by pulsed laser deposition. X-ray diffraction (XRD) studies suggest different structural properties of the films on the different substrates. Raman measurements corroborate the XRD findings. The thicknesses of the films are also different on the two substrates, suggesting different nucleation process on the two substrates. Interestingly on both the substrates, Fe is not in metal clusters, suggesting their possible incorporation in TiO2 matrix.

Structural And Dielectric Properties Of Y2(Ba0.5R0.5)2O7 (R = W, Mo) Ceramics

N.K. Singh; Pritam Kumar

Advanced Materials Letters, 2011, Volume 2, Issue 3, Pages 239-244
DOI: 10.5185/amlett.2011.1215

Defect pyrochlore-type Y2(Ba0.5R0.5)2O7 (R = W, Mo) oxides ceramics were prepared by using high-temperature solid-state reaction technique. Preliminary studies of X-ray diffraction (XRD) patterns and scanning electron micrographs (SEM) of the compounds at room temperature suggested that compounds have single phase orthorhombic structures and uniform grain distribution throughout the surface of the samples. Detailed studies of dielectric and electrical properties of the materials in a wide range of frequency (1 kHz–1MHz) and temperatures (23–344°C) showed that these properties are strongly temperature and frequency dependent. Variation of dielectric constant (ε') and tangent loss (tanδ) as a function temperatures showed the abnormal behavior around 132°C at 10 kHz and 141°C at 30 kHz of Y2(Ba0.5W0.5)2O7 and around 293°C at 10 kHz and 305°C at 30 kHz of Y2(Ba0.5Mo0.5)2O7 ceramics respectively.

Effect of H3PO4 reactant and NaF additive on the crystallization and properties of brushite

C. Sekar; K. Suguna

Advanced Materials Letters, 2011, Volume 2, Issue 3, Pages 227-232
DOI: 10.5185/amlett.2011.1217

Calcium hydrogen phosphate dihydrate (CaHPO4.2H2O, CHPD) or brushite crystal is a well known urinary substance found frequently in urinary stones. The CHPD crystals have been crystallized in sodium metasilicate gel (SMS) at room temperature under pH 6 in the presence of sodium fluoride. Here, H3PO4 and CaCl2 were used as reactants which resulted in simultaneous crystallization of mostly dentritic brushite crystals and a small quantity of hydroxyapatite (HA). On the other hand, use of Na2HPO4 and CaCl2 as reactants yielded the large quantity of HA along with platelet brushite crystals. In both the cases, addition of sodium fluoride is found to inhibit the nucleation and subsequent growth of brushite crystals. The crystal morphology, structure and elemental composition of the grown crystals have been analyzed using SEM-EDX and powder XRD studies. Functional groups present in the grown crystals have been confirmed from the vibrational frequencies of the recorded FTIR spectrum.

Comparative study of structure, dielectric and electrical behavior of Ba(Fe0.5Nb0.5)O3 ceramics and their solid solutions with BaTiO3

N.K. Singh; Pritam Kumar; Radheshyam Rai

Advanced Materials Letters, 2011, Volume 2, Issue 3, Pages 200-205
DOI: 10.5185/amlett.2010.11178

Dielectric properties of (1-x)Ba(Fe0.5Nb0.5)O3-xBaTiO3 (where x = 0.00, 0.05 and 0.10) solid solution ceramics at high temperature range of RT ~ 270 o C have been characterized in this paper. The above said polycrystalline ceramics with (x = 0.0, 0.05 and 0.10) have been produced via a mixed oxide route. The effects of BaTiO3 substitution on the structure and on the electrical and ferroelectric properties of Ba(Fe0.5Nb0.5)O3 samples have been studied by performing x-ray diffraction and dielectric measurements. The dielectric properties (e¢ and tan d) were investigated in the temperature range of 30-270 °C and in the frequency range of 100 Hz-5 MHz. The variation of relative dielectric permittivity (tan d) and tangent loss (tan d) has suggested a significant role of hopping of trapped charge carriers, which is resulted in an extra dielectric response in addition to the dipole response. It is observed that: (i) the relative dielectric permittivity and tangent loss (tan d) are dependent on frequency, (ii) the temperature of dielectric permittivity maximum shifts toward lower temperature side and (iii) dielectric permittivity and tangent loss rapidly increase by making solid solution of BFN with BaTiO3. X-ray diffraction analysis of the compound suggests the formation of single-phase compound with monoclinic structure. SEM photographs exhibit the uniform distribution of grains. The maximum ferroelectric transition temperature (Tc) of this system was 250-270 °C with the dielectric constant peak of 72500 at 1.09 kHz for x = 0.05.

Structural, dielectric and electrical properties of Lead zirconate titanate and CaCu3Ti4O12 ceramic composite

Arun Chamola; Hemant Singh; U.C. Naithani; Shubhash Sharma; Uday Prabhat; Pratiksha Devi; Anuradha Malik; Alok Srivastava; R.K. Sharma

Advanced Materials Letters, 2011, Volume 2, Issue 1, Pages 26-31
DOI: 10.5185/amlett.2010.12182

In the present work, structural, dielectric and electrical properties of lead zirconate titanate and CaCu3Ti4O12 ceramic composite with composition (1-x)Pb(Zr0.65Ti0.35)O3 - xCaCu3Ti4O12 (where x = 0, 0.20, 0.40 and 0.60) has been reported. The sample was prepared by employing a high-temperature solid-state reaction technique. X-ray diffraction studies confirm the formation of pure phase for x = 0.00 concentration and composite phases for the x = 0.40, 0.60 compositions. Doublet of diffraction peaks suggests structural change for x = 0.20 composition. Scanning electron micrographs show a uniform grain distribution and the grain size and shape modified upon CaCu3Ti4O12 addition. Dielectric measurement demonstrates a decrease in the dielectric constant with increase in CaCu3Ti4O12 percentage. The prepared ceramic composites have high dielectric constant and low dielectric loss. The temperature dependence of the ac conductivity indicated that the conduction process is due to singly ionized (in ferroelectric region) and doubly ionized (in paraelectric region).

X-ray and electrical properties of Ba(Gd0.5Nb0.5)O3 ceramic

Pritam Kumar; B.P. Singh; T.P. Sinha; N.K. Singh

Advanced Materials Letters, 2011, Volume 2, Issue 1, Pages 76-81
DOI: 10.5185/amlett.2010.11176

The complex perovskite oxide barium gadolinium niobate, Ba(Gd0.5Nb0.5)O3 (BGN) is synthesized by a solid-state reaction technique. The X-ray diffraction of the sample at room temperature shows a tetragonal phase. The scanning electron micrograph of the sample shows the average grain size of BGN ~ 1.92 mm. The frequency-dependent dielectric dispersion of BGN is investigated in the temperature range from 303 K to 463 K and in a frequency range from 50 Hz to 1 MHz by impedance spectroscopy. The logarithmic angular frequency dependence of loss peak is found to obey an Arrhenius law with activation energy of 0.70 eV. It is observed that: (i) the dielectric constant (e¢ ) and loss tangent (tan d) are dependent on frequency, (ii) the temperature of dielectric constant maximum shift toward lower temperature side, (iii) The scaling behavior of dielectric  loss spectra suggests that the relaxation describes the same mechanism at various temperatures.

Optical properties of MAl12O19:Eu (M = Ca, Ba, Sr) nanophosphors

Abhay D. Deshmukh; S. J. Dhoble; N.S. Dhoble

Advanced Materials Letters, 2011, Volume 2, Issue 1, Pages 38-42
DOI: 10.5185/amlett.2010.10171

The MAl12O19:Eu (M = Ca, Ba, Sr) phosphor were synthesized by combustion method and systematically characterized by photoluminescence excitation and emission spectra, concentration quenching, morphology and X-ray mapping with scanning electron microscopy. In SrAl12O19:Eu phosphor two PL emission peaks are observed at about 389 nm and another around 420 nm as well as BaAl12O19:Eu phosphor shows blue emission around 460 nm is observed in the blue region of the spectrum and CaAl12O19:Eu shows only red emission at 592 as well as 615 nm. Both phosphors can be efficiently excited in the wavelength range of 250-425 nm, where the near UV (~320 nm) solid state excitation is matched. By combining MAl12O19:Eu (M = Ca, Ba, Sr) phosphor with near UV chops emitting intense blue green (Ba), yellow-red (Ca) and blue purple (Sr) LEDs white LEDs can be produced.

Structural And Dielectric Properties Of Dy2(Ba0.5R0.5)2O7 (R = W, Mo) Ceramics

N. K. Singh; Pritam Kumar; Hemchand Kumar; Radheshyam Rai

Advanced Materials Letters, 2010, Volume 1, Issue 1, Pages 79-82
DOI: 10.5185/amlett.2010.3102

The polycrystalline samples of the pyrochlore-type Dy2(Ba0.5R0.5)2O7 (R = W, Mo) compounds have been prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction (XRD) studies and scanning electron micrographs (SEM) of the compounds at room temperature suggested that compounds have single phase orthorhombic crystal structures and grain distribution throughout the surface of the samples was uniform. Dielectric studies (dielectric constant (e´) and tangent loss (tan δ) obtained both as a function of frequency (4 kHz -1 MHz) at room temperature (RT) and temperature (RT 320 0 C) at 20 kHz and 100 kHz suggest that compounds do not have dielectric anomaly in the said frequency and temperature range.