Advanced Materials Letters

In Bangladesh, generally imported clays are used as the main ingredient in ceramicware industries. Though locally available clays can be refined and used instead of imported ones to minimize the high manufacturing cost. In this research, 3 locally available clays were investigated both mechanically and spectrally. The XRF analysis of local non-refined clays in contrast to imported clays has indicated the presence of excess SiO2 content (about 35%) in the form of free silica as well as TiO2 and iron oxide but the Al2O3 content are a presence in lower amount (around 8.7%). In the ceramic body, a high amount of silica content shows low plasticity which creates a crack and iron oxide could adversely affect the translucency of ceramic ware. After the refining process from those local clays, the amount of SiO2 content was reduced up to 40.2% along with 5.5% increment in Al2O3 content. From the mechanical analysis of those clays, hardness, impact and compressive strength show very good results compared with imported clays. Copyright © VBRI Press

This review article describes a series of studies on the glass-ceramic Na + superionic conductors with Na5YSi4O12 (N5)-type structure synthesized using the composition formula of Na3+3x-yR1-xP < em>ySi3-yO9 for a variety of rare earth elements, R, under the appropriate composition parameters. Recent researches on structural control of the Na + superionic conducting glass-ceramics are also introduced. The optimum conditions for crystallization were discussed with reference to the conduction properties and the preparation of crack-free N5-type glass-ceramics. The effects of Si substitution with the various elements with tetrahedral oxygen coordination structure and Y substitution with the various R elements were also discussed on ionic conductivity of N5-type glass-ceramics, respectively. 

The paper presents the results of investigations on hot pressure sintering under the alternating current. The powders of different grain sizes were used for the sintering to investigate the impact of the powder on the final sintered structure and relative density. The additional experiments were focused on the kinetics of the Al2O3 nanopowders sintering. They confirmed that the time of the process duration is dependent on the temperature and the applied pressure. However, compared to the powders of tungsten monocarbide, it depends on the temperature rise speed in rather small degree. Discussion of the results pointed out that the obtained data, both theoretical and experimental one, confirmed possibility that during the sintering process the dislocations might appear and spread. It seemed reasonable to assume that in the low voltage regime the activated sliding with diffusion accommodation prevails, while in the high voltage regime the dislocation creep does.

The present work demonstrates a simple and efficient route to synthesize a variety of barium titanate (BaTiO3) nanostructures including nanowires, nanoswords, nanostars, nanocubes, and nanoparticles by a facile hydrothermal approach. The experiments showed that different morphologies can easily be tuned by varying the concentration of precursors, i.e., hydrogen titanate (H2Ti3O7) and barium hydroxide octahydrate (Ba(OH)2.8H2O), while keeping the molar ratio, reaction temperature and time fixed. The structure and morphology of BaTiO3 were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results indicate that BaTiO3 nanowires are in cubic phase with an average diameter of 80-100 nm. The shape of BaTiO3 changes from nanowires to nanoparticles with an increase in Ba(OH)2.8H2O concentration from 0.08 M to 0.51 M. Two possible mechanisms, in-situ topotactic transformation reaction and dissolution-deposition reaction have been suggested for different morphologies of BaTiO3.  The synthesized 0-D and 1-D BaTiO3 nanostructures are promising materials for many applications because of their excellent dielectric, ferroelectric and piezoelectric properties. The present work will open a new route to single reaction parameter dependent synthesis of 0- and 1-D BaTiO3 nanostructures which can find a range of applications including electronics, catalysis, energy harvesting, etc.

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.

Lead based piezoelectric perovskite materials are well known for their excellent piezoelectric properties, which are extensively used in industrial applications. Though, considering the toxicity of lead and its compounds, there is a general awareness for the development of environmental friendly lead-free materials as evidenced from the legislation passed by the European Union in this effect. The different class of materials is now being considered as potentially attractive alternatives to lead zirconate titanate (PZT) based perovskites for various applications. In this review, we review the progresses made on lead-free piezoelectric materials emphasizing on their synthesis, structure–property correlation, etc. Advancement of the various piezo systems such as bismuth sodium titanate, alkali niobates etc. and non-perovskites for example bismuth layer-structured ferroelectrics has been deliberated. It is found that some lead-free compositions show stable piezoelectric responses though they are not as high as the PZT system. This subject is of current interest to the ceramic researchers worldwide as evidenced from the large number of research publications and has motivated us to come out with a critical overview of the field. This article would drive to the researchers to advance the piezoelectric properties of the non-lead based perovskite compounds to achieve materials at par with the PZT system.  

Polycrystalline samples of 1- x(Na0.5 K0.5)(Nb0.95 Ta0.05) ) -x(Bi Fe)O3 with x=0, 0.003, 0.005, 0.007) hereby denoted as NKNT-BF were prepared by the mixed oxide method. Preliminary structural studies carried out by X-ray diffraction technique showed the formation of perovskite structure with orthorhombic symmetry. Addition of BF in the NKNT system lowered the sintering temperature by 500C. The nature of the frequency dependence of ac conductivity of NKNT compounds follows Jonscher power law. Complex impedance and modulus spectra confirm the significant contribution of both grain and grain boundary to the electrical response of the materials. Above the ferroelectric–paraelectric phase transition temperature, the electrical conduction is governed by the thermal excitation of charge carriers from oxygen vacancies exhibiting Negative temperature coefficient (NTCR) behaviour. Detailed study on the multiferroic properties (where magnetism and ferroelectricity are strongly coupled together) of the system is under process which is likely to form key components in the development of future technology, for example, in memories and logic devices.

Multiferroic bismuth ferrites (BFO) and Ni substituted bismuth ferrites (BFNO) were synthesized by standard solid state reaction route. The structural and microstructural studies were carried out. The effect of Ni substitution on dielectric constant and dielectric loss of the samples was studied in a wide range of frequency (100 Hz- 1 MHz) and temperature (27 o C – 420 o C). It has been observed that the dielectric constant increases with increase in Ni doping concentration and attained a maximum value for BFNO(x = 0.075) sample while the dielectric loss has been found to decrease with the doping concentration. This implies a reduction in the conductivity and hence improved the dielectric properties of Ni doped BFO. The anomalous peaks in temperature dependent dielectric studies indicate the increase in antiferromagnetic ordering temperature and possible existence of spin glass states upon Ni substitution in place of Fe. The complex impedance spectroscopic analysis suggests purely the intrinsic nature of the dielectric anomalies. Temperature dependent non-Debye type of dielectric relaxation has also been observed. The Nyquist plots show the negative temperature coefficient of resistance behavior of these compounds. Further it would be interesting to study their magnetic and magnetoelectric properties with the aim of identifying new multifunctional device applications.

Pb1-xSmx(Zr0.45Ti0.55)1-x/4O3 (PSZT; x = 0.00, 0.03 and 0.06) ceramic samples were prepared by high temperature mixed oxide method. Using complex impedance spectroscopy (CIS) technique, the complex impedance (Z*) and modulus (M*) properties of the materials were analyzed within a wide range of temperature and frequency. Impedance analysis indicates the presence of mostly bulk resistive (grain) contributions which is found to decrease with the increase in temperature. It suggests about the negative temperature coefficient of resistance (NTCR) type behaviour of the materials. Complex modulus plots exhibit the presence of grain (bulk) as well as grain boundary contributions in the materials and also support their NTCR type behaviour. Both the complex impedance and complex modulus plots confirm the presence of non-Debye type of relaxation in the materials. At higher temperatures, bulk resistance is found to increase with the increase in Sm 3+ concentration in PSZT along with the increase in relaxation phenomenon.

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.

LaxBi1-xFeO3 (LBFO) samples were prepared by sol-gel route using citric acid as chelating agent for x = 0.0 - 0.4. The structure, dielectric and magnetic properties of the LBFO compounds were studied and compared with the corresponding properties of the materials prepared by a conventional solid state reaction. The use of the sol–gel method in preparation lowered the reaction threshold temperature by 200 °C. Effects of the preparation routes and conditions on the phase and microstructures of the materials were investigated in this study using XRD and SEM. The pure BFO without bismuth loss, which cannot be prepared by the solid state reaction, was obtained by the sol–gel method. Sol-gel synthesis could yield a pure phase material at relatively lower temperatures while the solid state method yielded powder with a small amount of the secondary Bi25FeO40 phase. Single phase LBFO prepared by sol-gel method (SG) revealed huge value of dielectric constant than same obtained by the solid state reaction method (SS). Maxwell-Wagner type dielectric dispersion is observed in sol-gel method. Dielectric constant and loss tangent are found to be higher for SG as compared to SS. Huge coercivity (HC) of the order of ~ 15 kOe is observed in both SG and SS samples due to the high anisotropy in these samples. The increase in the magnetization is observed due to the destruction of spin cycloid structure. The enhanced properties made LBFO a promising candidate for the applications in novel memory devices and spintronics.

The polycrystalline sample of ZnSb2O4 was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction (XRD) studies of powder sample of ZnSb2O4 showed the formation of single-phase compound at room temperature. The surface morphology of the pellet sample of ZnSb2O4 was recorded at room temperature using a scanning electron microscope (SEM). Detailed studies of dielectric properties (εr, tan δ) and impedance parameters of the material provide an insight into the electrical properties and understanding of types of relaxation process occurred in the material. Temperature variation of dc conductivity shows that this compound exhibits negative temperature coefficient of resistance (NTCR) and frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.

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.

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.

The polycrystalline Ba3Sr2GdTi3V7O30 material of tungsten bronze structural family was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction analysis exhibits the formation of single-phase compound with orthorhombic crystal system. Surface micrograph recorded by scanning electron microscopic (SEM) technique has well defined but non-uniformly distributed grains throughout the surface of the pellet sample. Detailed studies of dielectric properties as a function of temperature (306-773 K) and frequencies (10 2 -10 6 Hz) suggest that the compound has frequency independent diffused dielectric anomaly at a temperature ~620 K which may be related to ferroelectric phase transition which is confirmed from polarization study. The frequency and temperature dependence of impedance property of the material were analyzed using a complex impedance spectroscopy. The Nyquist plots confirmed the presence of grain and grain boundary effect in the material.

A new ferroelectric oxide (Li2Pb2Gd2W2Ti4Nb4O30) of the tungsten bronze structural family was synthesized using a high temperature solid-state reaction (i.e., mixed-oxide) method at 1100 o C. Room temperature structural analysis (XRD) shows the formation of a new compound in single phase. The ferroelectric phase transition temperature (much above the room temperature) was determined by the dielectric and polarization measurements. Impedance, modulus and electrical conductivity of the material exhibit a strong correlation between its micro-structure and electrical parameters. The existence of non-exponential-type of conductivity relaxation in the compound was confirmed by detailed studies of its transport properties.

First time novel complex strontium barium tantalate, Sr0.5Ba0.5Ta2O6 was successfully synthesized in 1D structure (nanorods) by citrate-nitrate gel route. Their structural properties were examined via X-ray diffractometry (XRD) and revealed the formation of tetragonal tungsten bronze (TTB) structure at as low as 1100ºC. Also, FT-IR, FT-Raman, UV-vis, SEM, TEM and PL were used to identify the structure and properties of powders. Well isolated nanorods of the average diameter of ~200nm can be fabricated by this route. PL spectrum showed strong and broad visible emission band around 439nm due to particles with little surface defects. The frequency dependent dielectric dispersion of SBT50 powders sintered at 1300°C/4 h was investigated in a frequency range from 1 kHz-1MHz and at different temperatures (25°C- 450°C). It is observed that: (i) the dielectric constant (ε') and loss tangent (tan δ) are dependent on frequency, (ii) the temperature of dielectric constant maximum shift toward lower temperature side and the maximum dielectric constant (ε) was observed to be 2400 at 1 kHz. The Tc was found to be ~444-449°C and ferroelectric relaxor or diffuse phase transition like behavior was observed at around 449°C.

Complex impedance analysis of new tungsten bronze ferroelectric vanadates, Na2Pb2R2W2Ti4V4O30 (R = Gd, Eu), was carried out on samples prepared relatively at low temperature using a mixed-oxide technique. The formation of the materials under the reported conditions has been confirmed by an X-ray diffraction technique. A preliminary structural analysis exhibits orthorhombic crystal structure of the materials at room temperature. The electrical properties of the materials have been studied using ac impedance spectroscopy technique. Detailed studies of impedance and related parameters exhibit that the electrical properties of the materials are strongly dependent on temperature, and bear a good correlation with their microstructures. The temperature dependence of electrical relaxation phenomenon in the materials has been observed. The bulk resistance, evaluated from complex impedance spectra, is found to decrease with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR) – type behavior similar to that of semiconductors. A small contribution of grain boundary effect was also observed. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The ac conductivity spectra exhibit a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.

The influence of Al, Si and B on the growth of TiC is studied in this article. It is found that the adsorption of Al is more favorable on TiC {111} than that on {001}. Therefore, under the influence of it, the growth rate of {111} will be accelerated and result in the decreasing of the relative growth rate between {001} and {111}. Therefore, TiC will grow into truncated-octahedron. But when TiC is formed under the influence of Si and B, they will grow into hexagonal platelets due to the preferential adsorption of Si and B on {011} and {001}.

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.

Cellulosic waste materials which include sawdust, wastepaper, corncob and sugarcane bagasse were converted into nanostructured ceramics and nanocomposites by submersion in silica colloidal suspension (sol) and subsequently by calcination of the cellulosic/SiO2 nanocomposites under controlled conditions. Depending on the calcination conditions used, nanostructured SiO2 ceramics and carbon/SiO2 nanocomposites were obtained. The morphology of resulting nanostructured ceramics and nanocomposites obtained from four types of cellulosic waste materials were characterized by Scanning Electron Microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and CHN elemental analyzer. The effect of cellulosic materials on the properties of nanostructured ceramics and nanocomposites formed were investigated. Copyright © 2011 VBRI press.

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).

Numerous metal oxide semiconductor materials were reported to be usable as semiconductor gas sensor, such as ZnO, SnO2, and TiO2 and so on. The samples of Zn and Cu doped SnO2 (SnZnO3 and SnCuO3) have been synthesized by solid-state reaction method. Some aspect of crystal structure of the compound at room temperature was studied using X-ray diffraction technique. The XRD study of the compound shows that there is a change in the basic crystal structure of SnO2 on substitutions of ZnO and CuO. The patterns of the SnO2 sample are indexed as tetragonal perovskite type with a = 7.3928 Å, c = 5.2879 Å but on substitution of ZnO and CuO the structure becomes orthorhombic with lattice constant a = 23.5237Å, b = 8.2183 Å and c =5.8017 Å or a = 21.8594 Å, b = 5.3200 Å, and c = 5.1803 Å, respectively. The temperature variation of resistance shows that compounds have negative temperature coefficient of resistance. The gas sensitivity for LPG (liquefied petroleum gas) showed a drastic change in conductivity.