N. Mykytenko; A. Kiv; D. Fuks
Abstract
A descriptor is constructed to predict the composition of ABO3 perovskites that do not contain transition metals and have a high level of ionic conductivity (s). The descriptor consists of two parts: the ratio of ionic radii, RA/RB and the ratio of ionization potentials, VB/VA for A- and B- cations. ...
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A descriptor is constructed to predict the composition of ABO3 perovskites that do not contain transition metals and have a high level of ionic conductivity (s). The descriptor consists of two parts: the ratio of ionic radii, RA/RB and the ratio of ionization potentials, VB/VA for A- and B- cations. Parameters for 100 perovskite compounds were considered to find the correlation dependences between the descriptor and the magnitude of s. Correlation selection approach is proposed to reveal a suitable correlation series. This approach allows determining the composition of perovskites that has a desirable ionic conductivity.
Bradha Madhavan; Anuradha Ashok
Abstract
The present work highlights a series of perovskites La0.8A0.2TiO3-δ, (where A= Ba, Ca, Sr), which includes a high dielectric constant, a low dielectric loss over a wide temperature, in a frequency range of 30 MHZ. Undoped and A-site doped LaTiO3-δ (with Ba 2+ , Sr 2+ and Ca 2+ ) perovskites ...
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The present work highlights a series of perovskites La0.8A0.2TiO3-δ, (where A= Ba, Ca, Sr), which includes a high dielectric constant, a low dielectric loss over a wide temperature, in a frequency range of 30 MHZ. Undoped and A-site doped LaTiO3-δ (with Ba 2+ , Sr 2+ and Ca 2+ ) perovskites were synthesised by solid state reaction method (ball milling). The perovskite phase formation of the milled precursor powders under thermal treatments was investigated by thermogravimetry/differential scanning calorimetry (TG/DSC). Structural analysis of the phase pure sintered pellets revealed an orthorhombic crystal structure for all perovskites. Surface morphology of the sintered pellets exposed the presence of nanosized grains. The oxidation states of La 3+ and Ti 3+ ions have been confirmed using X-ray Photoelectron Spectroscopy (XPS). The dielectric spectral analysis reveals that dielectric properties of the perovskites depend on temperature and frequency. Among the dopants Sr is found to be the most effective in increasing the dielectric properties of LaTiO3-δ. This makes it suitable as a high dielectric material for making capacitors operating at higher frequencies.
Usha Chandra; K. Asokan; V. Ganesan
Abstract
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 ...
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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.
David L. Fuks; Arnold E. Kiv
Abstract
Anchor Practically applicable approach for the fabrication of ABO3 perovskites with high rates of ionic transport is developed. The ionic transport in perovskites with transition metals at B – site is considered in terms of the theory of coordination compounds. It is shown that the structure of ...
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Anchor Practically applicable approach for the fabrication of ABO3 perovskites with high rates of ionic transport is developed. The ionic transport in perovskites with transition metals at B – site is considered in terms of the theory of coordination compounds. It is shown that the structure of these materials is sensitive to the values of the effective charge of the ions of transition metals (Z * ) and to the electronegativity (χ) of the surrounding cations. The magnitudes of Z * and χ can be varied by choosing the appropriate elements at sites A and B to induce a distortion of the short range order. This leads to reduction of potential barriers for formation and migration of structural defects including oxygen vacancies. In typical perovskites a correlation between the rates of the ionic transport and the estimated values of Z * and χ is found.