A. S. Bhalla

The perovskite structure—a review of its role in ceramic science and technology

Abstract Starting with the history of the fundamental science of the relation of structure to composition delineated completely by Goldschmidt, we use the perovskite structure to illustrate the enormous power of crystal chemistry-based intelligent synthesis in creating new materials.The perovskite structure is shown to be the single most versatile ceramic host. By appropriate changes in composition one can modify the most significant electroceramic dielectric (BaTiO3 and its relatives) phase in industry, into metallic conductors, superconductors or the highest pressure phases in the earth. After an historical introduction of the science, detailed treatment of the applications is confined to the most recent research on novel uses in piezoelectric, ferroelectric and related applications.

Dielectric and pyroelectric properties in the Pb(Mg1/3Nb2/3)O3-PbTiO3 system

Abstract Dielectric and pyroelectric properties of relaxor ferroelectric in the (1-x) Pb(Mg1/3Nb2/3)O3-xPbTiO3 solid solution series have been investigated. The dielectric constant (K) and loss of poled and unpoled ceramic samples were determined. The pyroelectric coefficient and the spontaneous polarization were measured by the static Byer-Roundy method as a function of temperature and for various compositions in the binary system PMN-PT. An important contribution to the dielectric and pyroelectric behavior for the solid solutions compositions close to the morphotropic phase boundary (x ∼ 0.4) between pseudocubic and tetragonal regions existing in the grains of the ceramic were observed. Anomalous dielectric and pyroelectric behaviors occurred for compositions x = 0.275 ∼ 0.35 mole% PT in the vicinity of morphotropic phase boundary.

Piezoelectric and strain properties of Ba(Ti1−xZrx)O3 ceramics

The polarization and strain behavior of Ba(Ti1−xZrx)O3 (x=0–0.3) ceramics are studied. The unipolar strain levels of ∼0.18% at 40 kV/cm and of ∼0.25% at ∼120 kV/cm with small hysteresis were obtained for the ceramics with 0.03⩽x⩽0.08. The remnant polarization is ∼13–18 μC/cm2 for 0.03⩽x⩽0.08 and below 2 μC/cm2 for 0.15⩽x⩽0.3 at room temperature. The electromechanical coupling coefficient K33=56.5% and the piezoelectric stain coefficient d33=236 pC/N were obtained for the ceramics with x=0.05. These results indicated that the Ba(Ti1−xZrx)O3 system is a promising lead-free high strain material for applications.

Classification and consequences of complex lead perovskite ferroelectrics with regard to B-site cation order

From a number of studies on ferroelectric and related materials based on complex lead perovskites [Pb(B x ′B 1− x ″)O 3 ], it is apparent that the B-site cation order influences the crystallography, phase transitions, and other physical properties. A classification of complex lead perovskites is presented based on the relative scale of long-range cation order. In particular, we discuss the implications of cation order in relation to relaxor and normal ferroelectric behavior.

Micro-Raman scattering and dielectric investigations of phase transition behavior in the BaTiO3–BaZrO3 system

In this study, the phase transition behavior of the BaTiO3–BaZrO3 system was studied using micro-Raman scattering and dielectric measurement techniques. BaZrxTi1−xO3 ceramics were prepared for x=0.00, 0.05, 0.08, 0.15, 0.20, and 1.00 compositions using a solid-state reaction technique. A single-phase perovskite structure of the ceramics was identified by the x-ray diffraction technique. The basic phase transition temperatures in these compositions were studied in the temperature range of 70–575 K. The tetragonal to cubic transition temperature was found to decrease with increasing Zr content. The orthorhombic to tetragonal transition temperature that increases with an initial increase in Zr content merges with the tetragonal–cubic transition for x⩾0.15 compositions. Raman spectra of rhombohedral and orthorhombic phases could not be distinguished. Excellent agreement between the crystallographic transition temperatures obtained by both techniques suggested that Zr substituted octahedra were uniformly distr...

Enhanced ferroelectric properties of Cr-doped BiFeO3 thin films grown by chemical solution deposition

Multiferroic Cr-doped BiFeO3 (BFO) thin films were prepared on Pt∕TiO2∕SiO2∕Si(100) substrates by a chemical solution deposition method. From the x-ray photoelectron spectroscopy measurements, it was observed that the valence number of Fe ion in undoped and Cr-doped BFO thin films was found to be almost 3+. It was found that Cr-doped BFO thin films exhibited good ferroelectric properties, such as improved leakage-current density and P-E hysteresis characteristics. The 3mol% Cr-doped BFO thin film showed a leakage-current density of 9.2×10−7A∕cm2 at 100kV∕cm and a large remanent polarization (Pr) of 61μC∕cm2 at room temperature.

Dielectric behavior of Ba(Ti1−xZrx)O3 single crystals

In this article, we report the successful growth of Ba(Ti1−xZrx)O3 (x=0.05–0.2) single-crystal fibers by the laser-heated pedestal growth technique. A single-phase perovskite structure of the materials has been identified by the x-ray diffraction technique. The phase diagram for Ba(Ti1−xZrx)O3 single crystals is established for x⩽0.2. Dielectric properties as function of temperature and frequency and room-temperature hysteresis loops are measured. The remnant polarization (Pr) and coercive fields (Ec) are obtained and compared for both single crystals and ceramics. The small dielectric relaxation has been observed for the lower-temperature phase transition (around 40 °C at 1 kHz) of the sample with x=0.08. The relaxation times follow the Arrhenius law with τ0=0.4×10−13 s and Erelax=0.53 eV. A common feature of the low-temperature relaxation mode in the sample is also observed, which follows the Arrhenius law with the τ0=0.8×10−10 s and Erelax=0.46 eV.

Ferroelectric-relaxor behavior of Ba(Ti0.7Zr0.3)O3 ceramics

Ferroelectric-relaxor behavior of Ba(Ti0.7Zr0.3)O3 ceramics is studied in the temperature range from 150 to 450 K. A broad dielectric peak with a high-dielectric maximum exhibits frequency dispersion. The dielectric relaxation rate follows the Vogel–Fulcher relation with E=0.21 eV and TVF=199.6 K. The polarization hysteresis loops were observed with a remnant polarization of 10 μC/cm2 at 175 K. The high-dielectric constant and high-polarization properties are expected to find practical applications at low temperatures.

Raman spectroscopy of Mg-Ta order-disorder in BaMg1/3Ta2/3O3

A complex perovskite-type material BaMg13Ta23O3 (BMT) with remarkable microwave dielectric properties was studied by microprobe Raman scattering in a wide temperature interval from 30 up to 1200 K. Two of the most appropriate practical forms of BMT materials, namely ceramics and single crystal fibers grown by the laser heated pedestal growth technique, were employed in the experiments. The way and degree of the B ion arrangement in complex compounds (Mg and Ta in the present BMT) or, in other words, the nano-microstructural composition have remained the most important questions for synthesis and practical applications of these complex materials. X-ray diffraction yields a simple cubic structure and no B-site ordering for the BMT ceramics the P3ml space group with 1:2 order for Mg and Ta ions and for fibers, which corresponds to the Pm3m symmetry on average. Comparison of the Raman spectra from both ceramics and fibers does not reveal any important difference. A careful consideration of some interdependent characteristics (the normal mode analysis and mode assignment, the mode positions and their behavior in comparison with related 1:1 compounds, no appropriate splitting of the degenerate modes) led us to conclude that the Mg and Ta ions with 1:1 composition are arranged on nanoscale regions of the Fm3m space symmetry. The selection rules for Raman scattering are controlled by this short-range regular arrangement so one can distinguish between three possibilities (Pm3m, Fm3m and P3ml) by Raman spectra. In this model, uncompensated charges should appear in both the 1:1 ordered regions and the rest of materials which becomes rich in Ta and pure in Mg. Several additional weak lines in the Raman spectra as well as slight splitting of the degenerate modes give evidence of some distortions in microstructures which could provide, at least partly, the charge compensation. These features seem to be mostly static. Dynamic changes were found on heating when the Raman spectra of BMT reduced in intensity up to the disappearance without any rearrangement in the B sublattice. We suppose that due to large phonon vibrations at high temperatures, the difference between two primary inequivalent oxygen octahedrons around Ta and Mg vanishes in average so that there is an equivalent change in the symmetry from Fm3m to Pm3m. No Raman-active modes of the first-order are allowed in the latter phase and this fact is in agreement with the experimental observation.

Morphotropic phase boundary in Pb (Mg13Nb23) O3-PbTiO3 system

Abstract Dielectric and pyroelectric properties in the solid solution (1 −x) Pb (Mg 1 3 Nb 1 3 ) O 3 : xPbTiO 3 across the morphotropic phase boundary compositions, x = 0.275–0.4, are studied as a function of temperature. The studies revealed that the true morphotropic boundary is in the vicinity of x≈ 0.3 and it has a small curvature.