Transmission electron microscopy studies of the (1-x)Pb(Mg1/3Nb2/3)O3-(x)PbTiO3 (PMN-PT (1-x)/x) crystalline solution have been performed for x=0.1, 0.2, 0.35, and 0.60. Bright-field imaging has revealed a common sequence of domain-like states with increasing x. Normal micron-sized ferroelectric domains were found for x>0.40. Tweed-like structures were found for x∼0.35. These tweedlike structures are similar to those previously reported in pre-martensitic states. Paraelectric clusters were found for x<0.30. The paraelectric cluster state was characterized by the lack of self-assembly amongst embryos and the presence of relaxor behavior in the macroscopic response characteristics. The composition PMN-PT 65/35 was then modified with La for a detailed study of the transition between the tweed-like precursor and paraelectric cluster states with increasing impurity content.

Addition of rare earth oxides affects several properties of barium titanate ceramics such as dielectric constant, Curie temperature and electrical conductivity. Electrical properties depend on the composition, firing conditions and mode of incorporation of rare earth ions into perovskite or perovskite-like lattice.

Incorporation of rare earth ions into the BaTiO3 lattice was studied by quantitative wavelength dispersive spectroscopy in combination with scanning electron microscopy and X-ray powder diffraction. Broad solubility regions between rare earth titanates and barium titanate were detected, influencing the properties.

In present review, phase equilibria and properties of rare earth (La,Nd,Ce) containing BaTiO3 ceramics are compared with particular emphasis on preparation conditions.

A combination of different empirical methods which allow the prediction of the dielectric properties of non-ferroelectric complex perovskites has been proposed and its present limits verified. The long term purpose is to engineer new microwave materials with increased relative permittivity ε0 and low thermal coefficient of the resonant frequency τf.

The estimation of the dielectric properties has been accomplished by means of structural predictions based on the tolerance factor and a microscopic model. Furthermore, the optical permittivity based on the Gladstone-Dale relation and the total polarisability according to the molecular/ion additivity rule were also estimated. Ceramics of new compositions were then fabricated and analysed to verify the dielectric properties predicted by the empirical methods. Results show good agreement with the expected structural features and optical permittivities, and the method is sufficiently reliable to estimate the end values, or at least to estimate trends of the dielectric properties induced by partial substitution of cations on site A. The importance of the electronic polarisability on the end value of τε has been demonstrated.

Previous research has demonstrated that the formation of nano-sized “1:1” cation ordered domains in Zr4+ substituted Ba(Zn1/3Ta2/3)O3 may be responsible for the anomalies in the dielectric loss properties of these perovskite ceramics. To explore the structure and crystal chemistry of these phases, the effect of a series of M4+ substitutions (Zr4+, Ce4+, Sn4+, and Ti4+) on the B-site cation ordering in Ba(Zn1/3Ta2/3)O3, Ba(Mg1/3Ta2/3)O3, and Sr(Mg1/3Ta2/3)O3 has been examined. In all cases the substitution of low levels (∼ 5 mole %) of “over-sized” tetravalent cations (e.g. Zr4+, Ce4+) promotes a transformation to a 1:1 ordered phase, while the introduction of “under-sized” cations (e.g. Ti4+) stabilizes a disordered perovskite. Using Rietveld methods the structures of the 1:1 ordered A(βI1/2βII1/2)O3 phases were found to conform to a “random layer” model in which the βII positions are occupied by Ta, and the βI sites by a random distribution of the Mg(Zn), M4+ and residual Ta cations.

Order-disorder phenomena on the simple-cubic B-site sublattice in A(B1/3B'2/3)O3 perovskites is examined. A simple cubic groundstate analysis in the cube approximation reveals that this approximation is inadequate for A(B1/3B'2/3)O3 perovskites, because it cannot predict a common experimentally-observed [111] superstructure. A partial vertex enumeration technique is used to demonstrate that a 12 interaction subset of the cube + linear triplet approximation is sufficient. First-principles calculations were performed for Ba(Zn1/3Ta2/3)O3 (BZT) and Pb(Mg1/3Nb2/3)O3 (PMN), two technologically interesting materials, in an effort to construct generalized Ising model Hamiltonians to enable simulations of these materials. Both ionic model (SSCAD) and pseudopotential (PP) calculations were done, enumerating the relative energies of a series of B-site superstructures. Structural hierarchies are reasonble and predict the [111] groundstate for both BZT and PMN, despite the fact that it is not observed in the latter. The pseudopotential results also indicate the possibility of metal-insulator transitions in BZT as a function of B-site configuration.

Addition to thermally activated flips of polar regions in relaxor ferroelectrics, a new polarization mechanism, which originates from the vibrations (breathing) of surface of polar regions, is introduced to explain the dielectric behavior of relaxor ferroelectrics. This new mechanism plays an important role in the dielectric behavior of such materials at low temperature. Based on the above assumption and general dielectric theory, a formula is given to characterize the temperature dependence of the dielectric constant. The correctness of the formula is verified by using it to fit the experimental results of the two typical relaxors. The fitted results show that the method is of high precision and that the temperature of the dielectric constant maximum is decided by the two polarization behavior. It also indicates that the new polarization is a resonance polarization.

A new approach based on the study of distortion in the AO3 layer of ABO3 perovskites is proposed with the aim to discuss their ferroelectric properties. Rhombohedral distortions exist for either A-O average distances shorter than 2.7 A (space group Nr.161) or A-O distances larger than 3 Å (space group Nr.160). In the case of small distortions tetragonal or orthorhombic symmetries are preferred. Moreover, a relationship between the dimension of the B cation and the distortion in this type of structure has been established. Preliminary results show interesting correlations between distortions in the AO3 plane and the critical temperature of ferroelectric materials.

A structural phase transformation from hexagonal to monoclinic has been found in an ordered perovskite compound (Ba, Sr)(Mg1/3Ta2/3)O3, (BSMT). The transformation temperature of BSMT increases and the dielectric constant also changes from 24 to 27 with an increase in Sr concentration. The temperature coefficient of the dielectric constant is also changed with the variation of Sr content. In order to apply BSMT for practical use of dielectric resonators these changes in the dielectric properties, which is dominated by the phase transformation, must be controlled. In order to clarify the relation between the dielectric constant change and the structural phase transformation, phonon mode of BSMT has been studied using Raman spectroscopy. Change in the Raman spectrum of BSMT is classified into four steps. The first and the fourth steps correspond to the phase transformation. The change in the phonon mode detected by Raman spectroscopy is discussed in connection with the structural change.

Compositions in the PNN-PMW-PT system can be tailored to give high dielectric constant for MLC applications. Low temperature firing of MLC is always advantageous in using the less expensive electrode systems. Controlled addition of LiNO3 reduces the sintering temperature, increases the fired density and influences the microstructure of the ceramics. It also raises the peak dielectric constant and shifts the Curie temperature. The possible role of Li+ in modifying the characteristics of the ceramics is discussed.

Compositions in the Ba(Mg1/3Nb2/3)O3-BazrO3 (BMN-BZ) pseudo-binary system were prepared to evaluate the effect of BaZrO3 on the B-site cation ordering. While pure BMN adopts a 1:2 ordered structure, space group , 5 to 15 mole% additions of BZ stabilize a cubic 1:1 ordered phase with a doubled perovskite repeat. At higher levels of substitution (>25 mole% BZ), the B-site cations are disordered. Analytical TEM studies revealed that the 1:1 ordering is limited to nanometer-sized domains and the microstructure was found to strongly depend on the thermal history of the ceramics. For example, a cooling rate of 300°C/hr from a sintering temperature of 1640°C produced a partially ordered microstructure comprised of 4–5nm 1:1 domains dispersed in a disordered matrix. A completely ordered structure with 30–40 nm domains could be achieved when the cooling rate was reduced to 10°C/hr. The structure of the ordered 1:1 phases is interpreted using a “random layer” model in which one site is occupied exclusively by Nb, and the second contains a random distribution of all the remaining cations. Similar thermal annealing experiments were also conducted in an attempt to grow the 1:1 ordered domains in PMN-type (PbMg1/3Nb2/303) relaxor ferroelectric ceramics. Through experiments on PbZr03 (PZ)-doped PMT (PbMg1/3Ta2/3O3), the first observation of thermally induced domain growth in this class of relaxor ceramics are presented. These results cannot be explained by the widely accepted “space charge” model for relaxor ferroelectrics, but instead favor a charge-balanced random layer model for the 1:1 cation order.

In a recent work on phase equilibria relations in the BaO:Fe2O3:TiO2 system the existence of sixteen ternary compounds was confirmed. Most of the new found compounds apparently have a new structural type. In this work we employed electron diffraction and high-resolution microscopy in attempt to understand the structures of the new compounds. Since the present work was done on the compounds prepared by solid-state reaction, it also provides a correlation with a single-crystal x-ray work on some of the similar compounds prepared by crystallization from a melt.

Pellets in the ternary solid-solution Ba6–3xNd8+2xTi18O54 (x=0.75) have been processed to near theoretical density by mixed-oxide synthesis, and their dielectric properties determined to be εr≈89, Qf> 10,000, and τf≈+60ppm/°C at microwave frequencies. Similar ceramics with Ca, Sr, and Pb partially substituted for Ba were also processed and analysed. Both Ca and Sr were found to increase εr to 100–105 but significantly lower Qf and inflate τf. While Pb substitution also lowered Qf, it had no significant effect on εr and beneficially suppressed τf to values from -16 to +8ppm/°C, tunable with Pb content, strongly suggesting that these materials may be useful for commercial applications.

The thermal processing schedules necessary to form phase pure Ba2TigO20, with and without substitutional solid solution were investigated. Undoped compositions formed the compound most easily under rapid (500°C/min) heating rates, where diffusional agglomeration of the. TiO2 batch constituent was minimized. The compound formed most easily with minor (0.82%) substitutions of SnO2 and ZrO2 for TiO2. The solubility of Sn in Ba2Ti9O20 was higher than that of Zr. Extended heat treatment (16 vs. 6 h at 1390°C) resulted in volitalization of grain boundary liquid phase, leading to a more porous and slightly degraded resonators. The effects of dopant concentrations and soak periods at 1390°C on dielectric constants and temperature-dependent quality factors are reported.

Dielectric measurements were carried out in single crystals of KTiOPO4, KTiOAsO4, RbTiOAsO4 and CsTiOAsO4. All of the materials exhibit a clear dielectric relaxation process in the low temperature range and a conductance mechanism in the high temperature range. The dielectric relaxation process can be well described by the Debye dielectric model with an activation energies of 0.8 eV, 0.5 eV and 0.4 eV respectively. The relaxation process is associated with the deviation of the alkali ions from its ideal lattice positions. The high temperature conductance is associated with the motion of the alkali ions from one lattice site to another. Therefore, both the low temperature relaxation process and the high temperature conductance originate from different features of defect behavior of alkali ions in the cage structure of these materials.

Ferroelectric SrBi2Ta2O9 (SBT) films were prepared by the spin coating technique on platinum, quartz and YBa2Cu3O7-x/LaA1O3 substrates from a methoxyethanol solution of bismuth isopropoxide (Bi(OCH(CH3)2)3) and strontium tantalum isopropoxide (SrTa2(OCH(CH3)2)12). X-Ray diffraction studies showed some crystallization occurred after annealing the films under oxygen flow at 600 °C and excellent crystallinity was achieved after annealing at 750 °C for 0.5 h. Electron microprobe analysis gave a composition close to that expected for SBT, and atomic force microscopy gave a root mean square surface roughness of 101 A. An hysteresis measurement (1 kHz) gave remnant polarization (2Pr), saturation polarization (Ps) and coercive field (Ec) values of 14.5 μC/cm2, 14.5 μ/cm2 and 59 kV/cm, respectively.

The structural and electrical properties of SrCe1-xYbxO3 ceramics have been studied as a function of temperature and Yb-concentration using x-ray diffraction and impedance techniques. The influence of Yb-dopants on electrical transport and structural disorder has been studied. A correlation between the structural properties, electrical conductivity is observed and discussed. These measurements allow us to determine the mechanism of charge carrier compensation and also the concentration and mobility of the electrical species.

Oxygen ion conducting yttria-stabilized zirconia and perovskite-type Sr-doped LaMnO3 have been widely used as solid electrolyte and cathode materials in solid oxide fuel cells. The electrochemical properties of the cathode depend largely on the nanostructure and the phase composition of the interface between cathode and electrolyte. Interfaces between single crystals of 9.5mol% Y2O3-stabilized ZrO2 and porous La0.85Sr0.15MnyO3 (y = 0.95…1.10) were investigated. Atomic force microscopy was used for interface studies of YSZ single crystals after removal of sintered perovskite cathodes. High resolution transmission electron microscopy, electron diffraction and electrochemical impedance spectroscopy were employed for interface characterization. Pyrochlore-type lanthanum zirconate formed at the interface during sintering at 1100°C. Nucleation, growth kinetics, and morphology were largely depending on cathode stoichiometry. Lanthanum zirconate formation was retarded in case of A-site deficient perovskite.

The oxygen nonstoichiometry of Pr0.545Ce0.455O2-x was studied by solid state coulometric titration and was found to be extensive (0 ≤ y ≤ 0.28) at temperatures of 400–600 °C. The Po2 - x curves showed evidence of the existence of a number of single and two phase regions. Electrical conductivity measurements, performed under similar conditions, exhibited a p-n transition for temperature of 500 °C and below. The activated p-type conductivity was modeled in terms of the small polaron hopping mechanism. The p-n transition was correlated with the onset of phase separation.

The results of structural and electrical measurements of nanocrystalline CeO2 thin films are presented. A correlation between the electrical conductivity and microstructure has been observed and discussed. The electrical properties of nanocrystalline CeO2 thin films are attributed to a dominant role of grain boundary phase.

Terbia doped yttria stabilized zirconia (Tb-YSZ) thin films have been deposited on various substrates by applying the electrostatic spray deposition (ESD) technique. Yttrium- and zirconium-acetylacetonate as well as terbium-acetate hydrate were used as precursors. Butyl carbitol-ethanol mixed alcohol's with ratios of 50:50 vol% and 80:20 vol% were used as solvents for precursor solutions with total metal concentrations between 0.09 M and 0.009 M. Tb-YSZ thin films were deposited at temperatures between 520 K and 730 K. Surface morphology, chemistry, and crystal structure were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD). The Tb-YSZ layers consist of a fully stabilized cubic phases. The surface morphology of deposited Tb-YSZ layers can be controlled by changing different deposition parameters. The adhesion of Tb-YSZ to the substrate can be improved by a high temperature treatment.