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The structural instability of SrTiO3 at T S = 105 K is reinvestigated experimentally and theoretically by birefringence measurements and within the self-consistent phonon approximation. Analogous to BaTiO3 the phase transition shows precursor dynamics starting approximately 60 K above the phase transition temperature. These rotational dynamic clusters compete with precursor effects stemming from the polar soft mode and appear on different length scales as compared to BaTiO3. [ABSTRACT FROM AUTHOR]

The following article is a personal, and probably self-indulgent, review of the development of the classification of tilted octahedra in perovskite structures and my role in it. This review is not intended to be a thorough account of the topic, which has in any case been covered elsewhere, but is offered as a historical account of how the description of perovskite tilt systems in use today originally came about. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to review and briefly discuss recent experimental results on the effect of high pressure (p > 1.5 GPa) on relaxor ferroelectrics, exemplified by Na½Bi½TiO3 and PbMg⅓Nb2/3O3. The main result is that relaxor ferroelectrics present important polar and structural pressure-instabilities, which lead to both phase transitions of the average structure and considerable changes of the local structure. It is in particular the observation of a pressure-induced suppression of the relaxorcharacteristic X-ray diffuse scattering that points to important changes in the local order. The complementary use of Raman spectroscopy, X-ray diffraction and X-ray diffuse scattering allows the proposition of a mechanism for the observed changes. [ABSTRACT FROM AUTHOR]

A detailed phase diagram of Pb(Mg⅓Nb2/3)(1-x)TixO3, conventionally abbreviated to PMN-PT, has been constructed around the morphotropic phase boundary from measurements taken from one single crystal possessing a composition gradient. Optical birefringence imaging was employed as a function of temperature to plot retardation and orientation information as a function of temperature and position within the crystal. Electron-probe microanalysis measured the composition across the crystal and this enabled the phase boundaries to be plotted to high precision. Cubic (C), rhombohedral (R), tetragonal (T) and monoclinic (M) phases were observed, with the a C-R-T critical point at a composition x = 0.275 (4) at 394.7 (5) K on heating and at the same composition at 386.5 (5) K on cooling, in close agreement with phase diagrams suggested by published dielectric and diffraction experiments. [ABSTRACT FROM AUTHOR]

In flux-grown (1-x)NaNbO3-(x)Gd⅓NbO3 solid solution crystals a diffusion of the dielectric permittivity ε maximum grows with x and increases dramatically when x exceeds a threshold value x0 ≈ 0.1. Optical studies by the rotating-polarizer method show that Gd-doping results in a very small mean size of twins and the distribution of the birefringence image becomes very messy. In the x < x0 range the changes of lattice parameters and birefringence corresponding to the ε(T) anomaly were revealed. The results obtained are in line with the assumption that phase transition diffusion in NaNbO3 is a result of the local strains stemmed from the impurities. [ABSTRACT FROM AUTHOR]

The present paper reports on the observation of the optical birefringence as a function of temperature of the langbeinite-type crystal K[SUB2]Mn[SUB2](SO[SUB4])[SUB3] by using an imaging version of the so-called rotating-polarizer method. This method provides separates moving images of the orientation of the optical indicatrix and the magnitude of the optical anisotropy, showing the domain-wall behaviour during temperature changes. Somenew results o the domain behaviour of the phase transition of K[SUB2]Mn[SUB2](SO[SUB4])[SUB3] have been obtained. It is concluded that the sample single crystal consists of local regions, indicating the coexistence of two phases in this langbeinite-type crystal. [ABSTRACT FROM AUTHOR]

The relaxor ferroelectric, Sodium Bismuth Titanate, (Na 0.5 Bi 0.5 TiO 3 ), NBT is an A-site substituted distorted perovskite. An extensive temperature-, pressure- and substitution-dependent study of the crystal structure and phase transitions in this compound has been carried out using neutron/x-ray diffraction techniques. This has been complemented with optical, Raman and computational modelling studies. The temperature-dependent investigation shows that NBT undergoes a first phase transition from the high-temperature cubic prototype (Pm &3macr; m) Phase I to Phase II of tetragonal symmetry (P4bm) and then a second one with strong diffuse character to Phase III of rhombohedral symmetry (R3c). The high-pressure study of NBT has revealed an interesting and unusual relaxor-to-antiferroelectric (R3c → Pnma) phase transition. Structural variations as a function of temperature and doping across the (Na 1-x K x ) 0.5 Bi 0.5 TiO 3 (NKBT) series have also been established. [ABSTRACT FROM AUTHOR]

Focuses on the use of conoscopic illumination in a microscope equipped with a rotating polarizer-circular analyzer system and monochromatic light. Separation of an interference pattern into constituent parts; Identification of the sign of the optical indicatrix and birefringence; Effect of computed images on observed images.

Details the structural phase transition nomenclature report on phase transition nomenclature. Essential crystallographic and physical characteristics of each phase in the sequence; Eliminating confusion associated with the preset multiple nomenclatures expected to stimulate general use of the proposed nomenclature.

Investigates the room-temperature crystal structure of the perovskite lead hafnate PbHfO[sub 3]. Use of low-temperature single crystal X-ray diffraction and polycrystalline neutron diffraction; Difficulties in determining the oxygen positions.

In 1947 Kathleen Lonsdale conducted a series of experiments on X-ray diffraction using a divergent beam external to a crystal sample. Unlike the Kossel technique, where divergent X-rays are excited by the presence of fluorescing atoms within the crystal, the use of an external divergent source made it possible to study non-fluorescing crystals. The resulting photographs not only illustrated the complexity of X-ray diffraction from crystals in a truly beautiful way, but also demonstrated unprecedented experimental precision. This long-forgotten work is repeated here using a synchrotron radiation source and, once again, considerable merit is found in Lonsdale's technique. The results of this experiment suggest that, through the use of modern 'third-generation' synchrotron sources, divergent-beam diffraction could soon enjoy a renaissance for highprecision lattice-parameter determination and the study of crystal perfection. [ABSTRACT FROM AUTHOR]

Comments on suggestions made for the nomenclature of quasicrystalline phases and their crystalline approximants. Characteristics of quasicrystalline phase; Definition for a crystalline approximant.