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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]

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]

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