The immanent chaotization of crystal structures and the resulting diffuse scattering. II. Crystallochemical conditions of perovskite chaotization

Abstract

In part I of this series the problem of immanent chaotization of crystal structures was described in simple models and the mathematical approach to the calculation of diffuse scattering (DS) was described. It was formulated that the loose packing of most real crystals appears to be the universal microscopical cause of DS. In the present paper the microscopical nature of chaotization is analysed and a quantitative description of the structural loose packing is given for cubic perovskites; these are particularly convenient examples because the most vivid and thorough experimental data on DS were obtained for such crystals: KNbO3, BaTiO~, NaNbO3, KMnF3.

Polar Nanoregions and Dielectric Properties of BaTiO3‐Based Y5V Multilayer Ceramic Capacitors

“…The multiple B‐site model was supported by experimental evidence as well as by theoretical consideration, and indeed is again confirmed by the present results (Fig. ) in RFE Y5V chips.…”

“…DS is common in loosely packed crystal structure such as perovskite ABO 3 . In particular, the unequal bonding between Ba 2+ over‐bonding by 28% and Ti 4+ under‐bonding by 12% creates a strong local chemical stress that the off‐centered Ti shifts away from its body‐centered position.…”

Crystal structure of KCaF3 determined by the Rietveld profile method

“…Consideration of ionic radius (Kassan-Ogly and Naish, 1986) shows conclusively that the distortion appearing in KCaF 3 is mainly due to tilting of the CaF 6 octahedra. Hence, the splitting of the main lines observed on the X-ray powder diagram was investigated based on Glazer's analysis (Glazer, 1972(Glazer, , 1975.…”

Calorimetric Investigation of Tricritical Behavior in Tetragonal Pb(ZrxTi1−x)O3

“…However, real perovskite structures admit a considerable range of t, with the most likely interval being 0.7074t41.225. The deviation from the ideal closepacked structure leads to an instability in the ion positions, to increased oscillations at high temperatures, and, under appropriate thermodynamic conditions, to static ion displacements from the cubic structure to structures of lower symmetry, i.e., displacive phase transitions (28).…”