The (Na1 - x Kx )0.5 Bi0.5 TiO3 perovskite solid solution is investigated using x-ray diffraction (XRD) and Raman spectroscopy in order to follow the structural evolution between the end members Na0.5 Bi0.5 TiO3 (rhombohedral at 300 K) and K0.5 Bi0.5 TiO3 (tetragonal at 300 K). The Raman spectra are analysed with special regard to the hard modes and suggest the existence of nano-sized Bi3+ TiO3 and (Na1 - 2x K2x )+ TiO3 clusters. The complementary use of XRD and Raman spectroscopy suggests, in contrast to previous reported results, that the rhombohedral tetragonal phase transition goes through an intermediate phase, located at 0.5 x 0.80. The structural character of the intermediate phase is discussed in the light of sub- and super-group relations.

(PZT) is one of the most important and widely used piezoelectric materials. The study of its local and average structures is of fundamental importance in understanding the origin of its high-performance piezoelectricity. Pair distribution function analysis and Rietveld refinement have been carried out to study both the short-and long-range order in the Zr-rich rhombohedral region of the PZT phase diagram. The nature of the monoclinic phase across the Zr-rich and morphotropic phase boundary area of PZT is clarified. Evidence is found that long-range average rhombohedral and both long-and short-range monoclinic regions coexist at all compositions. In addition, a boundary between a monoclinic (M A ) structure and another monoclinic (M B ) structure has been found. The general advantage of a particular monoclinic distortion (M A ) for high piezoactivity is discussed from a spatial structural model of susceptibility to stress and electric field, which is applicable across the wide field of perovskite materials science.

Close examination of published measurements of absolute configuration in inorganic crystals has revealed many mistakes, and only a small number of published correlations between optical rotation and chirality of crystal structure can be trusted. The sense of rotation of light is here traced to the hand of specific helices of atoms, provided that the latter are correctly chosen. Four principles are given for choosing the helices. The crystals described are: low-quartz, ~-A1PO4, ct-HgS, Ca2Sr(CzHsCOO)6, BitzSiO2o, NaC103, NaBrO 3 and ~-LiIO 3. The principles suggest that the published absolute configuration of ~t-LiIO3 must be incorrect {subsequently