CRYSTAL-STRUCTURES AND DIELECTRIC-PROPERTIES OF COMPOUNDS IN THE KTIOPO4-TLTIOPO4 AND RBTIOPO4-TLTIOPO4 SYSTEMS

The crystal structures of (K0.82Tl0.18)TiOPO4, (Rb0.77Tl0.23)TiOPO4 an d TlTiOPO4, all of which are orthorhombic (sp. gr. Pna2(1)) and isostr uctural KTiOPO4, have been determined from single-crystal X-ray diffra ction data and refined to R factors between 0.020 and 0.042. It has be en shown that Tl was not distributed equally on the M(1) and M(2) site s in KTTP but almost equally in RTTP crystals. In the pure TTP compoun d, an anharmonic probability density function was used for Tl to get t he best agreement with the experimental data. The influence of partial replacement of an alkaline cation in KTP on the character of the ferr oelectric phase transition and electric conductivity of the solid solu tions has been studied.