Reinvestigation and structural approach of the Ba-Pt-O system for 4/3 < Y=Ba/Pt < 5/2

摘要

A reinvestigation of the Ba-rich region of the Ba-Pt-O system has been undertaken. The existence of a solid solution, already mentioned, has been confirmed, and its true formulation has been determined: Ba-12[BaxPt3-x]Pt6O27 with 0 less than or equal to x less than or equal to 3. The structure of these phases can be schematically considered as being built up from the periodic stacking along the c direction of one close-packing [Ba3O9] layer, similar to those of the hexagonal perovskite, and three [Ba(3)A'O-6] layers, with A' = Ba, Pt. The stacking of these mixed layers is of hexagonal type, and then columns parallel to c are formed. They consist of octahedra and trigonal prisms, sharing faces, which are occupied by A' cations. For 0 less than or equal to x less than or equal to 1, the structure appears to be incommensurate and should be described as a composite crystal based on two subsystems: [Ba] and [(Ba, Pt)O-3]. For x > 1, the X-ray diffraction pattern can be explained using a three-dimensional cell, but the structure refinement attempts as well as the electron diffraction patterns seem to indicate these phases are commensurate modulated structufes. (C) 1998 Academic Press. [References: 16]