SYNTHESIS AND CRYSTAL-STRUCTURE OF THE PSEUDO-HOLLANDITE RB0.62CR5TE8AND ANALYSIS OF THE ELECTRONIC BAND STRUCTURES OF THE RBXCR5TE8 PHASES

Pseudo-hollandite Rb0.62Cr5Te8 was prepared from Rb2Te and elemental C r and Te at 850 degrees C. Its crystal structure mas refined from sing le crystal X-ray diffraction data, Rb0.62Cr5Te8 crystallizes in the mo noclinic system, C2/m space group, with a = 20.367(8), b = 3.902(2), c = 9.605(3) Angstrom, and beta = 104.386(9)degrees, V = 739.3(8) Angst rom(3), and Z = 2. The structure determination was carried out on 1404 reflections (I>3 sigma(I)) and refinement of 47 parameters yielded th e reliability factors R = 2.57% and R-w = 2.79%. The structure of pseu do-hollandite Rb0.62Cr5Te8 is analogous to the TlCr5Te8 structure, whi ch differs from that of hollandite Rb0.73Cr5Te8. An analysis of the el ectronic band structures of pseudo-hollandite Rb0.62Cr5Te8 and holland ite Rb0.73Cr5Te8, calculated by means of the self-consistent ab initio tight-binding linear-muffin-tin-orbital method in the atomic sphere a pproximation, is presented, Spin-polarized calculations indicate that the RbxCr5Te8 phases are not half-metallic ferromagnets, The rubidium nonstoichiometry and the RbxCr5Te8 relative stability are also discuss ed. (C) 1997 Academic Press.