AN X-RAY STUDY OF THE MIXED-LAYERED COMPOUNDS OF (GETE)(N)(SB2TE3)(M)HOMOLOGOUS SERIES

Single crystals of the Ge2Sb2Te5 (phase D), GeSb2Te4 (phase B) and GeS b4Te7 (phase C) ternary mixed-layered compounds have been investigated by X-ray diffraction. A dependence of the (c/N) average distance betw een two adjacent atomic layers (N is the number of layers per unit cel l) on the cation-to-anion ratio for the ternary phases and the GrTe an d Sb2Te3 binary compounds has been analyzed. It is found that the depe ndence is linear. Based on the dependence, the c lattice parameters we re also calculated for other members of the (GeTe)(n) (Sb2Te3)(m) homo logous series in the quasi-binary GeTe-Sb2Te3 system for which experim ental data were not reported, The GeSb2Te4 (B) crystal structure was d etermined using an automatic diffractometer 'Syntex P (1) over bar'. T he results obtained indicate that Gr and Sb atoms are statistically di stributed in octahedral interstices to form mixed-cation layers. The G e3Sb2Te6 (A) compound with 33-layer structure (c=6.2234(5) nm) and Ge4 Sb2Te7 (F) one with 39-layer structure (c=7.279(1) nm) have been found in the GeTe-Sb2Te3 system by X-ray diffraction. The Ge4Sb2Te7 compoun d is present as a miner admixture to the A phase. (C) 1998 Elsevier Sc ience S.A.