An X-ray study of the mixed-layered compounds of (GeTe) n (Sb 2Te 3) m homologous series

Abstract

Single crystals of the Ge 2Sb 2Te 5 (phase D), GeSb 2Te 4 (phase B) and GeSb 4Te 7 (phase C) ternary mixed-layered compounds have been investigated by X-ray diffraction. A dependence of the ( c/ N) average distance between two adjacent atomic layers ( N is the number of layers per unit cell) on the cation-to-anion ratio for the ternary phases and the GeTe and Sb 2Te 3 binary compounds has been analyzed. It is found that the dependence is linear. Based on the dependence, the c lattice parameters were also calculated for other members of the (GeTe) n (Sb 2Te 3) m homologous series in the quasi-binary GeTe–Sb 2Te 3 system for which experimental data were not reported. The GeSb 2Te 4 (B) crystal structure was determined using an automatic diffractometer `Syntex P1̄'. The results obtained indicate that Ge and Sb atoms are statistically distributed in octahedral interstices to form mixed-cation layers. The Ge 3Sb 2Te 6 (A) compound with 33-layer structure ( c=6.2234(5) nm) and Ge 4Sb 2Te 7 (F) one with 39-layer structure ( c=7.279(1) nm) have been found in the GeTe–Sb 2Te 3 system by X-ray diffraction. The Ge 4Sb 2Te 7 compound is present as a minor admixture to the A phase.