Single Structure Widely Distributed in a GeTe−Sb₂Te₃ Pseudobinary System:  A Rock Salt Structure is Retained by Intrinsically Containing an Enormous Number of Vacancies within its Crystal

Abstract

GeTe(1-x)-Sb2Te3(x) sputtered amorphous film was crystallized into a simple NaCl-type structure through instantaneous laser irradiation over a wide composition range from x = 0 to at least 2/3. When the ratio of Sb2Te3 increases, a vacancy is generated at every Na site for two Sb atoms. The fraction of vacancies, v(x), changes according to x/(1 + 2x), and the cubic root unit cell volume varies with a strong correlation to v(x). Through these created vacancies, valence electrons provided by adjacent Ge/Sb and Te atoms remain constant regardless of the composition, ensuring that these electrons occupy predominantly the bonding molecular orbitals. This results in crystal chemical stability, with the closed shell p-p bondings in the valence electrons arranging the crystal's atomic configuration into an NaCl-type structure.