Abstract
This article opens a series of publications devoted to the preparation and stabilization of new high-temperature (HT) semiconductor phases A (III) – B (VI), which have a large number of vacancies and possess a number of unique properties. In this first work from the proposed series, the T-x-diagram of the Ga–S system was investigated in the composition range x = (30.0–60.7) mol% S, and then the structural identification of new HT phases was carried out. For the Ga–S system, four polymorphic (α-, α′-, β-, γ-) Ga2S3 phases of different symmetry were found and displayed on the phase diagram near the Ga2S3 composition (x ～ 60.0 mol% S). For the first time, it became possible to obtain in-situ a reliable direct proof for the existence of equilibrium in narrow temperature range for the re-opened cubic phase γ-Ga2+δS3 (x ≈ 59.0 mol% S), which was isolated at room temperature in a fairly pure form. We also confirmed the presence of another hexagonal β(α)-Ga2S3 modification, existing at much higher temperatures than the cubic γ-Ga2+δS3 phase. It was shown that the polymorphic α-Ga2S3 and α′-Ga2S3 phases mentioned in the literature form superstructures from the parent β-Ga2S3 phase. The observed structural variants for all four Ga2S3 polymorphic phases, containing up to 1/3 of vacancies in the Ga sub-lattices, are closely related to different methods of ordering Ga vacancies. The reliability of our studies follows from the combination of the methods used: differential thermal analysis (DTA), microstructural local analysis (TEM, HREM, SAED), powder X-ray diffractometry (XRD), including high-temperature synchrotron XRD.
NSTL
Elsevier