Phase transitions in In2Se3 as studied by electron microscopy and electron diffraction

Abstract

Indium selenide undergoes several reversible inter‐ and intrapolytypic phase transitions, above and below room temperature. A number of superstructures of the hexagonal (or rhombohedral) room temperature phase have been discovered by means of electron diffraction. The transition at 200 °C which corresponds to the α → β transformation is accompanied by intense non‐radial diffuse scattering, which is attributed to anisotropic transverse acoustic phonons. On cooling, a one‐dimensional deformation modulated structure is formed, which is interpreted as the frozen‐in configuration of the predominant vibration mode, which becomes soft below the transition temperature in the range 60 to 200 °C. This transition shows a large hysteresis, which is also found in thermal expansion. A new low temperature phase, which is presumably orthorhombic, is discovered on cooling below −125 °C. The structure of this phase can alternatively be described as being the result of pairing of indium ions or as the frozen‐in configuration of a longitudinal mode. Both phases exhibit a domain structure, which in the case of the α‐phase can be revealed by lattice resolution. Several high temperature superstructures are observed by means of electron diffraction. A direct relationship with the β‐phase is established and in a number of cases the superperiods are directly imaged.

Revised and new crystal data for indium selenides

“…This c value is exactly 1.5 times larger than ours. Van Tendeloo & Amelinckx, 1975;Popovi6, ~elustka & Bidjin, 1971;Popovi6, (~elustka, Ru~i6-Toro~ & Broz, 1977; the present work):…”

“…~' is the low-temperature orthorhombic phase which can be described as a slight deformation of the ~ hexagonal matrix lattice with approximately (Van Landuyt, Van Tendeloo & Amelinckx, 1975) …”

“…By electron diffraction and electron microscopy and in situ heating (by applying short, intense heating pulses with the electron beam) and cooling experiments, Van Landuyt, Van Tendeloo & Amelinckx (1975) observed that, during cooling, a one-dimensional deformation-modulated superstructure of fl(designated as if) was formed, in the range 473 to --~ 330 K. After fast cooling from higher temperatures (,-,970 K), they also observed a superstructure of~/(y'). In our X-ray diffraction work, performed with slow heating and slow cooling of the samples, we have not observed these phenomena.…”

“…Data Semiletov (1960Semiletov ( , 1961, Slavnova (1963), Slavnova & Eliseev (1963) and Slavnova, Luzhnaya & Medvedeva (1963), who regarded this phase as the first high-temperature phase of In2Se3 (Van Landuyt, Van Tendeloo & Amelinckx, 1975;Popovi6, t~elustka, Ru,Ei6-Toro~ & Broz, 1977). By electron diffraction, Semiletov (1961 a, b, c) obtained the unit-cell parameters a = 7.11, c = 19.30 A and suggested that the space group was P65.…”

Thermal stability and oxidation of layer-structured rhombohedral In3Se4 nanostructures

“…27 Many investigations have been carried out to understand the thermal stability and oxidation behaviour of various bulk indium selenides. 15,16,20,21,[29][30][31][32][33][34] In contrast, however, there are very limited investigations on the thermal stability and oxidation of indium selenide nanostructures. For example, j-In 2 Se 3 nanowires were revealed to be stable up to 500 C by in-situ synchrotron X-ray diffraction (XRD).…”