Diatomic Ferroelectrics

Anharmonicity and atomic distribution of SnTe and PbTe thermoelectrics

“…While Pawley reported the temperature dependence of the TO mode from 6 to 300 K, their sample remained cubic at all temperatures, probably as a result of a high hole concentration. 29 The partial phonon densities of states (DOS) of Sn and Te were previously measured in rock-salt SnTe at 60 K using nuclear-resonant inelastic x-ray scattering, and it was found that the phonons are softer than similar materials in rhombohedral phase. 59 In addition, lattice dynamics study of SnTe using Mössbauer spectroscopy suggested the existence of low-temperature anharmonicity.…”

“…29 However, T C in SnTe is strongly dependent on the introduction of extrinsic carriers, which arises from a slight off-stoichiometry. 24 Samples of SnTe synthesized by solid-state reaction are commonly found to exhibit a small Sn-deficiency, owing to slightly incongruent melting of the rock-salt phase.…”

“…The strong anharmonicity causes this zone-center TO phonon to stiffen markedly as T increases in the cubic paraelectric phase, in a clear departure from a quasiharmonic lattice, 10,[23][24][25][26][27] but in general agreement with the soft-mode picture of the ferroelectric transition. 28,29 Recently, an asymmetry of peaks was reported in the pair-distribution-function (PDF) or radial distribution function (RDF) of PbTe, PbS, and SnTe, which was interpreted in terms of atomic off-centerings increasing with temperature. 1,2,11,30 However, it is important to note that these x-ray PDF/RDF measurements did not filter out the phonon contribution to the scattered intensity, or thermal diffusive scattering (TDS).…”

“…24 The ferroelectric distortion matches the displacement pattern (eigenvector) of the transverse-optic (TO) phonon at the zone center (Γ), and the transition has early been interpreted in terms of the soft-mode theory of ferroelectricity initially proposed by Cochran. 28,29 In this study, the phonon DOS of SnTe and PbTe were measured at a series of temperatures with INS. In addition, the atomic mean square displacements were measured with neutron diffraction, on both single-crystalline and powder samples.…”

Ferroelectric switching in epitaxial GeTe films

“…© 2014 Author (s Germanium telluride GeTe has long been known as the simplest ferroelectric material with just two atoms in the primitive cell. 1 The origin of the rhombohedral distortion and its effect on the properties of GeTe have been extensively studied by various groups. [2][3][4] Recently, there has been increased interest in GeTe, primarily driven by industrial application of GeTe-based compounds, such as quasibinary GeTe-Sb 2 Te 3 , in phase-change memory (PCM) alloys and also by the proposal that GeTe may exhibit a giant Rashba effect in the bulk phase.…”