Characterization and Decomposition of the Natural van der Waals SnSb₂Te₄ under Compression

Abstract

High pressure X-ray diffraction, Raman scattering and electrical measurements, together with theoretical calculations, which include the analysis of the topological electron density and electronic localization function, evidence the presence of an isostructural phase transition around 2 GPa, a Fermi resonance around 3.5 GPa and a pressure-induced decomposition of SnSb2Te4 into the high-pressure phases of its parent binary compounds (-Sb2Te3 and SnTe) above 7 GPa. The internal polyhedral compressibility, the behavior of the Raman-active modes, the electrical behavior and the nature of its different bonds under compression have been discussed and compared with their parent binary compounds and with related ternary materials. In this context, the Raman spectrum of SnSb2Te4 exhibits vibrational modes that are associated but forbidden in rocksalt-type SnTe; thus showing a novel way to experimentally observe the forbidden vibrational modes of some compounds. Here, some of the bonds are identified with metavalent bonding, which were already observed in their parent binary compounds. The behavior of SnSb2Te4 is framed within the extended orbital radii map of BA2Te4 compounds, so our results pave the way to understand the pressure behavior and stability ranges of other "natural van der Waals" compounds with similar stoichiometry.

Anomalous Raman modes in tellurides

“…iii) The FWHM of the first ARM is always larger than that of the second one as in trigonal Te and the FWHM of the two ARMs in Te precipitates is always larger than in pure Te as expected for layers of nanometric size. iv) The two strongest ARMs measured in some tellurides, like ZnTe, 7 CdTe, 7 α-As2Te3, 23 and SnSb2Te4, 40 show negative pressure coefficients as those reported for bulk trigonal Te. [65][66][67] Moreover, the first anomalous Raman mode shows a larger negative pressure coefficient than the second one, as in trigonal Te.…”

“…[65][66][67] Moreover, the first anomalous Raman mode shows a larger negative pressure coefficient than the second one, as in trigonal Te. 7,23,40 The negative pressure coefficients shown by the ARMs are clear fingerprints of the Te nature of the ARMs in tellurides. Therefore, all the above mentioned features clearly indicate that the ARMs in tellurides are related to the formation of nanocrystalline trigonal Te either in form of small grains or layers.…”

“…The most striking point is that most of the bands observed in the ARS of GaTe and GaGeTe, especially the two strongest ones, have been observed in a number of 2D and bulk Te-based chalcogenides with different laser wavelenghts (typically with green and red lasers), irrespective of their different compositions and crystalline structures. They have been observed in ZnTe, 7,8 CdTe, [9][10][11][12][13][14] GaTe, [15][16][17][18][19][20][21][22] As2Te3, 23 Sb2Te3, 24,25 Bi2Te3, 26,27 GeTe, 28,29 SnTe and PbTe, 30,31 GeTe2, [32][33][34][35] TiTe2, [36][37][38][39] GaGeTe, 6 SnSb2Te4, 40 and crystalline Ge2Sb2Te5, 41 to name a few. A search among different tellurides shows that in most cases the first and more intense ARM is observed between 119 and 130 cm -1 , while the second ARM is usually observed between 139 and 145 cm -1 .…”

“…grains or layers of pure trigonal Te segregated from the original sample. [7][8][9]11,14,23,30,40 In order to substantiate this hypothesis, we have compared the ARS in Figure 1 with the unpolarized RS (Figure 2) and polarized RS of crystalline trigonal Te for different polarizations (see Figure S3 in the SI). As regards our unpolarized and polarized RS of crystalline Te, they are similar to those reported in the literature 9,47,[53][54][55] and show three main bands around 91, 120 and 140 cm -1 corresponding to the three first-order Raman modes E 1 (TO), A1 and E 2 (TO) modes of trigonal Te.…”

High-Pressure Spectroscopy Study of Zn(IO3)2 Using Far-Infrared Synchrotron Radiation

“…The pressure coefficients in the low-pressure phase are comparable to pressure coefficients in Fe(IO 3 ) 3 [13], LiIO 3 [28], and KIO 3 [29] in the same frequency region, indicating that Zn(IO 3 ) 2 is extremely compressible, similar to these other iodates. Additionally, the pressure coefficients for the different HP phases are of the same order of magnitude as in the low-pressure phase, suggesting that the changes in the coordination polyhedra are not drastic and that the transition is probably related to gradual changes in cation coordination number [30]. Table 2.…”