Two anomalous broad bands are usually found in the Raman spectrum of bulk and 2D Te-based chalcogenides, which include binary compounds, like ZnTe, CdTe, HgTe, GaTe, GeTe, SnTe, PbTe, GeTe₂, As₂Te₃, Sb₂Te₃, Bi₂Te₃, NiTe₂, IrTe₂, and TiTe₂, as well as ternary compounds, like GaGeTe, SnSb₂Te₄, SnBi₂Te₄, and GeSb₂Te₅. Many different explanations have been proposed in the literature for the origin of the anomalous broad bands in tellurides, usually located between 119 and 145 cm⁻¹. They have been attributed to the intrinsic Raman modes of the sample, to oxidation of the sample, to the folding of Brillouin-edge modes onto the zone center, to the existence of a double resonance, like that of graphene, or to the formation of Te precipitates. In this paper, we provide arguments to demonstrate that such bands correspond to clusters or precipitates of trigonal Te in the form of nanosize or microsize grains or layers that are segregated either inside or at the surface of the samples. Several mechanisms for Te segregation are discussed and sample heating caused by excessive laser power during Raman scattering measurements is emphasized. Besides, we show that anomalous Raman modes related to Se precipitates also occur in selenides, thus providing a general vision for better characterization of selenides and tellurides by means of Raman scattering measurements and for a better understanding of chalcogenides in general.

Transition metal nitrides, particularly those of 5d metals, are known for their outstanding properties, often relevant for industrial applications. Among these metal elements, tungsten is especially attractive given its low cost. In this high‐pressure investigation of the W–N system, two novel ultra‐incompressible tungsten nitride superconductors, namely W₂N₃ and W₃N₅, are successfully synthesized at 35 and 56 GPa, respectively, through a direct reaction between N₂ and W in laser‐heated diamond anvil cells. Their crystal structure is determined using synchrotron single‐crystal X‐ray diffraction. While the W₂N₃ solid's sole constituting nitrogen species are N^3‐ units, W₃N₅ features both discrete N^3‐ as well as N₂^4‐ pernitride anions. The bulk modulus of W₂N₃ and W₃N₅ is experimentally determined to be 380(3) and 406(7) GPa, and their ultra‐incompressible behavior is rationalized by their constituting WN₇ polyhedra and their linkages. Importantly, both W₂N₃ and W₃N₅ are recoverable to ambient conditions and stable in air. Density functional theory calculations reveal W₂N₃ and W₃N₅ to have a Vickers hardness of 30 and 34 GPa, and superconducting transition temperatures at ambient pressure (50 GPa) of 11.6 K (9.8 K) and 9.4 K (7.2 K), respectively. Additionally, transport measurements performed at 50 GPa on W₂N₃ corroborate with the calculations.

In recent years, there has been a fervent search for room-temperature superconductivity within the binary hydrides. However, as the number of untested compounds dwindled, it became natural to begin searching within the ternary hydrides. This led to the controversial discovery of room-temperature superconductivity at only 1 GPa in nitrogen-doped lutetium hydride [Dasenbrock-Gammon et al., Nature (London) 615, 244 (2023)] and consequently provided much impetus for the synthesis of nitrogen-based ternary hydrides. Here, we report the synthesis of stable trigonal ${\mathrm{LuH}}_3$ by hydrogenating pure lutetium which was subsequently pressurized to $\sim 2$ GPa in a dilute-${\mathrm{N}}_2$/He-rich pressure medium. Raman spectroscopy and x-ray diffraction were used to characterize the structures throughout. After depressurizing, energy-dispersive and wavelength-dispersive x-ray spectroscopies characterized the final compound. Though our compound under pressure exhibits similar structural behavior to the Dasenbrock-Gammon et al. sample, we do not observe any nitrogen within the structure of the recovered sample at ambient pressure. We observe two cubic structures under pressure that simultaneously explain the x-ray diffraction and Raman spectra observed: The first corresponds well to $Fm\overline{3}m {\mathrm{LuH}}_{2+x}$, while the latter is an $Ia\overline{3}$-type structure.

We report a joint experimental and theoretical study of the low-pressure phase of α′-Ga ₂ S ₃ under compression. The structural, vibrational, topological and electronic properties have been evaluated to reveal the relevance of the vacancy channels and the single and double lone electron pairs in the pressure behaviour of this system.