Lattice Dynamics Study of HgGa₂Se₄ at High Pressures

Abstract

We report on Raman scattering measurements in mercury digallium selenide (HgGa 2 Se 4) up to 25 GPa. We also performed, for the low-pressure defect-chalcopyrite structure, lattice-dynamics ab initio calculations at high pressures which agree with experiments. Measurements evidence that the semiconductor HgGa 2 Se 4 exhibits a pressure-induced phase transition above 19 GPa to a previously undetected structure. This transition is followed by a transformation to a Raman-inactive phase above 23.4 GPa. On downstroke from 25 GPa till 2.5 GPa a broad Raman spectrum was observed, which has been attributed to a fourth phase, and whose pressure dependence was followed during a second upstroke. Candidate structures for the three phases detected under compression are proposed. Finally, we also report and discuss the decomposition of the sample by laser heating at pressures close to 19 GPa. As possible products of decomposition we have identified at least the formation of trigonal selenium nanoclusters and cinnabar-type HgSe.

Structural, Vibrational, and Electronic Study of α-As2Te3 under Compression

“…Furthermore, segregation of Se nanoclusters caused by laser-induced damage during HP-RS measurements has also been observed in several chalcogenides 97,98 . In our experiments, it is highly difficult to avoid such damage when performing experimental RS measurements, at least with the red He:Ne laser.…”

X-ray diffraction study on pressure-induced phase transformations and the equation of state of ZnGa2Te4

“…26 Therefore, on the basis of the reported results we can only state that decompression of ZnGa 2 Te 4 from the DR structure results in a metastable phase at ambient pressure whose structure is related to the DZ structure previously proposed for related compounds. 8,10,11,13,25 The crystal structure cannot be fully solved from HP powder XRD experiments and the accurate solution of the crystal structure of the recovered sample may probably need the performance of HP single-crystal experiments. 27 …”

Structural and Vibrational Properties of CdAl2S4 under High Pressure: Experimental and Theoretical Approach

“…It must be mentioned that the discrepancies in the assignment of the symmetry of highfrequency modes in OVCs are very common because of the observation of quasi-modes instead of pure modes in uniaxial crystals. 17,33,[53][54][55] For CdAl 2 S 4 , the high quality of our Raman spectra and the similarity of the experimental and theoretical pressure dependence of the modes allows a rather clear assignment of the mode symmetry on the light of our theoretical calculations and previous Raman studies. A comparison with previous studies, in particular, with the results of Burlakov et al 11 , show that our main difference is that in our case we were able to distinguish experimentally between the B 4 and A 3 modes but not between E 5 and B 5 LO modes.…”