Abstract
High-pressure Raman scattering measurements have been carried out in ZnGa2Se4 for both tetragonal defect chalcopyrite and defect stannite structures. Experimental results have been compared with theoretical lattice dynamics ab initio calculations and confirm that both phases exhibit different Raman-active phonons with slightly different pressure dependence. A pressure-induced phase transition to a Raman-inactive phase occurs for both phases; however, the sample with defect chalcopyrite structure requires slightly higher pressures than the sample with defect stannite structure to fully transform into the Raman-inactive phase. On downstroke, the Raman-inactive phase transforms into a phase that could be attributed to a disordered zincblende structure for both original phases; however, the sample with original defect chalcopyrite structure compressed just above 20 GPa, where the transformation to the Raman-inactive phase is not completed, returns on downstroke mainly to its original structure but shows a new peak that does not correspond to the defect chalcopyrite phase. The pressure dependence of the Raman spectra with this new peak and those of the disordered zincblende phase is also reported and discussed.
Highlights
Zinc digallium selenide (ZnGa2Se4) is a tetrahedrally coordinated semiconductor of the adamantine-type AIIB2IIIX4VI family of ordered-vacancy compounds (OVCs)
The Raman-inactive phase transforms into a phase that could be attributed to a disordered zincblende structure for both original phases; the sample with original defect chalcopyrite structure compressed just above 20 GPa, where the transformation to the Raman-inactive phase is not completed, returns on downstroke mainly to its original structure but shows a new peak that does not correspond to the defect chalcopyrite phase
Total-energy calculations were performed within the framework of the density functional theory (DFT) and the pseudopotential method using the Vienna ab initio simulation package (VASP) of which a detailed account can be found in Ref. 38 and references therein
Summary
Zinc digallium selenide (ZnGa2Se4) is a tetrahedrally coordinated semiconductor of the adamantine-type AIIB2IIIX4VI family of ordered-vacancy compounds (OVCs). Report that ZnGa2Se4 crystallizes in the partially disordered tetragonal defect stannite (DS) structure, known as defect famatinite, with SG I–42 m and higher symmetry than the DC phase8–12,21,26 [see Fig. 1(b)] In this compound, Zn and Ga atoms have similar x-ray scattering factors and both SG I–4 and I–42 m have the same crystallographic extinctions. The presence of two stages of disorder in OVCs at HP has been recently questioned on the basis of both theoretical and experimental studies.29–33 To this respect, in a recent work, we studied the different possible intermediate phases of partial disorder between the initial DC or DS phases and the DZ structure and discuss the possibility to find them by means of in situ vibrational spectroscopy..
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