High-pressure optical and vibrational properties of CdGa2Se4: Order-disorder processes in adamantine compounds

Abstract

High pressure structural stability of BaLiF3 J. Appl. Phys. 110, 123505 (2011) Pressure effects on the transitions between disordered phases in supercooled liquid silicon J. Chem. Phys. 135, 204508 (2011) Microfabrication of controlled-geometry samples for the laser-heated diamond-anvil cell using focused ion beam technology Rev. Sci. Instrum. 82, 115106 (2011) First-principles investigations of elastic stability and electronic structure of cubic platinum carbide under pressure J. Appl. Phys. 110, 103507 (2011) Additional information on J. Appl. Phys. High-pressure optical absorption and Raman scattering measurements have been performed in defect chalcopyrite (DC) CdGa 2 Se 4 up to 22 GPa during two pressure cycles to investigate the pressure-induced order-disorder phase transitions taking place in this ordered-vacancy compound. Our measurements reveal that on decreasing pressure from 22 GPa, the sample does not revert to the initial phase but likely to a disordered zinc blende (DZ) structure the direct bandgap and Raman-active modes of which have been measured during a second upstroke. Our measurements have been complemented with electronic structure and lattice dynamical ab initio calculations. Lattice dynamical calculations have helped us to discuss and assign the symmetries of the Raman modes of the DC phase. Additionally, our electronic band structure calculations have helped us in discussing the order-disorder effects taking place above 6-8 GPa during the first upstroke.

Vibrational study of HgGa2S4 under high pressure

“…In order to obtain more information on the pressureinduced order-disorder processes, we have analyzed (not shown) the pressure dependences of the Raman mode intensities and linewidths as previously done in other highpressure studies of OVCs. 13,14,23 No clear information on the order-disorder processes can be obtained from the pressure dependence of these data; however, it is interesting to note that there is a small increase of the intensity of the A 3 mode normalized to that of the A 1 mode with pressure. This fact is similar to that previously observed in CdAl 2 S 4 13 and in CdGa 2 Se 4 , 23 where this behaviour related to the transformation from the DC to the DS phase since it is coincident with the simultaneous decrease of the intensity of the A 2 mode (the mode that disappears at the DC-to-DS transition).…”

“…20 [23][24][25] The reason is that calculations with structures with fractional atomic occupations, like most DS and DZ phases with ab initio codes are of great difficulty (e.g., one can use a supercell to simulate disorder but calculations become very time consuming).…”

“…Details of the lattice dynamics calculations can be consulted in Ref. 23. In order to include the transversal-longitudinal optic (TO-LO) splitting in our study, we need to add the effect of the electric field that it is not included in the previous direct force method.…”

High-pressure Raman scattering study of defect chalcopyrite and defect stannite ZnGa2Se4

“…The properties of this ordered DS phase are detailed in Refs. 15,33,34, and 41 and the justification about why calculations for the DS phase were performed for this ordered DS phase was already discussed in Ref. 28.…”

“…However, 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][30][31][32][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. 34 In order to shed light on the pressure dependence of the Raman modes in DC-and DS-ZnGa 2 Se 4 and study how pressure affects order-disorder transitions in both phases, we report here HP Raman scattering measurements at room temperature (RT) for both DC and DS structures.…”