Raman scattering study of pressure-induced phase transitions in MIn2S4 spinels

Abstract

MIn2S4 (M = Mn, Cd, Mg) spinels were investigated by Raman scattering spectroscopy under hydrostatic pressure up to 20 GPa. These compounds were found to undergo a reversible phase transition to a Raman-inactive defect NaCl-type structure. Transition pressures of 7.2, 9.3, and 12 GPa were found for M = Mn, Cd, and Mg, respectively. From the analysis of the pressure behaviour of Raman-active modes, it was concluded that the phase transition from spinel to NaCl-type structure is direct in MnIn2S4 and CdIn2S4, while it occurs via an intermediate LiVO2-type NaCl superstructure in MgIn2S4. The observed differences in pressure and path of the pressure-induced phase transition between these indium sulphide spinels are discussed.

Structural and optical high‐pressure study of spinel‐type MnIn2S4

“…The inversion parameter at 3.9 GPa during downstroke is i = 0.12, that is, half of the value during upstroke. This result is consistent with the decrease of the inversion parameter in MnIn 2 S 4 under compression observed from Raman measurements under pressure [7], and suggests that with increasing pressure In is more compressible than Mn so they tend to their normal positions in the lattice. The unit cell volume as a function of pressure is well described by the Murnaghan equation of state [8] which yields the bulk modulus and its pressure derivative at ambient pressure: B 0 = 73(2) GPa and B′ = 2.8(6) for the spinel phase, and B 0 = 40(3) GPa and B′ = 5.1(5) for the high pressure LiTiO 2 -type phase.…”

“…At low pressures, the pre-edge feature suggests the absence of inversion symmetry at the Mn site, as it is the case in tetrahedral coordinated Mn. The absence of significant changes in the XAS spectra before the phase transition suggests that the predominant tetrahedral coordination for Mn is maintained up to the phase transition, in agreement with XRD and Raman results [7]. The lack of the pre-edge feature above 7 GPa is coherent with the octahedral coordination of Mn in the LiTiO 2 phase obtained in XRD measurements.…”

“…The ambient pressure pattern can be clearly attributed to the cubic spinel phase. A Rietveld refinement of the structure at 1 atm allows us to obtain a volume of 1233.5(5) Å 3 and an inversion parameter of i = 0.25 in agreement with previous Raman measurements under pressure [7]. The inversion parameter does not change appreciably with pressure.…”

“…Although it has not been possible to deduce the inversion parameter from EXAFS analysis, the rather high value of the pseudo DebyeWaller factor (~0.009 Å 2 ) reveal the presence of significant static disorder, which does not vary appreciably under high pressure, in agreement with XRD and Raman results [7]. On decreasing pressure the sample reverts to its original spinel phase.…”

Pressure‐induced structural phase transitions in materials and earth sciences

“…Spinel CdCr 2 Se 4 undergo a phase transition near 10 GPa to a phase with tetragonal symmetry [299], while spinels CdIn 2 S 4 , MgIn 2 S 4 and MnIn 2 S 4 undergo phase transitions to a double rocksalt phase of the LiTiO 2 type near 10 GPa [300][301][302]. On the contrary, a lot of interest is shown in ultrahard nitride spinels recently synthesized whose properties are being explored at high pressures [12,[303][304][305].…”