Lacunar spinels, GaM4X8 (M = V, Nb, Mo, Ta, W; X = S, Se, Te), constitute a rare class of compounds with multiferroic properties. Recently, one member of this family, GaV4S8, received global attention due to the Néel-type skyrmions discovered in this material. Previous investigations strongly indicate the important role of the structure behind the multiferroicity, for example, the strong impact of ferroelectric transition on the exchange interactions at ∼40 K. Inspired by the delicate entanglement of lattice, spin, and charge degrees of freedom, in the present work, we aimed to use pressure to alter the structure and thus change the material’s properties to establish the inter-relation between the structural, optical, and electrical properties for a better understanding of this skyrmion host material. Upon this objective, in situ high-pressure measurements of single crystal/powder X-ray diffraction, electrical conductivity, and Raman spectroscopy were carried out by using a diamond anvil cell. These studies revealed the pressure-induced structural transformation from cubic to orthorhombic, along with a transition from semiconductor to metallic state in GaV4S8. The phase changes coincide with the variation in the optical property in this material explored by Raman spectra. We also determined the bulk modulus of the two phases of GaV4S8 by fitting the data set of unit cell volumes against pressure with the second-order birth-Murnaghan equation of state, and explained the mechanisms of phase transitions by means of the Jahn–Teller effect and the anisotropic changes in bonding lengths during compression.
Yuejian Wang, Saqib Rahman, Elaine Sun, Christopher Knill, Dongzhou Zhang, Lin Wang, Vladimir Tsurkan, and István Kézsmárki The Journal of Physical Chemistry C Article ASAP DOI: 10.1021/acs.jpcc.0c10527 abstract
Visualization of the cubic phase of GaV4S8, including two polyhedrals, VS6 and GaS4, in which green, red, and yellow balls represent the atoms of Ga, V, and S, respectively.