Structural investigations in the system Ga0.5V2S4–Ga0.5V2Se4

Tuning of Metal−Metal Bonding and Magnetism via the Electron Count in GaxV4-yCryS8

“…7,8 One of the first known and most investigated ferromagnetic compounds with GaMo 4 S 8 structure is GaV 4 S 8 . [9][10][11][12][13][14] Apart from the V 4 cluster viewpoint, the structure may also be described as a cation-deficient spinel, where the ordered occupation of half of the tetrahedral sites reduces the space group symmetry from Fd3 hm to F4 h3m. A further important difference to the spinel structure is a shift of the vanadium atoms from the centers of the octahedra along [111] toward an empty tetrahedral site.…”

“…Compounds with the GaMo 4 S 8 structure represent a special class of Mott insulators, where electronic conduction takes place by hopping of electrons between widely separated tetrahedral M 4 clusters ( M = transition metal) instead between single atoms as in classical Mott insulators. These materials exhibit interesting structural, magnetic, and electronic properties, among them 4 d -ferromagnetism, , phase transitions, , heavy-fermion behavior, and superconductivity under high pressure. , One of the first known and most investigated ferromagnetic compounds with GaMo 4 S 8 structure is GaV 4 S 8 . − Apart from the V 4 cluster viewpoint, the structure may also be described as a cation-deficient spinel, where the ordered occupation of half of the tetrahedral sites reduces the space group symmetry from Fd 3̄ m to F 4̄3 m . A further important difference to the spinel structure is a shift of the vanadium atoms from the centers of the octahedra along [111] toward an empty tetrahedral site.…”

Unusual ferroelectricity induced by the Jahn-Teller effect: A case study on lacunar spinel compounds

“…Interestingly, a recent study indicates that the JT distortion in GaV4S8 leads to a ferroelectric polarization (~0.6 μC•cm -2 ) along the [111] direction [18,19]. GaV4S8 belongs to the family of lacunar spinels AM4Q8 compounds [20][21][22][23] (A = Ga and Ge; M = V, Mo, Nb and Ta; X = S and Se), which attract enormous research attention since they exhibit abundant physical phenomena, such as high pressure induced superconducting phase transition [24] and correlation-driven insulator-to-metal transition [25,26]. At room temperature, GaV4S8 takes the high symmetry lacunar spinel structure with the Td symmetry (i.e., non-centrosymmetric and non-polar).…”

Atomic order in the spinel structure – a group-theoretical analysis

“…A special case of an ordered spinel structure is the structure of the Chevrel phases. formula describes the structures of such substances as Ga 1.33 Cr 4 S 8 (Besnard et al, 2003) and Ga 0.5 V 2 S 2 Se 2 (Haeuseler et al, 2001). If there are no A 4a and A 4c atoms at all, or only some of these atoms are absent, various types of Chevrel phases can be obtained (Talanov, 2005;Besnard et al, 2003).…”