Low-temperature Crystal Structures and Magnetic Properties of the V₄-Cluster Compounds Ga_1-xGe_xV₄S₈

Abstract

Solid solutions Ga 1−x Ge x V 4 S 8 (x = 0− 1) were synthesized by solid-state reactions and characterized by temperature-dependent X-ray powder diffraction and static magnetic susceptibility measurements. The compounds crystallize in the cubic GaMo 4 S 8 -type structure (space group F43m), built up by heterocubane-like [V 4 S 4 ] (5−x)+ cubes and [Ga 1−x Ge x S 4 ] (5−x)− tetrahedra arranged in a NaCllike manner. The successive substitution of Ga 3+ by Ge 4+ increases the electron count in the molecular orbitals (MO's) of the V 4 -cluster gradually from seven to eight. We observe an almost linear increase of the magnetic moments, connected with a transition from ferromagnetic to antiferromagnetic ordering around x ≈ 0.5. Remarkably, low-temperature structural phase transitions as known from the ternary compounds were also detected in the solid solutions. The gallium-rich compounds (0 ≤ x < 0.5) undergo rhombohedral distortions like GaV 4 S 8 (space group R3m), whereas distortions to orthorhombic symmetry (space group Imm2) as known from GeV 4 S 8 occur in the germanium-rich part of the solid solutions (0.5 ≤ x ≤ 1).

Negative Colossal Magnetoresistance Driven by Carrier Type in the Ferromagnetic Mott Insulator GaV4S8

“…Powder and crystals of these compounds were synthesized as described in the Experimental Details section. It is worth noting that whereas the existence of a full solid solution 0 ≤ x ≤ 1 in Ga 1– x Ge x V 4 S 8 was already described, , the Ga 3+ /Zn 2+ substitution was much less studied. Therefore, we have first focused our study on the Ga 1– x Zn x V 4 S 8 solid solution.…”

Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo4Se8

“…This reduces the point symmetry of the B 4 tetrahedra from T d to C 2 v . Among lacunar spinels, only GeV 4 S 8 , GeV 4 Se 8 , and the Ge-rich members of Ga 1– x Ge x V 4 S 8 have been found to distort to Imm 2 instead of R 3 m . This can be understood as the HOMO degeneracy of the B 4 cluster splits differently through the Jahn–Teller transition, due to the additional electron per B 4 cluster.…”

Synthesis and Structural and Magnetic Properties of Polycrystalline GaMo4Se8

“…Figure 1 shows the valence molecular orbital diagrams of both V 4 and Mo 4 metal clusters, as well as the structure distortion from the cubic F 43m to the rhombohedral R3m space group. In the crystal structure, the V/Mo and S/Se atoms form a heterocubane arrangement (in red in Figure 1), while Ga-S/Se bonds group these atoms in a tetrahedral arrangement (in green in Figure 1) [6][7][8]. The rhombohedral angle α in the distorted phase is smaller than 60 • in the V lacunar spinels and larger than 60 • in the Mo lacunar spinels, which inverts the order of the a 1 and e orbitals resulting from the orbital splitting by the crystal field [6].…”