Abstract
Two polycrystalline V4-cluster compounds of GaV4S8 were prepared at different annealing temperatures (GaV4S8-1 sintered at 800 ∘C and GaV4S8-2 sintered at 500 ∘C). Their temperature-dependent resistivity and structural phase transformation temperature (45 K for GaV4S8-1 and 43 K for GaV4S8-2) are found to be very sensitive to the annealing condition. Above 320 K, activation energy e3 is calculated to be ∼0.23 eV which decreases to ∼0.18 eV around 300 K in GaV4S8-1 and GaV4S8-2 on cooling. According to percolation theory, the gradual decrease in e3 below 300 K is expected due to the increase in separation between V4-clusters are significantly different in GaV4S8-1 and GaV4S8-2. This statement is strongly supported by the calculated bandwidth Γ per cluster in GaV4S8 (∼0.342 eV in GaV4S8-1 and ∼0.374 eV in GaV4S8-2). A negative magnetoresistance (MR) is also found around 43 K in GaV4S8-2 at 6.0 T magnetic field associated with structural transition.
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