Low-temperature thermoelectric properties of alpha-Zn_4Sb_3 bulk crystals prepared by a gradient freeze method and a spark plasma sintering method

摘要

The low temperature thermoelectric properties of Zn_4Sb_3 samples prepared by the gradient freeze (GF) method and sintering have been characterized. With decreasing temperature a dramatic rise in the thermal expansion is observed associated with the structural transition from beta- to alpha-phase; DELTA l/l-2.8 S 10 ~(-4) at T_s~GF-257.4 K for GF and DELTA l/l-1.6 S 10~(-4) at T_s~S=236.5 K for sintered samples. Enhancement is observed in electrical conductivity and p-type thermopower at T_s~GF and T_s~S while a reduction is observed in the magnetic susceptibility. The GF sample exhibits higher thermoelectric performance than the sintered sample. The power factor of the alpha-phase Zn_4Sb_3 GF sample is twice as large as that of the beta-phase; it exceeds 20 mu W/cm centre dot K~2 between 120 and 240 K, indicating that the alpha-phase Zn_4Sb_3 is one of the prime candidates for thermoelectric materials for cryogenic use.