Thermoelectric properties and transport mechanism of Cu0.5In0.5Cr2Se4 and its Zn-doped samples

The thermoelectric properties and transport mechanism of Cu0.5In0.5Cr2Se4 and its Zn-doped samples were studied. In the middle and low temperature range, the electrical resistivity of Cu0.5In0.5Cr2Se4 decreases and Seebeck coefficient increases with the increase of temperature, indicating the fixed range hopping behavior of Anderson's localization. Two abnormal declines emerge simultaneously in resistivity and Seebeck coefficient at high temperatures, indicating a band regulation by temperature. After slight Zn-doping, the carrier concentration decreases slightly and the carrier mobility increases obviously, realizing electron delocalization. Both of resistivity and Seebeck coefficient decrease with further increasing Zn doping content due to the enhanced carrier concentration, resulting in the improved power factor. The thermal conductivity is extremely low in the pristine Cu0.5In0.5Cr2Se4 and increases with increasing Zn-doping. Due to the significant enlargement of power factor and relatively weak increase of thermal conductivity, the ZT value is enhanced by Zn doping from 0.30 of the pristine sample to 0.40 for the sample with 3.5% Zn doping at 773 K. Moreover, a factor of about 60% improvement of the average ZT is reported on the Zn-doped Cu0.5In0.5Cr2Se4 sample, reaching 0.26 over the temperature range between 323 K and 773 K