ELECTRICAL-PROPERTIES OF GA AND ZNS DOPED ZNO PREPARED BY MECHANICAL ALLOYING

A series of n-type ZnO alloys doped with Ga and ZnS were prepared by m echanical alloying. Densities of 95% Co 98% of theoretical density wer e achieved by hot pressing the milled powders at 1000 and 1200 degrees C, respectively. The electrical resistivity and Seebeck coefficient o f alloys containing 0.25-3.0 at, % Ga were characterized between 22 an d 1000 degrees C, The magnitude of the resistivity and Seebeck coeffic ient at 22 degrees C ranged from 0.2 m Omega cm and -25 mu V/degrees C for the most heavily doped specimen to 1.1 m Omega cm and -70 mu V/de grees C for the lightly doped material. The alloys exhibit a positive temperature coefficient of resistivity and Seebeck coefficient with a nearly constant slope over the temperature range studied. Thermal diff usivity measurements on a specimen containing 1.0 at. % Ga were perfor med over the same temperature range. The thermal conductivity appears to follow a T-1 dependence, decreasing from 180 mW/cm degrees C at 22 degrees C to 82 mW/cm degrees C at 1000 degrees C, An estimate of the maximum dimensionless thermoelectric figure of merit, ZT, in this syst em at 1000 degrees C gives a value of 0.26, a factor of three to four less than current state-of-the-art materials such as Si-Ge, A signific ant reduction in thermal conductivity would be required to make these alloys competitive with existing thermoelectric power generation mater ials. (C) 1998 American Institute of Physics. [S0021-8979(98)03011-4].