화학공학소재연구정보센터
Materials Research Bulletin, Vol.44, No.6, 1352-1359, 2009
Effect of the cooling rate on the thermoelectric properties of p-type (Bi0.25Sb0.75)(2)Te-3 and n-type Bi-2(Te0.94Se0.06)(3) after melting in the bismuth-telluride system
The p-type (Bi0.25Sb0.75)(2)Te-3 and n-type Bi-2(Te0.94Se0.06)(3) ingots were prepared by cooling at various cooling rates C after melting so that they have an intermediate state between the polycrystalline and Bridgman ingots which lowers their thermal conductivity kappa, where C was changed from 0.10 to 2375 K/min in an evacuated glass tube. When the ingots were cooled at C = 0.50 K/min under the uniaxial temperature gradient of 5 K/cm, it was observed that the c axis of some grains points to the freezing direction. The electrical resistivity rho, Seebeck coefficient alpha and K of ingots were measured at 298 K along the freezing direction, so that rho and kappa at C = 0.50 K/min were lower by 20-30% and 9% than those of the corresponding Bridgman ingots. The thermoelectric figure of merits ZT(=alpha T-2/rho kappa) estimated for the p- and n-type ingots then reached high values of 1.27 and 1.25 at 298 K, respectively. (C) 2008 Elsevier Ltd. All rights reserved.