THERMOELECTRIC PROPERTIES OF P-TYPE LEAD-TELLURIDE DOPED WITH SILVER OR POTASSIUM

Single crystals of p-type PbTe were prepared by the Bridgman method, w here either Ag2Te or K was doped as the source material of silver or p otassium, respectively. Carrier concentration and Hall mobility were m easured from 77 to 300 K. The hole concentration was successfully cont rolled in the range from 2.0 x 10(24) to 9.0 x 10(24) m(-3) by doping 100 to 700 mol ppm Ag2Te, while the conduction type changed from p- to n-type in the region more than 1000 mol ppm Ag2Te. In the case of K-d oping, the carrier concentration was controlled in the region of 8.0 x 10(24) to 4.0 x 10(25) m(-3) with 1000 to 25000 mol ppm it. Figure of merits (Z) of p-PbTe at 300 K were 8.0 x 10(-4) K-1 at a hole concent ration of 1.34 x 10(25) m(-3) (2400 mol ppm K) and 1.38 x 10(-3) K-1 a t 2.34 x 10(24) m(-3) (200 mol ppm Ag2Te). Diffusion lengths of dopant elements of Ag, K and Sn for p-type and I for n-type PbTe were estima ted using the literature data. The result indicates that long distance diffusion occurs in a short period in the case of Ag and K. Therefore , the stable functionally graded materials (FGM) of PbTe might be prep ared by gradient I doping or Sn alloying, while those by Ag or K dopin g will be soon changed into non-FGM due to the rapid diffusion resulti ng in the decreased efficiency of thermoelectric energy conversion.