Electrical transport properties of SnBi4Te7 and PbBi4Te7 with different deviations from stoichiometry

Polycrystalline samples of SnBi4Te7 and PbBi4Te7 with deviations from stoic hiometry in different sublattices were synthesized by melting and quenching followed by prolonged annealing and hot-pressing. At room temperature SnBi 4Te7 exhibits both n-type conductivity (Te deficiency and Sn or Bi excess) and p-type conductivity (Te excess and Sn or Bi deficiency) whereas only n- type conductivity samples were obtained for PbBi4Te7 regardless of the type of deviation from stoichiometry. Both compounds possess high carrier conce ntrations in the range 4 x 10(19)-4 x 10(20) cm(-3) and a relatively low ca rrier mobility of 35-70 cm(2) V-1 s(-1). The electrical resistivity and See beck coefficient have been measured over the temperature range 100-800 K on samples with different deviations from stoichiometry, The temperature depe ndence of the electrical transport properties of the compounds is typical o f heavily-doped semiconductors. The potential for thermoelectric applicatio ns using these compounds is discussed.