Effect of TeI4 content on the thermoelectric properties of n-type Bi–Te–Se crystals prepared by zone melting

n-Type (Bi2Te3)0.93(Bi2Se3)0.07 thermoelectric materials doped with various content of TeI4 (0, 0.05, 0.10, 0.13, and 0.15 wt.%) have been fabricated through the zone melting method. Electrical conductivity (σ), Seebeck coefficient (α) and thermal conductivity (κ) were measured along the crystal growth direction in the temperature range of 300–500 K. The influence of the variations of TeI4 content on thermoelectric properties was studied. The undoped (Bi2Te3)0.93(Bi2Se3)0.07 exhibited p-type conduction and it translated to n-type when TeI4 was doped. The increase of TeI4 content increased the carrier concentration and thus resulted in an increase of σ and a decrease of |α|. The maximum figure of merit ZT (ZT = α2σT/κ) of the zone-melted crystals in the direction parallel to the growth direction showed a value of 0.90 for the sample containing 0.10 wt.% TeI4.