Solid Solutions Based on Bismuth Telluride Doped with Graphene

The microstructure and thermoelectric properties of materials based on p-type Bi_0.5Sb_1.5Te₃ and n-type Bi₂Te_2.4Se_0.6 solid solutions doped with graphene are studied. The samples are obtained by spark plasma sintering of powders prepared by melt spinning and crushed in a ball mill together with graphene plates, which are introduced in an amount of 0.05, 0.1, and 0.15 wt %. Scanning electron microscopy is used to study the composition and microstructure. The samples with p-type conductivity have a fine-grained (on the order of hundreds of nanometers) structure with microsized tellurium-based eutectic inclusions. The samples with n-type conductivity contain grains with melted edges. The thermoelectric parameters are measured: Seebeck coefficient, electrical conductivity, thermal conductivity at room temperature and in the temperature range from 100 to 700 K; and the thermoelectric figure of merit is calculated. When adding 0.15 wt % of graphene plates to a p-type solid solution, the maximum thermoelectric figure of merit (ZT)_max of the material increases by 13% and is equal to 1.3 at 420 K. For a sample with n-type conductivity doped with graphene, the highest value of (ZT)_max = 0.83 at 470 K is obtained by adding 0.1 wt % of graphene plates.