Giant improvement of thermoelectric power factor of Bi 2 Te 3 under pressure

The pressure ( P ) dependencies of both the thermopower (Seebeck effect) S and the electrical resistance ( R ) for p -type single crystals of Bi 2 Te 3 and indium-doped bismuth telluride ( In x Bi 2 − x Te 3 , 0.04 ≤ x ≤ 0.10 ) are reported on a pressure range of 0-8.5 GPa. The thermoelectric power factor (efficiency) ( æ = S 2 / R ) exhibits two maxima: the first one near ∼ 1 GPa and the second near ∼ 2.5 - 4.5 GPa . These features evidence a giant increase in the power factor by a factor of ∼ 10 . Possible values of the dimensionless figure of merit under pressure are also estimated. The maxima are explained in terms of pressure-driven changes in an electron structure. The second feature may be also addressed to an intermediate high-pressure phase detected in x-ray diffraction studies.