초록/요약

The temperature dependences of the electrical conductivity (Formula presented.), Seebeck coefficient (Formula presented.), and heat capacity Cp(T) of polycrystalline samples of Bi2Te3, Bi2Te3+1%CuI, and Bi2Te3+1%(CuI+1/2Pb) are investigated in the temperature range below room temperature. Based on the temperature dependences of all investigated physical properties, it is discovered that phase transition occurs at 120–200 K. Investigation of single crystals shows that anomalies in the electrical resistivity (Formula presented.) occur only across the crystal growth axis (across the well-conducting Bi–Te plane). Investigation of the low-temperature dependence of electrical conductivity shows that all polycrystalline samples exhibit quasi-two-dimensional electron transport. Additionally, quasi-two-dimensional transport is detected in single crystals based on anisotropy analysis (Formula presented.) (where (Formula presented.) is the resistivity along the crystal growth axis, and (Formula presented.) is resistivity across the crystal growth axis) and temperature dependence (Formula presented.) below 50 K. The Fermi energy (Formula presented.) is estimated using the temperature dependence of (Formula presented.). It is discovered that an increase in (Formula presented.) at T > 200 K is associated with the phase transition. For single-crystal samples, the maximum thermoelectric figure of merit ZT, as observed along the crystal growth axis, increases with doping. A maximum ZT value of ∼1.1 is observed for the Bi2Te3+1%(CuI+1/2Pb) sample at room temperature ((Formula presented.)). © 2021 The American Ceramic Society