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The temperature dependences of the electrical conductivity (T), Seebeck coefficient (T), and heat capacity C p (T) of polycrystalline samples of Bi 2 Te 3 , Bi 2 Te 3 +1%CuI, and Bi 2 Te 3 +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 ( (T) = 1∕ (T)) 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 ⊥ (T)∕ ‖ (T): 10 (where ‖ (T) is the resistivity along the crystal growth axis, and ⊥ (T) is resistivity across the crystal growth axis) and temperature dependence (T): T 2 below 50 K. The Fermi energy E F is estimated using the temperature dependence of S(T). It is discovered that an increase in E F 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 Bi 2 Te 3 +1%(CuI+1/2Pb) sample at room temperature (T = 300 K).

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