Thermoelectric properties and phase transition of doped single crystals and polycrystals of Bi₂Te₃

Abstract

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).

Enhanced thermoelectric properties of polycrystalline CuCrS2−x Se x (x = 0, 0.5, 1.0, 1.5, 2) samples by replacing chalcogens and sintering

“…According to experimental data and preliminary theoretical calculations [4,[28][29][30][31][32][33][34][35][36][37][38] layered transition metal dichalcogenides are the excellent candidates for efficient thermoelectric energy converters. Our investigations of layered chalcogenides have demonstrated that effective ways to improve thermoelectric properties are substitutions in sublattices and, as a result, the changes in the morphology of crystallites in bulk sample [3,29,[32][33][34]39].…”

“…Single crystals in comparison with polycrystals have better thermoelectric properties [1][2][3][4][5][6][7]. But high cost and technological difficulties limit their use.…”

“…The aim of our investigation was to trace the change in the thermoelectric parameters of the CuCrS 2−x Se x (x = 0, 0.5, 1.0, 1.5, 2) compounds at temperatures below room temperature after replacement selenium to sulfur and sintering. Studies at temperatures below room temperature make it possible to elucidate the mechanisms of the observed processes due to the possibility of separating the contributions from different mechanisms to thermoelectric properties [3,4,29,[32][33][34]39]. This is due to the fact that at low temperatures the contributions of a number of mechanisms significantly decrease, while other contributions increase and dominate.…”

Effect of carbon nanotubes addition on thermoelectric properties of Ca3Co4O9 ceramics

“…The optimization of one parameter of thermal conductivity or electrical conductivity usually causes the reduction of the other parameter. In recent years, compared with intermetallic thermoelectric compounds, such as Bi 2 Te 3 , [3] PbTe, [4] etc., thermoelectric oxide material Ca 3 Co 4 O 9 (abbreviated as CCO) has attracted extensive attention because of its good stability, convenient preparation, green environmental protection and low cost. [5] At present, the ZT value of polycrystalline Ca 3 Co 4 O 9 still cannot meet the requirements of practical application, which limits its commercial applica-tion.…”

“…3 Co 4 O 9 and can be regarded as spherical particles. The effect of carbon nanotube addition on the effective thermal conductivity of Ca 3 Co 4 O 9 material can be discussed by using the model of formula(2).…”