Crystal structure and thermoelectric performance of p–type Bi0.86Ba0.14CuSeO/Cu2–ySe composites

Bi0.86Ba0.14CuSeO/xCu2–ySe (0.05 ≤ x ≤ 0.15; y = 0 and 0.2) composites were fabricated by spark plasma sintering, and the crystal structure and thermoelectric properties of the Bi0.86Ba0.14CuSeO/xCu2–ySe composites were studied. The composites contained Cu2–ySe (y = 0 and 0.2) nanoinclusions in a tetragonal Bi0.86Ba0.14CuSeO matrix. To increase the electrical conductivities of Bi0.86Ba0.14CuSeO, we introduced Cu2–ySe nanoinclusions with a high electrical conductivity into the matrix. The introduction of Cu2–ySe nanoinclusions reduced the structural distortion of CuSe4 tetrahedra and the effective mass, thereby enhancing the carrier mobility. A significant increase in electrical conductivities was achieved with increasing Cu2–ySe nanoinclusion, i.e., 117, 165, and 214 Ω−1cm−1 at 673 K for x = 0.05, 0.10, and 0.15 composites. The Cu2–ySe nanoinclusions reduced the lattice thermal conductivity because they strengthened the long–wavelength phonon scattering at the Bi0.86Ba0.14CuSeO/Cu2–ySe interface. The largest dimensionless figure–of–merit (0.33 at 673 K) was obtained for x = 0.15 composite, which was attributed to the highest electrical conductivity and the lowest lattice thermal conductivity.