High-performance thermoelectric mineral Cu_12-xNi _xSb₄S₁₃ tetrahedrite

X-ray structural analysis and high-temperature thermoelectric properties measurements are performed on polycrystalline samples of artificial mineral Cu_12-xNi_xSb₄S₁₃ tetrahedrite. Analysis of the atomic displacement parameter manifests low-energy vibration of Cu(2) out of CuS₃ triangle plane. The vibration results in low lattice thermal conductivity of less than 0.5 W K^-1 m ^-1. By tuning of the Ni composition x and decrease of electronic thermal conductivity, dimensionless thermoelectric figure of merit for x = 1.5 achieves 0.7 at 665 K, which is a considerably high value among p-type Pb-free sulfides. Because the tetrahedrite is an environmentally friendly material, it constitutes a good thermoelectric material for use in support of a sustainable society.