Excellent p-n control in a high temperature thermoelectric boride

Polycrystalline samples of YxAlyB14 (x ∼ 0.57) with different fractional occupancies y (0.41 ≤ y ≤ 0.63) were synthesized and their thermoelectric properties investigated. Electrical conductivities generally followed three-dimensional variable range hopping with a rapid delocalization indicated as electrons were increased. Positive Seebeck coefficients were obtained for the Al-poor sample, y = 0.41, which was shifted in the negative direction with increase of y. Maximum Seebeck coefficient values were approximately 400 μV K−1 at 850 K and −200 μV K−1 at 1000 K, for p-type and n-type, respectively. Excellent control of p-n characteristics was achieved in a system with the same crystal structure and consisting of the same elements.