Anisotropic thermoelectric power in single crystalline Mg1-xAlxB2 compounds

The thermoelectric power of single crystalline Mg1-xAlxB2 compounds is measured and analyzed along the main crystallographic directions (ab-plane and c-axis direction). It is shown that the classical model of thermoelectric power with phonon drag and diffusion terms provides satisfactory explanation of the temperature dependence of the Seebeck parameter S(T). Agreement of S(T) with the study of resistivity is achieved with some variation of the Debye temperature being a model-sensitive parameter. Presence of positive and negative charge carriers is observed and competing contributions of the pi and sigma bands are discussed.