Thermoelectric Properties of Metallic Hexaborides RB6 (R = La, Pr, Nd, Gd)

Seebeck coefficient has been studied on the single crystals of metallic hexaborides RB6 (R = La, Pr, Nd, Gd) at temperatures of 2–300 K. The experiment has shown that the signal is limited by the values |S| ≤ 1.5 μV/K for all tested materials. The data obtained for the systems LaB6 and GdB6 were approximated by phonon drag contribution caused by quasi-local (Einstein) mode with characteristic temperatures ΘE(LaB6) ≈ 240 K and ΘE(GdB6) ≈ 180 K. On the contrary, the crystalline electric field effect induces the inversion between negative and positive types of thermoelectricity, which complicates the simulation of phonon drag in the case of PrB6 and NdB6.