P-N control of YbB6

Possibility of p-n control of the divalent hexaborides is demonstrated using YbB₆. Theoretical calculations suggested that boron deficiency and metal atom deficiency in the divalent hexaborides lead to n-type and p-type conduction, respectively. In the alkaline-earth hexaborides, such as CaB₆, n-type Seebeck coefficient was observed but p-type one was not obtained. In the present study, YbB₆ was chosen because of its wide homogeneity range in composition, which is preferable to control the boron/metal ratio. Polycrystalline YbB_x (x=5.7, 5.9, 6.1, 6.3) were sintered, and their Seebeck coefficients were measured. As predicted, n-type Seebeck coefficient was observed in YbB_5.7 and YbB_5.9, and p-type one was observed in YbB_6.1 and YbB_6.3 at room temperature.