Thermoelectric Properties of p‐Type Semiconducting NaB5C with Hexaboride‐Type Structure, Compared to Layered MB2C2 (M = La, Ce)

Abstract

AbstractWhile hexaborides are known to exhibit n‐type semi‐conducting or metallic properties, the carbaboride NaB5C that crystallizes with the hexaboride‐structure type was found to be p‐type. It thus complements n‐type CaB6, which has almost identical structural features [s.g. Pm$\bar{3}$m, a = 409.25 pm and z/c(B) = 0.2034 for NaB5C and a = 415.37 and z/c(B) = 0.201 for CaB6]. Mono‐phasic samples were synthesized via solid state reactions of the elements and compacted by spark plasma sintering at high pressures. The thermoelectric properties (thermal diffusivities, electrical conductivities, Seebeck coefficients) were measured up to temperatures as high as 873 K (S = 80 μV·K–1) and compared to that of LaB2C2 and CeB2C2. These have layered structures and are metallic.