Pressure effect and superconducting properties of lithium ternary borides

Li₂Pd₃B and Li₂Pt₃B show superconducting transition at the temperatures, 7.4 K and 2.6 K, respectively. These materials have the same cubic structure (P4₃32) composed of distorted octahedrons, whose corners are occupied by Pd/Pt. This structure does not have mirror or inversion symmetry along any directions. It is a very interesting feature of those materials in relation to the symmetry of superconductivity. The samples were prepared by a two-stage arc-melting method. Their superconductivity is induced by Li addition. Controlling the Li stoichiometry is a key to synthesize high quality samples in the preparation process of arc-melting because Li is volatile at high temperatures. The specific heat measurements were carried out by heat-pulse relaxation and semi-adiabatic methods. Pressure effect was measured with a SQUID magnetometer using a low temperature hydrostatic micropressure cell at pressures up to around 1 GPa. The superconducting transition temperatures of both Li₂Pd₃B and Li₂Pt₃B decreased linearly with pressure. The pressure dependence, dT_c/dP, were 0.091 and 0.090 K/GPa, respectively.