Hydrogen effects on synthesis processes and electrical resistivities of LiBC

In this paper, we report on the effects of using LiH as a starting material or and hydrogen atmosphere on the synthesis processes and electrical resistivities of LiBC compound. We observed that, in argon atmosphere, the use of LiH was effective in synthesizing the LiBC-samples of high phase purity. In this case, the obtained LiBC phase is non-stoichiometric, Li-deficient. On the other side, samples prepared from LiH as starting material, under different hydrogen partial pressures (P _H2 = 0.01, 0.10 and 1.00 MPa), have shown a different behavior. Namely, sample prepared under P _H2 = 1.00 MPa has significantly lower concentration of impurity phases and the c-axis lattice parameter of LiBC is as of the stoichiometric phase (without Li-deficiency) that is usually observed and reported in the literature. The other samples prepared under lower hydrogen pressure (P _H2 = 0.01, 0.10) have an appreciable amount of impurity phases and Li-deficiency probably caused by the Li evaporation. Electrical resistance vs. temperature was measured for two almost single-phase LiBC samples with Li-deficiency and without Li-deficiency and it is about one order of magnitude lower for the sample with Li-deficiency, due to hole-doping effect. Both samples show semiconducting behavior and do not exhibit superconductivity down to 2.0 K, although superconductivity is predicted theoretically for the Li-deficient LiBC compound.