Synthesis and physical properties of LiBC intermetallics

Polycrystalline samples of LiBC compounds, which were predicted as possible candidate for high-T_c superconductivity, have been synthesised by a flux method for a wide range of flux compositions Li_xBC (x=0.5-2.4). Scanning electron microscopy and X-ray diffraction patterns showed a plate-like morphology and a single-phase nature of LiBC samples for the starting flux composition of Li_1.25BC. The lattice constants a, c display a systematic variation with x and a maximum volume of the hexagonal unit cell at x=1.25. Electrical resistivity measurements revealed an extrinsic semiconducting behaviour of the single-phase LiBC with an activation energy of 18 meV and a maximum specific resistivity of 2.5 Ω cm at 300 K. In contrast to the theoretical prediction of high T_c, no superconducting features were detected down to 2 K both, by measurements of electrical resistivity and magnetic susceptibility. However, the results do not allow to refute the theoretical prediction because of the lack of accurate chemical analysis methods for the LiBC compounds synthesised.