Fabrication and characterization of M2SnC (M = Ti, Zr, Hf and Nb)

Dense single phase polycrystalline samples of M2SnC, where M = Ti, Zr, Hf and Nb, were fabricated and preliminarily characterized for the first time. The fabrication process entailed the reactive hot-isostatic pressing of Sn powders with the appropriate transition metal and graphite powders. The fabrication of these ternaries is complicated by the fact that at low temperatures (≈1000°C) the reaction kinetics for their formation are slow, while at higher temperatures (≈1350°C) they tend to dissociate. The exact decomposition temperature varied but was in the range of 1330°C. The uniqueness of these layered compounds lies in the fact that they are all as readily machinable as graphite and are excellent electrical conductors with conductivities that range from 2.4 × 106 to 14 × 106 (Ω.m)-1, with the least conductive phase being Hf2SnC and the most conductive Ti2SnC and the other two in between. The temperature dependence of the resistivity was metallic-like, with temperature coefficients of resistivity that varied from 0.003-0.009 K-1 As a class these ternaries were found to posses hardnesses in the range 3-5 GPa and were as readily machinable as graphite.