Heat capacity and high temperature electrical transport properties of TbNiC2

The single phase polycrystalline TbNiC2 sample was obtained by annealing at 1073 K. The compound adopts structure of CeNiC2-type, confirmed by XRD Rietveld refinement: space group Amm2, a = 3.6000(2) angstrom, b = 4.5129(2) angstrom, c = 6.0563(3), R-B(I) = 3.72%, R-p = 5.46%. The orthorhombic CeNiC2 crystal structure prototype is shown to be derived from the hexagonal AlB2 one (space group P6/mmm) following the Badrnighausen formalism via translationengleiche. Zero-field heat capacity measurements of TbNiC2 in the range of 1.9-300 K reveal Sommerfeld coefficient gamma = 8(1) mJ mol(-1) K-2, phonon coefficient beta = 1.18(1).10(-4) J mol(-1) K-4 with the derived Debye temperature of Theta(D) approximate to 404 K and antiferromagnetic state below T-N = 25 K with a spin-wave excitation gap of Delta = 26(2) K. The 4f-electron contribution to the magnetic entropy change indicates a doublet ground state for a non-Kramer's Tb3+ ion. Thermopower and electrical resistivity of TbNiC2 have been measured in the range of 310-855 K and reveal values characteristic for metallic systems. Seebeck coefficient decreases with increasing temperature approximately linearly in the all studied interval, and its sign changes from positive to negative one at similar to 660 K, whereby the electrical resistivity increases from 310 K reaching maximum at-640 K and afterwards decreases slightly. Maximum power factor value of 27 mu W m(-1) K-2 has been observed at 310 K.