Heat capacity and high temperature electrical transport properties of TbNiC2

Abstract

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) Å, b = 4.5129(2) Å, c = 6.0563(3), RB(I) = 3.72%, Rp = 5.46%. The orthorhombic CeNiC2 crystal structure prototype is shown to be derived from the hexagonal AlB2 one (space group P6/mmm) following the Bärnighausen formalism via translationengleiche. Zero-field heat capacity measurements of TbNiC2 in the range of 1.9–300 K reveal Sommerfeld coefficient γ = 8(1) mJ mol−1 K−2, phonon coefficient β = 1.18(1)∙10−4 J mol−1 K−4 with the derived Debye temperature of ΘD ≈ 404 K and antiferromagnetic state below TN = 25 K with a spin-wave excitation gap of Δ = 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 ~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 μW m−1 K−2 has been observed at 310 K.