Heat capacity and other thermodynamic properties of CoTe2 from 5 to 1 030 K and of CoTe2.315 from 300 to 1 040 K

Abstract

The heat capacity of orthorhombic (marcasite-type structure) cobalt ditelluride has been measured from 5 to 1 030 K by adiabatic-shield calorimetry with alternate energy inputs and equilibrations. Above 900 K a marked increase in heat capacity occurs which probably signals a change in the composition of the CoTe2-phase towards higher tellurium content. Values at 298.15 and 1 000 K in J K−1 mol−1 of the heat capacity (Cp,m), entropy [S m ° (T)−S m ° (0)], andGibbs energy function − [G m ° (T)−H m ° (0)]T−1 are 75.23, 114.5, 49.93, and 132.4, 216.2, 139.17, respectively. Consistent with the metallic behavior of CoTe2, deviation of the heat capacity from theDebye T3-law was found at low temperatures. Comparison with the heat capacity of FeTe2 shows aSchottky-like deviation with a maximum of 7.3 J K−1 mol−1 at 80 K and evidences the influence of the additional 3 d-electron in cobalt compared to iron. Heat capacity measurements were made on CoTe2.33 to ascertain the existence range of the CoTe2+x-phase and the entropy of the associated structural disorder.