Thermal properties of Nb from acoustic and electrical resistivity measurements in the temperature range 60–340 K

Abstract

The thermal diffusivity and the relative difference in molar heat capacities, (Cp−Cv)/Cv, of polycrystalline niobium have been derived from acoustic measurements in the temperature range 60–340 K. The electrical resistivity has also been measured from 8 to 340 K; 0.833 μΩ cm, 18.7, and 9.25 K being the values of residual resistivity ρ0, resistance ratio ρ (300 K)/ρ0, and superconducting transition temperature, respectively. The thermal conductivity, Lorenz ratio, and molar heat capacity at constant volume have been calculated for the temperature range 60–340 K, using present values of thermal diffusivity, electrical resistivity, and literature values of specific heat Cp. A shallow maximum in the derived thermal conductivity curve is observed around 180 K where the Lorenz ratio assumes the maximum value 3.15×10−8 W Ω K−2. It is suggested that the thermal conductivity maximum may originate in the phonon contribution.