1980 Volume 88 Issue 1018 Pages 305-311
The heat capacity of a rutile (TiO2) single crystal of 99.99% purity has been measured between 80 and 1100K using the laser-flash calorimeter. The reproducibility of the data was ±0.5% below 800K, and ±1% above that. The smoothed heat capacity agrees with the values in JANAF Tables (1975) within ±0.7% up to 700K, above which the present data are lower by 0.3 to 0.7% than those in the Table. The accuracy of the data is believed to be nearly equal to the reproducibility above 130K.
The heat capacity of rutile has been analyzed in order to estimate a contribution from anharmonic lattice vibrations. The negative anharmonic heat capacity, which decreases linearly with temperature with the coefficient of -1.24×10-3J⋅mol-1⋅K-2, was obtained from the heat capacity at constant volume by subtracting a theoretical heat capacity based on the summation of the Debye and the Einstein function; the characteristic temperature of the latter was calculated to be 607K by considering three acoustic and fifteen optical branches of the lattice vibrations. It has been argued that the anharmonic heat capacity is semi-quantitatively correlated with the temperature derivatives of frequencies of the lattice vibrations at constant volume.
