Heat capacity and entropy of rutile and TiO2II: Thermodynamic calculation of rutile–TiO2II transition boundary

• The CP of rutile and TiO2II were measured in the temperature range of 5–465 K.
• The entropy of TiO2II at STP was experimentally determined for the first time.
• The phase transition boundary of rutile–TiO2II was calculated thermodynamically.

The heat capacity at constant pressure (CP) data of rutile and synthetic TiO2II were measured in the temperature range of 5–465 K using the heat capacity option of the physical property measurement system (PPMS) and by differential scanning calorimetry (DSC). The entropy values for rutile and TiO2II at standard temperature and pressure conditions calculated from the measured heat capacity data are 50.22 ± 0.20 and 47.50 ± 0.20 J mol−1 K−1, respectively. The CP for both phases were also calculated using the Kieffer model to extrapolate CP to higher temperatures beyond experimental range. These new thermodynamic data were used to calculate the phase transition boundary between rutile and TiO2II with the help of other parameters available in the literature. The calculated phase boundary is compared with previous experimental results and possible reasons for the differences are discussed.