Heat capacity and thermodynamic functions of TiO2(B) nanowires

Heat capacities of TiO2(B), 50 nm in diameter and several micrometers in length, containing given amounts of anatase were measured using a Quantum Design Physical Property Measurement System (PPMS) over a temperature range from 1.9 to 302 K. After eliminating the contribution from anatase, the heat capacities for TiO2(B) were fitted to a theoretical model in the low temperature range (T < 9 K), orthogonal polynomials in the middle temperature range (9 < T < 65 K), and a combination of Debye and Einstein functions in the high temperature range (T > 65 K). The standard molar heat capacity, molar entropy, and molar enthalpy for TiO2(B) at T = 298.15 K were determined to be (58.18 ± 0.81) J·K−1·mol−1, (52.31 ± 0.69) J·K−1·mol−1, and (9.03 ± 0.12) kJ·mol−1, respectively, leading to a Gibbs free energy of −(6.56 ± 0.09) kJ·mol−1. The heat capacity of TiO2(B) is found to be similar to brookite, but significantly higher than those of anatase and rutile when temperature is above 200 K.