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. (C) 2018 Elsevier Ltd