Heat capacity and thermodynamic functions of hollandite-type K0.17TiO1.9·0.061H2O

Highlights: • Hollandite-type K_0.17TiO_1.9 with traced water was synthesized. • A Schottky anomaly associated with the water at surface was discovered and discussed in heat capacity below T = 3 K. • Heat capacity data and thermodynamic properties for hollandite-type K_0.17TiO_1.9·0.061H₂O were determined. -- Abstract: The heat capacity of K_0.17TiO_1.9·0.061H₂O has been measured by the use of a Quantum Design Physical Property Measurement System (PPMS) in the temperature range from 1.9 K to 302 K. An upturn below 3 K and weak bump at 7 K are observed and ascribed to Schottky anomaly and boson peak, respectively. The experimental data for K_0.17TiO_1.9·0.061H₂O are fitted to a joint contributions of lattice vacancy, lattice vibration, Schottky anomaly and boson peak in the low temperature range (T < 9 K), orthogonal polynomials in the middle temperature range (9 < T < 63) K, and a combination of Debye and Einstein functions in the high temperature range (T > 63 K). The standard molar heat capacity, molar entropy, and molar enthalpy for K_0.17TiO_1.9·0.061H₂O at T = 298.15 K are determined to be (64.2 ± 0.7) J·K⁻¹·mol⁻¹, (65.7 ± 0.7) J·K⁻¹·mol⁻¹, and (10.5 ± 0.1) kJ·mol⁻¹, respectively, leading to a Gibbs energy of −(9.05 ± 0.09) kJ·mol⁻¹.