Thermodynamic properties of the Sb6O13 and Ca6Sb2O11-σ

This investigation employed high-temperature drop calorimetry to determine the high-temperature heat capacities ( C p ) of Sb 6 O 13 and three polymorphs of perovskite-type Ca 6 Sb 2 O 11-δ : cubic (Cub), tetragonal (Tet), and orthorhombic (Orth). The temperature-dependent C p relationships for Sb 6 O 13 , Cub-Ca 6 Sb 2 O 11 , Tet-Ca 6 Sb 2 O 11 and Orth-Ca 6 Sb 2 O 11-δ were derived as: C p (Sb6O13)  = 493.05 + 6.61 × 10 −11  T -9498750  T −2 (573–973 K); C p (Cub-Ca6Sb2O11)  = 550 + 2.00× 10 −6  T −22848000  T −2 (573–1273 K); C p (Tet-Ca6Sb2O11)  = 481.03 + 1.92 × 10 −9  T -7780332.5  T −2 (573–1273 K); C p (Orth-Ca6Sb2O11-δ)  = 492.474 + 3.63× 10 −9  T− 8940348.47  T −2 (573–1273 K), and then used for computing changes in entropy and Gibbs free energy.