Heat capacity, enthalpy and entropy of Sr {sub 14} Co {sub 11} O {sub 33} and Sr {sub 6} Co {sub 5} O {sub 15}

摘要: Highlights: • Heat capacity, enthalpy and entropy of ternary strontium cobalt oxides Sr{sub 14}Co{sub 11}O{sub 33} and Sr{sub 6}Co{sub 5}O{sub 15}. • Heat capacity by DSC calorimetry and heat-pulsed calorimetry. • Enthalpy increments by drop calorimetry. • Einstein–Debye model for low-temperature heat capacity. - Abstract: Heat capacity and enthalpy increments of two ternary strontium cobalt mixed oxides Sr{sub 14}Co{sub 11}O{sub 33} and Sr{sub 6}Co{sub 5}O{sub 15} were measured by the relaxation time method (2–250 K), DSC (258–355 K) and drop calorimetry (573–1173 K). Temperature dependencies of the molar heat capacity in the form C{sub pm} = 1359.46 + 0.355826·T–19.5816·10{sup 6}·T{sup −2} J K{sup −1}mol{sup −1} for Sr{sub 14}Co{sub 11}O{sub 33} and C{sub pm} = 515.81+ 0.313326·T–5.07872·10{sup 6}·T{sup −2} J K{sup −1}mol{sup −1} for Sr{sub 6}Co{sub 5}O{sub 15} respectively, were derived by the least-squares method from the experimental data. The heat capacity was analyzed in terms of a combined Debye–Einstein model. The molar entropies at 298.15 K, S{sub m}(298.15 K) = 1339.76 J K{sup −1}mol{sup −1} for Sr{sub 14}Co{sub 11}O{sub 33} and S{sub m}(298.15 K) = 578.77 J K{sup −1}mol{sup −1} for Sr{sub 6}Co{sub 5}O{sub 15} were evaluated from the low temperature heat capacity measurements.