Thermodynamic properties of Na2Ti6O13 and Na2Ti3O7: electrochemical and calorimetric determination |
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| Affiliation: | 1. Institut für Physikalische Chemie, Montanuniversität Leoben, Franz-Josef-Strasse 18, A-8700 Leoben, Austria;2. Max-Planck-Institut für Festkörperforschung, Heisenbergstr.1, D-70569 Stuttgart, Germany;1. Nanhu College, Jiaxing University, Jiaxing, Zhejiang, 314001, China;2. School of Biological and Chemical Engineering, Jiaxing University, Jiaxing, Zhejiang, 314001, China;3. College of Materials Science and Engineering, Guilin University of Technology, Guilin, 541004, China;1. CIC Energigune, Parque Tecnológico de Álava, Albert Einstein 48, 01510, Miñano, Spain;2. Scuola di Scienze e Tecnologie – Sezione Chimica, Università di Camerino, Via S. Agostino 1, 62032, Camerino, Italy;3. Departamento de Química Inorgánica, Universidad del País Vasco, UPV/EHU, P.O.Box.664, 48080, Leioa, Spain;1. Materials Science Centre, Indian Institute of Technology Kharagpur, Kharagpur 721302, India;2. School of Nano Science and Technology, Indian Institute of Technology Kharagpur, Kharagpur 721302, India;1. College of Materials and Chemical Engineering, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, China Three Gorges University, Yichang 443002, China;2. College of Electrical Engineering and New Energy, China Three Gorges University, Yichang 443002, China;3. Collaborative Innovation Center for Microgrid of New Energy, Yichang, Hubei 443002, China |
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| Abstract: | Standard values of Gibbs free energy, entropy, and enthalpy of Na2Ti6O13 and Na2Ti3O7 were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na–β″-alumina electrolyte. The central part of the anodic half cell consisted of Na2CO3, while two appropriate coexisting phases of the ternary system Na–Ti–O are used as cathodic materials. The cell was placed in an atmosphere containing CO2 and O2. By combining the results of emf-measurements in the temperature range of 573⩽T/K⩽1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15⩽T/K⩽300, the thermodynamic data were determined for a wide temperature range of 15⩽T/K⩽1100. The standard molar enthalpy of formation and standard molar entropy at T=298.15 K as determined by emf-measurements are ΔfHm0=(−6277.9±6.5) kJ · mol−1 and Sm0=(404.6±5.3) J · mol−1 · K−1 for Na2Ti6O13 and ΔfHm0=(−3459.2±3.8) kJ · mol−1 and Sm0=(227.8±3.7) J · mol−1 · K−1 for Na2Ti3O7. The standard molar entropy at T=298.15 K obtained from low-temperature calorimetry is Sm0=399.7 J · mol−1 · K−1 and Sm0=229.4 J · mol−1 · K−1 for Na2Ti6O13 and Na2Ti3O7, respectively. The phase widths with respect to Na2O content were studied by using a Na2O-titration technique. |
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