Phase relationships and transport in Ti-, Ce- and Zr-substituted lanthanum silicate systems |
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| Affiliation: | 1. Surface Analysis and Materials Engineering Research Group, School of Engineering and Information Technology, Murdoch University, Perth, WA 6150, Australia;2. College of Ibn-Alhaitham for Pure Science, University of Baghdad, Baghdad, Iraq;3. Chemical and Metallurgical Engineering and Chemistry, School of Engineering and Information Technology, Murdoch University, Perth, WA 6150, Australia;4. Newcastle University, Singapore, SIT Building @Ngee Ann Polytechnic, 537 Clementi Road #06-01, Singapore, 599493, Singapore;5. Department of Chemical Engineering, University of Riau, Pekanbaru, Indonesia;6. School of Engineering, Edith Cowan University, Joondalup, WA 6027, Australia;7. Faculty of Chemistry, Hanoi National University of Education, Building A4, 136 Xuan Thuy Road, Cau Giay Dist., Hanoi, Viet Nam;8. Department of Physics, Jahangirnagar University, Savar, Dhaka, 1342, Bangladesh;1. Department of Electroceramics, Instituto de Cerámica y Vidrio – CSIC, Kelsen 5, Campus de Cantoblanco, 28049, Madrid, Spain;2. POEMMA-CEMDATIC, ETSI Telecomunicación (UPM), 28040, Madrid, Spain;3. Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research: Materials Synthesis and Processing (IEK-1), 52425, Jülich, Germany;1. School of Materials Science and Engineering, Tianjin University, Tianjin Key Laboratory of Advanced Joining Technology, Key Lab of Advanced Ceramics and Machining Technology of Ministry of Education, No. 92, Weijin Road, Tianjin 300072, China;2. Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China;3. ICMMO/SP2M, UMR CNRS 8182, Université Paris-Sud, 91405 Orsay Cédex, France;1. State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China;2. University of Chinese Academy of Sciences, Beijing, 100049, PR China;3. Science and Technology Scramjet Laboratory, Beijing, 100074, PR China;1. Institute of Energy and Climate Research IEK-1, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany;2. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons ER-C, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany;3. Central Facility for Electron Microscopy GFE, RWTH Aachen University, 52074 Aachen, Germany;4. Instituto de Tecnología Química, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, Av. Naranjos s/n, E-46022 Valencia, Spain;5. Institute of Energy and Climate Research IEK-2, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany |
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| Abstract: | The solubility of Ti4+ in the lattice of apatite-type La9.83Si6−xTixO26.75 corresponds to approximately 28% of the Si-site density. The conductivity of La9.83Si6−xTixO26.75 (x = 1–2) is predominantly oxygen-ionic and independent of the oxygen partial pressure in the p(O2) range from 10−20 to 0.3 atm. The electron transference numbers determined by the modified faradaic efficiency technique are lower than 0.006 at 900–950 °C in air. The open-circuit voltage of oxygen concentration cells with Ti-doped silicate electrolytes is close to the theoretical Nernst value both under oxygen/air and air/10%H2–90%N2 gradients at 700–950 °C, suggesting the stabilization of Ti4+ in the apatite structure. Titanium addition in La9.83Si6−xTixO26.75 (x = 1–2) leads to decreasing ionic conductivity and increasing activation energies from 93 to 137 kJ/mol, and enhanced degradation in reducing atmospheres due to SiO volatilization. At p(O2) = 10−20 atm and 1223 K, the conductivity decrease after 100 h was about 5% for x = 1 and 17% for x = 2. The solubility of Zr4+ in the La9.83Si6−xZrxO26.75 system was found to be negligible, while the maximum concentration of Ce4+ in La9.4−xCexSi6O27−δ is approximately 5% with respect to the number of lanthanum sites. |
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