Effect of lanthanum doping on ceria fluorite structure and the relation with transport properties and catalytic performance on oxidative coupling of methane

Effect of lanthanum doping on ceria fluorite structure and the relation with transport properties and catalytic performance on oxidative coupling of methane

• Autor
• Sergio Damasceno
• Resumo

• Rare-earth-doped Ceria and its solid solution is a popular material widely investigated in energy process field, such as energy conversion and catalysis, and in devices, for instance, sensors and memristors. Ceria has a cubic fluorite structure, and the doping with lanthanum, a rare-earth oxide with lower valence (La3+), changes this structure to a disordered fluorite and/or a C-type structure, which depends on the doping level. Moreover, the doping level offers a path to tune the defect chemistry for applications in several fields. In this work we investigate solid solutions of lanthanum-doped ceria (Ce1-xLaxO2-x/2) with x from 0 to 50 at.% synthesized by a combustion route and the electrical properties and its correlation with defect chemistry and crystal structure. The as prepared powders were compacted into disks that were sintered at 1500 °C for 5 hours and were used to investigate the transport properties though electrochemical impedance spectroscopy. The results indicates an increase in electrical conductivity from 0 to 5 at.% which is kept constant up to 15 at.%. Above 20 at.% it start decreasing. This behavior is explained in terms of vacancy formation, whereas for lower lanthanum-doping the creation of vacancies improves the conductivity, however, above 20 at.% and higher concentrations of oxygen vacancies, the electrostatic and steric interactions between dopant and vacancies (defects) lead to clusters formation. This association process originates from the Coulomb interaction between vacancies and local relaxation in the crystal lattice. In this regard the activation energies decreases for lower doping and above 20 at.% it increases which indicates an increase in resistance for defect migration. X-ray powder diffraction is a technique that allows investigation of the different phases in materials structures, and is used to investigate the strain evolution, lattice parameter expansion, and phase concentration, through the Rietveld refinement, which is under date obtention. On the other hand, Raman spectroscopy has provided meaningful insights on structural changes on fluorite crystal structure, such as the appearance of a C-type phase. Moreover, local symmetry breaking and vibrational changes on its structure due to formation of oxygen vacancies and the different positions of oxygen in the lattice can be detected. Such chances influence the red shift in the main fluorite vibrational mode, F2g, and the effects on peak broadening and increase in asymmetry, which is under data obtention. 

   

  Sergio Damascenoa, Vanessa B. Vilelab, Raphael Anacletoa,b, Daniel Z. Florioa, Fabio C. Fonsecab, Marlu C. Steilc, Andre S. Ferlautoa,*

  a Center for Engineering, Modeling and Applied Social Sciences, Federal University of ABC, Santo André 09210-580, SP, Brazil

  b Nuclear and Energy Research Institute, IPEN-CNEN, São Paulo 05508-000, Brazil

  c Université de Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, 69626, Villeurbanne Cedex, France

   

• Palavras-chave
• Ceria, transport properties, crystalline structure
• Modalidade
• Pôster
• Área Temática
• Materiais Funcionais Avançados