Cerium doped barium titanate ceramics prepared by the sol-gel method

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Abstract
08-047 Catalina A STANCIU STANCIU, C.A.(University POLITEHNICA of Bucharest, Romania); IANCULESCU, A.C.(University POLITEHNICA of Bucharest, Romania); TRUSCA, R.(University POLITEHNICA of Bucharest, Romania); VASILE, B.S.(University POLITEHNICA of Bucharest, Romania); CERNEA, M.(National Institute of Materials Physics, Romania); PINTILIE, I.(National Institute of Materials Physics, Romania); Pure and cerium-doped barium titanate nanopowders described by the formulae Ba1-xCexTiO3 and Ba1-xCexTi1-x/4O3 for (x = 0.05 and 0.005) were prepared by the sol-gel method, using barium acetate, cerium nitrate and titanium isopropoxide as precursors. After annealing at 900 oC / 2hours, the non-stoichiometric powders with built-in Ti vacancies show single phase compositions for both samples (x = 0.05 and x = 0.005),while the stoichiometric powders show small amounts of secondary phases (Ba2TiO4 and BaTi2O5). SEM investigations of the ceramics sintered at 1300 oC /4 hours indicate significant changes of the microstructural features as a function of dopant content and stoichiometry. More homogeneous and denser microstructures were observed for the ceramics with built-in titanium vacancies no matter the Ce3+ concentration. The ceramic with x = 0.05 exhibits acceptable low dielectric losses (tan? ~ 0.010), smaller than the losses obtained for x = 0.005 (tan? ~ 0.03). A sharp ferroelectric-paraelectric transition is obtained for all the ceramics but the values of the Curie temperatures (TC) are very different. For x = 0.05, TC is close to room temperature (TC=24°C for Ba0.95Ce0.05TiO3, TC = 21 °C for Ba0.95Ce0.05Ti0.9875O3), while for x = 0.005, the TC is closer to the values obtained for pure BaTiO3 (TC = 129°C for Ba0.995Ce0.005TiO3 and TC = 133 °C for Ba0.995Ce0.005Ti0.99875O3). Due to the proximity of the paraelectric–ferroelectric phase transition, the ceramics with x = 0.05 present at room temperature higher dielectric permittivity values (?r = 5904, for the stoichiometric sample and ?r = 7698, for the sample with built-in Ti vacancies) than the permittivity values (?r = 1450 and 1163, respectively) obtained for the samples with lower Ce3+ content (x = 0.005).
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