PREPARATION AND CHARACTERISTICS OF THE SOL-GEL (Ba,La)TiO3 POWDERS AND RELATED CERAMICS

Reference Presenter Authors
(Institution)
Abstract
08-160 Vasile Adrian Surdu STANCIU, C.A.(University POLITEHNICA of Bucharest, Romania); Crisan, M.(Institute of Physical Chemistry Ilie Murgulescu, Romanian Academy); Surdu, V.A.(University POLITEHNICA of Bucharest); Dragan, N.(Institute of Physical Chemistry Ilie Murgulescu, Romanian Academy); Crisan, D.(Institute of Physical Chemistry Ilie Murgulescu, Romanian Academy); Mitoseriu, L.(Alexandru Ioan Cuza University); Curecheriu, L.(Alexandru Ioan Cuza University); Vasile, B.S.(University POLITEHNICA of Bucharest); IANCULESCU, A.C.(University POLITEHNICA of Bucharest, Romania); Pure and lanthanum-doped barium titanate nanopowders described by two different formulae: (i)Ba1-xLaxTiO3, for lower La concentrations (0  0.005) and Ba1-xLaxTi1-x/4O3 for higher donor dopant proportions (x = 0.025) were prepared by the alkoxide variant of the sol-gel method. Single phase compositions were obtained after annealing at 900°C/2h, in air, followed by slow cooling. The increase of the lanthanum content causes structural and morphological changes in the oxide powders. SEM investigations of the ceramics sintered at 1300°C for 4 hours indicate significant changes of the microstructural features (strong decrease of the average grain size and increase of the intergranular porosity) with the raise of La proportion. Lanthanum addition in the sol-gel barium titanate ceramics induces a more significant shift of the Curie temperature toward lower values, than that one reported in literature for ceramics of similar compositions, but processed by the conventional solid state method. The compositions with smaller La amount (x  0.005) show semiconducting properties at room temperature and high apparent dielectric permittivity values, while the undoped specimen and the ceramic sample with higher La content (x = 0 and 0.025) are good dielectrics. The ceramic with x = 0.025 exhibits acceptable low losses, a very diffuse ferroelectric-paraelectric transition and it is at room temperature in its Curie range, being thus susceptible of potential high tunability. The existence of multiple components in the complex impedance plots of the lightly-doped Ba1-xLaxTiO3 compositions (x  0.005) demonstrates the formation of grain core – grain boundary electric microstructures consisting of semiconducting cores and depleted boundary layers. However, the electrical resistivity evolution against temperature shows only small and diffuse PTCR jumps around the ferroelectric-paraelectric phase transition.
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