Evolution of microstructure and relaxor ferroelectric properties in (LazBa1−z)(Ti0.80Sn0.20)O3

We report a study on a series of lanthanum doped barium stannate-titanate ceramics towards correlating their microstructure with ferroelectric properties. The samples were prepared by solid state reaction technique and the X-Ray Diffraction analysis indicated predominantly single phase microstructure. Scanning Electron Microscopy revealed that while a low La doping of 1 atomic % yielded inhibited grain growth, higher amounts of La doping in barium stannate-titanate yield larger leafy grains. This peculiar grain growth and microstructure evolution could be attributed to the combination of the following two competing factors: (i) suppression of O vacancies due to La doping leading to grain growth inhibition and (ii) enhancement of mechanism leading to nucleation and growth of 2-dimensional (leafy) grains for La doping higher than 2 atomic % due to eutectic phenomena. Dielectric permittivity measurements indicate that addition of La enhances diffused phase transition in barium stannate-titanate, but its frequency dependence is observed only at 2 atomic % La doping. This signature relaxor behaviour and the increase in the intensity of a particular Raman peak with La doping, as well as non-saturated PE hysteresis loops confirm the presence of polar nano-regions for 2 and 3 atomic % La doped barium stannate-titanate. However significant enhancement in dielectric permittivity could not be achieved due to reduced grain size.