  We report a study on a series of lanthanum doped barium stannate-titanate
(LBTS) ceramics towards correlating their microstructure with ferroelectric
properties. The samples were prepared by solid state reaction technique and the
XRD analysis indicated predominantly single phase microstructure. Scanning
Electron Microscopy revealed that while a low La doping of 1 atomic % yielded
inhibited grain growth in 1LBTS, higher amounts of La doping 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-D
(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 BTS, 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 BTS. However significant enhancement in
dielectric permittivity could not be achieved due to reduced grain size.
