  The phase purity and crystal structure of PLTA samples (synthesized via
sol-gel process) were confirmed using synchrotron x-ray powder diffraction
(wavelength, lmbda= 0.44573 A. Rietveld analyses of powder x-ray diffraction
data confirmed the tetragonal structure for compositions with more than 0.18
and cubic structure for the sample with 0.25 composition. Temperature-dependent
XRD was performed to investigate the structural change from tetragonal to cubic
structure phase transition. Raman spectroscopy at room temperature also
confirmed this phase transition with composition. Field emission scanning
electron provided information about surface morphology while an energy
dispersive x-ray spectrometer attached with FESEM confirmed the chemical
compositions of samples. Temperature and frequency dependent dielectric studies
showed that the tetragonal to cubic phase transition decreased from 680 K to
175 K with the increase in the x from 0.03 to 0.25, respectively. This is
correlated with the structural studies. Electric field dependent spontaneous
polarization showed proper ferroelectric loop for 0.06 to 0.18 belonging to a
tetragonal phase while after 0.25 composition the spontaneous polarization
vanishes.Bipolar strain versus electric field revealed a butterfly loop for
0.06 to 0.18 compositions. Energy storage efficiency initially increases
nominally with substitution but beyond 0.18 composition enhances considerably.

Materials Science