Investigation of La and Al substitution on the spontaneous polarization and lattice dynamics of the Pb(1-x)LaxTi(1-x)AlxO3 ceramics

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.

Comment: 21 pages, 11 figures