The antiferrodistortive (AFD) phase transition for a pseudotetragonal composition of Pb(Zr0.530Ti0.470)O3 (PZT) doped with 6% Sr has been investigated using sound velocity (4 to 320K), high resolution synchrotron X-ray powder diffraction (100 to 800K
) and high resolution as well as high flux neutron powder diffraction measurements (4K) to settle the existing controversies about the true ground state of PZT in the morphotropic phase boundary (MPB) region. The multiplet character of the neutron diffraction profiles of (3/2 1/2 1/2)pc (pseudocubic or pc indices) and (3/2 3/2 1/2)pc superlattice peaks, appearing below the AFD transition temperature, rules out the rhombohedral R3c space group. The true ground state is confirmed to be monoclinic in the Cc space group in agreement with the predictions of the first principles calculations and earlier findings for pure PZT in the MPB region. 6% Sr2+ substitution and the use of high wavelength ({lambda}=2.44{AA}) neutrons have played key role in settling the existing controversies about the true ground state of PZT in the MPB region.
We report here the structure and dielectric studies on a new lead free (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution to explore the morphotropic phase boundary. The powder x-ray diffraction studies on (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution sugge
sts that structure is tetragonal (P4mm) for the composition with x=0.05 and cubic for the composition with x=0.30 and 0.40. Morphotropic phase boundary is observed in the composition range 0.10<x<0.30, where phase coexistence is observed and composition dependence of room temperature permittivity shows a peak. High temperature dielectric measurement for the composition with x=0.20 exhibits diffuse phase transition having peak temperature around ~ 396 K at 10 kHz. The diffuseness parameter ({gamma}) was obtained to be 1.68 for composition with x=0.20.
Temperature dependent structural changes in a nearly pure monoclinic phase composition (x=0.525) of Pb(Zr_xTi_1-x)O_3 (PZT) have been investigated using Rietveld analysis of high-resolution synchrotron powder x-ray diffraction data and correlated wit
h changes in the dielectric constant and planar electromechanical coupling coefficient. Our results show that the intrinsic piezoelectric response of the tetragonal phase of PZT is higher than that of the monoclinic phase. It is also shown that the high piezoelectric response of PZT may be linked with an anomalous softening of the elastic modulus (1/S_11) of the tetragonal compositions closest to the morphotropic phase boundary.
