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Phase Coexistence and the Structure of the Morphotropic Phase Boundary Region in (1-x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 Piezoceramics

Structure of the morphotropic phase and the phase coexistence region has been investigated in (1-x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 ceramics. The structure is cubic with space group Pm3m for the compositions with x<0.57 and tetragonal with space group P4mm for the compositions with x>0.59. For the compositions with 0.56<x<0.60, both the tetragonal and cubic phases coexist, which suggest very narrow morphotropic phase boundary region of compositional width Δx~0.03. Rietveld refinement of the structure using x-ray diffraction data confirms coexistence of the tetragonal and cubic phases in the MPB region and rules out the coexistence of tetragonal and rhombohedral structure reported by earlier workers. After poling appearance of significant value of electromechanical coupling coefficient in the cubic compositions (x=0.55, 0.56) suggests the presence of electric field induced transition from centrosymmetric cubic phase to noncentrosymmetric phase. Polarization- Electric field hysteresis loop measurement on the cubic composition with x=0.56 gives well saturated loop similar to that observed in Pb(Mg1/3Nb2/3)O3 relaxor below the freezing temperature.