Phase coexistence and the structure of the morphotropic phase boundary region in (1 − x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 piezoceramics

The structures of the morphotropic phase and the phase coexistence region have 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 suggests a very narrow morphotropic phase boundary (MPB) region of compositional width Δx ≈ 0.03. Rietveld refinement of the structure using X-ray diffraction data confirms the coexistence of the tetragonal and cubic phases in the MPB region and rules out the coexistence of tetragonal and rhombohedral structures reported by earlier workers. After poling, the appearance of a significant electromechanical coupling coefficient for the cubic compositions (x = 0.55, 0.56) suggests the presence of an electric-field-induced phase transition from centrosymmetric cubic phase to noncentrosymmetric phase. Polarization-electric field hysteresis loop measurement on the cubic composition with x = 0.56 gives a well-saturated hysteresis loop similar to that reported the in Pb(Mg1/3Nb2/3)O3 relaxor below the freezing temperature. Our dielectric studies on the composition with x = 0.56, in the temperature range 300-763 K, reveals a relaxor ferroelectric transition at ∼530 K with Vogel-Fulcher freezing temperature 482 K.