X-ray diffraction and dielectric studies across morphotropic phase boundary in (1 − x) [Pb(Mg0.5W0.5)O3]–xPbTiO3 ceramics

We present here the results of comprehensive X-ray diffraction and dielectric studies on several compositions of (1 − x)[Pb(Mg0.5W0.5)O3]–xPbTiO3 (PMW–xPT) solid solution across the morphotropic phase boundary. Rietveld analysis of the powder X-ray diffraction data reveals cubic (space group Fm3m) structure of PMW–xPT ceramics for the compositions with x ≤ 0.42, tetragonal (space group P4mm) structure for the compositions with x ≥ 0.72 and coexistence of the tetragonal and cubic phases for the intermediate compositions (0.46 ≤ x ≤ 0.68). Temperature dependence of the dielectric permittivity above room temperature exhibits diffuse nature of phase transitions for the compositions in the cubic and two phase region while the compositions with tetragonal structure at room temperature exhibit sharp ferroelectric to paraelectric phase transition. The PMW–xPT compositions with coexistence of tetragonal and cubic phases at room temperature exhibit two anomalies in the temperature dependence of the dielectric permittivity above room temperature. Using results of structural and dielectric studies a partial phase diagram of PMW–xPT ceramics is also presented.

Research highlights
► Structural studies reveal pseudocubic structure of PMW–xPT for the x ≤ 0.42, tetragonal for the x ≥ 0.72 and the coexistences of the two phases for intermediate compositions (0.46 ≤ x < 0.68).
► Temperature dependent dielectric constant shows diffuse nature of phase transition for the compositions lying in the cubic (x ≤ 0.42) and two phase region (0.46 ≤ x < 0.68).
► Normal ferroelectric transition is observed for tetragonal compositions (x > 0.68).
► Temperature dependent dielectric constant for compositions in the two phase region shows two dielectric anomalies above room temperature and not just one as reported by earlier workers.
► Rietveld structural analysis of PMW–xPT ceramics is presented for the first time to determine the fraction of the coexisting phases in MPB region.