Presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of multiferroic (1-x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 solid solution: A Rietveld study

We present here the results of structural studies on multiferroic (1 - x)Bi(Ni1/2Ti1/2)O-3-xPbTiO(3) solid solution using Rietveld analysis on powder x-ray diffraction data in the composition range 0.35 <= x <= 0.55. The stability region of various crystallographic phases at room temperature for (1 - x)Bi(Ni1/2Ti1/2)O-3-xPbTiO(3) is determined precisely. Structural transformation from pseudo-cubic (x <= 0.40) to tetragonal (x >= 0.50) phase is observed via phase coexistence region demarcating the morphotropic phase boundary. The morphotropic phase boundary region consists of coexisting tetragonal and monoclinic structures with space group P4mm and Pm, respectively, stable in composition range 0.41 <= x <= 0.49 as confirmed by Rietveld analysis. The results of Rietveld analysis completely rule out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase boundary region reported by earlier workers. A comparison between the bond lengths for "B-site cations-oxygen anions" obtained after Rietveld refinement, with the bond length calculated using Shannon-Prewitt ionic radii, reveals the ionic nature of B-O (Ni/Ti-O) bonds for the cubic phase and partial covalent character for the other crystallographic phases. (C) 2014 AIP Publishing LLC.