  We present here the results of structural studies on multiferroic
(1-x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 solid solution using Rietveld analysis on powder
x-ray diffraction data in the composition range 0.35 to 0.55. We have
determined precisely the stability region of various crystallographic phases at
room temperature for (1-x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 . Structural transformation
from pseudo-cubic to tetragonal phase is observed via phase coexistence region
demarcating the morphotropic phase boundary region. The morphotropic phase
boundary region consists of coexisting tetragonal and monoclinic structures
with space group P4mm and Pm respectively, stable in composition ranges 0.41 to
0.49 as confirmed by Rietveld analysis. The results of Rietveld analysis
completely rules 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 bonds for the
cubic phases and partial covalent character for the other crystallographic
phases.
