Structural evaluation in vicinity of composition induced non-ergodic to ergodic crossover in niobium doped (Na0.41 K0.09 Bi0.5)TiO3

A structural crossover from non-ergodic to ergodic phase in niobium doped (Na0.41K0.09Bi0.5)TiO3, i.e.,(Na0.41K0.09Bi0.50)(1-x/2)(Ti1-xNbx)O-3 was investigated using high resolution x-ray diffraction and Raman spectroscopy. The diffraction studies reveal the co-existence of cubic (Pm3m), rhombohedral (R3c), and tetragonal (P4bm) phases for lower concentrations of niobium, i.e., for x= 0.005 and the emergence of the pseudo-cubic (Pm3m) structure for higher niobium contents (for x= 0.0075). On the other hand, Raman spectroscopy reveals the augmentation of the tetragonal phase with niobium content. These observations advocate the crossover from the non-ergodic to ergodic phase with niobium content. The presence of the pseudo-cubic phase (Pm3m), especially for x = 0.0075, does not indicate the existence of the long-range cubic phase; rather, it models the contribution of nano-regions with the tetragonal symmetry as indicated in the Raman measurements. It further suggests that, with the incorporation of niobium, the size polar nano-regions diminish that leads to the crossover from the non-ergodic to ergodic phase.