Effect of Na-substitution on the dielectric behavior of layered K2−xNaxTi4O9 (0.05 ≤ x ≤ 0.15) ceramics

Layered and polycrystalline K2−xNaxTi4O9 (0.05 ≤ x ≤ 0.15) ceramics prepared using oxide mixing process have been investigated for their dielectric-spectroscopy. X-ray diffractograms (XRD) show the formation of these compounds in an orthorhombic crystal system with lattice constants evaluated. A schematic model has been proposed for the crystal structure of these compounds. While dielectric losses are attributed to strong dipole mechanism, space charges and electrical conduction, ɛr(T) plots reveal a sharp transition at 598 K for x = 0.15 composition which indicates some structural transition involving free dipoles. This may be credited to the ferroelectric to ferroelectric phase transition since increase in the unit cell volume destabilizes the paraelectric phase and boosts the possibility of another ferroelectric phase after transition. Moreover, relative permittivity and loss tangent values categorize them as ‘medium permittivity ceramics’.