Stabilization of anti-ferroelectric Pbcm phase over ferroelectric P21ma phase in intermittent ferroelectric NaNbO3 by incorporating CaTiO3

Abstract

This study focuses on the structural aspect of stabilization of anti-ferroelectric (AFE) Pbcm phase over ferroelectric P21ma phase by introducing CaTiO3 in NaNbO3 perovskite. For this work, Na1−xCaxNb1−xTixO3 (x = 0.00, 0.03, 0.04, 0.05) ceramic compositions are chosen for investigation. Structural and dielectric studies are performed on these compositions to see the effect of dopants on phase transitions involved. X-ray diffraction and their respective refinement results confirmed orthorhombic structure with Pbcm space group for all the compositions. Structures are generated using refined x-ray diffraction data in order to understand the effect of doping on octahedral tilting, which plays a huge role in increasing the energy gap required for Pbcm to P21ma conversion and is responsible for establishing stable antiferroelectric phase. To get more insights into the AFE-FE phase transition and stabilization of AFE phase with respect to composition, dielectric permittivity versus temperature and polarization versus electric field studies were performed for all the above-mentioned compositions. Based on PE and structural analysis, high electric field stable AFE phase can be established for x = 0.04 composition. Reasons for high electric field stable antiferroelectric phase at x = 0.04 are presented where it is argued that the octahedral tilt distortion of perovskite structure is responsible for the increase in energy barrier required for AFE ↔ FE transformation, thus stabilizing the antiferroelectric phase.