Composition induced relaxor to ferroelectric crossover in (1-x) Na0.5Bi0.5TiO3-xBiFeO3 (0 ≤ x ≤ 0.60)
Na0.5Bi0.5TiO3-based materials have been widely investigated in the past two decades due to their giant strain and stable mechanical quality factor, which render them as potential alternatives to lead-based materials. One of the limiting factors of these materials have been the relatively lower depolarization temperatures, which restrict their use in high power ultrasonics. This work explores the phase evolution, electromechanical and piezoelectric properties of (1-x)Na0.5Bi0.5TiO3-xBiFeO3 (x = 0~0.60, labelled as NBT-100xBFO) and demonstrates a composition-induced relaxor-to-ferroelectric crossover. All the samples maintain a R3c symmetry in the whole composition range and the unit cell volume monotonously increases with the increase in BiFeO3 concentration. However, electromechanical and piezoelectric properties indicate a criticality at x = 0.30, beyond which, NBT-100xBFO becomes ferroelectric. These results are further corroborated by the temperature dependent strain-field hysteresis and lamellar domain structure in the TEM images of unpoled NBT-50BFO, indicating a stable, long-range ferroelectric order. The outcome of this study indicates that NBT-BFO could be a potential high temperature ferroelectric, which can be further tailored to surpass the existing temperature limits of the NBT class of materials.