In this work, the dependency of the polarization (P) - electric field (E) loop area of lead free ferroelectrics Na_0.5Bi_0.5TiO₃ (NBT), K_0.5Bi_0.5TiO₃ (KBT), and Na_0.25K_0.25Bi_0.5TiO₃ (NKBT) on the amplitude (E₀) of the electric field is studied. Based on the nature of the hysteresis loop with increasing E₀, the lnA versus lnE₀ graph is divided into three stages and the scaling exponents of each stage are estimated. In the third stage, NBT, KBT, and NKBT show different shapes of P-E loops (square, slanted and pinched, respectively). Although, almost similar slopes in the third stage are obtained from the lnA versus lnE₀ graphs of KBT and NKBT, the formation of pinched P-E loop of NKBT is discussed based on the current-time curve under a complete cycle of the applied electric field. The shape of the P-E loop also affects the recoverable energy storage density (W_rec) of the material. Similar to the scaling of A, the variation of lnW_rec with lnE₀ of NBT, KBT and NKBT are examined. Interestingly, three stages are only noticed in the lnW_rec-lnE₀ curve of pinched P-E loop (NKBT), whereas lnW_rec linearly increases with lnE₀ for square and slanted P-E loop. Such type of behavior of W_rec of NKBT is explained based on the reversible domain switching mechanism of the pinched P-E loop.

This paper deals with an in-depth analysis on the role of the microstructure phase of titanium dioxide (TiO₂) precursor in sodium bismuth titanate (Na_0.5Bi_0.5TiO₃, hereafter represented as NBT) ceramics prepared through the hydrothermal method. The comparison of the grain size, microstructure, crystal structure, and electrical properties of the NBT ceramics is carried out using anatase and rutile TiO₂. NBT ceramics with anatase TiO₂ (denoted by NBT_A) displayed superior dielectric and ferro/piezoelectric properties along with the additional functionality in terms of photocatalysis. Systematic studies of functional properties such as piezoelectric, ferroelectric, and dielectric stressed the far-reaching influence of effects on grain size. The mechanisms and functional properties of grain quantitative effects are also discussed. Grain boundaries volume fraction increment has decreased the dielectric peak but increased the diffusiveness in the case of the NBT with rutile TiO₂ precursor (denoted as NBT_R). Similarly, elastic stiffness increment restricts the movement of the domain wall and led to a decrement in remnant polarization along with an increase in the values of the corresponding piezoelectric coefficient in fine-grain NBT_R samples.