Synthesis and Characterization of ST and NN modified BNT-KNN, BNT-BT-BKT Ceramics for Energy Storage Applications

Abstract

Ferroelectric (FE) ceramics have attracted immense attention because of their unique dielectric,piezoelectric, pyroelectric and FE properties, which make them suitable
for various device based applications. Generally, Pb-based FE ceramics are widely used in device based applications. However, toxicity of lead has made it imperative to searching for effective lead-free FEs, among which Bi0:5Na0:5TiO3 (BNT)-based systems have drawn great attention in recent years. Power generation from renewable
and non-conventional resources is required on a large scale. However, technology development for energy storage and power distribution is equally important in the energy
sector. Compared to FE materials and linear dielectrics, antiferroelectric (AFE) materials possess higher energy storage density due to their low remnant polarization (Pr) and low coercive field (Ec) values. But, AFE materials cannot withstand a large number of charge-discharge cycles. From literature survey, the above drawbacks of FE/AFE
systems related to energy storage applications, can be minimized by modifying potential FE material with the materials having paraelectric (PE) or AFE nature at room temperature (RT). In present work, we have chosen 0:93Bi0:5Na0:5TiO3 􀀀 0:07K0:5Na0:5NbO3
(0.93BNT-0.07KNN) and 0:884Bi0:5Na0:5TiO3 􀀀 0:036BaT iO3 􀀀 0:08Bi0:5K0:5TiO3 (0.884BNT-0.036BT-0.08BKT) ferroelectric systems and modified them with SrTiO3/ST
(PE) and NaNbO3/NN (AFE) systems.
Following ceramics were synthesized using solid state reaction (SSR) route.

(i) 0.93BNT-0.07KNN/BNT-KNN, (ii) 0.884BNT-0.036BT-0.08BKT/BNT-BT-BKT,
(iii) ST, (iv) NN, (v)(1-x)(0.93BNT-0.07KNN)-xST (x=0.04, 0.08, 0.12 and 0.16),
(vi) (1-x)(0.93BNT-0.07KNN)-xNN (x=0.04, 0.08, 0.12 and 0.16),
(vii) (1-x)(0.884BNT-0.036BT-0.08BKT)-xST (x=0.04, 0.08, 0.12 and 0.16),
(viii) (1-x)(0.884BNT-0.036BT-0.08BKT)-xNN (x=0.04, 0.08, 0.12 and 0.16).
BNT-KNN, BNT-BT-BKT, ST and NN ceramics were successfully synthesized in single
perovskite phase by SSR route. Deconvolution of (200) XRD peak revealed MPB nature
with _53% rhombohedral and _47% tetragonal structures in BNT-KNN ceramics while_31% rhombohedral and _69% tetragonal structures were obtained in BNT-BT-BKTceramics. Relaxor behaviour was observed in BNT-KNN ceramics and diffuse phase
transition near Curie temperature (TC) was observed in BNT-BT-BKT ceramics. High electric field induced strain (S) _0.6% and _0.63% were obtained in BNT-KNN and
BNT-BT-BKT ceramics, respectively, which suggested their usefulness for actuator applications. XRD study showed cubic structure of ST ceramics and orthorhombic structure
of NN ceramics. Dielectric study of ST ceramics revealed its paraelectric nature.All compositions of (1-x)(BNT-KNN)-xST and (1-x)(BNT-KNN)-xNN ceramics were successfully synthesized in single perovskite phase by SSRroute. XRD study confirmed pseudo cubic structure of (1-x)(BNT-KNN)-xST ceramics and confirmed the presence of MPB of rhombohedral-tetragonal structures in (1-x)(BNT-KNN)-xNN ceramics.
Low grain size, Ec _2.8kV /cm, Pr _1.6_C/cm2, saturation polarization (Ps) _20.8 _C/cm2, S% _0.09 and highest RT dielectic constant (ϵr) _2030, energy storage density (W1) _0.59 J/cm3, energy storage efficiency (_%) _64 were obtained in 0.84(BNT-KNN)-0.16ST ceramics. Highest value of maximum dielectric constant (ϵm) was obtained in 0.92(BNT-KNN)-0.08ST ceramics. Transition temperatures Td and TC
decreased with the increase of ST content in (1-x)(BNT-KNN)-xST ceramics. Highest RT ϵr _990, W1 _0.27 J/cm3 and _% _47 were obtained in 0.84(BNT-KNN)-0.16NN ceramics. Highest value of ϵm _2120 was obtained in 0.92(BNT-KNN)-0.08NN ceramics. Transition temperatures depolarization temperature (Td) and TC decreased with the increase of NN content in (1-x)(BNT-KNN)-xNN ceramics. Low value of Ec _8.41kV /cm, Pr _1.78_C/cm2, Ps _5.54_C/cm2, S% _0.17 and highest values of W1 _0.27 J/cm3 and _% _47 were obtained in 0.84(BNT-KNN)-0.16NN ceramics. All compositions of (1-x)(BNT-BT-BKT)-xST and (1-x)(BNT-BT-BKT)-xNN ceramics were successfully synthesized in single peovskite phase by SSR route. XRD study confirmed MPB nature of all ceramics with rhombohedral-tetragonal structures. Highest value of ϵm _3648, W1 _0.57 J/cm3 and _% _46 were obtained in
0.92(BNT-BT-BKT)-0.08ST ceramics and highest value of RT ϵr _1447 was obtained in 0.96(BNT-BT-BKT)-0.04ST ceramics. Transition temperature Td decreased with the
increase of ST content in (1-x)(BNT-BT-BKT)-xST ceramics. Relaxor behaviour was observed in 0.92(BNT-BT-BKT)-0.08ST ceramics and in (1-x)(BNT-BT-BKT)-xNN ceramics for x _ 0:08. Highest value of ϵm _3488 and W1 _0.72 J/cm3 were obtained
in 0.92(BNT-BT-BKT)-0.08NN ceramics. Temperature zone from Td to TC decreased with the increase of NN content in (1-x)(BNT-BT-BKT)-xNN ceramics. Low values of Ec
_7.3kV /cm, Pr _2.9 _C/cm2 and Ps _22.78 _C/cm2 and highest value of _% _47 were obtained in 0.84(BNT-BT-BKT)-0.16NN ceramics. Impedance study of BNT-BT-BKT ceramics revealed PTCR beahaviour below TC. Departed semicircles of impedance Cole-Cole plots and imaginary part of impedance Z′′(f)
fitting of BNT-BT-BKT ceramics and 0.92(BNT-BT-BKT)-0.08NN ceramics, confirmed non-Debye type relaxation behavior. Cole-Cole modulus plots of BNT-BT-BKT ceramics,
confirmed grain relaxation in low temperature region (below 300°C), grain and grain boundary relaxations in high temperature region (above 300°C). Low frequency plateau
(DC conductivity) and frequency dispersion (DC and AC conductivity) were confirmed from conductivity spectra of BNT-BT-BKT ceramics. Activation energies of _0.79,1.2 eV were attributed to grain, grain and grain boundary relaxations, respectively. Cation vacancies at lower temperatures and cation vacancies as well as oxygen vacancies at higher temperatures accounted for the conductivity mechanism of BNT-BT-BKT ceramics. In comparison with BNT-BT-BKT ceramics, PTCR zone increased and relaxation
phenomenon weakened in 0.92(BNT-BT-BKT)-0.08NN ceramics. Cole-Cole modulus plots of 0.92(BNT-BT-BKT)-0.08NN ceramics, confirmed grain relaxation in low temperature
region (below 400°C), grain and grain boundary relaxations in high temperature region(above 400°C). Activation energies of _0.37, 2.1 eV were attributed to grain, grain
and grain boundary relaxations, respectively. Variation in activation energies indicated increased number of vacancies in 0.92(BNT-BT-BKT)-0.08NN ceramics.XRD study confirmed the MPB nature with _72% rhombohedral and _28% tetragonal structures in microwave (MW) processed 0.92(BNT-BT-BKT)-0.08NNceramics. In comparison with conventionally processed ceramics, MW processed 0.92(BNT-BT-BKT)-0.08NN ceramics showed enhanced densification with fine grains,
high ϵr; Td, TC, energy storage density and low tanδ.