Original Article
Influence of BaSnO3 additive on the energy storage properties of Na0.5Bi0.5TiO3-based relaxor ferroelectrics

https://doi.org/10.1016/j.jeurceramsoc.2017.11.053Get rights and content

Abstract

(1-x)NBT-xBSN (0.1 ≤ x ≤ 0.35) ceramics were prepared by solid state methods and their energy storage properties and high-temperature capacitor applications were systematically investigated. All samples showed a perovskite structure and the structure transformed to lower symmetry orthorhombic phase (x ≥ 0.1) from rhombohedral phase (x < 0.1) to with the addition of BSN. The more addition content of BSN significantly decreases phase transition temperature Tm of NBT ceramics. The x = 0.25 sample exhibits a stable relative permittivity of 1605 ± 15% in a broad temperature range of 38 °C to 319 °C. With increasing BSN concentration, the slope of the P-E loops and the energy loss gradually decreases. When x = 0.25, a high breakdown strength of 190 kV/cm and the maximum discharge energy density of 1.91 J/cm3 were obtained, of which the energy efficiency was as high as 86.4%. Thus, it was believed that our work could provide a significant guidance for designing the new system for energy storage.

Introduction

Capacitors play a key role in most power electronics used to deliver very large amounts of energy in a very short time. The exploration of high energy storage density dielectric materials has become a research hotspot recently, mainly driven by the increasing demands for miniaturization of power electronics [1]. Generally, lead-contained dielectric materials have larger energy storage density [[2], [3], [4]]. However, increasing environmental awareness will limit the use of this material. Therefore, it is necessary to develop lead-free materials with high energy storage density [[5], [6], [7]].

Recently, advances in high-energy-density dielectrics have focused on Na0.5Bi0.5TiO3 (NBT) based relaxor ferroelectrics because of the high maximum polarization (Pm = 43 μC/cm2) under its dielectric breakdown strength (Eb) of 12 kV/mm, low sintering temperature (∼1100 °C) [8]. However, large leakage current, high remnant polarization(Pr = 38 μC/cm2) and coercive field(∼73 kV/cm) [9] are achilles heel for its application in energy storage. The polarization saturation at a field much lower than Eb and high remnant polarization reduce the energy storage quantity [10]. Thus, a dielectric for high energy storage capacitor is expected to possess high maximum polarization, high dielectric breakdown strength, postponed polarization saturation and low remnant polarization. For this, a practical strategy is devoted to introduction other perovskite structure compound into NBT to form solid solutions. Recently, various NBT-based solutions have been developed. Such as BNT-BT-CZ ceramic prepared by Li et al. [11]showed a high energy storage density of 0.7 J/cm3, a high energy storage density of 1.2 J/cm3 was obtained in BNTKNN ceramic [12]. Xu et al. [13] reported that 0.85(0.94BNT-0.06BT)-0.15NBN ceramic has a high energy storage density of 1.4 J/cm3. Zhao et al. [14] found a maximum energy storage density of 1.41 J/cm3 at 10.5 kV/mm in BNKT-0.08AN ceramic. Pu et al. [15] gained a high energy storage density of ∼1.62 J/cm3 at 18.97 kV/mm in 0.55NBT-0.45BCTZS5-5wt%MgO ceramic. Young et al. [5] achieved a high energy storage density of ∼1.70 J/cm3 at 17.2 kV/mm in 0.92BBNT-0.08NBN ceramic.

According to previous researches, shifting phase transition temperature (Tm) below operated temperature and enhanced the relaxor behavior is favorable for energy storage. A lead-free perovskite oxide, BaSnO3 (BSN) belongs to cubic perovskite crystal structure with a good temperature stability. The introduction of BaSnO3 into BaTiO3 could decrease the temperature of the dielectric peak Tm and enhances relaxor properties of BaTiO3 [16]. Tripathy S.N found the similar conclusion in (1-x)NBT-xBSN (0 ≤ x ≤ 0.15) ceramics [17]. However, a systematic investigation of realxor properties and energy storage behavior of (1-x)NBT-xBSN ceramics is not available in the literatures. [18]

In the present work, (1-x)NBT-xBSN ceramics were prepared by a conventional mixed oxide route. The effects of BSN content on densities, phase structure, microstructure, dielectric property, relaxor behavior and energy storage property of samples were systematically investigated. The results demonstrate that the (1-x)NBT-xBSN ceramics could be a good candidate for energy storage.

Section snippets

Experiment methods

The analytically pure BaCO3, SnO2, TiO2, Na2CO3 and Bi2O3 (Sinopharm Chemical Reagent Co., Shanghai), powders were used as starting powders. NBT and BSN powders were synthesized by solid state reaction, respectively. According to the chemical formula BSN and NBT, these powders were weighed, and then ball mixed with ZrO2 balls for 6 h using alcohol as the medium. The slurries were dried in oven at 80 °C for 24 h, and then the mixture BSN was calcined at 1200 °C for 4 h and the mixture NBT was

Results and discussions

Fig. 1 (a) shows the room temperature XRD patterns of (1-x)NBT-xBSN ceramics. It can be distinctly seen that all samples exhibit perovskite structure, indicating that BSN has diffused into NBT lattices and a stable solid solutions were formed between BSN and NBT. The enlarged patterns in 2Theta range of 55−60° are given in Fig. 1(b). With increasing BSN content, the (211) reflection peak shifts gradually to the low degree due to the expansion of cell volume according to Bragg’s law 2dsin θ=nλ.

Conclusions

In summary, (1-x)NBT-xBSN ceramics with a high energy storage density have been successfully prepared by solid state method. The Tm remarkably decreases to 46.16 °C from 256.8 °C with the addition of BSN, which provided an effective method to shift the phase transition temperature of NBT-based relaxors. When x = 0.25, a near plateau relative permittivity, 1605 ± 15%, extended across the temperature range, 38–319 °C. With increasing the BSN content, the BDS values is enhanced from 140 kV/cm to

Acknowledgements

This research was supported by the National Natural Science Foundation of China (51372144, 51641207), the Key Program of Innovative Research Team of Shaanxi Province (2014KCT-06). National Undergraduate Training Programs of China for Innovation and Entrepreneurship (201710708009)

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