Structure and electrical properties of lead-free Bi_0.5Na_0.5TiO₃-based ceramics for energy-storage applications

Abstract

optimum energy-storage properties were obtained in 0.90(BNT-BT)-0.10NT with energy-storage density of 1.2 J/cm 3 and energy-storage efficiency of 74.8% at 10 kV/mm. The results demonstrate that (1 -x)(BNT-BT)-xNT ceramics are promising candidate for high-temperature energy-storage application. IntroductionCapacitors play an important role in energy-storage system. Compared to batteries, capacitors possess faster charge-discharge time and higher power density [1,2]. However, the energy that capacitor dielectrics can store is much less than fuel cells or lithium ion batteries [3]. Thus, the development of new capacitor materials with high energy-storage capacity is a challenge for researchers. Additionally, since electronic equipment is often exposed to extreme temperatures in industrial applications, such as space exploration and deep oil / gas well drilling [4,5], the temperature reliability of capacitor materials is also very important. Bi 0.5 Na 0.5 TiO 3 (BNT) based ceramics have been actively studied for energy-storage application in recent years [6-10]. Among the reported systems, (1x)Bi 0.5 Na 0.5 TiO 3 -xBaTiO 3 (BNT-BT) binary solid solution at the morphotropic phase boundary (MPB, 0.06 ≤ x ≤ 0.10)[11] is a promising candidate for high-temperature energy-storage capacitors. On the one hand, the existence of double dielectric anomalies over the studied temperature range can help to improve the temperature stability of the dielectric properties. On the other hand, BNT-BT shows large maximum polarization, which is favorable for obtaining high energy-storage density. Modifications of BNT-based high-temperature energy-storage ceramics focus on expanding the temperature range with stable permittivity, as well as improving their energy-storage density and efficiency. Niobates are the most widely reported members to modify the dielectric and ferroelectric properties of BNT-based ceramics, such as NaNbO 3 [12, 13], KNbO 3 [14, 15], (Li, Ag)NbO 3 [16], Na 0.5 K 0.5 NbO 3 [17-20], and (Na, Bi)NbO 3 [21]. Tantalum and niobium belong to same family in the periodic table of elements. According to J. König [22] and M. Spreitzer [23], tantalate addition can significantly broaden the dielectric anomaly of BNT ceramics. However, the exact dielectric temperature stability has not been reported, neither has the effect of tantalate on the ferroelectric properties.To explore the potential use of tantalate modified BNT-based ceramics for temperature-stable energy-storage application, a new system based on (1x)(0.92Bi 0.5 Na 0.5 TiO 3 -0.08BaTiO 3 )-xNaTaO 3 ((1 -x)(BNT-BT)-xNT) ternary solid solution was prepared in this work. The effects of NT on the structure, dielectric stability, electrical properties, and energy-storage properties of the system were comprehensively investigated. Experimental Procedure(1 -x)(BNT-BT)-xNT (x = 0.01, 0.03, 0.05, 0.10, 0.15) ceramic samples were prepared by traditional solid-state reaction method [8,[24][25][26]. First, the raw powders Bi 2 O 3 (purity 99.0%), Na 2 CO 3 (purity 99.8%), TiO 2 (p...

High energy storage density over a broad temperature range in sodium bismuth titanate-based lead-free ceramics

“…It can be found that the first dielectric constant anomaly peak shifts to lower temperature and the magnitude of the anomaly peak decreases with increasing the value of x. It is due to the fact that large differences of ion valences and sizes among Ti 4+ , Zr 4+ and Nb 5+ in B-sites disturb the long range ferroelectric order of ceramics 10, 53, 54 . The second dielectric constant anomaly peak also decreases in magnitude while its position remains almost unchanged.…”

“…The first dielectric anomaly is located at a low temperature of ~170 °C (Fig. 3 (c)) and shows an obvious frequency dispersion, which is caused by the thermal evolution of R3c and P4bm PNRs coexisted in a wide temperature range for BNT-based ceramics 10, 47, 50 . The second dielectric constant anomaly is located at a higher temperature of ~360 °C (Fig.…”

“…This phenomenon is beneficial to improve the temperature stability of dielectric constant. We adopted temperature coefficient of capacitance ( TCC ) to evaluate the temperature stability of dielectric properties for (1-x)LLBNTZ-xNBN ceramics, as shown in Equation (2) 10 .where C T represents the capacitance at certain temperature within the measuring range, C Base Temp . is the capacitance at the base temperature.…”

“…For further evaluating energy storage performance of the (1-x)LLBNTZ-xNBN ceramics, the comparison of W 1 and BDS between (1-x)BBNT-xNBN ceramics and other lead-free ceramics in recently reported results are shown in Fig. 9  1, 4, 10, 14, 16, 22, 23, 37, 40, 69–75 . It can be seen that the values of W 1 and BDS for (1-x)LLBNTZ-xNBN ceramics are higher than those of other lead-free ceramics.

Figure 8Calculated energy storage density, energy loss density and energy storage efficiency as a function of electric field for the (1-x)LLBNTZ-xNBN ceramics at room temperature.

Figure 9Comparison of W 1 and BDS between (1-x)LLBNTZ-xNBN ceramics and other lead-free ceramics.

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“…Recently, for the needs of practical application, growing interests have been attracted on dielectrics, which have stable energy storage properties over a brode temperature range. Thus, the development of ceramic capacitor materials with high energy storage density and broad working temperature range is a challenge for researchers 10 .…”