Determination of depolarization temperature of (Bi1/2Na1/2)TiO3-based lead-free piezoceramics

Abstract

The depolarization temperature T d of piezoelectric materials is an important figure of merit for their application at elevated temperatures. Until now, there are several methods proposed in the literature to determine the depolarization temperature of piezoelectrics, which are based on different physical origins. Their validity and inter-correlation have not been clearly manifested. This paper applies the definition of depolarization temperature as the temperature of the steepest decrease of remanent polarization and evaluates currently used methods, both in terms of this definition and practical applicability. For the investigations, the lead-free piezoceramics (1-y)(Bi 1/2 Na 1/2 TiO 3 -xBi 1/2 K 1/2 TiO 3 )ÀyK 0.5 Na 0.5 NbO 3 in a wide compositional range were chosen. Results were then compared to those for BaTiO 3 and a commercial Pb(Zr,Ti)O 3 -based material as references. Thermally stimulated depolarization current and in situ temperature-dependent piezoelectric coefficient d 33 are recommended to determine T d according to the proposed definition. Methods based on inflection point of the real part of permittivity or the peak in dielectric loss give consistently higher temperature values.

The effects of Ba2+ content on depolarization temperature and pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3–0.06Ba1+xTiO3 ceramics

“…When the temperature rises from RT to T d , the phase transition from ferroelectric (FR) to relaxor antiferroelectric (relaxor AFR) started, and thus a sharp change in polarization resulted in a significant increase in p at T d [15]. The T d for Sample B (x = 0.01) and C (x = 0.02) is below 90°C and for Sample A (x = 0.00) and D (x = 0.03) above 90°C, which explained why Sample B and C had a greater increase in p than Sample A and D. According to Anton et al [7], the T d determination depends on the highest value of the dielectric loss tangent, which may consistently generate higher T d than other methods such as the thermally stimulated depolarization current; therefore the T d for Sample A and D might actually be less than *125 and *110°C, as a result that the observed increase in p for Sample A and D could be related to the beginning of the phase transition in these samples.…”

“…However, there are other definitions of T d such as the steep reduction of remnant polarization [7], or the phase transition temperature from ferroelectric (FE) to anti-ferroelectric (AFE) or to relaxor anti-ferroelectric or to relaxor [8,[22][23][24][25]. In this study, T d was identified from the measurement of the dielectric loss (tand) versus temperature.…”

“…These phase transition temperatures are well above room temperature. Hence it is necessary to bring the phase transition temperature down to near room temperature (RT) for many applications, and that can be achieved by using various dopants [7]. In NBT-based systems, there is a weakly polar intermediate phase [8], which occurs between the depolarization temperature T d and the temperature of maximum permittivity (T m ) [9][10][11][12].…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…The thermally stimulated loss of the electric field induced ferroelectric state of BNT-based materials has been generally recognized as a two-stage process. 108,109 Upon heating, the ferroelastic texture of the induced ferroelectric state of BNT-based materials is generally lost at the depolarization temperature . 108 Further temperature increase leads to domain fragmentation and PNRs formation at − .…”

“…Therefore, the ´´ local maxima observed at 1 kHz can be used to determine phase transitions, as previously suggested. 109 As an approximation, the high temperature anomaly of the system is considered as since a considerable thermal depolarization occurs at this temperature, as it will become apparent in subsequent sections. 333 , although the synthesis route and characterization techniques used to detect phase transitions differed.…”