Peculiar Properties of Phase Transitions in Na0.5Bi0.5TiO3-xBaTiO3 (0<x<6) Lead-free Relaxor Ferroelectrics Seen Via Acoustic Emission

Abstract

Na 0.5 Bi 0.5 TiO 3-xBaTiO 3 (0<x<6) relaxor ferroelectrics crystals were investigated by means of dielectric and acoustic emission methods. Dielectric curves exhibit the slightly visible small maxima near the depolarization temperatures, T d , and the wide maxima at the temperatures of T m , whereas the acoustic emission exhibits the sharp bursts, corresponding to T d , T lm , which is known to be a temperature exhibiting a strong frequency dispersion, T RE , which is known to be a temperature above which a frequency dispersion vanishes, and the T m and the T p manifesting a transition to the paraelectric phase. Based on the AE data it was established that all these characteristic temperatures shift down as x increases, but with different slopes. A mechanism of such the differences is discussed.

Unveiling the high-temperature dielectric response of $$\text {Bi}_{0.5}\text {Na}_{0.5}\text {TiO}_{3}$$

“…In the following, a broad dielectric peak develops around 610 K, where, as we earlier commented, no structural phase transformation has been found 18 . This anomaly, also reported elsewhere 22,[24][25][26][27][28] , is the dielectric response of interest in this report. Because of its broadness, this peak has been connected to a diffuse-like phase transition by some authors 21,24,26,[30][31][32][33]50 .…”

“…In last years, the analysis of the elastic constants and energy dissipation spectra of electroceramics materials by mechanical spectroscopy has been providing clear information about the occurrence and characteristics of phase transitions 16,22,[37][38][39][40][41] , especially in materials with ferroelastic nature like BNT, relaxation mechanisms [42][43][44] and defects mobility [44][45][46] . Nevertheless, only a few works in the literature address the use of this technique to investigate the phase transitions and other thermally stimulated processes in BNT-based materials 11,22,24,[47][48][49] .…”

Electric field-induced transformations in bismuth sodium titanate-based materials

“…The 0.90BNT-0.07BT-0.03KNN ceramics showed the additional acoustic emissions corresponding to the electric field-induced transition from the antiferroelectric-like phase to a ferroelectric state (Figure 34c) [272]. .06 exhibits an additional AE event, which has the largest intensity at the temperature T P >T m , which was attributed to the tetragonal-to-cubic phase transition [273]. The dependence of the acoustic emission intensity at T LM is characterized by the presence of two maxima with increasing bias field.…”

Detecting the Burns temperature in Na 0.5 Bi 0.5 TiO 3 -xBaTiO 3 lead-free relaxor ferroelectrics by means of acoustic emission

“…Indeed, the sequence of phase transitions in unpoled NBT-xBT above the intermediate temperature, T RE , is antiferroelectric P 4bm Tm ←→ paraelectric tetragonal ferroelastic P 4/mbm + P 4bm P N Rs Tp ←→ cubic P m 3m with local distortion ( [2,[22][23][24] and the literature therein). Recently it has been proved that T RE ≡ T * and T m of NBT-xBT is not equivalent to the one of Pb-based RFEs [25,26], and, thus, a determination of T B from the deviation of 1/ε from a straight line in NBT-xBT seems to be not relevant.…”

“…It is clearly seen that T B , measured by the dilatometric method, slightly increases instead of decreasing, whereas T B , measured by 1/ε , steeply decreases and tends to T c of BaTiO 3 , surprisingly, not T B , in contradiction with previously measured data [20,21], as x increases. It is very interesting to plot the dependence of the transition to the paraelectric phase, referred to as T p [25,26], on x, too, which cannot be plotted by technical reasons recently [26].…”