Peculiar properties of phase transitions in Na0.5Bi0.5TiO3−0.06BaTiO₃ lead-free relaxor ferroelectrics seen via acoustic emission

Abstract

Na[Formula: see text]Bi[Formula: see text]TiO3-0.06BaTiO3 relaxor ferroelectrics (RFEs) ceramic samples were investigated by means of dielectric and acoustic emission methods in the temperature range of 70–350[Formula: see text]C and in dependence on frequency. Dielectric curve exhibits two anomalies: strongly dispersive the local maximum, within 130–180[Formula: see text]C and slightly dispersive the smeared high-temperature maximum within 300–310[Formula: see text]C. Acoustic emission exhibits the five groups of bursts: near 123[Formula: see text]C, 150–180[Formula: see text]C, near 225[Formula: see text]C, 300–310[Formula: see text]C and 327[Formula: see text]C. The first and third groups of acoustic emission bursts correspond to phase transitions of R[Formula: see text]c-P[Formula: see text]bm phases coexisting in this temperature, range, while the fourth and fifth groups of acoustic emission bursts correspond to P[Formula: see text]bm-P[Formula: see text] /mbm-Pm[Formula: see text] m phase transitions. The second group of acoustic emission bursts corresponds to strongly dispersive local maximum at which no phase transition has been proved in Na[Formula: see text]Bi[Formula: see text]TiO3-0.06BaTiO3. The existence and the location of the intermediate temperature, [Formula: see text], in Na[Formula: see text]Bi[Formula: see text]TiO3-0.06BaTiO3 compound are discussed.

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

“…The ɛ' (T) curves exhibit two groups of smeared (diffused) humps and maxima: the low temperature humps corresponds to T lm , in the range of 150-200ºC and the high temperature maxima corresponds to T m in the range of 300-350ºC. These results are in good agreement with previous studies 10,19,21,[27][28][29][30][31]33 . For pure NBT the form of the ɛ' curve is not symmetric around T m : from the low temperature side it is steeper in comparison with the high temperature side, as observed previously 21 .…”

“…, except of NBT-6BT, in which it exhibits the sixth burst, corresponding to T p ≈ 330ºC ( ≈ 70 s -1 ). Two lowest bursts clearly separate the T d , exhibiting no frequency dispersion, from T lm , exhibiting the essential frequency dispersion 10,[18][19][20]27 and obeying the Vogel-Fulcher law 39 . For pure NBT both the T RE and T m are located close to each other what causes the non symmetric form of ɛ' curve around T m .…”

“…The waves are detected using a piezoelectric sensor, fairly often connected with the sample through a dielectric acoustic waveguide to avoid of its overheating 34 . Traditionally in FEs the AE is well proven in detection of the structural phase transitions, T c , due to arising of the domains and their mechanical interaction [35][36][37][38] as well as recently it is well proven in a study of all the characteristic temperatures in RFEs: T m , T* and T B due to arising of the PNRs and their mechanical interaction [4][5][6][7][8][9][10]33 . AE technique has been described previously elsewhere 11 .…”

“…Previously the dielectric constant, measured on heating in NBT-6BT crystals, clearly shows the low temperature "hump" of ɛ' 19,[27][28][29][30] between of 140 and 220°C, accompanied by AE bursts between of 127 and 225°C, which also exhibits the bursts corresponding to T m ≈ 290°C and T p ≈ 390°C, respectively 33 . Recently, using the AE, it was confirmed that the temperature of this "hump", ascribed as the T lm , exhibits the strong frequency dispersion, whereas the T d exhibits no dispersion, and all these characteristic temperatures of NBT-6BT: T d ≈ 123°C, T lm ≈ 150÷180°C, T RE ≈ 225°C, T m ≈ 300÷310°C and T p ≈ 327°C have been successfully detected by AE 10 , in good agreement with the early detected data 33 .…”

“…Being mobile the PNRs nucleate at high enough Burns temperature, T B , on cooling, below so-called intermediate temperature, T*, they begin to couple and merge into larger ones, become a long-lived and so the deviation from a Curie-Weiss law and a frequency dispersion starts 3 , and on further cooling the PNRs become frozen into a nonergodic dipole glass state below Vogel-Fulcher temperature, ascribed as freezing temperature, T f , some degrees below the T m [1][2][3] . While all these characteristic points: T B , T* and T m , were detected in Pb-based RFEs [4][5][6][7] as well as in some Pb-free RFEs 8,9 , in Pb-free relaxors of Na 0.5 Bi 0.5 TiO 3 -xBaTiO 3 (NBT-xBT) they have been established recently using an acoustic emission (AE) method 10 . Moreover, in the latter paper it was shown that the temperature T lm , corresponding to local dielectric maxima of ɛ', or so-called "hump", low temperature and frequency dependent one, plays a role of T m in the Pb-based RFEs and is caused by interaction between PNRs only, whereas the high temperature maximum of ɛ', ascribed as to be corresponding to T m , is caused of coexisting of some phases with which NBT-xBT is known to be rich.…”