Electric-Field-Induced Phase Transformation and Frequency-Dependent Behavior of Bismuth Sodium Titanate–Barium Titanate

Abstract

The electric field response of the lead-free solid solution (1−x)Bi0.53Na0.47TiO3–xBaTiO3 (BNT–BT) in the higher BT composition range with x = 0.12 was investigated using in situ synchrotron X-ray powder diffraction. An introduced Bi-excess non-stoichiometry caused an extended morphotropic phase boundary, leading to an unexpected fully reversible relaxor to ferroelectric (R–FE) phase transformation behavior. By varying the field frequency in a broad range from 10−4 up to 102 Hz, BNT–12BT showed a frequency-dependent gradual suppression of the field induced ferroelectric phase transformation in favor of the relaxor state. A frequency triggered self-heating within the sample was found and the temperature increase exponentially correlated with the field frequency. The effects of a lowered phase transformation temperature TR–FE, caused by the non-stoichiometric composition, were observed in the experimental setup of the freestanding sample. This frequency-dependent investigation of an R–FE phase transformation is unlike previous macroscopic studies, in which heat dissipating metal contacts are used.

The complex structural mechanisms behind strain curves in bismuth sodium titanate–barium titanate

“…Previous works investigating both lead and lead-free compositions suggested a self-heating of the sample caused by higher frequencies. 12,[29][30][31][32] At elevated temperatures, the necessary threshold electric field for the R-FE phase transformation was also found to increase. 30 Shi et al presented an electric field-temperature (E-T) phase diagram of BNT-12BT, based on temperature dependent permittivity and piezoelectric measurements.…”

“…9,10 Even though these BT-rich compositions are far away from the MPB with two coexisting phases, 11 a phase transformation can still be induced due to the changing properties in a non-stoichiometric material. 12 The long-ranged ferroelectricity (FE) is evoked by the application of a sufficiently large electric field, which transforms back into a relaxor (R) state once the field is lowered. 12 This reversible phase transformation is typically responsible for giant strain, previously shown in 0.02Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 -0.02(K 0.5 Na 0.5 )NbO 3 (BNT-BT-KNN) and manganese-doped BNT-BT.…”

“…12 The long-ranged ferroelectricity (FE) is evoked by the application of a sufficiently large electric field, which transforms back into a relaxor (R) state once the field is lowered. 12 This reversible phase transformation is typically responsible for giant strain, previously shown in 0.02Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 -0.02(K 0.5 Na 0.5 )NbO 3 (BNT-BT-KNN) and manganese-doped BNT-BT. [13][14][15] Additionally, Li et al showed that stoichiometric deviations in BNT lead to significant differences in the microstructural and electrical properties.…”

“…16,17 Introducing a non-stoichiometry, by increasing the Bi/Na ratio in BNT-BT, stabilizes the relaxor state at room temperature in favor of the tetragonal ferroelectric phase, which is expected in stoichiometric compositions based on the previously suggested phase diagrams. 12,[18][19][20] Although a large macroscopic strain can be achieved, the underlying structural effects and mechanisms in the bulk material remain unknown. For that, in situ synchrotron x-ray diffraction with data analysis using the STRAP (Strain, Texture and Rietveld Analysis for Piezoceramics) procedure 21 is utilized (see the supplementary material for Rietveld refinement details).…”

Spontaneous ferroelectric order in lead-free relaxor Na1/2Bi1/2TiVenkataraman1, Hinterstein2, Lee3 et al. 2020Phys. Rev. BSelf Cite15000View full textAdd to dashboardCite

“…In recent years, increase in the ferroelectric→relaxor (FE→ RE) transformation temperature (T F-R ) is reported for (1 − x)Na 1/2 Bi 1/2 TiO 3 -xBaTiO 3 (denoted as NBTzBT; z = 100x) based materials and attributed to the stabilization of ferroelectric order [22][23][24][25]. NBTzBT exhibits a morphotrophic phase boundary (MPB) between 5 and 12 mole % BT [20,[26][27][28]. The most widely investigated compositional range is between 5 and 7 mole % BT, which is identified to be a core-MPB composition [29][30][31] and typically exhibits pseudocubic x-ray diffraction profiles [31], while the off-MPB compositions exhibit noncubic (rhombohedral/tetragonal) distortions [30].…”