Structure and properties of Fe-modified Na0.5Bi0.5TiO3at ambient

Abstract

Sodium bismuth titanate (NBT) ceramics are among the most promising lead-free materials for piezoelectric applications. This work reports the crystal structure and phase evolution of NBT and Fe-modified NBT (from 0-2 at% Fe) using synchrotron X-ray diffraction and Raman spectroscopy, both at ambient and elevated temperatures. The crystallographic results are discussed with reference to permittivity and piezoelectric thermal depolarization measurements of the same compositions. Changes in the depolarization temperature due to Fe substitution were detected by Raman spectroscopy, and were found to correlate closely with depolarization temperatures obtained from converse piezoelectric coefficient and permittivity measured in situ. The depolarization temperatures obtained from direct piezoelectric coefficient measured ex situ as well as the phase transition temperatures obtained from synchrotron X-ray diffraction were found to be at higher temperatures. The mechanisms underlying the relationship between permittivity and piezoelectric depolarization to structural transitions observed in Raman spectroscopy and X-ray diffraction are discussed.

Structural evolution of bismuth sodium titanate induced by a-site non-stoichiometry: Neutron powder diffraction studies

“…Similarly, solid solution of BNT with BaTiO 3 exhibits rich structural phases 2,7 as a function of composition and poling field with enhanced ferroelectric response near the morphotropic phase boundary 5 . In addition, recent works report that a doping on perovskite A-and B-site [8][9][10] modifies physical properties such as depolarization temperature, T d and piezoelectric constant (d 33 ). For example, a doping of lanthanide ions 8,11 on the A-site decreases the depolarization temperature, T d .…”

Dramatic influence of Dy3+ doping on strain and domain structure in lead-free piezoelectric 0.935(Na1/2Bi1/2)TiO3−0.065BaTiO3 ceramics

“…Based on the aforementioned discussion, one can believe that the intricate variations of phonon modes are the operating mechanism for the ferroelectric phase transformation. 5,21 Figs. 2(a)-2(f) show polarization versus E-field (P-E) and strain versus E-field (S-E) measurements at room temperature.…”

“…The relatively broadening phonon bands [e.g., A 1 Raman modes could be observed due to the B-site disorder caused by Dy 3+ doping. 5 The mid-frequency region at about 420∼700 cm −1 is related to the vibration of the TiO 6 octahedra. 5,20 Note that changes in the region are related to the polar Ti-cation displacement and octahedron-tilt.…”

“…5 The mid-frequency region at about 420∼700 cm −1 is related to the vibration of the TiO 6 octahedra. 5,20 Note that changes in the region are related to the polar Ti-cation displacement and octahedron-tilt. Furthermore, one can see a red-shift in frequency for the A (3) 1 mode of 2%Dy:NBBT in comparison to NBBT, which is consistent with Dy-doped NBT.…”

“…[1][2][3][4] Around the morphotropic phase boundary (MPB), the Na 1/2 Bi 1/2 TiO 3 -BaTiO 3 (NBBT), Na 1/2 Bi 1/2 TiO 3 -K 1/2 Bi 1/2 TiO 3 -SrTiO 3 (NBT-KBT-ST), as well as Na 1/2 Bi 1/2 TiO 3 -BaTiO 3 -K 1/2 Na 1/2 NbO 3 (NBT-BT-KNN) are nonpolar and cubic above the Curie temperature (T c ), yet become spontaneously polarized and mechanically distorted below T c . [5][6][7] Indeed, typical ferroelectrics consist of complex domain patterns with different polarization directions, which can be switched under sufficiently large E-field. Accompanying the domain switching (90…”