Influence of Zn²⁺ doping on the morphotropic phase boundary in lead‐free piezoelectric (1 – x)Na_1/2Bi_1/2TiO₃‐xBaTiO₃

Abstract

A series of morphotropic phase boundary (MPB) compositions of (1-x) Na 1/2 Bi 1/2 TiO 3 -xBaTiO 3 (x = 0.05, 0.055, 0.06, 0.065, 0.07), with and without 0.5 mol% Zn-doping was synthesized using the solid-state route. The samples were characterized using X-ray diffraction, dielectric analysis, and electromechanical measurements (piezoelectric d 33 coefficient, coupling factor k p , mechanical quality factor Q m , and internal bias field E bias ). The increase in the ferroelectric-relaxor transition temperature upon Zn-doping was accompanied by a shift of the MPB toward the Na 1/2 Bi 1/2 TiO 3 -rich side of the phase diagram.Higher tetragonal phase fraction and increased tetragonal distortion were noted for Zn-doped (1 -x)Na 1/2 Bi 1/2 TiO 3 -xBaTiO 3 . In addition, ferroelectric hardening and the presence of an internal bias field (E bias ) were observed for all doped compositions. The piezoelectric constant d 33 and the coupling coefficient k p decreased by up to ∼30%, while a 4-to 6-fold increase in Q m was observed for the doped compositions. Apart from establishing a structure-property correlation, these results highlight the chemically induced shift of the phase diagram upon doping, which is a crucial factor in material selection for optimal performance and commercialization.

Effect of thermal depolarization on the poling‐induced domain texture and piezoelectric properties in Mg‐doped NBT‐6BT

“…Upon doping, the lattice distortion of the poled material is enhanced in the R 3 c and the P 4 mm phases at all the temperatures where these phases are present. These observations have been reported before for unpoled Zn‐ and Mg‐doped NBT‐BT together with an increase in tetragonal phase fraction 9,41,42 . Also in this study, Mg doping increases the tetragonal phase fraction in the poled state of the bulk material from 7% to 25% at 30°C (Figure 2).…”

“…These observations have been reported before for unpoled Znand Mg-doped NBT-BT together with an increase in tetragonal phase fraction. 9,41,42 Also in this study, Mg doping increases the tetragonal phase fraction in the poled state of the bulk material from 7% to 25% at 30 • C (Figure 2).…”

Texture-based ferroelectric hardening in Na1/2Bi1/2TiO3 -based piezoceramics

“…The highest piezoelectric activity is found around the MPB, where the tetragonal and rhombohedral phases coexist, both in the unpoled and poled states. NBT-xBT exhibits a piezoelectric coefficient, d 33 , of 125-167 pC/N at 6-7 mol % BT [10,12] and NBT-xKBT features a d 33 of 134-190 pC/N around 19-22 mol % KBT [13][14][15]. At the MPB, both materials are nonergodic relaxors, meaning a nonreversible ferroelectric state can be induced by application of an electric field or mechanical stress [16,17].…”

Influence of defect chemistry on the electromechanical strain properties of BNT–ST‐based ternary systems

“…41 These samples exhibit a high E c and low strain compared to the other two samples, which hints at a hardening effect that occurs despite the unusual oxygen mobility. 42,43 In other words, these data suggest that the nonergodicity in a relaxor can be stabilized with a high concentration of oxygen-vacancy-related defect complexes. 41,44 Accordingly, the domain mobility is restrained by the pinning effect, which is responsible for the depressed strain behavior in BNT-24ST ceramics.…”

“…Even though the high‐temperature conductivity is high, the BNT–24ST and 1CT samples can be poled and tested at room temperature 41 . These samples exhibit a high E c and low strain compared to the other two samples, which hints at a hardening effect that occurs despite the unusual oxygen mobility 42,43 . In other words, these data suggest that the nonergodicity in a relaxor can be stabilized with a high concentration of oxygen‐vacancy‐related defect complexes 41,44 .…”