Phase transition, microstructure and electric‐field‐induced large strain in Bi_0.5(Na_0.85K_0.15)_0.5TiO₃–BiAlO₃ lead‐free piezoelectric ceramics

Abstract

Lead-free (1 À x)(Bi 0.5 (Na 0.85 K 0.15 ) 0.5 TiO 3 )-xBiAlO 3 (abbreviated as BNKT15-BA, x ¼ 0, 0.025, 0.050, 0.075, 0.100) piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The phase-transition behavior in BNKT15-BA ceramics with respect to changes in composition were investigated using X-ray diffraction analysis, dielectric and ferroelectric characterizations, and electric-field-induced strain. The results of X-ray diffraction revealed that a pure perovskite phase was formed for x 0.050. A phase transition from the coexistence of rhombohedral and tetragonal to a pseudocubic phase was observed at x ¼ 0.050. The dielectric constant continuously decreased with increase in BA content, and the depolarization temperature (T d ) was shifted toward lower temperature. The polarization and strain hysteresis loops indicate that the ferroelectric order of BNKT15 ceramics is disrupted significantly with the addition of BA. The destabilization of ferroelectric order is accompanied by an enhancement of bipolar and unipolar strains, and a large electric-field-induced strain (S ¼ 0.21%) and a normalized strain (d à 33 ¼ S max /E max ¼ 276 pm/V) were obtained at x ¼ 0.050. These results suggested that the BNKT15-BA system can be employed in lead-free electromechanical devices.

Structure and electrical properties in the K1/2Bi1/2TiO3–K1/2Bi1/2ZrO3 solid solution (KBT–KBZ)

“…Among the different available materials, Bi‐based compounds such as Na 1/2 Bi 1/2 TiO 3 (NBT) and K 1/2 Bi 1/2 TiO 3 (KBT) present interesting dielectric and ferroelectric–piezoelectric properties 6, 7, 30–32. As for PZT, such properties can be easily modulated by binary or ternary solid‐solution formation, such as NBT–KBT 33–35, NBT–BaTiO 3 36, NBT–KBT–BaTiO 3 37, NBT–KBT–Li 0.5 Bi 0.5 TiO 3 38, 39, NBT–SrTiO 3 40, 41, double substitutions like for NBT–PbZrO 3 42, NBT–BiScO 3 42, NBT–BiFeO 3 42–44, NBT–KBT–BiAlO 3 45 or more comple x substitution on A‐sites 46. Some of these substitutions improve the piezoelectric properties of NBT and KBT, while some of them suppress the ferroelectricity, inducing sometimes interesting dielectric properties and/or relaxor behavior.…”

Dielectric, Piezoelectric Properties and Field-Induced Large Strain of Bi(Zn0.5Ti0.5)O3-Modified Morphotropic Phase Boundary Bi0.5(Na0.82K0.18)0.5TiO3Piezoelectric Ceramics

“…Ceramics without added BZT revealed a normalized strain (d à 33 ¼ 228 pm/V) in agreement with reported studies. 8,17) As the BZT content was increased, the d à 33 value increased linearly to x ¼ 0:07 and then decreased significantly. The highest d à 33 of 385 pm/V was obtained at x ¼ 0:07 in the studied composition range, suggesting that BNKT18-BZT is a promising lead-free candidate material.…”

“…Ceramics with x 0:050 had dielectric curves that exhibited two dielectric anomalies at all of the measured frequencies, one around 120 C and another around 270 C, similar to those of BNT and BNT-based ceramics. 5,9,17,18) The first inflection point/or peak is often called the depolarization temperature (T d ), where the ferroelectricity significantly decreases, while the latter is called the maximum temperature (T m ), at which the dielectric constant reaches a maximum. However, as can be seen from Fig.…”

“…These results suggest that the BZT concentration induced a phase transition from normal ferroelectrics to ferroelectric with a diffuse transition in the BNKT18-BZT ceramics similar to that observed in BNT-based ceramics. 17,18) Dielectric loss was nearly unaffected and varied between 0.03 and 0.05. Figure 3 shows polarization hysteresis loops of BNKT18-BZT ceramics at room temperature.…”