Correlations between structure, microstructure, density and dielectric properties of the lead-free ferroelectrics Bi_0.5(Na,K)_0.5TiO₃

Abstract

Solid solutions of the lead-free ferroelectric oxides Bi 0:5 Na 0:5 TiO 3 (BNT) and Bi 0:5 K 0:5 TiO 3 (BKT), represented as (1 À x)BNTxBKT, are studied for very close compositions in the range 0 x 0:36 to understand the correlation between the structure and the properties. Compositions are varied in steps of Áx ¼ 0:02 in the range 0 x 0:1 and 0:2 x 0:36 and Áx ¼ 0:01 in the range 0:1 x 0:2, to precisely locate the structural transition as well as the morphotropic phase boundary (MPB) region and the compositional region of best performance. Rietveld refinement analysis of the powder X-ray diffraction patterns showed monoclinic phase up to x = 0.17 and a mixture of monoclinic and tetragonal phases for x > 0:17. Similarly, the density and the dielectric constant showed linear variation up to x ¼ 0:17 and a large increase above this composition, showing maximum values in the compositional range 0:22 x 0:26, corresponding to the MPB region. Microstructural features also showed corresponding changes, indicating close relationship between the structure, microstructure and properties of the different compositions.

Effect of Li Substitution on the Structure and Dielectric Constant of Bi0.5(Na⁠1-xLix)0.5TiO⁠3 (0 ≤ x ≤ 0.20) Solid Solution Series

“…The maximum dielectric constant observed for the BNT-BLT compositions is 420. However this value is relatively small, when compared to the maximum dielectric constant observed for the BNT-BKT series which is 1800 [23]. For the BNT-BKT system, maximum dielectric constant is observed in the MPB region where the monoclinic and tetragonal phases co-exist.…”

“…S1, ESM). Since the changes in the lattice parameters are very small with increasing Li content, it may be concluded that there is no major structural phase transformation as observed in the case of (1-x)BNT-xBKT, where the structure is found to change from monoclinic to tetragonal at higher BKT content [23]. The small change in the variation of the lattice parameters around x ≈ 0.1 may be due to the local structural changes, arising from the inhomogeneous distribution of the substituted Li ions in the lattice for x < 0.1.…”

Correlation between the structure and dielectric constant of Bi0.5(Na1‐xLix)0.5TiO3 (0 ≤ x ≤ 0.20) solid solutions

“…Many other studies have also reported on the enhanced piezoelectric and dielectric performances of Bi 0.5 (Na 1‐ x K x ) 0.5 TiO 3 in the MPB region 14,21–23 . Anjali et al reported that the onset of the MPB region is at x = 0.16 and the MPB region corresponds to 0.16 ≤ x ≤ 0.24 where better performance parameters are observed 24,25 …”

Effect of the sintering technique on the ferroelectric and d33 piezoelectric coefficients of Bi0.5(Na0.84K0.16)0.5TiO3 ceramic

“…Lead-free piezoelectric ceramics exhibit superior electromechanical responses near the morphotropic phase boundary (MPB). It is reported that their high piezoelectric response is due to the phase coexistence of rhombohedral and tetragonal phases at the optimal composition, i.e., the MPB [3][4][5][6][7].…”