Enhancing piezoelectric of d₃₃ coefficient of new (1−x)BNKLLT–xNKLNST lead-free ceramics synthesized by the solid state combustion technique

ABSTRACT

The objective of this paper is to modify the piezoelectric properties of Bi_0.5(Na_0.68K_0.22Li_0.1)_0.5TiO₃+0.10 wt% of La₂O₃ (BNKLLT) ceramics by the addition of (K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.10Sb_0.06)O₃ (NKLNST) compound with forming solid state. Novel binary (1−x)BNKLLT–xNKLNST lead-free piezoelectric ceramics with an x content from 0 to 0.10 (step 0.02) were prepared via the solid state combustion technique with glycine used as the fuel. The affectation of x content on the structure evolution, morphology and electrical response of these ceramics were examined. The coexistence structure between rhombohedral and tetragonal was observed in the x = 0 sample. As x content increased between 0.02 and 0.04, the phase formation became a higher tetragonality structure. With x content ≥ 0.06, the phase formation began to change to a pseudo cubic phase. The microstructure exhibited a polyhedral grain shape in all samples. The average grain size of (1−x)BNKLLT–xNKLNST samples with various x content was in the same range (1.36–1.52 µm). The relative theoretical density increased from 96.7 to 97.2% when the NKLNST concentration was increased up to 0.04 and then decreased at higher concentrations. The reduction of T_FA, T_SA and the weak ferroelectric behaviour of these ceramics with increasing x content were observed. The resulting (1–x)BNKLLT–xNKLNST ceramics exhibited large piezoelectric coefficient of d₃₃ up to 266 pC/N near the rhombohedral-tetragonal MPB at x = 0.04.

KEYWORDS:

• BNT-based
• solid state combustion technique
• structure evolution
• piezoelectric properties

Acknowledgments

This work was supported by the Higher Education Research Promotion and National Research University project of Thailand, Office of the Higher Education Commission. The authors wish to thank the Department of Physics, Faculty of Science, Naresuan University for their supporting facilities. Thanks are also given to Dr. Kyle V. Lopin for his help in editing the manuscript.