Characteristics improvement of Li_0.058(K_0.480Na_0.535)_0.966(Nb_0.9Ta_0.1)O₃ lead-free piezoelectric ceramics by LiF additions

Abstract

In this study, a series of Li_0.058(K_0.480Na_0.535)_0.966(Nb_0.90Ta_0.10)O₃ + (x)LiF (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 wt%) lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method. The incorporation of LiF could significantly improve the sintering ability of LKNNT ceramics by reducing the optimal sintering temperature from 1090°C to 1020°C. The crystal phases and micro-structures were analyzed by means of the X-ray diffraction and scanning electronic microscopy, respectively. The impedance analyzer was used to measure the Curie temperature, phase transition point, and electro-mechanical coupling factor. And the d₃₃ meter was used to measure the piezoelectric constants.

From the results, due to the addition of 0.2 wt% LiF, uniform and condensed grains can be obtained and hence the sintering temperature can be lowered down. As the contents of LiF increased, the orthorhombic to tetragonal phase transition points T_O-T were almost no changed, but the Curie temperature T_C decreased from 425°C (x = 0) to 405°C (x = 0.5). And furthermore, the electro-mechanical coupling factor k_p and piezoelectric constant d₃₃ were all decreased with increases of LiF contents. Hence, even though the reducing of little amount of piezoelectric characteristics, the LiF addition can improve the sintering ability of the LKNNT ceramics effectively.

Keywords:

• Curie temperature
• lead-free
• LiF
• piezoelectric

Funding

This work will acknowledge the financial support of the Ministry of Science and Technology, R.O.C. (NSC 101-2632-E-218-001-MY3, MOST 104-2623-E-218-001-ET, and MOST 104-2221-E-218-023).