Enhancement of the dielectric, piezoelectric, and ferroelectric properties in BiYbO₃-modified (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ lead-free ceramics

Abstract

Lead-free (1−x)(Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃−xBiYbO₃ [(1−x)BCTZ−xBYO] piezoelectric ceramics in the range of BYO concentrations were prepared by the conventional oxide-mixed method, and the effect of BYO content on their microstructure, crystalline structure, density and electrical properties was investigated. A dense microstructure with large grain was obtained for the ceramics with the addition of BYO. The ceramics with x=0.1% exhibit an optimum electrical behavior of d₃₃~580 pC/N, r~10.9 Ω, k_p~56.4%, and tan δ~1.12% when sintered at a low temperature of ~1350 °C. When the measuring electric field is 40 kV/cm, the well-saturated and square-like P–E loops for the ceramics were observed with P_r~12.2 μC/cm² and E_c~1.83 kV/cm.

Introduction

Recently, due to environmental concerns, lead-free piezoceramics have been given to much attention [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. In the search for lead-free piezoceramics candidates, such as Bi_0.5Na_0.5TiO₃ [5], [6], [11] and K_0.5Na_0.5NbO₃ [7], [8], [12] materials have been extensively conducted to improve their piezoelectric properties, but their piezoelectric constants are lower than that of lead zirconate titanate (PZT) piezoelectric ceramics [13], [14], [15]. Therefore, it is necessary to develop lead-free piezoceramics systems with higher piezoelectric properties to replace PZT ceramics.

In recent years, an increasing amount of research has been done on the new piezoelectric materials of the BaTiO₃-based ceramics systems [1], [2], [3], [4], [16], [17], [18]. In these systems, Mn- and Cu-modified (1−x)BiFeO₃−xBaTiO₃ ceramics exhibited a high T_c of ~485 °C, but with a low-field piezoelectric properties of d₃₃~170 pC/N, k_p~34.2%, which was reported by Zhou [1]. In 2009, a surprisingly high piezoelectric property of d₃₃~620 pC/N has been reported for the BaTiO₃-based ceramics by Ren [18]. Since then, a new piezoelectric system (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCTZ) with a super high d₃₃ was extensively investigated [16], [19], [20], [21]. Hao et al. [22] showed that the samples with grain size >10 μm exhibit excellent piezoelectric properties as d₃₃~470 pC/N, k_p~48% using different sintering methods for BCTZ piezoceramics. Damjanovic et al. [17] reported that the temperature-induced anomalies in the dielectric, piezoelectric, elastic coefficients and Raman spectroscopy of BCTZ ceramics. The [(Ba_1−3x/2Bi_x)_0.85Ca_0.15](Ti_0.9Zr_0.1)O₃ ceramics with x=0.75% exhibits an optimum electrical behavior of d₃₃~361 pC/N and k_p~40.2% [23]. In our previous study, CeO₂-modified BCTZ ceramics exhibited improved electrical properties of d₃₃~600 pC/N, k_p~51%, tan δ~1.2% [24]. In addition, Shi [25] found (1−x)(0.36BiScO₃–0.64PbTiO₃)−xBiYbO₃ piezoelectric ceramics to exhibit a good piezoelectric constant d₃₃~443 pC/N with a high Curie temperature of T_c~450 °C. Feng et al. [26] stated that a very promising material of xBiYbO₃–(1−x)PbTiO₃ piezoelectric ceramics for a high Curie temperature (T_c up to 590 °C). And the BYO material has a high Curie temperature of T_c~650 °C [27].

In this present work, the microstructure, dielectric, piezoelectric, and ferroelectric properties of (1−x)BCTZ−xBYO ceramics were studied. With the optimized processing, the enhanced d₃₃ and tan δ in the (1−x)BCTZ−xBYO system were obtained. These results show that the (1−x)BCTZ−xBYO ceramics with good electrical properties are induced by doping an optimum BYO content.