Lead-Free Piezoceramics: Revealing the Role of the Rhombohedral–Tetragonal Phase Coexistence in Enhancement of the Piezoelectric Properties

Abstract

Until now, lead zirconate titanate (PZT) based ceramics are the most widely used in piezoelectric devices. However, the use of lead is being avoided due to its toxicity and environmental risks. Indeed, the attention in piezoelectric devices has been moved to lead-free ceramics, especially on (K,Na)NbO3-based materials, due to growing environmental concerns. Here we report a systematic evaluation of the effects of the compositional modifications induced by replacement of the B-sites with Sb(5+) ions in 0.96[(K0.48Na0.52)0.95Li0.05Nb1-xSbxO3]-0.04[BaZrO3] lead-free piezoceramics. We show that this compositional design is the driving force for the development of the high piezoelectric properties. So, we find that this phenomenon can be explained by the stabilization of a Rhombohedral-Tetragonal (R-T) phase boundary close to room temperature, that facilities the polarization process of the system and exhibits a significantly high piezoelectric response with a d33 value as high as ∼400 pC/N, which is comparable to part soft PZTs. As a result, we believe that the general strategy and design principles described in this study open the possibility of obtaining (K,Na)NbO3-based lead-free ceramics with enhanced properties, expanding their application range.

Fabrication of Biocompatible Potassium Sodium Niobate Piezoelectric Ceramic as an Electroactive Implant

“…There were small pores between the grains, which are favorable for the contact of the material with the surrounding body fluids [41]. The XRD pattern in Figure 5b revealed that KNN ceramic was in perovskite phase with orthorhombic-tetragonal phase coexistences, and the relative volume fractions (%) of the T (V T ) and O (V O ) of the two-phase coexistence in this system were calculated as 39 $\pm$ 3 and 61 $\pm$ 5, respectively, from the following equations [25,42]:V T = [I (002) T + I (200) T ]/[I (002) T + I (200) T + I (022) O + I (200) O ], V O = [I (022) O + I (200) O ]/[I (002) T + I (200) T + I (022) O + I (200) O ], where I (002) T , I (200) T , I (022) O and I (200) O are the integrated intensities of the tetragonal (002) and (200) peaks, orthorhombic (022) and (200) peaks.…”

“…Though it possesses passable bio-response according to the research, BT piezoelectric ceramic is difficult to apply because of its poor stability of temperature, and the cytotoxicity of barium and titanium ions cannot be ignored. At present, for potassium sodium niobate, researchers are more inclined to improving the piezoelectric properties by doping antimony (Sb), tantalum (Ta), bismuth (Bi), and other elements [24,25,26,27] with a view to replace lead zirconate titanate in industrial applications. Such doped potassium sodium niobate (KNN)-based piezoelectric ceramics have little potential in the field of implant materials due to the toxicity of the dopant elements, despite the high piezoelectric properties.…”

The NbO6 octahedral distortion and phase structural transition of Eu3+‐doped K0.5Na0.5NbO3–xLiNbO3 ferroelectric ceramics

“…On one hand, Raman is a traditional method to investigate the structure, which could tell the information about the internal modes associated with the NbO 6 octahedron. As Rubio‐Marcos et al reported, it is useful to study the relationship between the structures and the piezoelectric properties of KNN‐based ceramics using the Raman spectroscopy. On the other hand, it has been reported that the photoluminescence spectroscopy of trivalent europium ion (Eu 3+ ) can be used as a probe for small structural distortions caused by phase transition, which have been observed in both glasses and ceramics .…”

Modifying Temperature Stability of (K,Na)NbO3 Ceramics through Phase Boundary

“…As x increased up to 0.02, the intensity of (200) PC peak was higher than that of (002) PC peak (Figure 1a), signifying the involvement of T phase. [11] ε r -T curve of the ceramics with x = 0.02 displayed a board T R-O of −40 ± 20 °C and a T O-T of 72 °C (Figure 1b), suggesting the existence of O phase. Thus, an O-T phase coexistence was deduced in the ceramics with x = 0.02 at room temperature, which was also observed in other KNN-based ceramics.…”