Correlation between Phase Transitions and Piezoelectric Properties in Lead-Free (K,Na,Li)NbO₃–BaTiO₃ Ceramics

Abstract

In this manuscript, we report the polymorphic phase transitions, structural changes and piezoelectric properties of alkali niobate based lead-free ceramics. The phase transitions were characterized as a function of alkali niobate content at room temperature. The results clearly demonstrate that in this system high piezoelectric properties are achieved for a specific fraction of ferroelectric orthorhombic (O) and tetragonal (T) phases. Using Rietveld and powder diffraction analysis, a correlation was established among the piezoelectric response, the fraction of O and T phases, and KNN ratio for three different systems of (K,Na)NbO 3 -BaTiO 3 (KNN-BT), KNN-LiNbO 3 (LN), and (K,Na,Li)NbO 3 (KNLN)-BT.

X-ray analysis of phase coexistence and electric poling processing in alkaline niobate-based compositions

“…However, an orthorhombic symmetry with a ≈ c > b is usually characterized by the splitting of (2 0 0)/(0 0 2) and (0 2 0) peaks owing to the difference between a and b. Compared to (0 2 0) line, the (2 0 0) [15], where I Small-Brag and I Large-Brag are the intensities of (2 0 0) peaks with small Brag angles and large Brag angles, respectively, and SI T and SI O are the sums of peak intensities for tetragonal and orthorhombic phases, respectively, as summarized in Table 1. It can be found that the two-phase coexistence zone covers a broad composition range, which exhibits a different characteristic from that of an MPB.…”

Piezoelectric MEMS for energy harvesting

“…One of the strategies for achieving a higher piezoelectric response has been to modulate the composition such that the O/T transition lies close to room temperature. 73 Another strategy adopted for designing lead-free compositions is based upon the trend between the atomic weight ratio of A to B sites ( R w = W a / W b ) and the longitudinal piezoelectric constant d 33 , as shown in Figure 7b . 74 It can be observed that 1/ R w for KNN ceramics (for Na/K ratio of 0.5) is similar to R w for PZT ceramics at the MPB composition, and both of these materials exhibit high piezoelectric response.…”

Development of KNN-Based Piezoelectric Materials

“…To understand the structure -property correlation in KNN-based ceramics Ahn et al studied the interdependence of piezoelectric coefficient d 33 , tetragonal to orthorhombic transition temperature (T oÀt ) and fraction of tetragonality [80]. This analysis was conducted for three different systems namely KNN-BaTiO 3 (KNN-BT), KNN-LiNbO 3 (KNN-LN) and (K,Na,Li)NbO 3 -BaTiO 3 (KNLN-BT).…”