Phase coexistence and high electrical properties in (KxNa0.96−xLi0.04)(Nb0.85Ta0.15)O3 piezoelectric ceramics

Abstract

Articles you may be interested inPhase transitional behavior, microstructure, and electrical properties in Ta-modified [ ( K 0.458 Na 0.542 ) 0.96 Li 0.04 ] NbO 3 lead-free piezoelectric ceramics Improved temperature stability of CaTiO 3 -modified [ ( K 0.5 Na 0.5 ) 0.96 Li 0.04 ] ( Nb 0.91 Sb 0.05 Ta 0.04 ) O 3 lead-free piezoelectric ceramics J. Appl. Phys.͑K x Na 0.96−x Li 0.04 ͒͑Nb 0.85 Ta 0.15 ͒O 3 lead-free piezoelectric ceramics were produced by conventional solid-state reaction method. The effects of K/Na ratio on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics have been investigated. The phase structure of the ceramics undergoes a transition from orthorhombic to tetragonal phase with increasing x. A double-degenerate symmetric O-Nb-O stretching vibration v 1 and a triply degenerate symmetric O-Nb-O bending vibration v 5 are detected as relatively strong scattering in the Raman spectra. The peak shifts of v 5 and v 1 modes all have a discontinuity with x between 0.42 and 0.46, which may suggest the coexistence of orthorhombic and tetragonal phases in this range. Properly modifying x reduces the sintering temperature, promotes the grain growth behavior, and improves the density of the ceramics. The polymorphic phase transition ͑at T o-t ͒ is shifted to near room temperature by increasing x to 0.44 ͑K/Na ratio of about 0.85:1͒, and the coexistence of orthorhombic and tetragonal phases in the ceramics at x = 0.44 results in the optimized electrical properties ͑d 33 = 291 pC/ N, k p = 0.54, r = 1167, tan ␦ = 0.018, T o-t =35°C, T C = 351°C, P r = 27.65 C / cm 2 , and E c = 8.63 kV/ cm͒. The results show that the equal K/Na ratio is not an essential condition in obtaining optimized electrical properties in ͑K x Na 0.96−x Li 0.04 ͒͑Nb 0.85 Ta 0.15 ͒O 3 ceramics.

Excellent piezo-/pyro-/ferroelectric performance of Na 0.47 K 0.47 Li 0.06 NbO 3 lead-free ceramic near polymorphic phase transition

“…As expected from XRD and SEM, 1090 o C sintered NKLN ceramic resulted in a higher value of d 33, as 450 pCN À1 , which is comparable to the conventional PZT ceramic. The d 33 value obtained for the NKLN ceramic is much higher than the previously reported values of KNN-based ceramics [8][9][10][11][12][13]15,17] and some other lead-free materials [5,6]. The piezoelectric charge coefficient is relatively higher than the value obtained by Saito et al [14] in the textured LF4, which indicates that the 1090 o C sintered NKLN ceramic is a good lead-free alternative to PZT for piezoelectric applications such as transducers, ultrasonic sensors and actuators.…”

“…This PPT is quite similar to a classical MPB; in addition, it consists of two coexisting phases and hence shows temperature dependence [9]. Various reports suggest that highly improved piezoelectric properties in KNN-based ceramics can be obtained when this PPT is shifted to room temperature by adding an appropriate amount of Li at its A-site and Sb, Ta at its B-site [9][10][11][12][13]. A breakthrough was made by Saito et al [14] when they achieved a high piezoelectric charge coefficient (d 33 ) of 416 pCN À1 , which is comparable to that of PZT, in the textured Li, Ta, Sb-modified KNN abbreviated as LF4, due to its uniform brick-like quadrangular grains.…”

Improved piezoelectric properties of (KxNa1−x)0.94Li0.06NbO3 lead-free ceramics fabricated by combining two-step sintering

“…2. In KNN-based systems [9,12,13,17], ceramics with the mixed phase usually has a T o-t close to room temperature, and those with orthorhombic phase process a higher T o-t far away from room temperature. In the present work, the minimum T o-t value close to room temperature was obtained in samples with K/Na ratio $1 which corresponds to its coexistence of two phases.…”

“…To improve the densification and piezoelectric properties of KNN ceramics, many studies have been devoted to the property improvement by chemical modification [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], and found that Li substitution to K and/or Na sites plays an important role in enhancing the piezoelectric properties of the KNN system [5,14,15]. Moreover, changing K/Na ratio of KNNbased ceramics [13,16,17] can also be very helpful for fabricating high-performance ceramics by shifting the orthorhombic-tetragonal polymorphic phase transition (PPT) to near room temperature.…”

Effect of CaZrO3 on phase structure and electrical properties of KNN-based lead-free ceramics

“…Therefore, there is a great need to develop lead free piezoelectric ceramics with good piezoelectric properties for replacing the lead-based ceramics in various applications. [3][4][5] Many lead free ferroelectric materials such as barium titanate (BT), 6,7 potassium niobate(KN), 8 potassium sodium niobate(KNN), [9][10][11][12][13][14][15][16][17][18][19][20][21] potassium tantalate niobate(KTN) [22][23][24][25] and bismuth sodium titanate(BNT), [26][27][28] have been investigated. Among all the lead free materials, K 0.5 Na 0.5 NbO 3 (KNN), the solid solution of ferroelectric KNbO 3 and antiferroelectric NaNbO 3 , has been studied extensively, considered one of the most promising candidates for lead-free piezoelectric ceramics for its high Curie temperature, outstanding piezoelectric and ferroelectric properties, and large electromechanical coupling coefficients as well as its better environmental compatibility than other lead-free piezoelectric ceramics, which superior piezoelectric attribute to orthorhombic-tetragonal polymorphic phase transition(PPT) around room temperature, and considered to be closely associated with phase coexistence in a way similar to that morphotropic phase boundary (MPB)-a phase boundary that a narrow composition region with orthorhombic or monoclinic phase separating rhombohedral and tetragonal phases in solid solutions-for widely used PZT-based ceramics.…”