Phase coexistence and high piezoelectric properties in (K_0.40Na_0.60)_0.96Li_0.04Nb_0.80Ta_0.20O₃ceramics

Abstract

Lead-free (KxNa1−x)0.96Li0.04 Nb0.80Ta0.20O3 ceramics with x = 0.10–0.70 were prepared by the conventional solid-state reaction technique. The influence of the K/Na ratio on the microstructure, crystallographic structure, phase transition and piezoelectric properties was investigated. It has been disclosed that the phase transition temperature TO–T drastically decreases with x in the narrow compositional range of x = 0.30–0.40 and the phase coexistence of the orthorhombic structure and the tetragonal structure occurs near x = 0.40. The ceramics with x = 0.40 shows high piezoelectric properties (d33 = 254 pC N−1, kp = 51.5%, kt = 49.4% and k33 = 66.6%, respectively) with low dielectric loss (tan δ = 1.5%) and weak temperature dependence between 10 and 85 °C. In particular, the piezoelectric properties remain almost unchanged in the thermal ageing test from −125 to 300 °C. Therefore, this ceramic is considered to be a very promising lead-free piezoelectric material for practical applications. The relation of piezoelectric properties with morphotropic phase boundary and polymorphic phase transition was discussed.

Polymorphic phase transition and excellent piezoelectric performance of (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 lead-free ceramics

“…Figure 3 delineates representatively the piezoelectric temperature stability in terms of k p and k 33 changes with temperature. In contrast to the results previously obtained for other KNN-based ceramics, 6,8,13,[17][18][19][20][21][22] both k p and k 33 show weak temperature dependence over a wide measured temperature range from Ϫ50 to 150°C. In particular, little change in k p and k 33 is seen over the common usage temperature interval between Ϫ40 and 85°C, where k p and k 33 show values larger than 0.46 and 0.61, respectively.…”

“…However, in contrast to the classical behaviors of nearly temperature-independent MPBs, such as in Pb͑Zr, Ti͒O 3 ceramics, strong piezoelectric temperature dependence is usually observed in KNN-based ceramics with high piezoelectric properties. 6,8,13,[17][18][19][20][21][22] This temperature dependence is an obstacle to practical applications. It is therefore very important from both scientific and technological viewpoints to clarify whether KNN-based ceramics that simultaneously possess high piezoelectric properties and good piezoelectric stability can exist when a polymorphic phase transition occurs around room temperature.…”

“…This paper reports our experimental results for a KNNbased ceramic with the unique chemical composition of ͑K 0.55 Na 0.45 ͒ 0.965 Li 0.035 Nb 0.80 Ta 0.20 O 3 ͑KNLNT͒, which not only deviates largely from the well-believed essential compositional condition of a nearly equal molar ratio of K/Na 3-5,7 but also is K-rich instead of the previously investigated Na-rich compositions that show high piezoelectric properties. 2,[13][14][15] The ceramic shows outstanding perfor-mance with high piezoelectric properties and weak piezoelectric temperature dependences over the common usage temperature interval between Ϫ40 and 85°C. Moreover, its piezoelectric properties are highly stable in the severe thermal aging test down to the experimental limit of −150°C and up to about 300°C.…”

“…The preparation and characterization procedures adopted in this study were the same as those used in previous studies. 10,13 Sintering was carried out under ambient conditions at 1120°C for 4 h. Poling was accomplished in silicon oil at 120°C under a dc field of 3.5 kV mm −1 for 30 min. Then, piezoelectric and dielectric measurements were performed 24 h after poling.…”

Phase transition and electrical properties of lead free (Na0.5K0.5)NbO3–BiAlO3 ceramics

“…The base for achieving intrinsically enhanced properties is on the formation of a MPB between orthorhombic and tetragonal (or rhombohedral) phases. It has been basically believed that more spontaneous polarization states are available owing to a coexistence of two kinds of ferroelectric phases [14].…”