Dingquan Xiao

Piezoelectric and ferroelectric properties of [Bi0.5(Na1−x−yKxLiy)0.5]TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics Bi0.5(Na1-x-yKxAgy)0.5TiO3 [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K+ and Ag+ on the electrical properties were examined. X-ray diffraction patterns indicate that K+ and Ag+ ions partially substitute for the Na+ ions in Bi0.5Na0.5TiO3 and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric constant d33=189 pC/N, electromechanical coupling factor kp=35.0%, remanent polarization Pr=39.5 μC/cm2, and coercive field Ec=3.3 kV/mm, respectively. The curves of the dielectric constant er and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase decreases with increasing the K+ content for the compositions researched. The dependencies of kp and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature Td of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d33=134 pC/N, kp=32.5%) and strong ferroelectricity (Pr=39.5 μC/cm2, Ec=4.1 kV/mm) at room temperature, is above 160 °C.

Effects of K∕Na ratio on the phase structure and electrical properties of (KxNa0.96−xLi0.04)(Nb0.91Ta0.05Sb0.04)O3 lead-free ceramics

(KxNa0.96−xLi0.04)(Nb0.91Ta0.05Sb0.04)O3 (x=0.32–0.56) lead-free piezoelectric ceramics were prepared by conventional sintering. The effects of K∕Na ratio on the phase structure and electrical properties of the ceramics were studied. These results indicate that the phase structure undergoes a transition from orthorhombic to tetragonal phase with increase of x. The ceramics with x=0.38 exhibit enhanced electrical properties (d33∼306pC∕N; kp∼48%; kt∼49%; Tc∼337°C; ϵr∼1327; tanδ∼2.5%; Pr∼34.9μC∕cm2; Ec∼11.3kV∕cm). Enhanced electrical properties of the ceramics should be attributed to the polymorphic phase transition near room temperature. These results show that the ceramic with x=0.38 is a promising lead-free piezoelectric material.

Lead-free Piezoelectrics Based on Potassium–Sodium Niobate with Giant d33

High-performance lead-free piezoelectrics (d33 > 400 pC/N) based on 0.96(K0.5Na0.5)0.95Li0.05Nb1-xSbxO3-0.04BaZrO3 with the rhombohedral-tetragonal (R-T) phase boundary have been designed and prepared. The R-T phase boundary lies the composition range of 0.04 ≤ x ≤ 0.07, and the dielectric and piezoelectric properties of the ceramics with the compositions near the phase boundary are significantly enhanced. In addition, the ceramic with x = 0.07 has a giant d33 of ~425 pC/N, which is comparable to that (~416 pC/N) of textured KNN-based ceramics (Saito, Y.; Takao, H.; Tani, T.; Nonoyama, T.; Takatori, K.; Homma, T.; Nagaya, T.; Nakamura, M. Nature 2004, 432, 84). The underlying physical mechanisms for enhanced piezoelectric properties are addressed. We believe that the material system is the most promising lead-free piezoelectric candidates for the practical applications.

Effects of Ag content on the phase structure and piezoelectric properties of (K0.44−xNa0.52Li0.04Agx)(Nb0.91Ta0.05Sb0.04)O3 lead-free ceramics

(K0.44−xNa0.52Li0.04Agx)(Nb0.91Ta0.05Sb0.04)O3 lead-free piezoelectric ceramics were prepared by normal sintering. The effects of Ag content on the phase structure and piezoelectric properties of the ceramics were mainly studied. These results show that the phase structure undergoes a transition from orthorhombic to tetragonal phase with increasing x from 0.00 to 0.06. The optimum Ag content enhances the piezoelectric properties, and the Curie temperature increases with increasing x. The ceramics with x=0.02 exhibit enhanced electrical properties (d33∼263pC∕N, kp∼45.3%, TC∼353°C, er∼1478, and tanδ∼2.3%) and good aging characteristics. These results show that the ceramic with x=0.02 is a promising lead-free piezoelectric material.

Compositional dependence of phase structure and electrical properties in (K0.42Na0.58)NbO3-LiSbO3 lead-free ceramics

(1−x)(K0.42Na0.58)NbO3-xLiSbO3 [(1−x)KNN-xLS] lead-free piezoelectric ceramics were prepared by the conventional mixed oxide method. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases was identified in the composition range of 0.04<x<0.06. The ceramics near the MPB exhibit a strong compositional dependence and enhanced piezoelectric properties. The ceramics with 5 mol. % LS exhibit enhanced electrical properties (d33∼270 pC/N, kp∼47.2%, Tc∼364 °C , To-t=35 °C, er∼1412, tan δ∼2.8%, and Pr∼25.7 μC/cm2; Ec∼11.1 kV/cm) and possess low dielectric loss (<2%) at 10 and 100 kHz at high temperature (250–400 °C). The low dielectric loss at high temperature is very important for high-temperature application of the ceramics. The related mechanism of the enhanced electrical properties of the ceramics was also discussed. These results show that (1−x)KNN-xLS (x=0.05) ceramic is ...

The structural origin of enhanced piezoelectric performance and stability in lead free ceramics

Lead-based piezoelectric materials are currently facing global restrictions due to their lead toxicity. Thus it is urgent to develop lead-free substitutes with high piezoelectricity and temperature stability, among which, potassium-sodium niobate [(K,Na)NbO3, KNN] has the most potential. It is very difficult to simultaneously achieve high piezoelectric performance and reliable stability in KNN-based systems. In particular, the structural/physical origin for their high piezoelectricity is still unclear, which hinders property optimization. Here we report the achievement of high temperature stability (less than 10% variation for electric field-induced strain from 27 °C to 80 °C), good fatigue properties (stable up to 106 cycles) as well as an enhanced piezoelectric coefficient (d33) of 525 pC N−1 in (1 − x)(K1−yNay)(Nb1−zSbz)O3–xBi0.5(Na1−wKw)0.5HfO3 (KNNS–BNKH) ceramics through manipulating the rhombohedral–tetragonal (R–T) phase boundary. The structural origin of their high piezoelectric performance can be attributed to a hierarchical nanodomain architecture, where the local structure inside nanodomains comprises R and T nanotwins. The physical origin can be attributed to low domain wall energy and nearly vanishing polarization anisotropy, facilitating easy polarization rotation among different states. We believe that the new breakthrough will open a window for the practical applications of KNN-based ceramics.

Giant d33 in (K,Na)(Nb,Sb)O3-(Bi,Na,K, Li)ZrO3 based lead-free piezoelectrics with high Tc

In this work, a lead-free piezoelectric system based on (1−x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-xBi0.5(Na0.7K0.2Li0.1)0.5ZrO3 [(1−x)KNNS-xBNKLZ] is developed, and a rhombohedral-tetragonal phase boundary is constructed in this system. The relationship between the phase boundary and the piezoelectric properties of the (1−x)KNNS-xBNKLZ ceramics is illuminated. The coexistence of a tetragonal phase and a rhombohedral phase is identified in the composition range of 0.03   300 pC/N) of ∼210 °C. We believe that the (1−x)KNNS-xBNKLZ system is very promising for lead-free piezoelectric applications.

Effects of K content on the dielectric, piezoelectric, and ferroelectric properties of 0.95(KxNa1−x)NbO3−0.05LiSbO3 lead-free ceramics

The effects of K content on the dielectric, piezoelectric, and ferroelectric properties of 0.95(KxNa1−x)NbO3−0.05LiSbO3 (0.95KxNN−0.05LS) (x=0.25–0.75) lead-free piezoelectric ceramics prepared by conventional solid-state sintering were studied. The experimental results show that the dielectric, piezoelectric, and ferroelectric properties strongly depend on K content in the 0.95KxNN−0.05LS ceramics. The 0.95KxNN−0.05LS (x=0.40) ceramics exhibit enhanced electrical properties (d33≈280 pC/N; kp≈49.4%; Tc∼364 °C; To-t=25 °C; er≈1463; tan δ≈2.3%; Pr∼30.8 μC/cm2; Ec∼14.0 kV/cm). The enhanced electrical properties of 0.95KxNN−0.05LS (x=0.40) ceramics are attributed to the polymorphic phase transition near room temperature. These results show that 0.95KxNN−0.05LS (x=0.40) ceramic is a promising lead-free piezoelectric material.

Synthesis and piezoelectric properties of lead-free piezoelectric [Bi0.5(Na1−x−yKxLiy)0.5]TiO3 ceramics

Abstract A new group of lead-free piezoelectric ceramics, [Bi 0.5 (Na 1− x − y K x Li y ) 0.5 ]TiO 3 , were invented. These ceramics were prepared by conventional ceramic sintering technique. The results of X-ray diffraction (XRD) data show that the ceramics possess almost pure perovskite phase with a little unknown phase when y ≤0.20. The measurements of dielectric and piezoelectric properties reveal that the ceramics with high amount of K + and low amount of Li + provide relatively high piezoelectric charge constant d 33 (up to 180 pC/N) and high planar electromechanical coupling factor k p (up to 35.0%). The fabrication technique for these ceramics is stable. It is obvious that the ceramics can be used in practical applications.

Piezoelectric Properties of LiSbO3-Modified (K0.48Na0.52)NbO3 Lead-Free Ceramics

Lead-free piezoelectric (1-x)(K0.48Na0.52)NbO3–xLiSbO3 [(1-x)KNN–xLS] ceramics were prepared by conventional sintering. A morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases was identified in the composition range of 0.04<x<0.06. The ceramics near the MPB exhibit a strong compositional dependence, and good piezoelectric properties, temperature stability, and aging characteristics. It was found that the samples with 5 mol % LS exhibited enhanced electrical properties (d33~262 pC/N, kp~46%, Tc~373 °C, To–t~60 °C). These results show that (1-x)KNN–xLS ceramic is a promising lead-free piezoelectric material.