Wenfeng Liang

Lead-free piezoelectric ceramics based on (0.97 − x)K0.48Na0.52NbO3-0.03Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3-xB0.5Na0.5TiO3 ternary system

In this work, the ternary system of potassium-sodium niobate has been designed to enhance the piezoelectric properties without sacrificing the Curie temperature greatly, and (0.97 − x)K0.48Na0.52NbO3-0.03Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3-xB0.5Na0.5TiO3 ceramics have been prepared by the conventional solid-state method. The effect of B0.5Na0.5TiO3 content on the microstructure and electrical properties of the ceramics is studied. The phase diagram shows a phase boundary of the rhombohedral-tetragonal (R-T) phase coexistence in the composition range of 0.5% < x < 1.5%, and then an enhanced dielectric, ferroelectric, and piezoelectric behavior is obtained at such a phase boundary zone. The ceramic with x = 0.01 has an optimum electrical behavior of d33 ∼ 285 pC/N, kp ∼ 0.40, er ∼ 1235, tan δ ∼ 0.031, Pr ∼ 14.9 μC/cm2, and Ec ∼ 15.2 kV/cm, together with a high Curie temperature of ∼347 °C. The large d33 in such a ternary system is due to a composition-induced R-T phase transition and a higher ɛrPr, and the thermal...

Effect of New Phase Boundary on the Dielectric and Piezoelectric Properties of K0.5Na0.5NbO3- xBaZrO3- yBi0.5Na0.5TiO3Lead-free Ceramics

(1-x-y)K0.5Na0.5NbO3- xBaZrO3- yBi0.5Na0.5TiO3 ceramics (abbreviated as KNN-x, y) were prepared by the conventional solid state reaction method. BaZrO3 results in the increase of T R-O, and Bi0.5Na0.5TiO3 leads to the decrease of T O-T. The ceramics co-modified with these two additives exhibit a new phase boundary. With the shrinkage of O phase in the R–O–T phase structure, the first order O-T phase transition evolved to the secondary order R-T phase transition according to the thermal hysteresis. Enhanced piezoelectric properties (d 33 = 348 pC/N and k P = 43.2%) were obtained near the new phase boundary when x = 0.04 and y = 0.025.

Origin of high mechanical quality factor in CuO-doped (K, Na)NbO3-based ceramics

The origin of a high mechanical quality in CuO-doped (K, Na)NbO3-based ceramics is addressed by considering the correlations between the lattice positions of Cu ions and the hardening effect in K0.48Na0.52 + xNbO3-0.01CuO ceramics. The Cu ions simultaneously occupy K/Na and Nb sites of these ceramics with x = 0 and 0.02, only occupy the K/Na site of the ceramics with x = −0.02, and mostly form a secondary phase of the ceramics with x = −0.05. The Cu ions lead to the hardening of ceramics with an increase of EC and Qm by only occupying the K/Na site, together with the formation of double hysteresis loops in un-poled compositions. A defect model is proposed to illuminate the origin of a high Qm value, that is, the domain stabilization is dominated by the content of relatively mobile O2− ions in the ceramics, which has a weak bonding with CuK/Na defects.

Enhanced Electrical Properties of Bi4Ti3O12-modified (K0.5N0.5)NbO3 Lead-free Piezoceramics

Lead-free piezoceramics (K0.5N0.5)NbO3-x wt% Bi4Ti3O12 were fabricated, and effects of Bi4Ti3O12 on the properties of (K0.5N0.5)NbO3 ceramics were investigated. The results show that the orthorhombic and tetragonal transition temperature of the ceramics shifts toward room temperature and a small amount of Bi4Ti3O12 cannot influence the symmetry of (K0.5N0.5)NbO3 ceramics but improve their electrical properties. Optimum piezoelectric properties are owned by (K0.5N0.5)NbO3–0.50 wt% Bi4Ti3O12: d 33 = 135 pC/N, k p = 36.4%, and T C = 406°C, whereas the relatively superb ferroelectric properties are obtained by (K0.5N0.5)NbO3–0.75 wt% Bi4Ti3O12: P r = 27.2 μC/cm2, E c = 7.6 kV/cm, and T C = 398°C.

Effect of Bi0.5(Na0.9K0.1)0.5TiO3 on Phase Structure and Electrical Properties of (K0.5Na0.5)NbO3 Lead-free Ceramics

(1−x)(K0.5Na0.5)NbO3-xBi0.5(Na0.9K0.1)0.5TiO3 ((1−x)KNN-xBNKT) lead-free ceramics were prepared by the conventional solid state reaction technique, and the effects of BNKT on the phase structure, microstructure, ferroelectric and piezoelectric properties of (1−x)KNN-xBNKT ceramics were investigated. The addition of BNKT strongly affects the microstructure of these ceramics, and changes the crystalline structure of these ceramics from an orthorhombic phase with x < 0.02 to a tetragonal phase with x ≥ 0.03 at room temperature. A coexistence of orthorhombic and tetragonal phases was identified in the range of 0.02 ≤ x < 0.03. 0.975KNN-0.025BNKT ceramics show the optimum piezoelectric properties of d 33∼170 pC/N and k p∼0.38.

Piezoelectric Properties of (1-x)(K0.52Na0.48)1-x Li x NbO3-x (Bi0.5Na0.5)0.9Ca0.1TiO3 with Higher Curie Temperature

The polymorphic phase transition (PPT) near room temperature can induce enhanced electrical properties of KNN-based lead-free piezoelectric ceramics, limiting their temperature stability. In this paper, the 0.98(K0.52Na0.48)1-x Li x NbO3–0.02(Bi0.5Na0.5)0.9 Ca0.1TiO3 (KNLN x -BNCT) lead-free piezoelectric ceramics were prepared by the conventional sintering technique, and the electrical properties and phase structure can be tailored by modifying Li content. The polymorphic phase transition (PPT) from orthorhombic and tetragonal phase around room temperature was identified in the composition range 0.01 ≤ x ≤ 0.02, resulting in improved electrical properties (d 33∼262 pC/N, k p ∼ 0.36, ϵ r ∼ 715, and tan δ∼ 0.03). Moreover, KNLN x -BNCT (x0.02) ceramics with tetragonal structure possess a pertinent temperature stability and a broader application range owing to its higher T C (>400°C).

Piezoelectric properties of 0.99[(Na x K 1−x )Nb 0.955 O 3 -0.045LiSbO 3 ]-0.01CaTiO 3 lead-free ceramics

0.99[(Na<inf>x</inf>K<inf>1-x</inf>)Nb<inf>0.955</inf>O<inf>3</inf>-0.045LiSbO<inf>3</inf>]-0.01CaTiO<inf>3</inf> (NKNLS-CT) lead-free piezoelectric ceramics have been prepared by the conventional mixed oxide method. The effect of the K/Na ratio on the electrical properties of NKNLS-CT ceramics was investigated. When x = 0.52, the ceramics possess optimum properties: piezoelectric constant d<inf>33</inf>=266 pC/N, planar electromechanical coupling factors k<inf>p</inf>=48.7 %. These results show that the NKNLS-CT ceramics may be regarded as the promising lead-free piezoelectric materials.