Wangfeng Bai

Phase transitions, relaxor behavior, and large strain response in LiNbO3-modified Bi0.5(Na0.80K0.20)0.5TiO3 lead-free piezoceramics

The effect of LiNbO3 (LN) addition on the ferroelectric behavior and piezoelectric properties of Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT20) lead-free piezoceramics were systematically investigated. Results showed that the LN substitution into BNKT20 induced a transition from coexistence of ferroelectric tetragonal and rhombohedral phases to relaxor pseudocubic phases, which is accompanied by the significant disruption of ferroelectric order and with the shift of the ferroelectric-relaxor transition temperature TF-R down to room temperature. Accordingly, a large accompanying normalized strain of ∼0.38% (corresponding to a large signal d33* of ∼475 pm/V) were obtained in BNKT20 with 2.5 mol. %LN addition near the phase boundary. Temperature-dependent measurements of both polarization and strain from room temperature to 120 °C suggested that the origin of the large strain is due to a reversible field-induced ergodic relaxor-to-ferroelectric phase transformation. Moreover, an attractive property for application as hi...

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

(1 − x)[0.93(K0.5Na0.5)NbO3–0.07LiNbO3]–xCaZrO3 (KNN–LN–xCZ) lead-free piezoelectric ceramics have been prepared by the conventional solid state reaction method and investigated to differentiate the effects of polymorphic phase transition. The crystal structure of the ceramics changed from orthorhombic to tetragonal at x ≥ 0.04, and then both the orthorhombic and tetragonal phases coexisted in the region of 0.04 < x < 0.08 composition, and the orthorhombic–tetragonal phase transition temperature was modified to around room temperature. Remarkably, piezoelectric and ferroelectric properties have been obtained for KNN–LN–xCZ ternary system with x = 0.04, in which the piezoelectric parameter of d*33 was 320 pm V−1 with Curie temperature Tc = 350 °C, strain level = 0.16% at 50 kV cm−1 and remnant polarization Pr = 27.2 μC cm−2.

Fabrication and Electrical Properties of Ba(Zr,Ti)O3 Textured Ceramics by Templated Grain Growth

The (h00) textured Ba(Zr0.085Ti0.915)O3 (BZT) ceramics were fabricated by templated grain growth using anisotropically shaped BaTiO3 (BT) templates. A high orientation degree (Lotgerings factor) of 85% calculated from X-ray diffraction (XRD) patterns was obtained. The dielectric, ferroelectric, piezoelectric properties of the random and textured BZT ceramics have been studied. The Curie temperature of the textured BZT ceramics was 94 °C, which was higher than that of the random BZT ceramics. The textured BZT ceramics exhibited excellent piezoelectric performance with the piezoelectric coefficient d33 = 234 pC/N, strain levels of 0.22% at 40 kV/cm, normalized strain (Smax/Emax) level of 550 pm/V calculated from the unipolar strain–electric field (S–E) hysteresis loops and remnant polarization Pr = 11.46 µC/cm2 sintered at 1450 °C for 4 h with 85% of Lotgerings factor.

Effect of Different Templates on Electrical Properties of Textured KNN-Based Ceramics

Platelike and perovskite structure NaNbO3 (NN) with orthorhombic, SrTiO3 (ST) with cubic and BaTiO3 (BT) with tetragonal were used as templates to fabricate grain-oriented 0.94(K0.5Na0.5)NbO3-0.06LiSbO3 (0.94KNN-0.06LS) ceramics by templated grain growth (TGG). The effects of different templates on the grain orientation, ferroelectric, dielectric, piezoelectric properties and strain behavior of 0.94KNN-0.06LS ceramics were systematically investigated. Textured ceramics with high orientation factor were obtained successfully when the platelike NN was used as a template, while high degree of grain orientation cannot be obtained with ST and BT template. The templated growth of <00l> oriented grains on the NN template resulted in textured ceramics with brick significantly high <00l> texture degree corresponding to 87% Lotgering factor at 5 mol% NN templates. Textured ceramics with NN templates exhibited excellent piezoelectric properties as compared to the random counterparts due to high degree of grain orientation, while ceramics used ST templates shown excellent strain behavior.

Effect of LaNiO3 Buffer Layer on Ferroelectric Properties of Ba(Zr,Ti)O3 Thin Films

BaZrxTi(1-x)O3 (x = 0∼0.15) (BZT) thin films were prepared by chemical solution deposition. LaNiO3 buffer layer was introduced to modify the structure and ferroelectric properties of the films. Results show that the BZT films deposited on Pt/Ti/SiO2/Si substrate have random orientation, but those on LaNiO3 buffered Pt/Ti/SiO2/Si substrate have highly (100) preferred orientation. Grain size and leakage current of the BZT films decrease with increase of Zr content. The BZT films with LaNiO3 buffer layer exhibit larger grain size and have higher remanent polarization, dielectric constant and tunability. This work reveals the promising application of highly (100) oriented BZT films in multifunctional ferroelectrics.

Microstructure and Piezoelectric Properties of Lead-Free (K0.5Na0.5)NbO3-LiNbO3-SrTiO3 Ceramics

(1−x)[0.93(K0.5Na0.5)NbO3-0.07LiNbO3]-xSrTiO3 ((1-x)KNN-LN-xST) system ceramics with ABO3structure were synthesized by conventional solid state reaction route and investigated to differentiate the effects of polymorphic phase transition. The crystal structure of (1-x)KNN-LN-xST ceramics was changed from orthorhombic to tetragonal at x≥0.04, then became a morphotropic phase boundary in which both the orthogonal and tetragonal phases coexisted at 0.04<x<0.08, and was converted to tetragonal structure at x≥0.08. At phase boundary, the dielectric and piezoelectric properties of these ceramics change obviously. The Curie temperature decreased with increasing of x in the temperature range from 200°C to 400°C.The polymorphic phase transition between the orthorhombic and tetragonal phases plays a very important role in enhancement of the piezoelectric properties of (1-x)KNN-LN-xST ceramics.