Piezoelectric and mechanical properties of CaO reinforced porous PZT ceramics with one-dimensional pore channels

The formation of capillaries in sodium alginate gels is a dissipative process driven by unidirectional diffusion of divalent cations into sodium alginate sols. In the present work, we have prepared 3-1 type porous lead zirconate titanate (PZT) ceramics with oxides (CaO) being doped on a molecular level from the dissipative process by incorporating PZT particles into the sodium alginate gel matrix. By varying the concentration of cation solutions (CaCl₂) from 0.5 mol/L to 2.5 mol/L, both the microstructure, doping amount of oxides (CaO) and crystalline phase of the porous PZT ceramics were tailored. Accordingly, increase in the concentration of Ca²⁺ has led to a reduction in the relative permittivity (ε_r) first, and then an increase, while the piezoelectric coefficient (d₃₃ and d₃₁) demonstrated an opposite variation tendency. The prepared samples possessed a maximal HFOM value of 4755×10^–15 Pa⁻¹ when the concentration of Ca²⁺ was 1.0 mol/L. Addition of CaO was found to improve the compressive strength of porous PZT ceramics, which was preferential to promoting the stability and reliability for application.     

Sb doping effects on the piezoelectric and ferroelectric characteristics of lead-free Na0.5K0.5Nb1−x SbxO3 piezoelectric ceramics

The piezoelectric, phase structure and ferroelectric properties of lead-free Na_0.5K_0.5Nb_1−xSb_xO₃ piezoelectric ceramics were systematically investigated. (Na_0.5K_0.5)Nb_1−xSb_xO₃ ceramics were synthesized using the conventional solid-state reaction method. The effect of B-site Sb⁵⁺ substitution for Nb⁵⁺ on the structural characteristics and piezoelectric properties of samples was determined. According to XRD patterns, the phase gradually changes from tetragonal to orthorhombic with increasing Sb content. At x = 0.03, the tetragonal and orthorhombic phases coexist and relatively high piezoelectric properties were obtained. The relatively high Q_m value obtained after substitution with Sb⁵⁺ ions might be due to the increased electronegativity and decreased ionic radius at the morphotropic phase boundary (MPB) at x = 0.03. However, the Q_m value decreases with further Sb addition. Relatively high piezoelectric properties at x = 0.03 of k_p = 0.42, k_t = 0.48, ?_r = 446, Q_m = 143, tan δ = 2.3%, and density = 4.31 g/cm³, d₃₃ = 123 pC/N, were obtained.     

Effects of pore size and orientation on dielectric and piezoelectric properties of 1-3 type porous PZT ceramics

Porous PZT ceramics have drawn an increasing amount of interest in recent years due to their superior properties compared with the dense material. However, researchers have usually dedicated effort to 0-3 and 3-3 type porous PZT ceramics and little attention has been focused on 1-3 type. The 1-3 type porous PZT ceramics with high porosity were fabricated in this study by freeze-casting process. All samples possessed high piezoelectric coefficient (d₃₃) with high porosity owing to the special one-dimensional ordered porous structure along the poling direction. The d₃₃ values increased by either improving the pore channel orientation level or decreasing pore size. The relative permittivity improved only with the enhancement of pore channel orientation level. The acoustic impedances ranged from 1.45 to 1.35 MRayls which could match well with those of biological tissue or water; therefore, this material would be beneficial in hydrophone applications.     

Microstructure and piezoelectric properties of CuO added (K, Na, Li)NbO3 lead-free piezoelectric ceramics

Lead-free Na_0.5K_0.5NbO₃ (NKN) and Na_0.475K_0.475Li_0.05NbO₃ (NKLN) ceramics doped with CuO were prepared by the mixed oxide route. The powders were calcined at 850-930 °C and sintered at 850-1100 °C. Small additions of CuO reduced the sintering temperature and increased the density to 96% theoretical. Cu first appears to enter the A site then the B site. In NKLN the orthorhombic-tetragonal and tetragonal-cubic phase transitions are approximately 150 °C lower and 50 °C higher, respectively than in NKN. With increasing addition of Cu to NKN and NKLN the remanent polarization (P_r) increased and coercive field (E_c) decreased. NKLN prepared with 0.4 wt% CuO exhibited a saturation polarization (P_sat) of 30 μC/cm², remanent polarization (P_r) of 27 μC/cm² and coercive field (E_c) of 1.0 kV/mm. CuO caused the NKLN ceramics to harden considerably; the mechanical quality factor (Q_m) increased from 50 to 260, d₃₃ ∼ 285 and piezoelectric coupling factors were >0.4.     

Microstructure and piezoelectric properties of CuO-doped 0.95(K0.5Na0.5)NbO3-0.05Li(Nb0.5Sb0.5)O3 lead-free ceramics

The effects of sintering temperature and the addition of CuO on the microstructure and piezoelectric properties of 0.95(K_0.5Na_0.5)NbO₃-0.05Li(Nb_0.5Sb_0.5)O₃ were investigated. The KNN-5LNS ceramics doped with CuO were well sintered even at 940 °C. A small amount of Cu²⁺ was incorporated into the KNN-5LNS matrix ceramics and XRD patterns suggested that the Cu²⁺ ion could enter the A or B site of the perovskite unit cell and replace the Nb⁵⁺ or Li⁺ simultaneously. The study also showed that the introduction of CuO effectively reduced the sintering temperature and improved the electrical properties of KNN-5LNS. The high piezoelectric properties of d₃₃ = 263 pC/N, k_p = 0.42, Q_m = 143 and tan δ = 0.024 were obtained from the 0.4 mol% CuO doped KNN-5LNS ceramics sintered at 980 °C for 2 h.     

ZnO和CuO烧结助剂对KNN压电陶瓷性能的影响

以微波水热法制备的KNN粉体为原料,添加1mol%ZnO、1mol%CuO烧结助剂,采用传统电子陶瓷制备方法,研究了烧结助剂对KNN陶瓷的陶瓷体积密度、显微结构和电性能的影响,结果表明:添加烧结助剂ZnO和CuO可以降低KNN陶瓷的烧结温度,提高KNN陶瓷的体积密度;与此同时,ZnO和CuO添加后降低了KNN无铅压电陶瓷的压电常数d33、介电常数ε33T/ε0,但机械品质因数Qm得到很大的提高,介电损耗tanδ明显降低。其中CuO烧结助剂可以使KNN陶瓷的d33由142 pC/N降低至118 pC/N,Qm值由82提高至427,tanδ由2.46%降低至0.64%。     

Fabrication and piezoelectric properties of BaTiO3/BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 composites

We fabricated xBaTiO₃ (BT)/(1-x)[BaTiO₃-Bi(Mg_1/2Ti_1/2)O₃-BiFeO₃] (BT-BMT-BF)?+?0.1?wt%MnCO₃ composites by spark plasma sintering and investigated the effect of BT content x, BT powder size, and BT-BMT-BF composition on piezoelectric properties. For xBT/(1-x)(0.3BT-0.1BMT-0.6BF) +?0.1?wt%MnCO₃ (x?=?0–0.75) composites with a 0.5-µm BT powder, the dielectric constant was increased with x, and the relative density was decreased at x?=?0.67 and 0.75, creating optimum BT content of x?=?0.50 with a piezoelectric constant d₃₃ of 107?pC/N. When a larger 1.5-µm BT powder was utilized for the composite with x?=?0.50, the d₃₃ value increased to 150?pC/N due to the grain size effect of the BT grains. To compensate for a compositional change from the optimum 0.3BT-0.1BMT-0.6BF due to partial diffusion between the BT and 0.3BT-0.1BMT-0.6BF grains, a 0.5BT/0.5(0.275BT-0.1BMT-0.625BF)?+?0.1?wt%MnCO₃ composite with the 1.5-µm BT powder was fabricated. We obtained an increased d₃₃ value of 166?pC/N. These results provided a useful composite design to enhance the piezoelectric properties.     

Coexistence of three ferroelectric phases and enhanced piezoelectric properties in BaTiO3–CaHfO3 lead-free ceramics

Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO₃-xCaHfO₃ was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO₃ (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d₃₃～400 pC/N), inverse piezoelectric coefficient (d₃₃^*～547 pm/V) and planar electromechanical coupling factor (k_p～58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response.     

减小压电陶瓷驱动电源纹波的一种有效方法

为了解决直流放大式压电陶瓷驱动电源在实际应用中存在输出电压纹波较大且幅值随输出电压大小而改变的问题，对其工作原理进行了深入分析，在此基础上提出了采用恒流源代替基在级电路负载的方法。实验表明，这种有效地抑制了电源的纹波及其变化。