Fabrication and properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 ceramics and their multilayer piezoelectric actuators

The lead‐free ceramics with nominal composition (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCTZ) were prepared by a conventional solid‐state reaction combined with a liquid precursor mixing method. Structural, dielectric, piezoelectric, and ferroelectric properties of the ceramics were systematically investigated. Excellent electrical properties of T_c ~ 101°C, tanδ ~ (0.003–0.05), k_p ~ 0.46, d₃₃ ~ 560 pC/N, P_s ~17 μC/cm² and a large strain of 0.43% were reproducibly obtained for the BCTZ ceramics. In addition, BCTZ‐based monolithic multilayer piezoelectric actuators were successfully fabricated by alternately laminating the claimed piezoelectric ceramics and internal‐binder. The actuators show large displacements under low driven voltage. These results highlight that the BCTZ ceramics are excellent candidate for multilayer piezoelectric devices.     

Influence of ferroelectric domain texture on the performance of multilayer piezoelectric actuators

Lead zirconate titanate (PZT)-based multilayer piezoelectric actuators (MAs) present a maximum in their piezoelectric properties when pre-stressed with a low mechanical load (ca. 50 MPa) along the longitudinal axis of the actuator. In this work, we investigate this phenomenon by combining polarised Raman spectroscopy with a Reverse Monte Carlo (RMC) method in order to quantify the domain orientation distribution of PZT-based MAs, both in-situ and at the remanent state, under combined applied electric field and mechanical load. Our study shows that the performance maximum of MAs is the result of two competing effects: (i) an increasing reservoir for non-180° domain switching for increasing applied compressive pre-stress and (ii) a large activation energy for domain switching at high pre-stresses. Hence, our study uncovers structure-property relationships in piezoceramic components that could be used to finely tune the electromechanical response of actuators.     

Enhanced piezoelectric property in Mn-doped K0.5Na0.5NbO3 ceramics via cold sintering process and KMnO4 solution

Through mixing the KMnO₄ solution with K_0.5Na_0.5NbO₃ (KNN) powders, cold sintering process (CSP) was employed to fabricate high-density Mn-doped KNN green pellets and ceramics. The microstructure, doping effect of Mn and electrical properties of these ceramics were studied in detail. Compared with conventional sintering (CS), the CSP supports the homogeneity of dopants and then promotes grain growth and ceramic densification; thus the Mn-doped KNN ceramics prepared by CSP show the obviously higher density and larger grain size. Besides, the less alkalis volatilization and oxygen vacancies result in more Mn³⁺ but less Mn⁴⁺ in CSP ceramics compared to CS ones, which endows the pinning effect and good poling characteristics in CSP ceramics. All the previous results contribute to the high dielectric constant and remnant polarization in CSP ceramics, which support the enhanced piezoelectric coefficient and are much superior than Mn-doped KNN ceramics prepared by CS. This work reveals that CSP can be a new doping strategy to perform chemical modification of electrical properties in KNN ceramics.     

A low-cost multilayer piezoelectric actuator for ultrasonic motor stator driving fabricated by a low-temperature co-fired ceramic process

Multilayer piezoelectric ceramics have wide application prospects in the fields of precision driving and intelligent sensing owing to their low driving voltages and large strains. However, high sintering temperatures and expensive noble metal electrodes limit their application as multilayer piezoelectric ceramic actuators (MLAs) in conventional devices. In this study, a modified piezoelectric ceramic powder and Ag inner electrode were used to prepare a low-cost MLA with a low sintering temperature of 900 °C. The MLA showed superior piezoelectric properties with d₃₃ = 3015 pC/N and a large electric-field-induced strain of 0.13% at 22.2 kV/cm. Moreover, the stator of the ultrasonic motor composed of this MLA produced the ideal vibration mode, and the maximum rotation speed of the ultrasonic motor was 192 r/min under a 50 g load, which verifies the applicability of this component in practical minimised devices. These results demonstrate a strategy for fabricating low-cost and high-precision micro-actuators for precision driving.     

Defect engineering of high‐performance potassium sodium niobate piezoelectric ceramics sintered in reducing atmosphere

Reducing atmosphere fired (K_0.5Na_0.5)NbO₃‐based ceramics open up an important opportunity for manufacturing lead‐free multilayer piezoelectric devices cofiring with the base metal inner electrode. In this study, the effects of sintering atmosphere on the piezoelectric, dielectric, and insulating properties in Sn‐doped (Na_0.52K_0.44Li_0.04)NbO₃ (KNN) were investigated. To establish the relationship between the defect structure and electrical properties, the thermally stimulated depolarization current (TSDC) technique was implemented. The electrical properties degrade severely when the pure KNN ceramics are sintered in reducing atmosphere, compared with the ceramics sintered in air. The reason is that the oxygen vacancy concentration in reduced fired ceramics is much higher than that in air fired ceramics. However, the 0.6 mol% Sn‐doped KNN ceramics sintered in reducing atmosphere exhibit comparable electrical properties to the air fired ceramics. From the TSDC analysis, the reducing atmosphere fired ceramics have approximately the same oxygen vacancy concentration as the air fired ceramics because B‐site substituted Sn works as an acceptor.     

A novel piezoelectric ceramic with high Curie temperature and high piezoelectric coefficient

0.02Pb(Sb_1/2Nb_1/2)O₃-0.98Pb_1-xBa_x(Zr_0.53Ti_0.47)O₃ (PSN-PB_xZT) ceramics with high Curie temperature and high piezoelectric properties were prepared by traditional solid state reaction measurement to meet the requirements for high temperature applications, and the crystal structure, dielectric, piezoelectric and ferroelectric properties were investigated. All the samples show a tetragonal crystal structure at room temperature and there was no noticeable change with the increasing of Ba²⁺ content. Doping of Ba²⁺ markedly improved piezoelectric properties of PSN-PZT, the maximum d₃₃~560 pC/N, T_c ~317 °C at x = 0.05. Their outstanding piezoelectric properties will drive the development of high temperature industrial applications.     

Dispersion and rheology for direct writing lead-based piezoelectric ceramic pastes with anisotropic template particles

Controlling the rheology of direct writing pastes is essential for producing high quality printed ceramics. Ceramic pastes were formulated to explore the relation between surface chemistry and rheology of complex pastes of Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT) powder, large BaTiO₃ (BT) platelet particles, and a commercial poly(acrylic) acid-based binder system. Zeta potential of the ceramic powder, the conformation of the poly(acrylic) acid, and the effect of these factors on rheology were evaluated as a function of suspension pH. Effective dispersion and amenable rheology for direct writing were achieved at mixing pH 5. Additions of 0.3 to 2.6 vol% BT tabular particles dramatically altered the rheology of the pastes due to the shear alignment of the BT particles. Powder-organic interactions and the size and concentration of BT platelet particles can be tailored to direct write either space-filling filaments to form dense ceramics or non-flowing filaments to form spanning ceramic structures.     

(Na1/2Bi1/2)TiO3-based lead-free co-fired multilayer actuators with large strain and high fatigue resistance

Large-strain multilayer actuators (MLAs) were fabricated by tape-casting 0.91(Na_1/2 Bi_1/2)TiO₃–0.06BaTiO₃–0.03AgNbO₃ (NBT-BT–3AN) lead-free incipient piezoceramics co-fired with Pt inner electrodes. Microstructures, dielectric properties, unipolar and bipolar strain, as well as fatigue properties of the MLAs were investigated. It was found that the actuator consisting of 15 ceramic layers with individual thicknesses of 114 μm could output a large unipolar strain of 0.3% and a dynamic displacement of 5 μm at 6 kV/mm at room temperature. It exhibited excellent cycling stability and provided a high strain of 0.23% after 10⁷ cycles at 6 kV/mm. Moreover, these MLAs still can deliver a strain of 0.20% at 125°C.     

Tape casting system for ULTCCs to fabricate multilayer and multimaterial 3D electronic packages with embedded electrodes

A 3D multilayer structure built by two ultra‐low temperature co‐fired ceramic (ULTCC) compositions with silver embedded electrodes are co‐fired at a temperature of 450°C. The 3D multilayer module is prepared by laminating the ULTCC green tapes with a new binder system, which organics can be completely burned out at temperature of 250°C before the sintering of the ULTCC 3D modulus. High‐density microstructures are achieved for the sintered module. In this study, the ULTCC feasible binder system is introduced. Also, ULTCC multilayers and multimaterial structures with surface and embedded silver electrodes are fabricated. This research opens up a new horizon for fabrication of electroceramic devices with embedded electrodes in multimaterial devices.     

Interfacial development and microstructural imperfection of multilayer ceramic chips with Ag/Pd electrodes

The interfacial microstructure between Ag/Pd electrodes and PMN–PZN–PT relaxor ferroelectric ceramics in cofired multilayer ceramic devices was investigated by transmission electron microscopy and scanning electron microscopy. Disadvantageous interfacial defects, such as delaminations, warping, gas holes and exaggerated grain growth, were identified. In addition to the preparation process, the composition of the inner electrode paste and the sintering densification compatibility between the layers played important roles in the interfacial development. The relationship of the interfacial microstructure to the reliability of the device is discussed.     

Properties of Low‐Temperature Sintering PNN–PMW–PSN–PZT Piezoelectric Ceramics with Ba(Cu1/2W1/2)O3 Sintering Aids

Piezoelectric ceramics Pb(Ni_1/3Nb_2/3)O₃–Pb(Mg_1/2W_1/2)O₃–Pb(Sb_1/2Nb_1/2)O₃–Pb(Zr_0.39Ti_0.61)O₃ with Ba(Cu_1/2W_1/2)O₃ sintering aids were fabricated using economical industrial oxide powders and their piezoelectric, dielectric, and ferroelectric properties were investigated in order to develop low‐temperature sintering ceramics for multilayer piezoelectric actuators. A quadratic formula and the Curie–Weiss law reveal that the ceramics are typical displacive‐type ferroelectric relaxors. The ceramics sintered as low as 900°C have good piezoelectric properties of d₃₃ = 551 pC/N, k_p = 0.52, ε_r = 3583, tgδ = 0.02, and T_C = 161°C, which is much promising to manufacture multilayer piezoelectric transducers.     

The effects of sintering atmospheres on piezoelectric performances of Co-doped Ba0.88Ca0.12Zr0.12Ti0.88O3 ceramics

This work investigates the effects of content ratio Co³⁺/Co²⁺ on piezoelectric properties of lead-free Ba_0.88Ca_0.12Zr_0.12Ti_0.88O₃ (BCZT) ceramics. For this purpose, 0.10 wt% Co ions using a CoO powder doped BCZT ceramics were sintered under various atmospheres (ranging from pure nitrogen to 100 vol% oxygen concentration) to vary the ratio value Co³⁺/Co²⁺. X-ray photoelectron spectroscopy analysis revealed the coexistence of Co³⁺ and Co²⁺ for oxygen concentration below 40 vol% and the single oxidation state of Co³⁺ for oxygen concentration over 50 vol%. Co²⁺ substitution could induce more oxygen vacancy to accelerate densification and grain growth, whereas Co³⁺ substitution usually leads to larger lattice distortion to generate a stable asymmetric structure. When oxygen concentration was 30 vol% and Co³⁺/Co²⁺ near to 1.0, the respective superiority of Co³⁺ and Co²⁺ is brought into full play, and the ceramic showed the highest piezoelectric constant d₃₃^* ∼ 518 pm/V (380 pm/V for undoped BCZT) and the relatively high Curie temperature T_c ∼ 105°C (95°C for undoped BCZT). This study suggests that optimizing sintering atmosphere might be an effective way to enhance the piezoelectric properties for some composition-modified piezoelectric BCZT ceramics.     

Effect of TiO2 doped Ni electrodes on the dielectric properties and microstructures of (Ba0.96Ca0.04)(Ti0.85Zr0.15)O3 multilayer ceramic capacitors

The effects of TiO₂-doped Ni electrodes on the microstructures and dielectric properties of (Ba_0.96Ca_0.04)(Ti_0.85Zr_0.15)O₃ multilayer ceramic capacitors (MLCCs) have been investigated. Nickel paste with a TiO₂ dopant was used as internal electrodes in MLCCs based on (Ba_0.96Ca_0.04)(Ti_0.85Zr_0.15)O₃ (BCTZ) ceramic with copper end-termination. The microstructures and defects were analysed by microstructural techniques (SEM/HRTEM) and energy-dispersive spectroscopy (EDS). The continuity of the electrode of the MLCC was measured using a scanning electron microscope, which showed that the continuity of the electrode for the MLCC with a TiO₂-doped Ni electrode was approximately 90%. However, continuity of the electrode for a conventional MLCC was below 80%. The continuity of the TiO₂-doped Ni electrode showed significant improvement in the MLCC, which was due to no reaction between Ni and BCTZ.