Ion-Pair Engineering-Induced High Piezoelectricity in Bi4Ti3O12-Based High-Temperature Piezoceramics

Superior Piezoelectric Performance in Textured CaBi2Nb2O9 Ferroelectric Ceramics through Rare-Earth Gadolinium Doping and Spark Plasma Sintering

High-performance piezoelectric ceramics with excellent thermal stability are crucial for high-temperature piezoelectric sensor applications. However, conventional fabrication processes offer limited enhancements in piezoelectric performance. In this study, we achieved a significant breakthrough in the piezoelectric performance of highly textured CaBi2Nb2O9 (CBN) ceramics by incorporating rare-earth gadolinium doping and utilizing spark plasma sintering. The resulting Ca0.97Gd0.03Bi2Nb2O9 (CBN-3Gd) ceramics exhibited superior piezoelectric properties, with a high piezoelectric constant d33 of 26 pC/N and a high Curie temperature TC of 946 °C. We employed piezoresponse force microscopy (PFM) to observe the morphology and dimensions of the ferroelectric domains, revealing a rod-shaped 3D domain configuration. This configuration facilitated polarization rotation in the textured ceramics, as analyzed using X-ray photoelectron spectroscopy (XPS) and polarization-electric field (P-E) hysteresis loops. Furthermore, the textured CBN-3Gd ceramics demonstrated exceptional thermal stability and reliability. The piezoelectric constant d33 decreased by only 11.8% over a temperature range of room temperature to 500 °C, and the DC electrical resistivity remained at 6.7 × 105 Ω cm at 600 °C. This work not only highlights the great potential of textured CBN-based ceramics for high-temperature piezoelectric sensors but also provides a viable strategy for enhancing the performance of piezoelectric materials with large aspect ratio micromorphology.

Electromechanical Performance Optimization of Ni-Doped Bi(Sc, Zr)O3-PbTiO3 Ceramics and Microstructure Analysis

BiScO3-PbTiO3-based ceramics show great potential in high-temperature piezoelectric applications. However, their high dielectric loss tan δ and low mechanical quality factor Qm have to be optimized. In this paper, a ceramic system of (1-y)Bi(Sc0.975Zr0.025)O3-yPb(Ti1-xNix)O3 (BSZ-yPT-xNi, x = 0, 0.015, 0.025, and 0.035 and y = 0.62, 0.63, 0.64, and 0.65) was systematically investigated. Increase in x or y values leads to the enhancement of the tetragonal phase and tetragonal lattice distortion. The rhombohedral/tetragonal morphotropic phase boundary (MPB) locates in the vicinity of y = 0.64 for the x = 0 and 0.015 samples, and y = 0.63 for the x = 0.025 and 0.035 samples. For these MPB samples, the substitution of Ni2+ for Ti4+ causes domain refinement, evolving from the submicrometer lamellar domains to hierarchical domains, and finally to the high-density stripe-like nanodomains, which benefits the domain wall motion and makes the coercive field reduced. However, the alignment of defect dipoles (NiTi''-VO••) after the sufficient poling and aging treatment induces the noticeable internal bias field, which increases with the addition of Ni2+. Apparent piezoelectric "hardening" occurred, evidenced by the increase in Qm and the reduction in tan δ. Among the MPB samples, the x = 0.025/y = 0.63 ceramic shows the superior comprehensive electromechanical performance with the d33 of 380 pC/N, kt of 0.51, Qm of 112, and tan δ of 0.010. Besides, excellent temperature stability was achieved with the d33 of 367-380 pC/N, Qm of 106-112, and tan δ ≤ 0.010 in the temperature range of 25-250 °C.

Enhanced Electrical Conductivity of (001) Oriented Sr0.9La0.1TiO3 Microplatelets for Thermoelectric Applications

Two-dimensional perovskite microplatelets have played an important role in various applications, especially acting as a template to guide grains' epitaxial growth in the preparation of textured ceramics. The (001) oriented Sr0.9La0.1TiO3 microplatelets with a high aspect ratio of ∼20 were synthesized and obtained from Aurivillius Bi4Ti3O12 precursors. To reveal the mechanism of topochemical microcrystal conversion of Bi4Ti3O12 to Sr0.9La0.1TiO3, the reaction interface, morphology development, and phase composition evolution of the (001) oriented Sr0.9La0.1TiO3 microplatelets were investigated. When the temperature of the molten salt is above 753 °C, multiple Sr0.9La0.1TiO3 topological nucleation events took place. At 950 °C, the polycrystalline aggregate of (001)-oriented Sr0.9La0.1TiO3 crystallites grew in place of the original single crystal Bi4Ti3O12 platelets. When the temperature reached 1150 °C, the Sr0.9La0.1TiO3 platelets preserved the shape of a high aspect ratio and exhibited not only enhanced electrical conductivity with a carrier concentration of 3.518 × 1020 cm-3 and carrier mobility of 8.460 cm2·V-1·s-1 but also significantly decreased thermal conductivity ranging from 5.65 W·m-1·K-1 at 300 K to 2.54 W·m-1·K-1 at 1073 K. It can be widely applied in the field of template grain growth methods for preparing textured thermoelectric ceramics to improve their thermoelectric properties.

Enhancing piezocatalytic H2O2 production through morphology control of graphitic carbon nitride

Piezocatalytic H₂O₂ production has attracted significant attention as a green alternative to traditional anthraquinone methods with heavy environmental pollution and high energy consumption. However, since the efficiency of piezocatalyst in producing H₂O₂ is poor, searching for a suitable method to improve the yield of H₂O₂ is of great interest. Herein, a series of graphitic carbon nitride (g-C₃N₄) with different morphologies (hollow nanotube, nanosheet and hollow nanosphere) are applied to enhance the piezocatalytic performance in yielding H₂O₂. The hollow nanotube g-C₃N₄ exhibited an outstanding H₂O₂ generation rate of 262 umol·g^-1·h^-1 without any co-catalyst, which is 1.5 and 6.2 times higher than nanosheets and hollow nanospheres, respectively. Piezoelectric response force microscopy, piezoelectrochemical tests, and Finite Element Simulation results revealed that the excellent piezocatalytic property of hollow nanotube g-C₃N₄ is mainly attributed to its larger piezoelectric coefficient, higher intrinsic carrier density, and stronger external stress absorption conversion. Furthermore, mechanism analysis indicated that piezocatalytic H₂O₂ production follows a two-step single-electro pathway, and the discovery of ¹O₂ furnishes a new insight into explore this mechanism. This study offers a new strategy for the eco-friendly manufacturing of H₂O₂ and a valuable guide for future research on morphological modulation in piezocatalysis.

Realizing an Ultrahigh Depolarization Temperature near the Curie Point and Large d33 with Superior Temperature Stability in Lead-Free Ceramics via a Sandwich Structure Design

An imminent challenge of lead-free Bi_0.5Na_0.5TiO₃-based (BNT) piezoceramics is that the giant piezoelectric constant (d₃₃) caused by the morphotropic phase boundary is incompatible with a high depolarization temperature (T_d) and ultralow temperature coefficient (T_tc) of the real-time d₃₃, which severely hinders their industrial application in the field of elevated temperatures. Herein, a sandwich-structured 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃/0.89Bi_0.5Na_0.5TiO₃-0.11BaTiO₃/0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (SWS-6/11/6BT-y, where y refers to the weight fraction of the BNT-11BT solid solution) ceramic composite is engineered for mitigating the conflict between d₃₃, T_d and T_tc. Following this strategy, ultrahigh T_d near the Curie point (225 °C, close to that of the BNT-11BT layer) and relatively large d₃₃ (130 pC/N, close to that of the BNT-6BT layer) are simultaneously realized in a SWS-6/11/6BT-40%-Q ceramic composite. More importantly, the ultralow T_tc (0.07%) of real-time d₃₃ is also achieved in this work. The structural heterogeneity yields the high piezoresponse, and the built-in field resulting from layer-type ceramic composites provides the driving force to promote the diffused ferroelectric-relaxor phase transition and the resultant ferroelectric order with high T_d. The above synergistic contributions realize the remission of the d₃₃-T_d-T_tc conflict in a sandwich-structural SWS-6/11/6BT-40% ceramic composite. Thus, our work provided a path for designing the BNT-based piezoceramics with potential for industrial applications.

An Experimental Investigation on Polarization Process of a PZT-52 Tube Actuator with Interdigitated Electrodes

The manipulator is the key component of the micromanipulator. Using the axial expansion and contraction properties, the piezoelectric tube can drive the manipulator to achieve micro-motion positioning. It is widely used in scanning probe microscopy, fiber stretching and beam scanning. The piezoceramic tube actuator used to have continuous electrodes inside and outside. It is polarized along the radial direction. There are relatively high polarization voltages, but poor axial mechanical properties. A new tubular actuator is presented in this paper by combining interdigitated electrodes and piezoceramic tubes. The preparation, polarization and mesoscopic mechanical properties were investigated. Using Lead Zirconate Titanate (PZT-52) as a substrate, the preparation process of interdigitated electrodes by screen printing was studied. For initial polarization voltage determination, the local characteristic model of the actuator was extracted and the electric field was analyzed by a finite element method. By measuring the actuator's axial displacement, we measured the actuator's polarization effect. Various voltages, times and temperatures were evaluated to determine how polarization affects the actuator's displacement. Optimal polarization conditions are 800 V, 60 min and 150 °C, with a maximum displacement of 0.88 μm generated by a PZT-52 tube actuator with interdigitated electrodes. PZT-52 tube actuators with a continuous electrode cannot be polarized under these conditions. The maximum displacement is 0.47 μm after polarization at 4 kV. Based on the results, the new actuator has a more convenient polarization process and a greater axial displacement from an application standpoint. It provides technical guidance for the preparation and polarization of the piezoceramic tube actuator. There is potential for piezoelectric tubular actuators to be used in a broader range of applications.

Gd/Mn Co-Doped CaBi4Ti4O15 Aurivillius-Phase Ceramics: Structures, Electrical Conduction and Dielectric Relaxation Behaviors

In this work, Gd/Mn co-doped CaBi₄Ti₄O₁₅ Aurivillius-type ceramics with the formula of Ca_1-xGd_xBi₄Ti₄O₁₅ + xGd/0.2wt%MnCO₃ (abbreviated as CBT-xGd/0.2Mn) were prepared by the conventional solid-state reaction route. Firstly, the prepared ceramics were identified as the single CaBi₄Ti₄O₁₅ phase with orthorhombic symmetry and the change in lattice parameters detected from the Rietveld XRD refinement demonstrated that Gd³⁺ was successfully substituted for Ca²⁺ at the A-site. SEM observations further revealed that all samples were composed of the randomly orientated plate-like grains, and the corresponding average grain size gradually decreased with Gd content (x) increasing. For all compositions studied, the frequency independence of conductivity observed above 400 °C showed a nature of ionic conduction behavior, which was predominated by the long-range migration of oxygen vacancies. Based on the correlated barrier hopping (CBH) model, the maximum barrier height W_M, the dc conduction activation energy E_dc, as well as the hopping conduction activation energy E_p were calculated for the CBT-xGd/0.2Mn ceramics. The composition with x = 0.06 was found to have the highest E_dc value of 1.87 eV, as well as the lowest conductivity (1.8 × 10^-5 S/m at 600 °C) among these compositions. The electrical modules analysis for this composition further illustrated the degree of interaction between charge carrier β increases, with an increase in temperature from 500 °C to 600 °C, and then a turn to decrease when the temperature exceeded 600 °C. The value of β reached a maximum of 0.967 at 600 °C, indicating that the dielectric relaxation behavior at this temperature was closer to the ideal Debye type.