Domain Engineering of Lead‐Free Li‐Modified (K,Na)NbO3 Polycrystals with Highly Enhanced Piezoelectricity

Aging and re‐poling induced enhancement of piezoelectricity are found in (K,Na)NbO₃ (KNN)‐based lead‐free piezoelectric ceramics. For a compositionally optimized Li‐doped composition, its piezoelectric coefficient d₃₃ can be increased up to 324 pC N^?1 even from a considerably high value (190 pC N^?1) by means of a re‐poling treatment after room‐temperature aging. Such a high d₃₃ value is only reachable in KNN ceramics with complicated modifications using Ta and Sb dopants. High‐angle X‐ray diffraction analysis reveals apparent changes in the crystallographic orientations related to a 90° domain switching before and after the aging and re‐poling process. A possible mechanism considering both defect migration and rotation of spontaneous polarization explains the experimental results. The present study provides a general approach towards piezoelectric response enhancement in KNN‐based piezoelectric ceramics.     

An analog notch filter for piezoelectric optical scanner

The optical scanner is one of the most important components in free-space optical communications,airborne and space-based lidars,adaptive optics,and so on.The performance of an optical scanner is frequently limited by the presence of mechanical resonances.This paper presents an analog notch filter with adjustable function to reject the mechanical resonances of the optical scanner.First of all,the structure and work principle of the piezoelectric optical scanner are introduced.Furthermore,the frequency sweep method based on virtual instruments is used to gain the natural frequency of the piezoelectric optical scanner.Then,the notch filters in series are used to reduce the oscillation of the scanner at the resonance frequencies.A variety of scanning experiments were carried out.After the introduction of the notch filter,the non-linearity was reduced to±1.1% from ±2.1%.The linearity performance was greatly improved.     

提高钻井泵陶瓷缸套使用寿命的研究

高压泥浆泵是油田钻井工作台的＂心脏＂,而缸套是泥浆泵的重要磨损部件。工程陶瓷以其高硬度、高耐磨性,耐腐蚀性、表面性能好等优点,在钻井泵缸套中已得到广泛应用。但目前陶瓷缸套的使用寿命相对较短,如何提高陶瓷缸套的使用寿命,已成为陶瓷缸套研究中亟待解决的问题。本研究通过对钻井泵缸套的分析,提出了长寿命陶瓷缸套的要求,从陶瓷材料的选择,力学性能及其微观结构等方面探讨了提高陶瓷缸套使用寿命的方法,为陶瓷缸套生产企业提供改善产品质量的依据和方法。     

陶瓷成型加工技术新进展

陶瓷材料以其优异的耐高温?高强度?耐磨损?耐腐蚀等性能和优点被广泛应用在各个领域中。文中介绍了陶瓷成型加工技术的新方式?新特点和新进展。     

新型压电式传感器前置放大电路的设计

在油气井出砂检测中,压电式传感器检测到的出砂信号弱、频率高,常用的电荷放大器不能满足要求。基于此问题,文中开展了针对出砂信号的前置放大电路的研究,该电路由电荷放大器、带通滤波器、过载指示等电路组成,其中电荷放大器电路选用高阻型的运放AD823实现,带通滤波器的带宽设计为100kHz～1MHz,并且利用EWB电路仿真软件对电荷放大器和滤波电路进行了仿真,仿真结果与设计指标一致,验证了参数选取的合理性。最后,给出了该电路在出砂检测系统中的试验情况,结果表明参数选择合理、性能稳定。     

High-power piezoelectric energy harvester produced using [0 0 1]-textured (Na,K)NbO3-based lead-free piezoceramics

High-power piezoelectric energy harvesters (PEHs) require piezoceramics with a large k_p and d₃₃ but small ε^T₃₃/ε₀ values. The [0 0 1]-textured 0.96(Na, K)(Nb_1−xSb_x)–0.04SrZrO₃ piezoceramics (x = 0.025 and 0.045) exhibited the improved electromechanical coupling factor (k_p) and piezoelectric charge constant (d₃₃); however, the increase of dielectric constant (ε^T₃₃/ε₀) was not significant. Further, the textured piezoceramic with x = 0.045 shows the large d₃₃ × g₃₃ value of 21.5 pm²/N, where g₃₃ is piezoelectric voltage constant, indicating that texturing is a good technique to fabricate the piezoceramics for PEH. The impedance curve of the PEH consisting of the metal substrate and textured piezoceramic shows a piezoelectric resonance peak at a low frequency, which is the same as the mechanical resonance frequency of the PEH. Hence, the PEH can be considered a piezoelectric material. The figure of merit of the PEH was determined using the mechanical quality and electromechanical coupling factor calculated from the impedance curve of the PEH. A large power output of 1.7 mW was obtained from the type-1 PEH at the resonance frequency produced using the textured thick film (x = 0.045). Hence, this PEH can be used as a permanent power source for microelectronic devices in the Internet of Things.     

Effect of CaO doping on densification and microstructure control of highly transparent La0.4Gd1.6Zr2O7 ceramics

Calcium oxide (CaO) as sintering additive was first used to fabricate La_0.4Gd_1.6Zr₂O₇ transparent ceramics by a simple solid-state reaction and one-step vacuum sintering method. The effects of CaO dopant amount on the densification, as well as sintering behaviors and microstructure evolution of the as-fabricated La_0.4Gd_1.6Zr₂O₇ ceramics, were systematically investigated. Under the different sintering temperatures, the relationships during the sintering process between grain growth and zpore elimination were analyzed as well. It was found that 0.1 wt% CaO doping can effectively control the rate of grain growth and promote densification dominated by surface diffusion. Furthermore, Ca²⁺ entered the lattice of La_0.4Gd_1.6Zr₂O₇ ceramics to accelerate ion diffusion and suppress grain boundary migration. With the introduction of 0.1 wt% CaO doping, the highly transparent La_0.4Gd_1.6Zr₂O₇ ceramics (T = 80.4% at 1100 nm) were successfully fabricated at the traditional sintering temperature (1850°C).     

High-entropy carbide-based ceramic cutting tools

In this study, a novel high-entropy carbide-based ceramic cutting tool was developed. The cutting performance of three kinds of high-entropy carbide-based ceramic tools with different mechanical properties for the ISO C45E4 steel were evaluated. Although the pure (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8 ceramic cutting tool exhibited the highest hardness of 25.06 ± 0.32 GPa, the cutting performance was poor due to the chipping and catastrophic failure caused by the low toughness (2.25 ± 0.27 MPa m^1/2). The (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8–15 vol% cobalt cutting tool with highest fracture toughness (6.37 ± 0.24 MPa m^1/2) and lowest hardness (17.29 ± 0.79 GPa) showed the medium cutting performance due to the low wear resistance caused by the low hardness. The (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8–7.7 vol% cobalt cutting tool showed the longest effective cutting life of ∼67 min due to the high wear resistance and chipping resistance caused by the high hardness (21.05 ± 0.72 GPa), high toughness (5.35 ± 0.51 MPa m^1/2), and fine grain size (0.60 ± 0.15 μm). The wear mechanisms of the cobalt-containing (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C_0.8 ceramic cutting tools included adhesive wear and abrasive wear and oxidative wear. This research indicated that the high-entropy carbide-based ceramics with high hardness and high toughness have potential use in the field of cutting tool application.     

Fast preparation of porous anatase material via CuO-mediated glass crystallization and acid-leaching

As an attempt to facilitate the mass production of porous anatase catalysts in industry, in this work, frits with molar ratios of MgO:TiO₂:P₂O₅ = 20:32:24 and an extra addition of CuO (0, 8, 16, and 24 mol%) were first prepared by melt water-quenching method. The frits were further heat- and acid-treated, forming porous anatase consisting of nanosheets. The study showed that the CuO-containing samples had increasing crystallization of anatase and even the crystallization of CuO nano-rods. The easy dissolution of CuO nano-rods and the abundant grain boundaries in the heat-treated samples provided path for the acid-leaching and greatly accelerated the selective dissolution of the crystallized samples, reducing the acid-leaching time from 48 h for the CuO-free sample to 3 h for the sample containing 24 mol% CuO to form a similar porous structure. The preformed anatase acted as nucleus to induce the in situ growth of anatase nanosheets. As a result, CuO greatly fastened the formation of porous anatase, making the industrial production of porous anatase possible.     

Crystal structure and microwave dielectric properties of temperature stable (CoxZn1–x)TiNb2O8 ceramics

(Co_xZn_1–x)TiNb₂O₈ (x = 0.2–0.8) microwave dielectric ceramics were synthesized via the conventional solid-state reaction route, and the correlation of microwave dielectric properties on the crystal structure was discussed. Crystal structures of ceramic samples were systematically investigated by X-ray powder diffraction. Moreover, composition-induced phase transitions were confirmed via the following sequence: for x ≤ 0.2, single-phase orthorhombic ixiolite (ZnTiNb₂O₈) was formed, whereas for 0.3 ≤ x<0.8, ixiolite and rutile coexisted. When x ≥ 0.8, only single-phase rutile was detected. For the (Co_xZn_1–x)TiNb₂O₈ ceramics, the microwave dielectric properties were changed with the crystal structural transitions: the dielectric constant (ε_r) and the temperature coefficient of resonant frequency (τ_f) increased upon increasing the Co²⁺, but the quality factor (Q) decreased. A near-zero τ_f = +1.6 ppm/°C was obtained in the Co_0.38Zn_0.62TiNb₂O₈ ceramics with ε_r = 40.7 and high Q × f = 16 790 GHz. These research outcomes are expected to have great significance for developing microwave dielectric ceramics in practical applications.