掺杂后导致晶界融化，压电常数是不是会下降

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Grain boundary segregation plays a critical role in determining the properties of polycrystalline materials, yet its influence on piezoelectric performance remains underexplored. In this work, bismuth layer-structured piezoceramic W6+-doped CaBi2Nb2O9 (WCBN) was chosen to investigate the effect of grain boundary segregation on the piezoelectric properties through multiscale structural characterization and phase-field simulations. The results reveal that improper grain boundary segregation can induce internal stress fields that restrict domain switching dynamics, leading to deterioration of the piezoelectric response. Therefore, a novel poling process was developed, which effectively alleviated the segregation-induced stress constraints and enhanced the piezoelectric coefficients by 180%. More importantly, optimizing the preparation process significantly enhances the mechanical properties, particularly increasing the fracture toughness of WCBN ceramics to 2.73 MPa m1/2, which is more than twice that of traditional Pb(Zr, Ti)O3 piezoceramics. These findings establish direct correlations between grain boundary segregation, internal stress, and domain switching behavior, providing fundamental insights for the design of piezoelectric materials that integrate both high piezoelectric and mechanical properties, which could be greatly beneficial to long-term stable operation in harsh environments with high temperatures and complex vibrations for bismuth layer-structured piezoceramics.

Reducing mechanical losses and suppressing self‐heating are critical characteristics for high‐power piezoelectric applications. For environmentally friendly Pb‐free piezoelectric ceramics, traditional acceptor doping or annealing treatments have successfully improved the mechanical quality factor (Qm) based on a ceramic matrix with a poor piezoelectric coefficient (d33<100 pC/N). Nevertheless, a ceramic with high Qm and d33 values has not been reported owing to the inverse relationship between Qm and d33. Herein, a novel hardening method called grain boundary diffusion is used to develop Pb‐free potassium sodium niobate ceramics, where Qm increased by more than two‐fold (from 51 to 132) and a high d33 value (d33 = 360 pC/N) is maintained. Significantly, d33 retained 98% of its initial value after 180 days, exhibiting improved aging stability. The established properties are associated with the formation of the core‐shell microstructure and the full gradient composition distribution using structural characterizations and phase‐field simulations, where the core maintains a high d33 and the shell provides a hardening effect. The novel hardening effect in piezoelectric materials, known as grain boundary diffusion hardening, highlights the enhancement of the mechanical quality factor with high piezoelectricity, providing a new paradigm for the design of functional materials.

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The piezoelectric properties of Pb(Zr,Ti)O3 (PZT)‐based piezoceramics can be improved by doping with heterovalent ions at the A/B sites. Nd3+ ions were codoped at the A site and Ta5+ ions were doped into the B site of Pb(Zr0.5Ti0.5)(Mg0.5W0.5)(Ni1/3Nb2/3)O3 (xNd2O3‐PZTMWNN) ceramics sintered at a low temperature of 940°C. The number of Ta5+ ions at site B remained constant, whereas the number of Nd3+ ions at site A changed. The degree of deviation from the Curie–Weiss law (∆Tm) and the degree of diffuseness of the ferroelectric relaxors (γ) have a direct and close relationship. Combined analysis of the grain size, phase structure, domain structure, and activation energy (Ea) for domain wall movement was used to understand the mechanism of the piezoelectric improvement in PZT‐based ceramics. The high proportion of the tetragonal phase in the coexisting tetragonal–rhombohedral phases is closely related to the low Ea, which promotes domain rotation and leads to high piezoelectricity. The xNd2O3–PZTMWNN (x = 2.0, 2.5) ceramics have a very low Ea, but the clamping effect caused by the fine grain boundaries hinders the motion of the domain wall. The xNd2O3–PZTMWNN (x = 1.0) ceramics with low Ea, striped nanodomains, and large grains exhibited the highest piezoelectric activity.

In this experiment, a new lead-free piezoelectric ceramics (1−x)K0.45Na0.55Nb0.965Sb0.035O3−x(0.9Bi0.5Li0.5ZrO3−0.1SrSnO3) were prepared by the conventional solid-phase method, and the effects of the doping amount of 0.9Bi0.5Li0.5ZrO3−0.1SrSnO3 on the K0.45Na0.55Nb0.965Sb0.035O3 ceramics on the crystal structure, microstructure, microscopic structure and electrical properties. All the doping ions entered the KNN lattice and formed a dense solid solution with a single-phase structure, and the phase structure of the ceramics coexisted from orthorhombic (O) to orthorhombic-tetragonal (O-T) phases in the range of 0 ≤ x ≤ 0.03, and transitioned to rhombohedral-tetragonal (R-T) phase coexistence when 0.035 ≤ x ≤ 0.05. The electrical properties of the ceramics were analyzed and the polymorphic phase boundary (PPB) region was obtained at x = 0.035 and had the best overall properties: d 33 = 324pC/N, k p = 49%, ε r = 1479, tanδ = 3.21%, P r = 31.98 μC/cm2, E c = 16.83 kV cm−1 and T C = 293°C. By The microstructural analysis of the ceramics showed that the appropriate amount of compound doping of the second element enhances the denseness of the ceramics as well as makes the grains uniformly distributed. These results indicate that the ceramics of this system have great prospects for future applications in the field of lead-free piezoelectric ceramics.

Lead-free piezoelectric ceramic of (0.94-x)[(Bi0.5Na0.5)TiO3] + 0.06BaTiO3 + xSrTi0.875Nb0.1O3 (abbreviated as BNBT-xSTN) with x equal 0.0, 0.1, 0.2, 0.3, and 0.4 were synthesized using solid state reaction. The mixing of raw materials was ball milled in alcohol for 24 hours and then calcined at 850 oC for 2 hours to form BNBT-xSTN powder. The BNBT-xSTN powders were further shaped and sintered at 1175 °C with a heating rate of 5 °C per minute and held at the sintering temperature for 2 hours. The crystal structure, microstructure, dielectric, ferroelectric, strain, and energy storage density of the BNBT-xSTN ceramics were systematically investigated. The BNBT-xSTN ceramic materials were analyzed using X-ray diffraction (XRD), all samples show a typical perovskite structure without any trace of secondary phase with a crystal structure coexisting in rhombohedral and tetragonal phases (R&T). Scanning electron microscopy (SEM) images showed the grain boundaries and porosity. The highest dielectric constant was 2511 at x equal 0.2. On the other hand, polarization and strain of STN doped on BNBT were induced with various electric fields E equal 40 to 60 kV/cm, the electric field-induced strain curves of the analyzed samples show a phase transition from a ferroelectric phase to a relaxor phase when the STN is doped. The x equal 0.1 sample showed the maximum energy storage density of 0.3 J/cm3 at E equal 60 kV/cm, corresponding to the Wrec/Emax value of approximately 5 × 10- 3 J/(kV.cm2). 

Polycrystalline Ge thin films have attracted considerable attention as potential materials for use in various electronic and optical devices. We recently developed a low-temperature solid-phase crystallization technology for a doped Ge layer and achieved the highest electron mobility in a polycrystalline Ge thin film. In this study, we investigated the effects of strain on the crystalline and electrical properties of n-type polycrystalline Ge layers. By inserting a GeOx interlayer directly under Ge and selecting substrates with different coefficients of thermal expansion, we modulated the strain in the polycrystalline Ge layer, ranging from approximately 0.6% (tensile) to − 0.8% (compressive). Compressive strain enlarged the grain size to 12 µm, but decreased the electron mobility. The temperature dependence of the electron mobility clarified that changes in the potential barrier height of the grain boundary caused this behavior. Furthermore, we revealed that the behavior of the grain boundary barrier height with respect to strain is opposite for the n- and p-types. This result strongly suggests that this phenomenon is due to the piezoelectric effect. These discoveries will provide guidelines for improving the performance of Ge devices and useful physical knowledge of various polycrystalline semiconductor thin films.

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Lead-free piezoelectric ceramics are widely used in actuators, sensors, and transducers due to high piezoelectric coefficients and thermal stability. However, the commonly used strategies for improving the piezoelectric coefficients, such as morphotropic phase boundary (MPB) and polymorphic phase transition (PPT), are ineffective in improving temperature stability. In this work, defect dipoles were introduced into barium titanate to enhance both its piezoelectric coefficient and temperature stability. Donor Nb5+ and acceptor Li+ were doped into BaTiO3 as defect dipoles, resulting in an increase of piezoelectric coefficient to 267 pC/N and a significant improvement in thermal stability. The decrease in flat free energy and grain size, induced by the doping effect, led to a rise in piezoelectric coefficient. Furthermore, the defect dipoles produce an internal bias field (Ei), thus improving thermal stability by stabilizing the domain. This research provides a hopeful strategy for lead-free piezoelectric ceramics with both high thermal stability and a large dielectric coefficient.

Acceptor doping is a common method for hardening modified piezoelectric ceramics. The mechanism through which the hardening effect can be improved has been widely studied and verified. However, the effect of defects caused by different valence states of the B‐site ions on the properties of multicomponent piezoelectric ceramics remains to be discussed. Therefore, in this work, a novel Pb(Ni1/3Nb2/3)O3–Pb(In1/2Nb1/2)O3–Pb(Mn1/3Nb1/2)–PbTiO3 quaternary hard ceramic with excellent performance is prepared and studied. The interaction between grain‐boundary defects and defect dipoles is proposed to be the mechanism behind the observed excellent performance. It is found that different types of defects improve the hardening effect in various ways. These results can provide a theoretical basis for the preparation of multicomponent piezoelectric ceramics with better properties.

Defects generation in ceramics by element substitution or doping may improve their properties. However, different results will be obtained even though the same element is involved due to different mechanisms. Ceramics Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) is one of the potential candidates to replace lead-based material PZT. However, the conventional method requires high-temperature calcination and sintering process to synthesize this material. Thus, Lithium (Li) can act as the sintering aid to lower the temperature at the same time, the properties of piezoelectric can be enhanced. In this paper, the structural, physical, and piezoelectric performance of lead-free Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) ceramics with Lithium Li substitution and doping, synthesized by the solid-state reaction method were studied. The substitution of Li increases the density, ρ and piezoelectric coefficient, d33 of BCZT which are 4.075 g/cm3 and 304.6 pC/N, respectively. These results demonstrate that Li substitution is more beneficial to the piezoelectric properties than doping because it produces higher grain boundary resistance and activation energy and has lower conductivity than doping. This can provide a definite strategy during the chemical composition design and manufacture of BCZT ceramics.

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Lead-free potassium sodium niobate [(K0.5Na0.5)NbO3, KNN]-based piezoceramics have emerged as promising alternatives to lead-based counterparts. Although grain-size effects in KNN ceramics have been widely investigated, most prior studies relied on doping strategies, introducing additional variables that complicate interpretation. The intrinsic microscopic mechanisms of their grain size effects remain inadequately understood. In this work, the influence of grain size on domain structures and ferroelectric properties was systematically investigated in pure KNN ceramics with controlled uniform grain sizes (∼0.5, ∼3, and ∼9 μm). Comprehensive characterization combining piezoresponse force microscopy and macroscopic ferroelectric measurements reveals that although saturated polarization is similar across different grain sizes, polarization switching responses to applied electric fields vary substantially. Small grains predominantly exhibit simplified 180° domain configurations resulting from elevated grain-boundary-induced residual stresses, leading to higher coercive fields and reduced domain growth dynamics (growth rate, ∼169 nm2 V−1). Conversely, large grains feature diverse non-180° domains, which facilitate polarization switching at lower electric fields with an enhanced domain growth of ∼270 000 nm2 V−1. These results demonstrate that different grain boundary densities critically affect internal stress distributions and domain structures, thereby determining domain switching kinetics and macroscopic electromechanical performances. This study provides essential insights into the microscopic mechanisms underlying grain size effects in lead-free piezoelectric ceramics.

The perovskite-structured materials Pb0.75Ba0.251−xCax(Zr0.7Ti0.3)O3 for x = 1 and 2 at.% were synthesized using the conventional mixed-oxide method and carbonates. Microstructural analysis, performed using a scanning electron microscope, revealed rounded grains with relatively inhomogeneous sizes and distinct grain boundaries. X-ray diffraction confirmed that the materials exhibit a rhombohedral structure with an R3c space group at room temperature. Piezoelectric resonance measurements were conducted to determine the piezoelectric and elastic properties of the samples. The results indicated that a small amount of calcium doping significantly enhanced the piezoelectric coefficient d31. The calcium-doped ceramics exhibited higher electrical permittivity across the entire temperature range compared to the pure material, as well as a significant value of remanent polarization. These findings indicate that the performance parameters of the base material have been significantly improved, making these ceramics promising candidates for various applications.

Mechanical behaviors are specifically important considerations for piezoelectric materials in practical applications. As promising high‐temperature piezoelectric materials, CaBi4Ti4O15 (CBT) ceramics have been studied for many years, and significant progress has been made in enhancing their electrical performance. However, the mechanical properties of CBT ceramics have received scant attention from researchers to date. In this study, the hardness and fracture toughness of Nb/Mn co‐doped CBT ceramics were systematically examined. The effects of ion doping and electric poling on plastic deformation and crack propagation, as well as fracture behaviors, were revealed in detail. The results demonstrate that numerous layered ferroelectric domains with nanoscale dimensions are observed on the surface of plate‐like grains, and the corresponding domain boundaries are further confirmed as 180°‐like domain walls by high‐resolution transmission electron microscopy (HRTEM). Nanoindentation and Vickers indentation tests reveal that the Nb/Mn co‐doped CBT ceramics with smaller grain size and higher density possess greater hardness and higher resistance to deformation. The poling process tends to decrease hardness due to the presence of micro‐defects and stress concentration after domain rearrangement under applied electric field. Yet, the crack propagation along the poling direction is retarded by ferroelastic deformation around the crack tip, exhibiting significant fracture toughening. R‐curve analysis further elaborates on intrinsic and extrinsic toughening behaviors and indicate that ceramics with higher doping levels possess enhanced toughening behaviors and improved fracture resistance. This work not only deepens our understanding of the mechanical behaviors of CBT piezoelectric ceramics, but also offers valuable guidance for the design and development of high‐performance piezoelectric materials for practical applications.

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In this work, we systematically studied the deposition, characterization, and crystal structure modeling of ScAlN thin film. Measurements of the piezoelectric device’s relevant material properties, such as crystal structure, crystallographic orientation, and piezoelectric response, were performed to characterize the Sc0.29Al0.71N thin film grown using pulsed DC magnetron sputtering. Crystal structure modeling of the ScAlN thin film is proposed and validated, and the structure–property relations are discussed. The investigation results indicated that the sputtered thin film using seed layer technique had a good crystalline quality and a clear grain boundary. In addition, the effective piezoelectric coefficient d33 was up to 12.6 pC/N, and there was no wurtzite-to-rocksalt phase transition under high pressure. These good features demonstrated that the sputtered ScAlN is promising for application in high-coupling piezoelectric devices with high-pressure stability.

We investigate the melting process of polycrystalline copper doped with hydrogen atoms by using the newly developed Cu/H ReaxFF force field. Hydrogen atoms are found to effectively promote the melting of copper, and even make it happen at temperatures below the equilibrium melting temperature of copper during rapid heating. The enhanced melting is closely relevant to the interaction of hydrogen atoms with the grain boundary. We find that host Cu atoms perform cooperative vibration around the grain boundaries as the precursor of premelting. The doping of hydrogen atoms is shown to drive the vibration more violent so that the grain boundary becomes broader and the premelting is prematurely triggered. Meanwhile, hydrogen atoms segregated in grain boundaries massively diffuse into the bulk region with increasing temperature, resulting in intensification of lattice distortion of the bulk phase. This facilitates the rapid advancement of the liquid-solid interface during melting in contrast to the slow and discontinuous interface advancement in hydrogen-free polycrystalline copper. Our results suggest that even a small amount of hydrogen atoms is expected to significantly affect the thermodynamic properties of metals with the existence of structural defects.

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In this study, Cd1−xNaxCu3Ti4O12 (x = 0, 0.02, 0.04, 0.06, and 0.08) ceramics were prepared via a solid-state method. The phase composition, microstructure, and defect characteristics as well as optical, dielectric, and nonlinear properties of the ceramics were systematically studied. A CuO second phase was detected in doped samples. Grain boundary precipitates, Na with a low melting point, and oxygen and cation vacancies together caused the grain size to first increase and then decrease with an increase in the Na+ doping amount. The abundant emerging cation vacancies with an increase in Na+ content led to a decrease in the optical energy band. The sample with x = 0.04 exhibited the highest ε′ value (∼35 800) due to its largest grain size. Moreover, it possessed a lower tan δ (∼0.053) at 10 kHz, which was attributed to the multiplication of insulating grain boundaries. The huge dielectric constant originated from Maxwell–Wagner polarization at low frequencies and followed the internal barrier effect model. The lowest tan δ (∼0.037) and optimal nonlinear properties (α = 3.66 and Eb = 3.82 kV cm−1) were obtained in the sample with x = 0.08, which were associated with its highest grain boundary resistance and barrier height. Electric modulus data proved that dielectric relaxation at low frequencies was associated with grain boundaries. Dielectric anomalies in the high temperature range were attributed to oxygen vacancies.

This work shows the influence of admixture on the basic properties of the multicomponent PbZr1−xTixO3 (PZT)-type ceramics. It presents the results of four compositions of PZT-type material with the general chemical formula, Pb0.99M0.01((Zr0.49Ti0.51)0.95Mn0.021Sb0.016W0.013)0.9975O3, where, in the M position, a donor admixture was introduced, i.e., samarium (Sm3+), gadolinium (Gd3+), dysprosium (Dy3+) or lanthanum (La3+). The compositions of the PZT-type ceramics were obtained through the classic ceramic method, as a result of the synthesis of simple oxides. The X-ray diffraction (XRD) pattern studies showed that the obtained multicomponent PZT materials have a tetragonal structure with a P4mm point group. The microstructure of the obtained compositions is characterized by a well crystallized grain, with clearly visible grain boundaries. The composition with the admixture of lanthanum has the highest uniformity of fine grain microstructure, which positively affects its final dielectric and piezoelectric properties. In the multicomponent PZT-type ceramic, materials utilize the mixed (acceptor and donor) doping of the main compound. This dopiong method has a positive effect on the set of the electrophysical parameters of ceramic materials. Donor dopants W6+ (at positions B) and M3+ = Sm3+, Gd3+, Dy3+, and La3+ (at positions A) increase the dielectric and piezoelectric properties, while the acceptor dopant Sb3+ (at positions B) increases the time and temperature stability of the electrophysical parameters. In addition, the suitable selection of the set of admixtures improved the sinterability of the ceramic samples, as well as resulted in obtaining the required material with good piezoelectric parameters for the poling process. This research confirms that all ceramic compositions have a set of parameters suitable for applications in micromechatronics, for example, as actuators, piezoelectric transducers, and precision microswitches.

No abstract available