掺杂导致剩余极化强度升高，但是压电常数降低的原因

Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) films were grown on single crystal SrTiO 3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO 3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.

In this work, an attempt is made for improving the piezoelectric properties of a lead-free (Na[Formula: see text]K[Formula: see text]Li[Formula: see text](Nb[Formula: see text]V[Formula: see text]O3 ceramic system by doping manganese in it. The Rietveld analysis of XRD micrographs of the ceramics indicates the samples crystallizing into 99.86% of orthorhombic phase and very small traces of tetragonal phase around room temperature. The Curie temperature ([Formula: see text]) is hardly affected by the incorporation of Mn[Formula: see text] into the system. At the manganese concentration of 0.02[Formula: see text]wt.%, the ceramic system attains the peak values in its density, dielectric constant at room temperature ([Formula: see text]), planar electromechanical coefficient ([Formula: see text], piezoelectric coefficient ([Formula: see text]), and remnant polarization ([Formula: see text]). The optimum piezoelectric properties of [Formula: see text]% and [Formula: see text] pC/N are observed for this composition. The study reveals that the modification of (Na[Formula: see text]K[Formula: see text]Li[Formula: see text]) (Nb[Formula: see text]V[Formula: see text]O3 with an appropriate quantity of Mn[Formula: see text] can produce the desired changes in the crystallographic properties and densification so as to eventually improve its piezoelectric properties.

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The high mechanical quality factor (Qm) of KNN-based ceramics is usually achieved by acceptor doping. However, this hardening effect has serious limitations due to the increased mobility of oxygen vacancies under large electric fields and hence is difficult to use in high-power applications. In this work, the hardening mechanism is demonstrated by the development composites of the 0.957(K0.48Na0.52)Nb0.94Ta0.06O3-0.04(Bi0.5Na0.5)ZrO3-0.003BiFeO3 (KNNT-BNZ-BFO) matrix with the K4CuNb8O23 (KCN) phase using the two-step ball-milling method. A decrease in remnant polarization and dielectric constant and an increase in resistivity and Qm are observed compared to that in the KNNT-BNZ-BFO sample. A high Qm of 160, Curie temperature, TC, of 310 °C, and piezoelectric coefficient, d33, of 330 pC/N can be obtained simultaneously in the composite with a 0.008 mole ratio of KCN. This can be explained by the mechanical clamping effect of KCN due to strain incompatibility and the domain wall pegging that traps charges at the KNNT-BNZ-BFO/KCN interface. This composite approach is considered a general hardening concept and can be extended to other KNN-based ceramic systems.

In this work, a series of lead-free 0.97(Bi0.5Na0.5)TiO3-0.03BaTiO3-xPr6O11 (BNBT-xPr) piezoelectric materials with x=0, 0.1, 0.3, 0.5, and 0.7 wt.% were created by the solid-state combustion route, to enhance their electric properties. The investigation on the phase evolution, microstructure, and electrical behavior of the specimens were carried out. The powders and ceramics were calcined and sintered for two hours at 800℃ and 1180℃, correspondingly. All examples displayed a perfect perovskite lattice and no detectable impurity phase. XRD pattern examination for the ceramics disclosed the existence of rhombohedral and tetragonal phases in all examples. The rhombohedral phase was boosted by rising the doping levels, as established by the Rietveld refinement study. As the x content rose, the average grain size and measured density began to decrease from 0.90±0.10 to 0.73±0.07 µm and 6.13 to 6.05 g/cm3, correspondingly. It was noticed that Pr6O11 doping, decreased dielectric properties. The remnant polarization (Pr) of the samples rises from 22.2 to 27.7 µC/cm2 with x rises from 0 to 0.3 and then dropped. The coercive field (Ec) of the ceramics rises significantly when Pr6O11 was incorporated. The BNBT lead-free ceramics doped with 0.3wt%Pr6O11, with a high Pr value, could be a promising candidate for memory applications to replace Pb-based ceramics.  

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Piezocatalysis has emerged as a promising technology for environmental remediation by harnessing mechanical energy to drive redox reactions. In this study, Sm2O3-doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) solid solutions have been synthesized via a facile solid-state reaction to systematically investigate the effects of Sm3+ doping on the phase structure, defect chemistry, and piezocatalytic activity. Rietveld refinement, transmission electron microscopy, and Raman spectroscopy all confirm the coexistence of rhombohedral, orthorhombic, and tetragonal phases. The morphotropic phase boundary (MPB) promotes polarization rotation and enhances the piezoelectric response. The thermally stimulated depolarization current (TSDC) measurements reveal that the lowest defect (particularly oxygen vacancy) density is found in the BCZT samples doped with 0.02 wt % Sm2O3, which enable the materials to possess exceptional piezocatalytic performance, yielding a high degradation efficiency (96.8%) of rhodamine B within 30 min at a rate constant of 0.1156 min-1. Carrier separation and migration capabilities have been boosted through electrochemical and band structure analyses. This work indicates that Sm2O3 doping introduces local structural heterogeneity and optimizes the defect state for the host materials, providing an effective strategy for designing high-performance eco-friendly piezocatalysts.

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Ferroelectric hafnium oxide thin films—the most promising materials in microelectronics’ non-volatile memory—exhibit both unconventional ferroelectricity and unconventional piezoelectricity. Their exact origin remains controversial, and the relationship between ferroelectric and piezoelectric properties remains unclear. We introduce a new method to investigate this issue, which consists in a local controlled modification of the ferroelectric and piezoelectric properties within a single Hf0.5Zr0.5O2 capacitor device through local doping and a further comparative nanoscopic analysis of the modified regions. By comparing the ferroelectric properties of Ga-doped Hf0.5Zr0.5O2 thin films with the results of piezoresponse force microscopy and their simulation, as well as with the results of in situ synchrotron X-ray microdiffractometry, we demonstrate that, depending on the doping concentration, ferroelectric Hf0.5Zr0.5O2 has either a negative or a positive longitudinal piezoelectric coefficient, and its maximal value is −0.3 pm/V. This is several hundreds or thousands of times less than those of classical ferroelectrics. These changes in piezoelectric properties are accompanied by either improved or decreased remnant polarization, as well as partial or complete domain switching. We conclude that various ferroelectric and piezoelectric properties, and the relationships between them, can be designed for Hf0.5Zr0.5O2 via oxygen vacancies and mechanical-strain engineering, e.g., by doping ferroelectric films.

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With the wide application of ultrasonic transducers, microacoustic devices, and other technologies in industrial production, the design and preparation of high-quality ferroelectric ceramic materials required for their core are receiving more and more attention. These applications put forward higher requirements for the performance of ferroelectric ceramics, such as higher dielectric and piezoelectric properties, higher Curie temperature and so on. The structural characteristics and electrical properties of 0.7PFN–0.3PT ferroelectric ceramics were systematically evaluated with emphasis on the role of Fe3+/Nb5+ co-doping. X-ray diffraction measurements and microscopic morphology tests show that the 0.7PFN-0.3PT ceramics exhibit a pure chalcocite structure and a high densification. As the frequency increases, both the dielectric constant and the loss tangent decrease, suggesting that PFN–PT displays characteristic ferroelectric dielectric dispersion. The maximum dielectric constant εr of the 0.7PFN-0.3PT ceramic sample at 1 kHz is 1480, the Curie temperature at 1 kHz is 138°C, the saturation polarization constant Ps is 30.94 µC/cm2, the coercivity field Ec is 27.10 kV/mm and the piezoeleceric constant d33 is 58 pC/N.

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