Search

BaTiO nanoparticles were prepared for the first time employing a solvothermal process from the synthetic precursors of KTiO nano-whiskers. The obtained samples were characterized by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and high-resolution transmission electron microscopy, etc. The results indicate that well-crystallized single-phase BaTiO nanoparticles are synthesized using KTiO as precursors under solvothermal conditions at as low as 0.9 M. The solvothermal method facilitates the crystallinity and formation of the BaTiO nanoparticles. However, the K ions cannot be completely replaced by Ba by the hydrothermal method even at 10 M due to its unique and extremely stable 'tunnel' structure. The solvothermal method provides new avenues for the ion-exchange synthesis of a variety of other perovskite-type materials such as MTiO (M = Pb, Sr, Ca, etc.). [ABSTRACT FROM AUTHOR]

Pure (K,Na)NbO (KNN) powders have been successfully prepared by using traditional hydrothermal method and high-temperature mixing method (HTMM) under solvothermal and hydrothermal conditions. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to show the change of phase, morphology, and size of the as-prepared particles with the alkalinity of the starting solution. Compared with the traditional hydrothermal method, smaller particles with higher phase purity are prepared using HTMM under hydrothermal conditions. It is found that the alkalinity has significant effects on the crystal size. The KNN grain size first increases and then decreases with increasing alkalinity. Typical samples solvothermally synthesized in a mixed solvent with isopropanol/deionized water ratio of 50/50 by volume were made of well-crystallized single-crystalline nanoparticles with size of about 500 nm. [ABSTRACT FROM AUTHOR]

Dielectric ceramics have attracted ever-increasing interest in energy storage applications due to their high-power density and fast charge–discharge speed. In particular, AgNbO3-based antiferroelectric ceramics are considered potential substitutes for lead-based ceramics. AgNbO3 ceramics sintered with fine hydrothermal-synthesized powders show the advantage of high breakdown strength. However, the fine grains lead to the decreased polarization, which harms the recoverable energy density. In this work, a little amount over-stoichiometrical WO3 and MnO2 were introduced to synergistically improve the polarization and dielectric breakdown strength of obtained AgNbO3 ceramics. The dependences of structures and dielectric properties on WO3 doping were explored. A maximum polarization of 49.4 μC/cm2 and Eb as large as 285 kV/cm were achieved in 0.1 wt % WO3 and MnO2 co-doped AgNbO3 ceramic. The corresponding Wrec reached 2.75 J/cm3, which was 1.3 times larger than that of pristine AgNbO3 ceramics. Moreover, benign thermal stability with Wrec = 2.2–2.7 J/cm3 over 30–150 °C at 240 kV cm−1 was also achieved in 0.1 wt.% WO3 and MnO2 co-doped AgNbO3 ceramics. [ABSTRACT FROM AUTHOR]

(KNa)NbO piezoelectric ceramics can be sintered at a temperature as low as 750 °C for 5 h by incorporating LiCO + BiO + ZnO as the sintering aid, whereas the conventional sintering temperature is around 1,100 °C. The optimal 'soft' piezoelectric properties are obtained for ceramics sintered at 850 °C for 5 h. The dielectric permittivity ( ε), piezoelectric coefficient ( d), electromechanical coupling ( k) and mechanical quality factors ( Q) of (K, Na)NbO modified with 5.5 wt% sintering aids are 1,436, 90 pC/N, 0.3 and 10, respectively. These values are similar to the values obtained for (KNa)NbO ceramics sintered above 1,100 °C. The underlying mechanism for abrupt change of dielectric permittivity is explained. [ABSTRACT FROM AUTHOR]

Dielectric materials with high permittivity are strongly demanded for various technological applications. While polarization inherently exists in ferroelectric barium titanate (BaTiO3), its high permittivity can only be achieved by chemical and/or structural modification. Here, we report the room-temperature colossal permittivity (~760,000) obtained in xNd: BaTiO3 (x = 0.5 mol%) ceramics derived from the counterpart nanoparticles followed by conventional pressureless sintering process. Through the systematic analysis of chemical composition, crystalline structure and defect chemistry, the substitution mechanism involving the occupation of Nd3+ in Ba2+ -site associated with the generation of Ba vacancies and oxygen vacancies for charge compensation has been firstly demonstrated. The present study serves as a precedent and fundamental step toward further improvement of the permittivity of BaTiO3-based ceramics. [ABSTRACT FROM AUTHOR]

This paper develops analytical electromechanical formulas to predict the mechanical deformation of ionic polymer-metal composite (IPMC) cantilever actuators under DC excitation voltages. In this research, IPMC samples with Pt and Ag electrodes were manufactured, and the large nonlinear deformation and the effect of curvature on surface electrode resistance of the IPMC samples were investigated experimentally and theoretically. A distributed electrical model was modified for calculating the distribution of voltage along the bending actuator. Then an irreversible thermodynamic model that could predict the curvature of a unit part of an IPMC actuator is combined with the electrical model so that an analytical electromechanical model is developed. The electromechanical model is then validated against the experimental results obtained from Pt- and Ag-IPMC actuators under various excitation voltages. The good agreement between the electromechanical model and the actuators shows that the analytical electromechanical model can accurately describe the large nonlinear quasi-static deflection behavior of IPMC actuators. [ABSTRACT FROM AUTHOR]

A magnetoelectric composite of Pb(ZrTi)O film-on-CoFeO ceramic was prepared by spin-coating Pb(ZrTi)O films of 300 nm in thickness on the LaNiO-buffered highly dense CoFeO ceramics. The X-ray diffraction, ferroelectric loops, piezoelectric curves, and magnetoelectric coupling effects were all measured at room temperature to investigate the effect of LaNiO thickness on the magnetoelectric response of the composites. The introduction of the metallic oxide LaNiO efficiently enhanced the magnetoelectric coefficient α by improving the electric-related outputs. However, too thick LaNiO layer would also hinder the strain (stress) transferring across the interface between the Pb(ZrTi)O and CoFeO phases. A peak α value was obtained in the sample with a LaNiO thickness of about 60 nm, which was 2.5 times larger than that in the composite of Pb(ZrTi)O film on the CoFeO ceramic without the LaNiO layer. Further enhancement could be anticipated by optimizing the LaNiO layer and/or Pb(ZrTi)O films. [ABSTRACT FROM AUTHOR]

A piezoelectric driving method for rover vehicles is proposed in this paper. Employing this method, a tracked vehicle driven by friction forces from a frame mounted with piezoelectric elements was developed. The vehicle is designed with no driver sprocket, no idler-wheel and no supporting bogie wheels, and the vehicle thus requires no lubrication and has potential application in planetary exploration. The frame consists of a pair of piezoelectric transducers. Each transducer comprises four annular parts jointed by beams adhered with piezoelectric ceramics. The tracks are set to the outer surface of the annular parts by means of track tension. Traveling rotating waves are generated by piezoelectric transducers in the annular parts, which generate microscopic elliptical motions at the interface of the tracks. The microscopic elliptical motions from the piezoelectric transducers drive the track vehicle to move. Finite elements analysis was carried out to verify the operation principle using commercial software ANSYS. Piezoelectric transducers were fabricated, assembled and tested to validate the concepts of the proposed rover vehicle and confirm the simulation results. A prototype vehicle with mass of 0.57 kg moves at a speed of 4.3 mm/s at a driving voltage of 250 V and operating frequency of 65.53 kHz. [ABSTRACT FROM AUTHOR]