Intrinsically tunable bulk acoustic wave resonators based on sol-gel grown PMN-PT films

Intrinsically tunable bulk acoustic wave resonators, based on sol-gel 0.70Pb(Mg1/3Nb2/3)O3- 0.30PbTiO3 (PMN-PT) thin films, with high effective electromechanical coupling coefficient of 13% and tunability of the series resonance frequency up to 4.0% are fabricated and characterized. The enhanced electroacoustic properties of the PMN-PT resonators are attributed to the mechanism of polarization rotation occurring in the region of the morphotropic phase boundary. Electroacoustic performance of the PMN-PT resonators is analyzed using the theory of dc fieldinduced piezoelectric effect in ferroelectrics. Extrinsic acoustic loss in the PMN-PT resonators is analyzed using the model of the wave scattering at reflections from rough interfaces. Mechanical Q-factor of the resonators is up to 70 at 4.1 GHz and limited mainly by losses in the PMN-PT film

Nickel manganite-carbonized alginate composite for use as energy storage electrodes

Nickel-manganite is a versatile material used in many technology applications. One of the established uses is as a supercapacitor electrode. The advantage of this type of material is the abundance of required metals, compared to noble metals, the synthesis methods' simplicity, and high redox activity. Metal-oxide battery materials are usually combined with activated carbon to enhance the specific surface area and add to energy storage capacity via surface charge accumulation. In the current work, nickel manganite was synthesized via the sol-gel combustion synthesis method with glycine as fuel and nitrate ions as oxidizers. The post-combustion amorphous powder was calcined at temperatures between 300 and 800 °C. Powders were structurally characterized. Obtained materials were tested as energy storage electrodes in a three-electrode cell setup in 6 M KOH aqueous solution as electrolyte. Methods embedded in electrochemical characterization were cyclic voltammetry (CV), electric impedance spectroscopy (EIS) and constant current chronopotentiometry at different current densities to obtain galvanostatic charge-discharge (GCD) curves. Results show considerable charge storage activity, which can be ascribed to oxido reduction reactions of manganese ions and charge accumulation on the surface of the activated carbon

INFLUENCE OF CALCINATION TEMPERATURE ON THE STRUCTURE, MORPHOLOGY AND OPTICAL PROPERTIES OF ELECTROSPUN PSEUDOBROOKITE NANOFIBERS

Novel crystalline iron-titanate fibers were synthesized for the first time to the best of our knowledge, through a simple, low cost electrospinning method followed by calcination treatment at different temperatures (500–750 °C for 3 h and at 500 °C for 6 h and at 550 °C for 4 h). The fibers were prepared from a precursor solution containing polyvinylpyrrolidone (PVP), iron(III) nonahydrate, titanium isopropoxide, N,N-Dimethylformamide and ethanol. As spun fibers were smooth, straight, beadless and uniform forming a nonwoven fibrous mat, with an average diameter of ca. 205 nm. Upon calcination in air the PVP matrice was removed and XRD and FTIR analysis showed that the duration of the calcination process, besides the temperature, had a direct influence on phase formation. Pure phase of pseudobrookite was obtained at 600 °C, 500 °C for 6 h and at 550 °C for 4 h. In addition, the morphology of obtained nanofibers was directly affected by the calcination temperature. The surface of fibers obtained after calcination was no longer smooth and the fiber diameter decreased due to complete degradation of PVP. At 700 oC and 750 °C, fibers were thicker which can be attributed to growth of Fe2TiO5 nanoparticles and simultaneous coalescence of small particles. All samples exhibited a type IV nitrogen adsorption isotherm with a type- H3 indicating slit-shaped mesoporous structure. The BET surface areas of 500 oC for 6 h, 550 oC for 4 h and 600 oC for 3 h were estimated to be 62, 38.7 and 33.2 m2/g, respectively

Tunable FBARs based on sol-gel grown PMN-PT films

In this work possibilities of using of sol-gel grown PMN-PT films in tunable film bulk acoustic wave resonators are considered. More than 4% tuning of resonance frequency under DC field less than 15 V/μm is demonstrated. Linear and nonlinear electrostriction and induced piezoelectric coefficients of the PMN-PT films are evaluated

Simultaneous heteroepitaxial growth of SrO (001) and SrO (111) during strontium-assisted deoxidation in the Si (001) surface

International audienceEpitaxial integration of transition-metal oxides with silicon brings a variety of functional properties to the well-established platform of electronic components. In this process, deoxidation and passivation of the silicon surface are one of the most important steps, which in our study were controlled by an ultra-thin layer of SrO and monitored by using transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), synchrotron X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) methods. Results revealed that an insufficient amount of SrO leads to uneven deoxidation of the silicon surfacei.e.formation of pits and islands, whereas the composition of the as-formed heterostructure gradually changes from strontium silicide at the interface with silicon, to strontium silicate and SrO in the topmost layer. Epitaxial ordering of SrO, occurring simultaneously with silicon deoxidation, was observed. RHEED analysis has identified that SrO is epitaxially aligned with the (001) Si substrate both with SrO (001) and SrO (111) out-of-plane directions. This observation was discussed from the point of view of SrO desorption, SrO-induced deoxidation of the Si (001) surface and other interfacial reactions as well as structural ordering of deposited SrO. Results of the study present an important milestone in understanding subsequent epitaxial integration of functional oxides with silicon using SrO

Large direct and inverse electrocaloric effects in lead-free Dy doped 0.975KNN-0.025NBT ceramics

International audienceUndoped and Dy3+ doped 0.975 K1/2Na1/2NbO3-0.025Na1/2Bi1/2TiO3 (0.975KNN-0.025NBT) ceramics were synthesized using the solid-state synthesis method. X-ray diffraction analysis revealed pure perovskite structure without any secondary phases. The dielectric investigations of both ceramics revealed low dielectric losses in the dysprosium doped ceramic, particularly for temperatures higher than 100 degrees C. The dielectric loss anomaly around room temperature corroborates the polymorphic phase boundary (PPB) between orthorhombic and tetragonal phases detected by XRD investigations. The electrocaloric effect (ECE) was investigated using the indirect method based on the Maxwell equation and thermal P-E hysteresis loops. The maximum ECE value was found equal to 0.63 K at 83 degrees C for KNNBT0.025. However, in Dy doped KNNBT0.025 ceramics, both direct and inverse ECE responses were found with values of 1.01 K at 118 degrees C and -1.79 K at 80 degrees C, respectively. Besides, yellow light emission was detected under an excitation wavelength of 350 nm. The simultaneous existence of high ECEs, good dielectric performance, and photoluminescence properties makes KNNBT-Dy a promising candidate for solid-state refrigeration and optoelectronic devices