The electrocaloric effect (ECE) of multilayer ceramic capacitor (MLCC) of Y5V type was directly measured via a differential scanning calorimetry (DSC) method and a reference resistor was used to calibrate the heat flow due to the heat dissipation. The results are compared with those calculated from Maxwell relations by using the polarization data obtained from the polarization - electric field hysteresis loops. The direct method shows a larger ECE temperature change, which is accounted for the situation approaches an ideal condition. For the indirect method using Maxwell relations, only the polarization projection along the electric field was taken into account, which will be less than the randomly distributed real polarizations that contribute to the ECE. The MLCCs exhibit a broad peak of ECE around 80 °C, which will be favorite for the practical ECE cooling devices.
Nowadays, polycrystalline Pb(Zr, Ti)O3 (PZT) thin films are widely used in various applications such as piezoelectric actuators, sensors and Ferroelectric Random Access Memory. In this later case an important issue is the switching speed capability at low voltage of the ferroelectric domains as well as their size. The switching speed control of nano-sized domain is mandatory for the application of ferroelectric nanostructures in new more efficient devices. In the last years, many studies have been done on the switching dynamics of epitaxial PZT ferroelectric thin films via Piezoresponse Force Microscopy (PFM). PFM is a powerful technique to study ferroelectric materials at the nanoscale level as the domain structures can be controlled in a non-destructive way and the orientation of the polarization can be studied locally. We report here the switching dynamic study in polycrystalline PZT thin films with two different thicknesses on a large time scale (from 1 s down to 10-9 s). Both films present a similar grain size (Rmean≈45 nm) and allowed the observations of two different regimes for the polarization switching speed. We could evidence a tight connection of the nucleation and growth of nano-domains as well as of their success rate with the film thickness and grain structure.
The paper considers a focusing piezoelectric transducer in the form of a spherical segment with technological hole in the center and with separated electrodes. This transducer is designed to generate high-intensity ultrasonic fields with controllable characteristics in the focal spot in the external acoustic medium. In order to enhance the efficiency of the acoustic wave excitation, porous piezoceramics is suggested as an active material for the transducer. The simulation of the working process for piezoelectric transducers was done with the use of multiscale finite element technologies in computational package ANSYS. On the results of calculations, it was concluded that the multi-electrode coating allows controlling the characteristics of the focal area at the working acoustic medium and, thus, improve the efficiency of the transducer with a powerful ultrasound.
In this work, we present analytical and finite element method (FEM) modeling to describe the time dependence of the pyroelectric current of embedded piezoelectrics generated by a laser pulse. Analytical solutions of the one-dimensional heat transfer equation consider a two-layer model, account for the experimentally derived heat pulse shape and the heat loss to the environment. They serve as a proof of the more complex FEM modeling which allows the consideration of three-layer models. It provides an understanding of the heat transfer in structurally complex devices excited by laser pulses.
In the late 80ths we constructed a light fibre interferometer, which could measure the voltage-induced thickness variations of piezoelectric samples down to some few picometres. The principle of the interferometer is explained and four methods to minimize noise. With this sensor, we started a home-made PFM in February 1993. The very first pictures are shown together with locally measured polarization cycles. We found out that the inverse piezoelectric effect dominates the first harmonic of the PFM.
In this present study, the issue of lead volatility in (Pb 0.92 La 0.08 )(Zr 0.60 Ti 0.40 )O 3 (PLZT 8/60/40) ceramics is addressed by the combinatorial approach of high energy ball milling and microwave sintering. The XRD patterns were used for the phase analysis. Higher relative density (~99%) and uniform grain distribution (~1.2 μm) were found for PLZT 8/60/40 ceramics, which was microwave sintered at 1150°C. The dielectric constant for the unpoled PLZT ceramics was found to be ~2100 at 1 kHz frequency with very low dielectric loss (~0.03). The saturated P-E and S-E ferroelectric hysteresis loops as well as the domain switching current peak in I-E loop confirms the ferroelectric nature of PLZT ceramics. The high remnant polarization ~33 μC/cm 2 , low coercive field ~10 kV/cm and high strain ~0.26%, was shown by the ceramics which was microwave sintered at 1150°C. The piezoelectric charge (d 33 ) was found to be ~575 pC/N.
In the present work theoretical calculations on surface acoustic wave (SAW) propagation characteristics and acousto-optic diffraction efficiency of ZnO/IDT/AlN/Sapphire is performed. The proposed layered structure with ZnO and AlN is found to be a promising high performance SAW device, as it possess an enhanced electromechanical coupling coefficient with an appreciable SAW phase velocity and is temperature stable. Also, the proposed layered structure found to exhibits very high diffraction efficiency and very high acousto optical figure of merit coupled with nearly temperature stable characteristics indicating a bonding device for acousto optic applications.
Electromechanical characterization of piezoceramic bulk elements around resonance is usually done with low-level continuous excitation signals at room temperature, but in real applications such elements are driven with different types of electrical signals, usually at higher levels and at different ambient temperatures. Both homemade and commercial soft and hard PZT piezoceramic elements were characterized using the established characterization methods that include the measurements of electrical admittance and surface displacement of the piezoceramic elements around the series resonance frequencies of two modes of vibration (radial and thickness extensional). The measurements included fast frequency sweeps at constant voltage excitation levels, burst measurements, at different temperatures and at different levels of excitation. A novel method for electromechanical characterization of piezoceramic elements that utilizes the resonance frequency tracking at different excitation levels (electric fields up to 5 kV/m, currents up to 1.3 A at resonance) and temperature conditions (up to 150 °C) has been proposed. The main idea is to keep the investigated element in resonance as the excitation level changes by constant tracking of its resonance frequency. The electromechanical parameters of the considered elements change mostly due to the nonlinear effects and the changes due to different thermodynamic conditions can be neglected when fast algorithm is applied. The decrease of the input electrical admittance magnitude is more expressed than the change of the resonance frequency when algorithm is applied.
The Ferroelectric strontium barium niobate (SBN) thin films are prepared using Pulsed Laser Deposition (PLD) technique. XRD spectra of the prepared films indicate the polycrystalline growth confirming the formation of tetragonal tungsten bronze structure. A waveguide is fabricated so as to guide the light in SBN thin film. The EO measurements for the SBN thin films have been carried out using Senarmont Compensation method in order to examine the dynamic variation of EO coefficient of the prepared films. The value of dynamic EO coefficient is found to be 198pm/V.
The channel mobility in graphene field-effect transistors (G-FETs) is usually strongly degraded by Coulomb scattering caused by charged impurities. Additional issue is the zero-bandgap in monolayer graphene, which limits the power gain of the G-FETs. The both issues can be effectively addressed by using ferroelectric as a G-FET substrate [1,2]. We show that, at the same residual concentration of the charge carriers, the mobility in monolayer G-FETs on LiNbO3 substrate is higher than that on the SiO2/Si substrate (Fig. 1). The effect is associated with reduction of Coulomb scattering via screening the charged impurity field by the field induced in the ferroelectric substrate, but significant only for mobilities below 1000 cm2/Vs. Raman spectra analysis [3] and correlations established between mobility and microwave loss tangent [4] of the Al2O3 gate dielectric indicate that the charged impurities are located predominantly in the gate dielectric and/or at the gate dielectric interface and likely associated with oxygen vacancies. The measured characteristic frequencies of the G-FETs on LiNbO3 substrates are approx. 2 GHz (Fig. 2) and limited mainly by parasitic capacitance at the source/drain electrode side walls. The corresponding intrinsic cutoff frequency is more than 10 GHz.
La-doped lead zirconate titanate (Pb,La)(Zr,Ti)O 3 (PLZT) films were prepared via chemical solution deposition. Then, Pt, Al-doped ZnO (AZO), or Sn-doped In 2 O 3 (ITO) top electrodes were deposited on the PLZT films to investigate ferroelectric properties. Three kinds of ferroelectric capacitors were annealed in 3% D 2 (with N 2 as a balance gas) to compare hydrogen-induced degradation of ferroelectric properties. Deuterium ion in ferroelectric capacitor was evaluated by time of flight secondary ion mass spectrometry. For ferroelectric capacitor with Pt top electrode, deuterium ion was detected in PLZT films after 5 min D 2 annealing. On the other hands, deuterium ion was slightly detected with AZO and was not detected at all with ITO even after 120 min D 2 annealing.
Hexagonal ErFeO 3 thin films were fabricated by a pulsed laser deposition method. A high-field magnetization measurement and the Mössbauer spectroscopy under a magnetic field were conducted. It revealed that the magnetic moment of Fe ion lay almost in the ab plane of the thin film forming the 120° structure. The obtained spectrum was explained with the coexistence of two domains with the opposite cant direction of the net magnetic moments along the c axis. The increase of the quadrupole coupling constant with a magnetic field would suggest the displacement of Fe ion by a magnetic field.
DC bias field dependent high overtone resonances are observed in a metal insulator metal (MIM) structure based on Ba 0.5 Sr 0.5 TiO 3 (BST) thin films on a sapphire substrate. The microwave measurement shows the bias dependent nature of the device, wherein without any bias it acts like a MIM capacitor but upon biasing resonant peaks start appearing in its frequency spectra, which is typical of a response given by a high overtone bulk acoustic wave resonator (HBAR). Acoustic velocity of the sapphire substrate is calculated to be 11440 m/s and the HBAR exhibits a high quality factor of 4370 around 1.39 GHz.
The tunable planar capacitors based on the BST film deposited onto the silicon carbide (SiC) substrate are presented. Thin BST films on SiC substrates were obtained by RF magnetron sputtering of a ceramic target with Ba 0.4 Sr 0.6 TiO 3 composition. X-ray diffraction has shown a well-formed perovskite structure with (100) growth texture. The capacitance of planar BST capacitors was estimated as 0.5 pF (that corresponds to BST film permittivity about ε ≅ 500), the dielectric losses as 0.02 and the tunability at the 60 V/μm as n ≅ 1.7. Microwave investigation at the elevated MW signal up to 3 var of the reactive power on the capacitor had demonstrated that the power handling capability of the FE tunable capacitors on the SiC substrate is limited rather by the electric non-linearity than the overheating.
Relaxor-based piezoelectric single crystals have experienced three generations of development, from binary (e.g. PMN-PT) through ternary (e.g. PIN-PMN-PT) to doped ternary (e.g. Mn:PIN-PMN-PT). With improved composition and other relevant factors, these materials exhibit an extraordinary degree of piezoelectricity and ultrahigh electromechanical coupling coefficients, making them suitable for applications requiring high sensitivity and high bandwidth. With further increases in rhombohedral-to-tetragonal phase transition temperature (T RT ), coercive field (E C ) and mechanical quality factor (Q m ), these piezocrystals can now be expected to work at elevated temperature, T, and pressure, P, and with high electric field drive. However, in operation, material properties can vary and performance can degrade significantly because of these elevated conditions, and the situation can be exacerbated by losses in the materials, necessitating proper characterisation of loss factors. In this paper, we report an investigation of three different loss characterisation methods then propose one combined method, demonstrating its use on TE-mode plates of PIN-PMN-PT and Mn:PIN-PMN-PT. Characterisation was performed using impedance spectroscopy for 20°C ≤ T ≤ 100°C and 0 MPa ≤ P ≤ 60 MPa. Results relating to dielectric, elastic and piezoelectric losses are reported, with detailed analysis and comparisons.
Inkjet printing is a deposition technique capable of direct patterning of functional materials on selected substrates. We demonstrate the inkjet printing of tantalum-oxide-based dielectric structures on conductive indium-tin-oxide-coated glass. The viscosity of the ink consisting of Ta-, Al-, and Si- alkoxide precursors dissolved in 2-methoxyethanol (2MOE) could be adjusted by adding highly viscous glycerol (GLY) or 1,3-propanediol (PD). Inks with optimized physical properties showed excellent jetting performance and could be printed even after several months. However, the ink design based merely on adjusting the physical properties proved to be insufficient as the drying of such inks resulted in an irregular surface morphology. We show that the adjustment of the ink's solvent composition with respect to the volatility of a particular solvent improves the uniformity of dried deposits. The optimized ink formulation with the 65:25:10=2MOE:GLY:PD solvent ratio enabled printing of flat and uniform thin-film capacitors with the performance comparable to the spin-coated films of the same composition.
In this work, we have grown GaN nanowires using Plasma assisted Molecular beam epitaxy (PA-MBE) on Si (111) substrate. High resolution X-ray diffraction (HRXRD) characterization and scanning electron microscopy (SEM) studies were carried out to investigate the crystal structure, morphology and uniformity of the grown nanowires. These studies confirm wurtzite crystal structure and uniform growth. The diameter of nanowires was observed to be in the range of 100 - 200 nm with length between 1 - 2 μm. Piezoresponse force microscopy (PFM) was used in Dual AC Resonance Tracking (DART) mode for imaging the height and phase response from the grown nanowires. A switching spectroscopy PFM (SS-PFM) was employed to measure the piezoresponse from individual nanowires. It shows repetitive Displacement-voltage (D-V) loops at multiple points which demonstrates the defect free and high quality growth. An effective piezoelectric coefficient, d33 in the range of 14 - 20 pm/V was calculated for GaN nanowires. Further, we have also simulated piezoresponse of GaN thin films and nanowires for comparison and confirmed that size dependence (polarization/volume) is a dominant factor for increase in the piezoresponse. This study demonstrates the usability of GaN nanowires for sensing, actuation and energy harvesting for high temperature applications.
A prototype flexural ultrasound transducer capable of operating at high temperatures was designed for noncontact measurement applications. A doped bismuth titanate was used as the piezoelectric element; the construction of the transducer was designed using materials and bonding capable of operating at temperatures up to 500°C. The bismuth titanate was characterised by X-ray diffraction, differential thermal analysis and impedance analysis; the transducer response was measured using laser interferometry at room temperature. The resulting frequency spectrum showed clear resonance peaks, indicative of an operational flexural transducer.
A novel bridge transducer based on the cymbal design has been developed for energy harvesting from impact loading by vehicle-induced deformations in pavement. The bridge transducer consists of a 2 mm thick 32×32 mm square soft PZT ceramic and hardened steel end caps. A novel electrode design is used to polarize the piezoelectric ceramic along its length, effectively utilizing d33 mode for enhanced energy generation. A prototype module with 64 bridge transducers were fabricated and loaded repeatedly to simulate vehicle traffic on a highway. When compared to the conventional transducer design, horizontal poling increases energy and voltage considerably. Each loading of the prototype transducer module generates 0.83 mJ of energy. Loading under simulated traffic conditions at 5 Hz generated 2.1 mW at a resistive load of 400 kOhm.
