Meysam Sharifzadeh Mirshekarloo

Large strain and high energy storage density in orthorhombic perovskite (Pb0.97La0.02)(Zr1−x−ySnxTiy)O3 antiferroelectric thin films

Antiferroelectric (Pb0.97La0.02)(Zr1−x−ySnxTiy)O3 (PLZST) thin films with orthorhombic perovskite structure were prepared on Si substrates by a chemical solution deposition process. A secondary pyrochlore phase, which was not detectable with x-ray diffraction, was revealed with transmission electron microscopy. The pyrochlore phase was effectively suppressed by the introduction of polyethylene glycol (PEG) in the precursor solution and applying PbO capping layer on the surface of the films. With the persistent and detrimental pyrochlore phase removed completely, our PLZST antiferroelectric thin films exhibited excellent electrical and electromechanical properties. A large energy storage density up to 13.7 J/cm3 was exhibited from the polarization measurement, and a strain of 0.49% under the clamping of the substrate was also achieved in the thin film with high Zr content.

Nonlinear dielectric thin films for high-power electric storage with energy density comparable with electrochemical supercapacitors

Although batteries possess high energy storage density, their output power is limited by the slow movement of charge carriers, and thus capacitors are often required to deliver high power output. Dielectric capacitors have high power density with fast discharge rate, but their energy density is typically much lower than electrochemical supercapacitors. Increasing the energy density of dielectric materials is highly desired to extend their applications in many emerging power system applications. In this paper, we review the mechanisms and major characteristics of electric energy storage with electrochemical supercapacitors and dielectric capacitors. Three types of in-house-produced ferroic nonlinear dielectric thin film materials with high energy density are described, including (Pb_0.97La_0.02)(Zr_0.90Sn_0.05Ti_0.05)O₃ (PLZST) antiferroelectric ceramic thin films, Pb(Zn_1/3Nb_2/3)O_3-Pb(Mg_1/3Nb_2/3) O_3-PbTiO₃ (PZN-PMN-PT) relaxor ferroelectric ceramic thin films, and poly(vinylidene fluoride) (PVDF)-based polymer blend thin films. The results showed that these thin film materials are promising for electric storage with outstandingly high power density and fairly high energy density, comparable with electrochemical supercapacitors.

Nanoconfinement induced crystal orientation and large piezoelectric coefficient in vertically aligned P(VDF-TrFE) nanotube array

Vertically aligned piezoelectric P(VDF-TrFE) nanotube array comprising nanotubes embedded in anodized alumina membrane matrix without entanglement has been fabricated. It is found that the crystallographic polar axes of the P(VDF-TrFE) nanotubes are oriented along the nanotubes long axes. Such a desired crystal orientation is due to the kinetic selection mechanism for lamellae growth confined in the nanopores. The preferred crystal orientation in nanotubes leads to huge piezoelectric coefficients of the P(VDF-TrFE). The piezoelectric strain and voltage coefficients of P(VDF-TrFE) nanotube array are observed to be 1.97 and 3.40 times of those for conventional spin coated film. Such a significant performance enhancement is attributed to the well-controlled polarization orientation, the elimination of the substrate constraint, and the low dielectric constant of the nanotube array. The P(VDF-TrFE) nanotube array exhibiting the unique structure and outstanding piezoelectric performance is promising for wide applications, including various electrical devices and electromechanical sensors and transducers.

Fieldlike spin-orbit torque in ultrathin polycrystalline FeMn films

Field-like spin orbit torque in FeMn/Pt bilayers with ultra-thin polycrystalline FeMn has been characterized through planar Hall effect measurements. A large effective field is obtained for FeMn in the thickness range of 2 to 5 nm. The experimental observations can be reasonably accounted for by using a macro-spin model under the assumption that the FeMn layer is composed of two spin sublattices with unequal magnetizations. The large effective field corroborates the spin Hall origin of the effective field considering the much smaller uncompensated net moments in FeMn as compared to NiFe. The effective absorption of spin current by FeMn is further confirmed by the fact that spin current generated by Pt in NiFe/FeMn/Pt trilayers can only travel through the FeMn layer with a thickness of 1 to 4 nm. By quantifying the field-like effective field induced in NiFe, a spin diffusion length of 2 nm is estimated in FeMn, in consistence with values reported in literature by ferromagnetic resonance and spin-pumping experiments.

Lead-Free Piezoelectric Ceramic Coatings Fabricated by Thermal Spray Process

This paper starts from a review on the progress in fabrication of piezoelectric ceramic coatings by thermal spray method. For our experimental work, two types of lead-free piezoelectric ceramic coatings, including potassium-sodium niobate-based and bismuth sodium titanate-based, are fabricated by thermal spray process, and their structure, morphology, and piezoelectric properties are characterized. Our obtained lead-free ceramic coatings exhibit single phase of perovskite structure, relatively dense morphology, and competitive piezoelectric coefficients. The mechanism of forming the piezoelectric perovskite crystalline phase by thermal spray involving melting-recrystallization process is analyzed in comparison to that of ceramic synthesis through solid-state reaction. Suppression of volatile loss and decomposition at high temperature due to the extremely high melting and cooling rate in the thermal spray process, and the impact on the resulting structure are discussed. Significant advantages of the thermal spray method over alternative processing methods for forming piezoelectric ceramic coatings are summarized. The combination of environmentally friendly lead-free compositions and the scalable thermal spray processing method will promote more applications of piezoelectric ceramic coatings for producing distributive sensors and transducers, and forming advanced smart structures and systems.

Hybrid local piezoelectric and conductive functions for high performance airborne sound absorption

A concept of hybrid local piezoelectric and electrical conductive functions for improving airborne sound absorption is proposed and demonstrated in composite foam made of porous polar polyvinylidene fluoride (PVDF) mixed with conductive single-walled carbon nanotube (SWCNT). According to our hybrid material function design, the local piezoelectric effect in the PVDF matrix with the polar structure and the electrical resistive loss of SWCNT enhanced sound energy conversion to electrical energy and subsequently to thermal energy, respectively, in addition to the other known sound absorption mechanisms in a porous material. It is found that the overall energy conversion and hence the sound absorption performance are maximized when the concentration of the SWCNT is around the conductivity percolation threshold. For the optimal composition of PVDF/5 wt. % SWCNT, a sound reduction coefficient of larger than 0.58 has been obtained, with a high sound absorption coefficient higher than 50% at 600 Hz, showing their...

Magneto-optical Kerr effect investigation on magnetoelectric coupling in ferromagnetic/antiferroelectric multilayer thin film structures

Magnetoelectric (ME) membranes comprising soft ferromagnetic Ni and antiferroelectric (AFE) (Pb,La)(Zr,Sn,Ti)O3 (PLZST) layers were proposed and fabricated through a bulk micro-machining process on silicon wafers. An AC-mode magneto-optical Kerr effect technique was proposed to examine the magnetoelectric coupling in the multilayer membranes, in which the electric field-induced magnetization rotation was analyzed for understanding the underlying coupling mechanisms. The AFE to ferroelectric phase transformation of PLZST induced a rotation of magnetization of about 0.5° in Ni, persuaded by strain-induced anisotropy of about −0.5 kJ/m3.