89 research outputs found
Room temperature surface piezoelectricity in SrTiO3 ceramics via piezoresponse force microscopy
SrTiO3 ceramics are investigated by piezoresponse force microscopy.
Piezoelectric contrast is observed on polished surfaces in both vertical and
lateral regimes and depends on the grain orientation varying in both sign
(polarization direction) and amplitude. The observed contrast is attested to
the surface piezoelectricity due to flexoelectric effect (strain
gradient-induced polarization) caused by the surface relaxation. The estimated
flexoelectric coefficient is approximately one order of magnitude smaller as
compared to those recently measured in SrTiO3 single crystals. The observed
enhancement of piezoresponse signal at the grain boundaries is explained by the
dipole moments associated with inhomogeneous distribution of oxygen vacancies
Domain Dynamics in Piezoresponse Force Microscopy: Quantitative Deconvolution and Hysteresis Loop Fine Structure
Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is
studied using the combination of local hysteresis loop acquisition with
simultaneous domain imaging. The analytical theory for PFS signal from domain
of arbitrary cross-section is developed and used for the analysis of
experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest
formation of oblate domain at early stage of the domain nucleation and growth,
consistent with efficient screening of depolarization field within the
material. The fine structure of the hysteresis loop is shown to be related to
the observed jumps in the domain geometry during domain wall propagation
(nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.Comment: 17 pages, 3 figures, 2 Appendices, to be submmited to Appl. Phys.
Let
Li transport in fresh and aged LiMn2O4 cathodes via electrochemical strain microscopy
Transport properties of Li+ mobile ions in fresh and aged LiMn2O4 battery cathodes were studied at the nanoscale via electrochemical strain microscopy (ESM), time spectroscopy, and voltage spectroscopy mapping. Both Vegard and plausible non-Vegard contributions to the ESM signal were identified in electrochemical hysteresis loops obtained on fresh and aged samples. In the fresh cathodes, the Vegard contribution dominates the signal, while in the aged samples different shape of hysteresis loops indicates an additional plausible non-Vegard contribution. Non-uniform spatial distribution of the electrochemical loop opening in LiMn2O4 particles studied in the aged samples indicates stronger variation of the Li diffusion coefficient at the microscale as compared to the fresh specimens. Time spectroscopy measurements revealed a suppression of the local Li diffusivity in aged samples. The mechanisms of the cathode aging are discussed in the context of observed nanoscale ESM response. (C) 2015 AIP Publishing LLC
Fixed Volume Effect on Polar Properties and Phase Diagrams of Ferroelectric Semi-ellipsoidal Nanoparticles
For advanced applications in modern industry it is very important to reduce
the volume of ferroelectric nanoparticles without serious deterioration of
their polar properties. In many practically important cases fixed volume
(rather than fixed size) corresponds to realistic technological conditions of
nanoparticles fabrication. The letter is focused on the theoretical study of
the behavior of ferroelectric polarization, paramagnetoelectric coefficient and
phase diagrams of semi-ellipsoidal nanoparticles with fixed volume V. Our
approach combines the Landau-Ginzburg-Devonshire phenomenology, classical
electrostatics and elasticity theory. Our results show that the size effects of
the phase diagrams and polarization of semi-ellipsoidal BiFeO3 nanoparticles
nontrivially depends on V. These findings provide a path to optimize the polar
properties of nanoparticles by controlling their phase diagrams at a fixed
volume.Comment: 15 pages, 5 figures, we added the section IV. Paramagnetoelectric
(PME) coefficient at fixed volume in this version and changed title and
abstract accordingl
A comparative study of structural and electrical properties in lead-free BCZT ceramics: Influence of the synthesis method
In the present work, various grain size phenomena were studied in promising lead-free piezoelectric ceramics (Ba0.85Ca0.15) (Zr0.10Ti0.90)O3 fabricated via chemical and conventional oxide methods. Phase composition was ascertained by the Rietveld refinement. Average grain size estimated from the microstructure was ∼1.5 μm in the sol-gel derived ceramic (SG-BCZT) which was much smaller than that obtained in coarse grained (∼27 μm) sample prepared by solid state method (SS-BCZT). Systematic investigation of various functional properties viz. dielectric, ferroelectric, piezoelectric and impedance emphasized the profound influence of grain size effects. The increase in grain boundary volume fraction enhanced diffuseness while lowered the dielectric peak in SG-BCZT. Similarly, increase in elastic stiffness and progressive hindrance to domain wall movements, resulted in a decrease of the remnant polarization and the associated piezoelectric charge coefficient values in small-grained SG-BCZT sample. Accordingly, higher Young's modulus value of 158.3 GPa was observed in SG-BCZT as compared to 117.9 GPa in SS-BCZT. Local-area piezoresponse force microscopy (PFM) images revealed lamellar domains with periodicity 250 ± 90 nm in SS-BCZT while small sized fractal-like irregular domains with an estimated domain width of 150 ± 60 nm were registered in SG-BCZT. Complex impedance spectroscopy results along with grain boundary conductivity were also guided by grain size effect. The mechanisms of grain size driven effects and their impact on the functional properties were discussed.publishe
Low-frequency magnetic sensing by magnetoelectric metglas/bidomain LiNbO3 long bars
We present an investigation into the magnetic sensing performance of magnetoelectric bilayered metglas / bidomain LiNbO3 long thin bars operating in a cantilever or free vibrating regime and under quasi-static and low-frequency resonant conditions. Bidomain single crystals of Y+128o-cut LiNbO3 were engineered by an improved diffusion annealing technique with a polarization macrodomain structure of the “head-to-head” and “tail-to-tail” type. Long composite bars with lengths of 30, 40 and 45 mm, as well as with and without attached small tip proof masses, were studied. ME coefficients as large as 550 V/cm∙Oe, corresponding to a conversion ratio of 27.5 V/Oe, were obtained under resonance conditions at frequencies of the order of 100 Hz in magnetic bias fields as low as 2 Oe. Equivalent magnetic noise spectral densities down to 120 pT/Hz1/2 at 10 Hz and to 68 pT/Hz1/2 at a resonance frequency as low as 81 Hz were obtained for the 45 mm long cantilever bar with a tip proof mass of 1.2 g. In the same composite without any added mass the magnetic noise was shown to be as low as 37 pT/Hz1/2 at a resonance frequency of 244 Hz and 1.2 pT/Hz1/2 at 1335 Hz in a fixed cantilever and free vibrating regimes, respectively. A simple unidimensional dynamic model predicted the possibility to drop the low-frequency magnetic noise by more than one order of magnitude in case all the extrinsic noise sources are suppressed, especially those related to external vibrations, and the thickness ratio of the magnetic-to-piezoelectric phases is optimized. Thus, we have shown that such systems might find use in simple and sensitive room-temperature low-frequency magnetic sensors, e.g., for biomedical applications.publishe
Interface modulated currents in periodically proton exchanged Mg doped lithium niobate
Conductivity in Mg doped lithium niobate (Mg:LN) plays a key role in the reduction of photorefraction and is therefore widely exploited in optical devices. However, charge transport through Mg:LN and across interfaces such as electrodes also yields potential electronic applications in devices with switchable conductivity states. Furthermore, the introduction of proton exchanged (PE) phases in Mg:LN enhances ionic conductivity, thus providing tailorability of conduction mechanisms and functionality dependent on sample composition. To facilitate the construction and design of such multifunctional electronic devices based on periodically PE Mg:LN or similar ferroelectric semiconductors, fundamental understanding of charge transport in these materials, as well as the impact of internal and external interfaces, is essential. In order to gain insight into polarization and interface dependent conductivity due to band bending, UV illumination, and chemical reactivity, wedge shaped samples consisting of polar oriented Mg:LN and PE phases were investigated using conductive atomic force microscopy. In Mg:LN, three conductivity states (on/off/transient) were observed under UV illumination, controllable by the polarity of the sample and the externally applied electric field. Measurements of currents originating from electrochemical reactions at the metal electrode-PE phase interfaces demonstrate a memresistive and rectifying capability of the PE phase. Furthermore, internal interfaces such as domain walls and Mg:LN-PE phase boundaries were found to play a major role in the accumulation of charge carriers due to polarization gradients, which can lead to increased currents. The insight gained from these findings yield the potential for multifunctional applications such as switchable UV sensitive micro-and nanoelectronic devices and bistable memristors. (C) 2016 AIP Publishing LLC
Ferroelectric characterization of aligned barium titanate nanofibres
We report the synthesis, structural and ferroelectric characterization of continuous well-aligned nanofibres of barium titanate produced by the electrospinning technique. The fibres with average diameter of 150–400 nm consist of connected nanoparticles of BaTiO 3 stacked together to form the shape of a long filament. The tetragonal phase in the obtained nanofibres was revealed by the x-ray diffraction and Raman spectroscopy and has been also confirmed by the second harmonic generation (SHG) and piezoresponse force microscopy (PFM). The temperature dependence of the SHG in the vicinity of the paraelectric–ferroelectric phase transition suggests that barium titanate nanofibres are indeed ferroelectric with an apparent glass-like state caused by metastable polar nanoregions. The existence of domain structure and local switching studied by PFM present clear evidence of the polar phase at room temperature.Fundação para a Ciência e a Tecnologia (FCT
The strain-induced transitions of the piezoelectric, pyroelectric and electrocaloric properties of the CuInPS films
The low-dimensional ferroelectrics, ferrielectrics and antiferroelectrics are
of urgent scientific interest due to their unusual polar, piezoelectric,
electrocaloric and pyroelectric properties. The strain engineering and strain
control of the ferroelectric properties of layered 2D Van der Waals materials,
such as CuInP(S,Se) monolayers, thin films and nanoflakes, are of
fundamental interest and especially promising for their advanced applications
in nanoscale nonvolatile memories, energy conversion and storage, nano-coolers
and sensors. Here, we study the polar, piezoelectric, electrocaloric and
pyroelectric properties of thin strained films of a ferrielectric
CuInPS covered by semiconducting electrodes and reveal an unusually
strong effect of a mismatch strain on these properties. In particular, the sign
of the mismatch strain and its magnitude determine the complicated behavior of
piezoelectric, electrocaloric and pyroelectric responses. The strain effect on
these properties is opposite, i.e., "anomalous", in comparison with many other
ferroelectric films, for which the out-of-plane remanent polarization,
piezoelectric, electrocaloric and pyroelectric responses increase strongly for
tensile strains and decrease or vanish for compressive strains.Comment: 16 pages, 5 figures, to be presented at the VI Lithuanian-Polish
Meeting on Physics of Ferroelectric
Electromagnetic energy harvesting using magnetic levitation architectures: a review
Motion-driven electromagnetic energy harvesters have the ability to provide low-cost and customizable electric powering. They are a well-suited technological solution to autonomously supply a broad range of high-sophisticated devices. This paper presents a detailed review focused on major breakthroughs in the scope of electromagnetic energy harvesting using magnetic levitation architectures. A rigorous analysis of twenty-one design configurations was made to compare their geometric and constructive parameters, optimization methodologies and energy harvesting performances. This review also explores the most relevant models (analytical, semi-analytical, empirical and finite element method) already developed to make intelligible the physical phenomena of their transduction mechanisms. The most relevant approaches to model each physical phenomenon of these transduction mechanisms are highlighted in this paper. Very good agreements were found between
experimental and simulation tests with deviations lower than 15%. Moreover, the external motion excitations and electric energy harvesting outputs were also comprehensively compared and critically discussed. Electric power densities up to 8 mW/cm^3 (8 kW/m^3) have already been achieved; for resistive loads, the maximum voltage and current were 43.4 V and 150 mA, respectively, for volumes up to 235 cm^3. Results highlight the potential of these harvesters to convert mechanical energy into electric energy both for large-scale and small-scale applications. Moreover, this paper proposes future research directions towards efficiency maximization and minimization of energy production costs.in publicatio
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