A5067461277- Ferroelectric and Piezoelectric Materials
- Acoustic Wave Resonator Technologies
- Multiferroics and related materials
- Electronic and Structural Properties of Oxides
- Microwave Dielectric Ceramics Synthesis
- Solid-state spectroscopy and crystallography
- Nonlocal and gradient elasticity in micro/nano structures
- Dielectric materials and actuators
- Force Microscopy Techniques and Applications
- Ultrasonics and Acoustic Wave Propagation
- Mechanical and Optical Resonators
- Semiconductor materials and devices
- Advanced MEMS and NEMS Technologies
- Advanced Sensor and Energy Harvesting Materials
- Physics of Superconductivity and Magnetism
- Photorefractive and Nonlinear Optics
- Magnetic and transport properties of perovskites and related materials
- Dielectric properties of ceramics
- Ferroelectric and Negative Capacitance Devices
- Geophysics and Sensor Technology
- Optical and Acousto-Optic Technologies
- Liquid Crystal Research Advancements
- Material Dynamics and Properties
- Superconducting Materials and Applications
- High-pressure geophysics and materials
École Polytechnique Fédérale de Lausanne
2014-2024
University of Lausanne
2023
Physico-Technical Institute
1990-2021
Ioffe Institute
1985-2019
Politecnico di Milano
2019
ETH Zurich
2019
Nagoya University
2019
Physical and Technical Institute
2019
Euclid Techlabs (United States)
2009
Fermi National Accelerator Laboratory
2009
A phenomenological thermodynamic theory of ferroelectric thin films epitaxially grown on cubic substrates is developed using a new form the potential, which corresponds to actual mechanical boundary conditions problem. For single-domain ${\mathrm{BaTiO}}_{3}$ and ${\mathrm{PbTiO}}_{3}$ films, ``misfit-temperature'' phase diagrams are constructed. It found that 2D clamping apart from shift temperature transition, results in change its order. sequence phases appearance forbidden bulk crystals...
Flexoelectricity—the coupling between polarization and strain gradients—is a universal effect allowed by symmetry in all materials. Following its discovery several decades ago, studies of flexoelectricity solids have been scarce due to the seemingly small magnitude this bulk samples. The development nanoscale technologies, however, has renewed interest flexoelectricity, as large gradients often present at can lead strong flexoelectric effects. Here we review fundamentals solids, discuss...
Piezoelectricity in pyroelectrics and the linear response of polarization to a strain gradient?lexoelectricity) are discussed framework unified approach. It was pointed out by Born Huang Martin, that there difference between piezoelectric for cases sound wave uniform finite crystal, only ``proper'' parts constants coincided these cases. is shown this paper no such if an accurate definition piezoelectricity applied. The theory flexoelectricity solid crystalline dielectrics developed. general...
The flexoelectric effect is the response of electric polarization to a mechanical strain gradient. It can be viewed as higher-order with respect piezoelectricity, which itself. However, at nanoscale, where large gradients are expected, becomes appreciable. Besides, in contrast piezoelectric effect, flexoelectricity allowed by symmetry any material. Due these qualities has attracted growing interest during past decade. Presently, its role physics dielectrics and semiconductors widely...
The reduction in switchable polarization of ferroelectric thin films due to electrical stress (polarization fatigue) is a major problem nonvolatile memories. There large body available experimental data and number existing models which address this issue, however the origin phenomena still not properly understood. This work synthesizes current data, models, approaches order draw conclusions on relative importance different macro- microscopic scenarios fatigue. Special attention paid role...
A Landau-Ginsburg-Devonshire-type theory is used to describe the mechanical substrate effect on equilibrium states and phase transitions in ${\mathrm{SrTiO}}_{3}$ epitaxial thin films. The misfit strain-temperature diagram of films developed taking into account existence two coupled instabilities (antiferrodistortive ferroelectric) this crystal. It shown that remain paraelectric down 0 K only a narrow range small negative strains between...
The switching kinetics in ferroelectric thin films has been intensively studied during the past decade. It is widely accepted that this basically governed by dynamics of domain coalescence (the Kolmogorov-Avrami-Ishibashi model). This conclusion mainly supported fitting time dependence currents to predicted model, fit being typically performed a 1--2 decade interval time. present paper reports on study modified $\mathrm{Pt}/\mathrm{Pb}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_{3}/\mathrm{Pt}$ as...
Hetero interfaces between metal-oxides display pronounced phenomena such as semiconductor-metal transitions, magnetoresistance, the quantum hall effect and superconductivity. Similar effects at compositionally homogeneous including ferroic domain walls are expected. Unlike hetero interfaces, can be created, displaced, annihilated recreated inside a functioning device. Theory predicts existence of 'strongly' charged that break polarization continuity, but stable conduct steadily through...
This article reviews the existing theoretical models describing interface-induced phenomena which affect switching characteristics and dielectric properties of ferroelectric thin films. Three groups effects are addressed—namely, “passive-layer-type” effects, ferroelectric-electrode contact potential poling effect interface. The experimental data on film capacitors discussed in context reviewed theories. Special attention is paid to case internal bias field effects.
Abstract We review the current theory of intrinsic dielectric loss, that is loss in a perfect crystal due to anharmonic interaction a.c. electric field with phonon system crystal. Both ordinary dielectrics and displacive ferroelectrics are considered. The predicts dependence on frequency ω temperature T. This very sensitive symmetry For dielectrics, results presented tabulated for all 32 groups, except non-symmorphic groups. existing experimental date analysed explained basis theory.
While commonly used piezoelectric materials contain lead, non-hazardous, high-performance piezoelectrics are yet to be discovered. Charged domain walls in ferroelectrics considered inactive with regards the response and, therefore, largely ignored this search. Here we demonstrate a mechanism that leads strong enhancement of dielectric and properties increasing density charged walls. We show an incomplete compensation bound polarization charge at these creates stable built-in depolarizing...
Abstract The charged domain wall is an ultrathin (typically nanosized) interface between two domains; it carries bound charge owing to a change of normal component spontaneous polarization on crossing the wall. In contrast hetero-interfaces different materials, walls (CDWs) can be created, displaced, erased, and recreated again in bulk material. Screening with free carriers often necessary for stability CDWs, which result giant two-dimensional conductivity along Usually nominally insulating...
The low frequency dielectric response of relaxor ferroelectrics is analyzed. Following the conventional approach this considered as a sum those relaxators having an exponentially wide and smooth spectrum relaxation times. It shown that Vogel-Fulcher relationship for positions temperautre maximum real imaginary parts permittivity can be obtained direct consequence gradual broadening with decreasing temperature. such Vogel-Fulcher--type does not necessarily imply ``freezing'' in system.
A zero-field spontaneous relaxor-ferroelectric transition is reported in Pb(Sc0.5Ta0.5)O3 (PST). This behavior different from that of other relaxors, where such transitions occur only under the field. highly disordered PST has wide relaxation spectrum typical relaxors shown to transform spontaneously into a macroscopic ferroelectric state. Introduction defects (lead vacancies) material impedes resulting usual relaxor behavior. Dielectric properties PST, with and without defects, are...
Abstract The basic properties of electric polarization response in crystalline dielectrics are theoretically analysed. Spontaneous polarization, pyroelectricity, piezoelectricity, flexoelectricity (polarization to strain gradient) and thermopolarization effect temperature discussed on the basis a unified approach. Special attention is paid problem adequate theoretical definition these phenomena. sample termination considered detail. Key Words: Electric polarizationthermal...
The switching of the sandwich structure ‘‘ferroelectric+thin dielectric layer’’ is theoretically studied. behavior remanent polarization, Pr, coercive field, Ec, maximal polarization on loop, Ps, and slope hysteresis loop at Ec as a function both, relative thickness layer (the divided by ferroelectric) amplitude measuring analyzed. It shown that effect Pr qualitatively different from Ps. As result this analysis set characteristic features with variable have been formulated. These can be used...
Stress-induced changes in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3 (PZT)-based capacitors have been studied using piezoresponse force microscopy. Visualization polarization distribution d33-loop measurements individual 1×1.5-μm2 before after stress application, generated by substrate bending, provided direct experimental evidence stress-induced switching. Mechanical caused elastic with direction resulting determined sign applied stress. In addition, application turned...
We report a first-principles investigation of ultrathin BaTiO(3) films with SrRuO(3) electrodes. find that the ionic relaxations in metal-oxide electrode play crucial role stabilizing ferroelectric phase. Comparison frozen-phonon calculations shows degree softness lattice has an essential impact on screening polarization BaTiO(3). The critical thickness for ferroelectricity is found to be 1.2 nm. results our provide possible explanation beneficial oxide electrodes switching and dielectric...
Direct evidence for freezing in two relaxor ferroelectrics, PbMg1/3Nb2/3O3 and PbSc1/2Ta1/2O3, at a certain temperature Tf≠0 K was obtained from the dependence of maximum relaxation time, τmax. It shown that τmax(T) follows Vögel–Fulcher (VF) law, tends toward infinity as approaches Tf. The Tf derived coincides with value fit frequency, ω, temperature, Tmax, dielectric permittivity to same VF law. Thus, this result solves controversy law ω(Tmax) may not correspond spectrum.
The size, shape, and polarization orientation of fatigued areas formed during the suppression switchable (Prs) (fatigue) in Pt–PZT–Pt ferroelectric capacitors (FECAPs), were observed by means atomic force microscopy imaging phase piezoelectric vibration induced a low ac field applied between top bottom electrodes. In virgin state (FECAP as prepared), pattern domains with opposite was randomly distributed typical sizes 1–3 μm. application dc larger than coercive (Ec) enabled to fully orient...