The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

J F Scott - One of the best experts on this subject based on the ideXlab platform.

  • polarization vortex domains induced by switching electric field in Ferroelectric Films with circular electrodes
    Physical Review B, 2014
    Co-Authors: Laurent Baudry, Anais Sene, I Lukyanchuk, Laurent Lahoche, J F Scott
    Abstract:

    We describe Ferroelectric Thin Films with circular electrodes and develop a thermodynamic theory that explains exotic experimental results previously reported. It is found to be especially useful for restricted geometries such as microstructures for which boundary conditions are well known to play an important role in Ferroelectric properties. We have explored a switching mechanism that consists of an inhomogeneous rotational motion of the polarization and leads to a vortex state. The vortex appearance exhibits characteristic properties of a first-order field-induced phase transition with three critical electric fields and the possibility of hysteresis behavior.

  • flux closure vortexlike domain structures in Ferroelectric Thin Films
    Physical Review Letters, 2010
    Co-Authors: Yachin Ivry, J F Scott, Daping Chu, Colm Durkan
    Abstract:

    Enhanced piezoresponse force microscopy was used to study flux closure vortexlike structures of 90° ferroelastic domains at the nanoscale in Thin Ferroelectric lead zirconium titanate (PZT) Films. Using an external electric field, a vortexlike structure was induced far away from a grain boundary, indicating that physical edges are not necessary for nucleation contrary to previous suggestions. We demonstrate two different configurations of vortexlike structures, one of which has not been observed before. The stability of these structures is found to be size dependent, supporting previous predictions.

  • influence of mechanical boundary conditions on the electrocaloric properties of Ferroelectric Thin Films
    Journal of Applied Physics, 2008
    Co-Authors: G Akcay, S P Alpay, George A Rossetti, J F Scott
    Abstract:

    A thermodynamic analysis of the electrocaloric (EC) effect in BaTiO3 Ferroelectric Thin Films has been carried out under differing mechanical boundary conditions. It is shown that both the magnitude of the electrocaloric effect and temperature at which it is maximized depend not only on the extent of the applied field change but also on the value of the initial field. For initial fields smaller than a critical value the EC effect is largest at the phase transition temperature but the effect is a strong function of temperature. For external electrical fields larger than this value, conversely, the EC effect is the largest at a higher temperature and is a weak function of temperature. Perfect lateral clamping transforms the first-order phase transition into a second-order transition, lowering the magnitude of the electrocaloric effect and dependence on temperature. Compressive and tensile misfit strains also alter the nature of the phase transition and affect the electrocaloric properties in an analogous wa...

  • influence of mechanical boundary conditions on the electrocaloric properties of Ferroelectric Thin Films
    Journal of Applied Physics, 2008
    Co-Authors: G Akcay, S P Alpay, George A Rossetti, J F Scott
    Abstract:

    A thermodynamic analysis of the electrocaloric (EC) effect in BaTiO3 Ferroelectric Thin Films has been carried out under differing mechanical boundary conditions. It is shown that both the magnitude of the electrocaloric effect and temperature at which it is maximized depend not only on the extent of the applied field change but also on the value of the initial field. For initial fields smaller than a critical value the EC effect is largest at the phase transition temperature but the effect is a strong function of temperature. For external electrical fields larger than this value, conversely, the EC effect is the largest at a higher temperature and is a weak function of temperature. Perfect lateral clamping transforms the first-order phase transition into a second-order transition, lowering the magnitude of the electrocaloric effect and dependence on temperature. Compressive and tensile misfit strains also alter the nature of the phase transition and affect the electrocaloric properties in an analogous way. A compressive misfit strain shifts the maximum in the EC effect to higher temperatures, reduces its magnitude, and reduces its dependence on temperature, while tensile misfit strain results in the opposite effects. Control of the misfit strain by appropriate choice of substrate provides potential means to vary both the magnitude and the temperature sensitivity of the EC effect for use in cooling or thermodielectric power conversion devices.

  • polarization relaxation kinetics and 180 domain wall dynamics in Ferroelectric Thin Films
    Physical Review B, 2001
    Co-Authors: C S Ganpule, Ramamoorthy Ramesh, V Nagarajan, Alexander L Roytburd, B K Hill, Satishchandra Ogale, E D Williams, J F Scott
    Abstract:

    The time-dependent relaxation of remanant polarization in epitaxial lead zirconate titanate [Pb(Zr 0 . 2 Ti 0 . 8 )O 3 .PZT] Ferroelectric Thin Films, containing a uniform two-dimensional grid of 90° domains (c axis in the plane of the film). is examined using voltage-modulated scanning force microscopy. 90° domain walls preferentially nucleate 180° reverse domains during relaxation, which grow and coalesce as a function of relaxation time. Relaxation is seen to saturate at different levels depending on the write voltage. Late (saturation) stages of relaxation are accompanied by pinning and faceting of the domain walls (drastically reducing the wall mobility). which is direct evidence of the role of defect sites and crystallographic features on polarization relaxation. The kinetics of relaxation is modeled through the nucleation and growth Johnson-MehlAvrami-Kolmogorov theory with a decreasing driving force.

A K Tagantsev - One of the best experts on this subject based on the ideXlab platform.

  • polarization charge as a reconfigurable quasi dopant in Ferroelectric Thin Films
    Nature Nanotechnology, 2015
    Co-Authors: Arnaud Crassous, A K Tagantsev, Tomas Sluka, N Setter
    Abstract:

    Charged domain walls can be created and manipulated at the nanoscale so that their polarization charge can be used to dope Ferroelectric Thin Films at selected locations in a reversible way.

  • controlling domain wall motion in Ferroelectric Thin Films
    Nature Nanotechnology, 2015
    Co-Authors: L J Mcgilly, A K Tagantsev, P V Yudin, L Feigl, N Setter
    Abstract:

    The nucleation and position of multiple domain walls in Thin Films of Pb(Zr,Ti)O3 can be controlled by voltage pulses applied to a top Pt electrode. Domain walls in ferroic materials have attracted significant interest in recent years, in particular because of the unique properties that can be found in their vicinity1,2,3. However, to fully harness their potential as nanoscale functional entities4,5, it is essential to achieve reliable and precise control of their nucleation, location, number and velocity. Here, using piezoresponse force microscopy, we show the control and manipulation of domain walls in Ferroelectric Thin Films of Pb(Zr,Ti)O3 with Pt top electrodes. This high-level control presents an excellent opportunity to demonstrate the versatility and flexibility of Ferroelectric domain walls. Their position can be controlled by the tuning of voltage pulses, and multiple domain walls can be nucleated and handled in a reproducible fashion. The system is accurately described by analogy to the classical Stefan problem6, which has been used previously to describe many diverse systems and is here applied to electric circuits. This study is a step towards the realization of domain wall nanoelectronics utilizing Ferroelectric Thin Films.

  • interface induced phenomena in polarization response of Ferroelectric Thin Films
    Journal of Applied Physics, 2006
    Co-Authors: A K Tagantsev, G Gerra
    Abstract:

    This article reviews the existing theoretical models describing the interface-induced phenomena which affect the switching characteristics and dielectric properties of Ferroelectric Thin Films. Three groups of interface-induced effects are addressed—namely, “passive-layer-type” effects, Ferroelectric-electrode contact potential effects, and the poling effect of the Ferroelectric-electrode interface. The existing experimental data on dielectric and switching characteristics of Ferroelectric Thin film capacitors are discussed in the context of the reviewed theories. Special attention is paid to the case of internal bias field effects.

  • non kolmogorov avrami switching kinetics in Ferroelectric Thin Films
    Physical Review B, 2002
    Co-Authors: A K Tagantsev, N Setter, Igor Stolichnov, Jeffrey S Cross, Mineharu Tsukada
    Abstract:

    The switching kinetics in Ferroelectric Thin Films has been intensively studied during the past decade. It is widely accepted that this kinetics is basically governed by the dynamics of domain coalescence (the Kolmogorov-Avrami-Ishibashi model). This conclusion is mainly supported by fitting the time dependence of the switching currents to that predicted by this model, the fit being typically performed in a 1-2 decade interval of time. The present paper reports on a study of the switching kinetics in modified Pt/Pb(Zr,Ti)O-3/Pt Thin Films as a function of time and applied voltage, performed in time intervals from 10 ns to 1s. Our experimental data show that both the time and applied field dependences of the switching polarization (when monitored over a wide enough time interval) are in a strong qualitative disagreement with the predictions of the Kolmogorov-Avrami-Ishibashi approach. For the interpretation of our result, an alternative approach is forwarded. In contrast to Kolmogorov-Avrami-Ishibashi approach, we assume that the film consists of many areas, which have independent switching dynamics. The switching in an area is considered to be triggered by an act of the reverse domain nucleation. The switching kinetics is described in terms of the distribution function of the nucleation probabilities in these areas. The developed approach enables a good description of the polarization dynamics in typical Ferroelectric Thin Films for memory applications.

  • polarization fatigue in Ferroelectric Films basic experimental findings phenomenological scenarios and microscopic features
    Journal of Applied Physics, 2001
    Co-Authors: A K Tagantsev, Igor Stolichnov, E L Colla, N Setter
    Abstract:

    The reduction in switchable polarization of Ferroelectric Thin Films due to electrical stress (polarization fatigue) is a major problem in Ferroelectric nonvolatile memories. There is a large body of available experimental data and a number of existing models which address this issue, however the origin of this phenomena is still not properly understood. This work synthesizes the current experimental data, models, and approaches in order to draw conclusions on the relative importance of different macro- and microscopic scenarios of fatigue. Special attention is paid to the role of oxygen vacancy migration and electron injection into the film and it is concluded that the latter plays the predominant role. Experiments and problems for theoretical investigations, which can contribute to the further elucidation of polarization fatigue mechanisms in Ferroelectric Thin Films, are suggested.

Longqing Chen - One of the best experts on this subject based on the ideXlab platform.

  • giant resistive switching via control of Ferroelectric charged domain walls
    Advanced Materials, 2016
    Co-Authors: Jason Britson, Jacob R Jokisaari, Longqing Chen, Yi Zhang, Carolina Adamo, Alexander Melville, Darrell G Schlom, Xiaoqing Pan
    Abstract:

    Controlled switching of resistivity in Ferroelectric Thin Films is demonstrated by writing and erasing stable, nanoscale, strongly charged domain walls using an in situ transmission electron microscopy technique. The resistance can be read nondestructively and presents the largest off/on ratio (≈10(5) ) ever reported in room-temperature Ferroelectric devices, opening new avenues for engineering Ferroelectric Thin-film devices.

  • first order morphological transition of ferroelastic domains in Ferroelectric Thin Films
    Acta Materialia, 2014
    Co-Authors: Jason Britson, Xiaoqing Pan, Christopher B Nelson, Longqing Chen
    Abstract:

    Ferroelastic domains are common defects in epitaxial Ferroelectric Thin Films, being typically observed around interfacial dislocations due to attractive elastic interactions. Because of their large stress fields, domain size and shape can influence local Ferroelectric switching behavior. Here the morphology of ferroelastic domains in Pb(Zr0.2 ,T i 0.8)O3 Thin Films is investigated as a function of film thickness and substrate strain using phase field modeling in combination with transmission electron microscopy. Increasing film thickness or strain is found to induce switching from typical ferroelastic domains extending to the free surface of the film to nanosized domains localized near the substrate interface. An analysis of thermodynamic properties reveals hysteretic and discontinuous changes in the first derivatives of the free energy resulting from competing electrostatic and elastic energies. Such first-order morphological transitions are expected to be very common in epitaxial Thin Films during switching under an external electric or stress field. 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • atomic scale mechanisms of ferroelastic domain wall mediated Ferroelectric switching
    Nature Communications, 2013
    Co-Authors: Peng Gao, Jason Britson, Jacob R Jokisaari, Christopher T Nelson, Seunghyub Baek, Yiran Wang, C B Eom, Longqing Chen, Xiaoqing Pan
    Abstract:

    In Ferroelectric Thin Films, ferroelastic domains affect the features of polarization switching. Gao et al. perform real-time transmission electron microscopy measurements and show that ferroelastic domains can hinder the switching via formation of a transient interface layer with a dipole glass structure.

  • phase field method of phase transitions domain structures in Ferroelectric Thin Films a review
    Journal of the American Ceramic Society, 2008
    Co-Authors: Longqing Chen
    Abstract:

    This article briefly reviews recent applications of phase-field method to Ferroelectric phase transitions and domain structures in Thin Films. It starts with a brief introduction to the thermodynamics of coupled electromechanical systems and the Landau description of Ferroelectric transitions in homogeneous Ferroelectric single crystals. The thermodynamic potentials of a homogeneous crystal under different mechanical boundary conditions are presented, including the Thin-film boundary conditions. The phase-field approach to inhomogeneous systems containing domain structures is then outlined. It describes a domain structure using the spatial distribution of spontaneous polarization. The evolution of a domain structure towards equilibrium is driven by the reduction in the total-free energy of an inhomogeneous domain structure including the chemical driving force, domain wall energy, electrostatic energy as well as elastic energy. A number of examples are discussed, including phase transitions and domain stability in Ferroelectric Thin Films and superlattices. It is demonstrated that using a set of independently measured thermodynamic parameters for the corresponding bulk single crystals, the phase-field approach is able to quantitatively predict not only the strain effect on phase transition temperatures but also the correct Ferroelectric domain structures for a given strain and temperature.

  • strain tuning of Ferroelectric Thin Films
    Annual Review of Materials Research, 2007
    Co-Authors: D G Schlom, Longqing Chen, Karin M Rabe, S K Streiffer, Jeanmarc Triscone
    Abstract:

    Predictions and measurements of the effect of biaxial strain on the properties of epitaxial Ferroelectric Thin Films and superlattices are reviewed. Results for single-layer Ferroelectric Films of biaxially strained SrTiO3, BaTiO3, and PbTiO3 as well as PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices are described. Theoretical ap- proaches, including first principles, thermodynamic analysis, and phase-field models, are applied to these biaxially strained materials, the assumptions and limitations of each technique are explained, and the predictions are compared. Measurements of the effect of biax- ial strain on the paraelectric-to-Ferroelectric transition temperature (TC) are shown, demonstrating the ability of percent-level strains to shift TC by hundreds of degrees in agreement with the predic- tions that predated such experiments. Along the way, important ex- perimental techniques for characterizing the properties of strained Ferroelectric Thin Films and superlattices, as well as appropriate sub- strates on which to grow them, are mentioned.

Ramamoorthy Ramesh - One of the best experts on this subject based on the ideXlab platform.

  • dynamics of ferroelastic domains in Ferroelectric Thin Films
    Nature Materials, 2003
    Co-Authors: V Nagarajan, Orlando Auciello, Longqing Chen, Alexander L Roytburd, A Stanishevsky, S Prasertchoung, T Zhao, J Melngailis, Ramamoorthy Ramesh
    Abstract:

    Dynamics of domain interfaces in a broad range of functional Thin-film materials is an area of great current interest. In Ferroelectric Thin Films, a significantly enhanced piezoelectric response should be observed if non-180° domain walls were to switch under electric field excitation. However, in continuous Thin Films they are clamped by the substrate, and therefore their contribution to the piezoelectric response is limited. In this paper we show that when the Ferroelectric layer is patterned into discrete islands using a focused ion beam, the clamping effect is significantly reduced, thereby facilitating the movement of ferroelastic walls. Piezo-response scanning force microscopy images of such islands in PbZr0.2Ti0.8O3 Thin Films clearly point out that the 90° domain walls can move. Capacitors 1 μm2 show a doubling of the remanent polarization at voltages higher than ∼15 V, associated with 90° domain switching, coupled with a d33 piezoelectric coefficient of ∼250 pm V−1 at remanence, which is approximately three times the predicted value of 87 pm V−1 for a single domain single crystal.

  • polarization relaxation kinetics and 180 domain wall dynamics in Ferroelectric Thin Films
    Physical Review B, 2001
    Co-Authors: C S Ganpule, Ramamoorthy Ramesh, V Nagarajan, Alexander L Roytburd, B K Hill, Satishchandra Ogale, E D Williams, J F Scott
    Abstract:

    The time-dependent relaxation of remanant polarization in epitaxial lead zirconate titanate [Pb(Zr 0 . 2 Ti 0 . 8 )O 3 .PZT] Ferroelectric Thin Films, containing a uniform two-dimensional grid of 90° domains (c axis in the plane of the film). is examined using voltage-modulated scanning force microscopy. 90° domain walls preferentially nucleate 180° reverse domains during relaxation, which grow and coalesce as a function of relaxation time. Relaxation is seen to saturate at different levels depending on the write voltage. Late (saturation) stages of relaxation are accompanied by pinning and faceting of the domain walls (drastically reducing the wall mobility). which is direct evidence of the role of defect sites and crystallographic features on polarization relaxation. The kinetics of relaxation is modeled through the nucleation and growth Johnson-MehlAvrami-Kolmogorov theory with a decreasing driving force.

  • polarization relaxation kinetics and 180 domain wall dynamics in Ferroelectric Thin Films
    Physical Review B, 2001
    Co-Authors: C S Ganpule, Ramamoorthy Ramesh, V Nagarajan, Alexander L Roytburd, B K Hill, Satishchandra Ogale, E D Williams, J F Scott
    Abstract:

    The time-dependent relaxation of remanant polarization in epitaxial lead zirconate titanate $[{\mathrm{P}\mathrm{b}(\mathrm{Z}\mathrm{r}}_{0.2}{\mathrm{Ti}}_{0.8}{)\mathrm{O}}_{3},\mathrm{P}\mathrm{Z}\mathrm{T}]$ Ferroelectric Thin Films, containing a uniform two-dimensional grid of 90\ifmmode^\circ\else\textdegree\fi{} domains (c axis in the plane of the film), is examined using voltage-modulated scanning force microscopy. 90\ifmmode^\circ\else\textdegree\fi{} domain walls preferentially nucleate 180\ifmmode^\circ\else\textdegree\fi{} reverse domains during relaxation, which grow and coalesce as a function of relaxation time. Relaxation is seen to saturate at different levels depending on the write voltage. Late (saturation) stages of relaxation are accompanied by pinning and faceting of the domain walls (drastically reducing the wall mobility), which is direct evidence of the role of defect sites and crystallographic features on polarization relaxation. The kinetics of relaxation is modeled through the nucleation and growth Johnson-Mehl-Avrami-Kolmogorov theory with a decreasing driving force.

  • scanning force microscopy of domain structure in Ferroelectric Thin Films imaging and control
    Nanotechnology, 1997
    Co-Authors: Alexei Gruverman, Orlando Auciello, Ramamoorthy Ramesh, Hiroshi Tokumoto
    Abstract:

    Scanning force microscopy (SFM) has been used to perform nanoscale studies of domain structures and switching behaviour of (PZT) Thin Films. An SFM piezoresponse mode, based on the detection of the piezoelectric vibration of a Ferroelectric sample, was shown to be suitable for high resolution imaging of Ferroelectric domains in Thin Films. The lower limit of the piezoresponse mode imaging resolution depends on the radius of the probing tip and is estimated to be of the order of several nanometers. The effect of the film microstructure on the imaging resolution is discussed. The ability of effective control of domains as small as 50 nm by means of SFM has been demonstrated. It is shown that SFM can be used in the investigation of electrical degradation effects in Ferroelectric Thin Films. Formation of regions with unswitchable polarization as a result of fatigue, wiThin grains of submicron size, was experimentally observed.

  • Nanoscale imaging of domain dynamics and retention in Ferroelectric Thin Films
    Applied Physics Letters, 1997
    Co-Authors: Alexei Gruverman, Hideki Tokumoto, Orlando Auciello, Ramamoorthy Ramesh, A. S. Prakash, Manfred Wuttig, S. Aggarwal, Thangam Venkatesan
    Abstract:

    We report results on the direct observation of the microscopic origins of backswitching in Ferroelectric Thin Films. The piezoelectric response generated in the film by a biased atomic force microscope tip was used to obtain static and dynamic piezoelectric images of individual grains in a polycrystalline material. We demonstrate that polarization reversal occurs under no external field i.e., loss of remanent polarization via a dispersive continuous-time random walk process, identified by a stretched exponential decay of the remanent polarization.

Lane W Martin - One of the best experts on this subject based on the ideXlab platform.

  • defect induced dis order in relaxor Ferroelectric Thin Films
    Physical Review Letters, 2019
    Co-Authors: Sahar Saremi, Lane W Martin, Jieun Kim, Anirban Ghosh, D Meyers
    Abstract:

    The effect of intrinsic point defects on relaxor properties of 0.68 PbMg_{1/3}Nb_{2/3}O_{3}-0.32 PbTiO_{3} Thin Films is studied across nearly 2 orders of magnitude of defect concentration via ex post facto ion bombardment. A weakening of the relaxor character is observed with increasing concentration of bombardment-induced point defects, which is hypothesized to be related to strong interactions between defect dipoles and the polarization. Although more defects and structural disorder are introduced in the system as a result of ion bombardment, the special type of defects that are likely to form in these polar materials (i.e., defect dipoles) can stabilize the direction of polarization against thermal fluctuations, and in turn, weaken relaxor behavior.

  • local control of defects and switching properties in Ferroelectric Thin Films
    Physical Review Materials, 2018
    Co-Authors: Sahar Saremi, Joshua C Agar, Lane W Martin, Ran Gao, Frances I Allen, Joshua Maher, Peter Hosemann
    Abstract:

    Electric-field switching of polarization is the building block of a wide variety of Ferroelectric devices. In turn, understanding the factors affecting Ferroelectric switching and developing routes to control it are of great technological significance. This work provides systematic experimental evidence of the role of defects in affecting Ferroelectric-polarization switching and utilizes the ability to deterministically create and spatially locate point defects in $\mathrm{PbZ}{\mathrm{r}}_{0.2}\mathrm{T}{\mathrm{i}}_{0.8}{\mathrm{O}}_{3}$ Thin Films via focused-helium-ion bombardment and the subsequent defect-polarization coupling as a knob for on-demand control of Ferroelectric switching (e.g., coercivity and imprint). At intermediate ion doses ($0.22--2.2\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{ions}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$), the dominant defects (isolated point defects and small clusters) show a weak interaction with domain walls (pinning potentials from $200--500\phantom{\rule{0.16em}{0ex}}\mathrm{K}\phantom{\rule{0.16em}{0ex}}\mathrm{MV}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$), resulting in small and symmetric changes in the coercive field. At high doses ($0.22--1\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.16em}{0ex}}\mathrm{ions}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$), on the other hand, the dominant defects (larger defect complexes and clusters) strongly pin domain-wall motion (pinning potentials from 500 to $1600\phantom{\rule{0.16em}{0ex}}\mathrm{K}\phantom{\rule{0.16em}{0ex}}\mathrm{MV}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$), resulting in a large increase in the coercivity and imprint, and a reduction in the polarization. This local control of Ferroelectric switching provides a route to produce novel functions; namely, tunable multiple polarization states, rewritable pre-determined 180\ifmmode^\circ\else\textdegree\fi{} domain patterns, and multiple zero-field piezoresponse and permittivity states. Such an approach opens up pathways to achieve multilevel data storage and logic, nonvolatile self-sensing shape-memory devices, and nonvolatile Ferroelectric field-effect transistors.

  • microwave a c conductivity of domain walls in Ferroelectric Thin Films
    Nature Communications, 2016
    Co-Authors: Alexander Tselev, Lane W Martin, Sergei V Kalinin, Liv R Dedon, Ye Cao, Petro Maksymovych
    Abstract:

    Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in Ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in Thin Films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. This demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale.

  • new modalities of strain control of Ferroelectric Thin Films
    Journal of Physics: Condensed Matter, 2016
    Co-Authors: Anoop R Damodaran, Joshua C Agar, Lane W Martin, Shishir Pandya, Zuhuang Chen, Liv R Dedon, Brent A Apgar, Sahar Saremi
    Abstract:

    Ferroelectrics, with their spontaneous switchable electric polarization and strong coupling between their electrical, mechanical, thermal, and optical responses, provide functionalities crucial for a diverse range of applications. Over the past decade, there has been significant progress in epitaxial strain engineering of oxide Ferroelectric Thin Films to control and enhance the nature of Ferroelectric order, alter Ferroelectric susceptibilities, and to create new modes of response which can be harnessed for various applications. This review aims to cover some of the most important discoveries in strain engineering over the past decade and highlight some of the new and emerging approaches for strain control of Ferroelectrics. We discuss how these new approaches to strain engineering provide promising routes to control and decouple Ferroelectric susceptibilities and create new modes of response not possible in the confines of conventional strain engineering. To conclude, we will provide an overview and prospectus of these new and interesting modalities of strain engineering helping to accelerate their widespread development and implementation in future functional devices.

  • large built in electric fields due to flexoelectricity in compositionally graded Ferroelectric Thin Films
    Physical Review B, 2013
    Co-Authors: J Karthik, R V K Mangalam, Joshua C Agar, Lane W Martin
    Abstract:

    We investigate the origin of large built-in electric fields that have been reported in compositionally graded Ferroelectric Thin Films using PbZr${}_{1\ensuremath{-}x}$Ti${}_{x}$O${}_{3}$ ($0.2lxl0.8$) as a model system. We show that the built-in electric fields that cause a voltage offset in the hysteresis loops are dependent on strain relaxation (through misfit dislocation formation) and the accompanying polarization distribution wiThin the material. Using a Ginzburg-Landau-Devonshire phenomenological formalism that includes the effects of compositional gradients, mechanical strain relaxation, and flexoelectricity, we demonstrate that the flexoelectric coupling between the out-of-plane polarization and the gradient of the epitaxial strain throughout the thickness of the film, not other inhomogeneities (i.e., composition or polarization), is directly responsible for the observed voltage offsets. This work demonstrates the importance of flexoelectricity in influencing the properties of Ferroelectric Thin Films and provides a powerful mechanism to control their properties.