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K Iwano, Y Shimoi, T Miyamoto, D Hata, M Sotome, N Kida, S Horiuchi, H Okamoto
Croconic acid crystals show proton displacive-type ferroelectricity with a large spontaneous polarization reaching 20  μC/cm^{2}, which originates from the strong coupling of proton and π-electron degrees of freedom. Such a coupling makes us expect a large polarization change by photoirradiations. Optical-pump second-harmonic-generation-probe experiments reveal that a photoexcited croconic-acid crystal loses the ferroelectricity substantially with a maximum quantum efficiency of more than 30 molecules per one absorbed photon...
March 10, 2017: Physical Review Letters
T Morimoto, T Miyamoto, H Yamakawa, T Terashige, T Ono, N Kida, H Okamoto
A rapid polarization control in paraelectric materials is important for an ultrafast optical switching useful in the future optical communication. In this study, we applied terahertz-pump second-harmonic-generation-probe and optical-reflectivity-probe spectroscopies to the paraelectric neutral phase of an organic molecular dielectric, tetrathiafulvalene-p-chloranil and revealed that a terahertz pulse with the electric-field amplitude of ∼400  kV/cm produces in the subpicosecond time scale a large macroscopic polarization whose magnitude reaches ∼20% of that in the ferroelectric ionic phase...
March 10, 2017: Physical Review Letters
Antonio J Dos Santos-García, Elena Solana-Madruga, Clemens Ritter, Adrián Andrada-Chacón, Javier Sánchez-Benítez, Federico J Mompean, Mar Garcia-Hernandez, Regino Sáez-Puche, Rainer Schmidt
Multiferroic materials exhibit two or more ferroic orders and have potential applications as multifunctional materials in the electronics industry. A coupling of ferroelectricity and ferromagnetism is hereby particularly promising. We show that the synthetic melanostibite mineral Mn2 FeSbO6 (R3‾ space group) with ilmenite-type structure exhibits cation off-centering that results in alternating modulated displacements, thus allowing antiferroelectricity to occur. Massive magnetoelectric coupling (MEC) and magnetocapacitance effect of up to 4000 % was detected at a record high temperature of 260 K...
March 23, 2017: Angewandte Chemie
Vladimir S Bystrov, Igor K Bdikin, Maksim Silibin, Dmitry Karpinsky, Svitlana Kopyl, Ekaterina V Paramonova, Gil Goncalves
Molecular modeling of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene (G) or graphene oxide (GO) were performed using the semi-empirical quantum approximation PM3 in HyperChem. The piezo properties of the composites were analyzed and compared with experimental data obtained for P(VDF-TrFE)-GO films. Qualitative agreement was obtained between the results of the modeling and the experimental results in terms of the properties of the measured effective piezoelectric coefficient d 33eff and its decrease in the presence of G/GO in comparison with the average computed piezoelectric coefficient <d 33>...
April 2017: Journal of Molecular Modeling
Alexander J Brath, Francesco Simonetti, Peter B Nagy, Geir Instanes
Ultrasonic guided wave tomography (GWT) methods for the detection of corrosion and erosion damage in straight pipe sections are now well advanced. However, successful application of GWT to pipe bends has not yet been demonstrated due to the computational burden associated with the complex forward model required to simulate guided wave propagation through the bend. In a previous paper [Brath et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Contr., vol. 61, pp. 815-829, 2014] we have shown that the speed of the forward model can be increased by replacing the three-dimensional pipe bend with a two-dimensional rectangular domain in which guided wave propagation is formulated based on an artificially inhomogeneous and elliptically anisotropic (INELAN) acoustic model...
March 15, 2017: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
J A Mundy, J Schaab, Y Kumagai, A Cano, M Stengel, I P Krug, D M Gottlob, H Dog Anay, M E Holtz, R Held, Z Yan, E Bourret, C M Schneider, D G Schlom, D A Muller, R Ramesh, N A Spaldin, D Meier
Ferroelectric domain walls hold great promise as functional two-dimensional materials because of their unusual electronic properties. Particularly intriguing are the so-called charged walls where a polarity mismatch causes local, diverging electrostatic potentials requiring charge compensation and hence a change in the electronic structure. These walls can exhibit significantly enhanced conductivity and serve as a circuit path. The development of all-domain-wall devices, however, also requires walls with controllable output to emulate electronic nano-components such as diodes and transistors...
March 20, 2017: Nature Materials
Kenta Shimamoto, Saumya Mukherjee, Sebastian Manz, Jonathan S White, Morgan Trassin, Michel Kenzelmann, Laurent Chapon, Thomas Lippert, Manfred Fiebig, Christof W Schneider, Christof Niedermayer
A current challenge in the field of magnetoelectric multiferroics is to identify systems that allow a controlled tuning of states displaying distinct magnetoelectric responses. Here we show that the multiferroic ground state of the archetypal multiferroic TbMnO3 is dramatically modified by epitaxial strain. Neutron diffraction reveals that in highly strained films the magnetic order changes from the bulk-like incommensurate bc-cycloidal structure to commensurate magnetic order. Concomitant with the modification of the magnetic ground state, optical second-harmonic generation (SHG) and electric measurements show an enormous increase of the ferroelectric polarization, and a change in its direction from along the c- to the a-axis...
March 20, 2017: Scientific Reports
Jin Jung Kweon, Riqiang Fu, Eun Sang Choi, Naresh S Dalal
Variable temperature magic angle spinning (MAS) NMR measurements are reported on (1)H and (31)P nuclei in KH2PO4 (KDP) in the vicinity of its paraelectric-ferroelectric phase transition temperature, T c, of 123 K, to examine the transition mechanism, in particular if this is a model order-disorder type or whether it also involves a displacive component. It has been well established that the temperature variation of the isotropic chemical shift, δ iso, in NMR measurements of the nuclei directly involved in the transition should remain constant or change smoothly through T c for an order-disorder type transition but it should show an anomalous change for a displacive one...
April 26, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Qingteng Zhang, Eric M Dufresne, Pice Chen, Joonkyu Park, Margaret P Cosgriff, Mohammed Yusuf, Yongqi Dong, Dillon D Fong, Hua Zhou, Zhonghou Cai, Ross J Harder, Sara J Callori, Matthew Dawber, Paul G Evans, Alec R Sandy
Ferroelectric-dielectric superlattices consisting of alternating layers of ferroelectric PbTiO_{3} and dielectric SrTiO_{3} exhibit a disordered striped nanodomain pattern, with characteristic length scales of 6 nm for the domain periodicity and 30 nm for the in-plane coherence of the domain pattern. Spatial disorder in the domain pattern gives rise to coherent hard x-ray scattering patterns exhibiting intensity speckles. We show here using variable-temperature Bragg-geometry x-ray photon correlation spectroscopy that x-ray scattering patterns from the disordered domains exhibit a continuous temporal decorrelation due to spontaneous domain fluctuations...
March 3, 2017: Physical Review Letters
Zongquan Gu, Dominic Imbrenda, Andrew L Bennett-Jackson, Matthias Falmbigl, Adrian Podpirka, Thomas C Parker, Daniel Shreiber, Mathew P Ivill, Vladimir M Fridkin, Jonathan E Spanier
We show how finite-size scaling of a bulk photovoltaic effect-generated electric field in epitaxial ferroelectric insulating BaTiO_{3}(001) films and a photo-Hall response involving the bulk photovoltaic current reveal a large room-temperature mean free path of photogenerated nonthermalized electrons. Experimental determination of mesoscopic ballistic optically generated carrier transport opens a new paradigm for hot electron-based solar energy conversion, and for facile control of ballistic transport distinct from existing low-dimensional semiconductor interfaces, surfaces, layers, or other structures...
March 3, 2017: Physical Review Letters
M A Helal, M Aftabuzzaman, S Tsukada, S Kojima
In relaxor ferroelectrics, the role of randomly orientated polar nanoregions (PNRs) with weak random fields (RFs) is one of the most puzzling issues of materials science. The relaxation time of polarization fluctuations of PNRs, which manifests themselves as a central peak (CP) in inelastic light scattering, is the important physical quantity to understand the dynamics of PNRs. Here, the angular and temperature dependences of depolarized and polarized CPs in 0.44Pb(Mg1/3Nb2/3)O3-0.56PbTiO3 single crystals with weak RFs have been studied by Raman and Brillouin scattering, respectively...
March 16, 2017: Scientific Reports
Alexander L Roytburd, Jun Ouyang, Andrei Artemev
A review of theoretical models, phase field modeling and experimental studies of domain structures in epitaxial films is presented. The thermodynamic theory of such domain structures is presented within the macroscopic thermo-mechanical framework. The theory allows for the evaluation of the main parameters of the domain structure using the energy minimization approach applied to the energy of elastic interactions. For homophase (polytwin) films, the thermodynamic theory provides a quantitative tool that can be used to estimate domain fractions in the film and the type of domain structure architecture...
April 26, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Katrine L Svane, Aron Walsh
Hybrid organic-inorganic materials are mechanically soft, leading to large thermoelastic effects which can affect properties such as electronic structure and ferroelectric ordering. Here we use a combination of ab initio lattice dynamics and molecular dynamics to study the finite temperature behavior of the hydrazinium and guanidinium formate perovskites, [NH2NH3][Zn(CHO2)3] and [C(NH2)3][Zn(CHO2)3]. Thermal displacement parameters and ellipsoids computed from the phonons and from molecular dynamics trajectories are found to be in good agreement...
January 12, 2017: Journal of Physical Chemistry. C, Nanomaterials and Interfaces
Andrey M Vyunishev, Anatoly S Chirkin
We study the frequency doubling in a quadratic nonlinear photonic crystal consisting of periodically poled structures mediated by uniform layers with random lengths. These structures can be formed by new local impact methods for ferroelectric crystal structuring. The statistical frequency doubling theory is developed for such structures. The effect of the number of random layers and variation in their thicknesses on the second-harmonic conversion efficiency is clarified. It is demonstrated that a proper choice of the intermediate layer thickness can enhance or suppress the conversion efficiency...
March 15, 2017: Optics Letters
Lingmin Yao, Zhongbin Pan, Jiwei Zhai, Haydn H D Chen
Nanocomposites in capacitors combining highly aligned one dimension ferroelectric nanowires with polymer would be more desirable for achieving higher energy density. However, the synthesis of the well-isolated ferroelectric oxide nanorod arrays with a high orientation has been rather scant, especially using glass-made substrates. In this study, a novel design that is capable of fabricating a highly [110]-oriented BaTiO3 (BT) nanorod array was proposed first, using a three-step hydrothermal reaction on glass-made substrates...
March 15, 2017: Nanoscale
Ádám Butykai, Sándor Bordács, István Kézsmárki, Vladimir Tsurkan, Alois Loidl, Jonathan Döring, Erik Neuber, Peter Milde, Susanne C Kehr, Lukas M Eng
GaV4S8 is a multiferroic semiconductor hosting Néel-type magnetic skyrmions dressed with electric polarization. At Ts = 42 K, the compound undergoes a structural phase transition of weakly first-order, from a non-centrosymmetric cubic phase at high temperatures to a polar rhombohedral structure at low temperatures. Below Ts, ferroelectric domains are formed with the electric polarization pointing along any of the four 〈111〉 axes. Although in this material the size and the shape of the ferroelectric-ferroelastic domains may act as important limiting factors in the formation of the Néel-type skyrmion lattice emerging below TC = 13 K, the characteristics of polar domains in GaV4S8 have not been studied yet...
March 15, 2017: Scientific Reports
Takahiro Shimada, Tao Xu, Yasumitsu Araki, Jie Wang, Takayuki Kitamura
Ultrathin multiferroics with coupled ferroelectric and ferromagnetic order parameters hold promise for novel technological paradigms, such as extremely thin magnetoelectric memories. However, these ferroic orders and their functions inevitably disappear below a fundamental size limit of several nanometers. Herein, we propose a novel design strategy for nanoscale multiferroics smaller than the critical size limit by engineering the dislocations in nonmagnetic ferroelectrics, even though these lattice defects are generally believed to be detrimental...
March 14, 2017: Nano Letters
Wei Xia, Christian Peter, Junhui Weng, Jian Zhang, Herbert Kliem, Yulong Jiang, Guodong Zhu
Ferroelectric polymer based devices exhibit great potentials in low-cost and flexible electronics. To meet the requirements of both low voltage operation and low energy consumption, thickness of ferroelectric polymer films is usually required to be less than, for example, 100 nm. However, decrease of film thickness is also accompanied by the degradation of both crystallinity and ferroelectricity and also the increase of current leakage, which surely degrades device performance. Here we report one epitaxy method based on removable poly(tetrafluoroethylene) (PTFE) templates for high-quality fabrication of ordered ferroelectric polymer thin films...
March 21, 2017: ACS Applied Materials & Interfaces
Xing Liao, Yi-Kai Huang, Chad A Mirkin, Vinayak P Dravid
Reliably obtaining nanostructures of complex oxides over large area with nanoscale resolution and well-controlled shape, spacing, and pattern symmetry remains a major challenge. In this communication, millions of nanowells have been routinely generated by beam pen lithography. Each attoliter volume nanowell functions as a "nano-reactor", inside which oxide nanostructures are synthesized from their sol-gel precursors. Importantly, these nanometer scale entities are in single crystalline or textured forms and epitaxial to the underlying substrates, which promises functionalities including ferroelectricity, ferromagnetism and multiferroicity...
March 13, 2017: ACS Nano
Se Young Park, Anil Kumar, Karin M Rabe
The structure and properties of the 1∶1 superlattice of LaVO_{3} and SrVO_{3} are investigated with a first-principles density-functional-theory-plus-U (DFT+U) method. The lowest energy states are antiferromagnetic charge-ordered Mott-insulating phases. In one of these insulating phases, layered charge ordering combines with the layered La/Sr cation ordering to produce a polar structure with a large nonzero spontaneous polarization normal to the interfaces. This polarization, comparable to that of conventional ferroelectrics, is produced by electron transfer between the V^{3+} and V^{4+} layers...
February 24, 2017: Physical Review Letters
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