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Chang, Hye Jung,Kalinin, Sergei V.,Morozovska, Anna N.,Huijben, Mark,Chu, Ying‐,Hao,Yu, Pu,Ramesh, Ramamoorthy,Eliseev, Evgeny A.,Svechnikov, George S.,Pennycook, Stephen J.,Borisevich, Albina Y WILEY‐VCH Verlag 2011 Advanced Materials Vol.23 No.21
<P><B>Direct atomic displacement mapping at ferroelectric interfaces</B> by aberration corrected scanning transmission electron microscopy(STEM) (a‐STEM image, b‐corresponding displacement profile) is combined with Landau‐Ginsburg‐Devonshire theory to obtain the complete interface electrostatics in real space, including separate estimates for the polarization and intrinsic interface charge contributions. </P>
Electric modulation of conduction in multiferroic Ca-doped BiFeO<sub>3</sub> films
Yang, C.-H.,Seidel, J.,Kim, S. Y.,Rossen, P. B.,Yu, P.,Gajek, M.,Chu, Y. H.,Martin, L. W.,Holcomb, M. B.,He, Q.,Maksymovych, P.,Balke, N.,Kalinin, S. V.,Baddorf, A. P.,Basu, S. R.,Scullin, M. L.,Rames Nature Publishing Group 2009 Nature materials Vol.8 No.6
Many interesting materials phenomena such as the emergence of high-Tc superconductivity in the cuprates and colossal magnetoresistance in the manganites arise out of a doping-driven competition between energetically similar ground states. Doped multiferroics present a tantalizing evolution of this generic concept of phase competition. Here, we present the observation of an electronic conductor–insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO<SUB>3</SUB> through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p–n junction can be created, erased and inverted in this material. A ‘dome-like’ feature in the doping dependence of the ferroelectric transition is observed around a Ca concentration of ∼1/8, where a new pseudo-tetragonal phase appears and the electric modulation of conduction is optimized. Possible mechanisms for the observed effects are discussed on the basis of the interplay of ionic and electronic conduction. This observation opens the door to merging magnetoelectrics and magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom already present in the multiferroic BiFeO<SUB>3</SUB>.
D.L. Aminin,I.G. Agafonova,V.I. Kalinin,A.S. Silchenko,S.A. Avilov,V.A. Stonik,P.D. Collin,C. Woodward 한국식품영양과학회 2008 Journal of medicinal food Vol.11 No.3
Frondoside A, a major triterpene glycoside from North Atlantic commercially harvested sea cucumber Cucumaria frondosa, possesses strong immunomodulatory properties in subtoxic doses. Frondoside A stimulates lysosomal activity of mouse macrophages in vivo at a maximal effective stimulatory dose of 0.2 μg per mouse and is maintained over 10 days. This glycoside also shows a 30% stimulation of lysosomal activity in mouse macrophages in vitro at concentrations of 0.1–0.38 μg/mL. Frondoside A enhances macrophage phagocytosis of the bacterium Staphylococcus aureus in vitro at a maximal effective concentration of 0.001 μg/mL. Frondoside A stimulates reactive oxygen species formation in macrophages in vitro at a maximal effective concentration of 0.001 μg/mL. Frondoside A stimulates an increase in the number of antibody plaque-forming cells (normally B-cells in spleen) in vivo with a maximal stimulatory effect at a concentration of 0.2 μg per mouse (stimulatory index, 1.86). Frondoside A has a weak effect upon immunoglobulin (Ig) M production after immunization with sheep erythrocytes in mice. Frondoside A does not stimulate Ig production in mice and does not significantly enhance the ovalbumin-stimulated IgM and IgG antibody levels in ovalbumin-immunized mice. Hence frondoside A is an immunostimulant of cell-based immunity including phagocytosis without a significant effect on amplification of humoral immune activity or adjuvant properties. Therefore, frondoside A may provide curative and/or preventive treatment options against diseases wherein a depleted immune status contributes to the pathological processes.
Morozovska, Anna N.,Eliseev, Eugene A.,Genenko, Yuri A.,Vorotiahin, Ivan S.,Silibin, Maxim V.,Cao, Ye,Kim, Yunseok,Glinchuk, Maya D.,Kalinin, Sergei V. American Physical Society 2016 Physical Review B Vol.94 No.17
<P>We explore the role of flexoelectric effect in functional properties of nanoscale ferroelectric films with mixed electronic-ionic conductivity. Using a coupled Ginzburg-Landau model, we calculate spontaneous polarization, effective piezoresponse, elastic strain and compliance, carrier concentration, and piezoconductance as a function of thickness and applied pressure. In the absence of flexoelectric coupling, the studied physical quantities manifest well-explored size-induced phase transitions, including transition to paraelectric phase below critical thickness. Similarly, in the absence of external pressure flexoelectric coupling affects properties of these films only weakly. However, the combined effect of flexoelectric coupling and external pressure induces polarizations at the film surfaces, which cause the electric built-in field that destroys the thickness-induced phase transition to paraelectric phase and induces the electretlike state with irreversible spontaneous polarization below critical thickness. Interestingly, the built-in field leads to noticeable increase of the average strain and elastic compliance in this thickness range. We further illustrate that the changes of the electron concentration by several orders of magnitude under positive or negative pressures can lead to the occurrence of high-or low-conductivity states, i.e., the nonvolatile piezoresistive switching, in which the swing can be controlled by the film thickness and flexoelectric coupling. The obtained theoretical results can be of fundamental interest for ferroic systems, and can provide a theoretical model for explanation of a set of recent experimental results on resistive switching and transient polar states in these systems.</P>
Kim, Young-Min,Morozovska, Anna,Eliseev, Eugene,Oxley, Mark P.,Mishra, Rohan,Selbach, Sverre M.,Grande, Tor,Pantelides, S. T.,Kalinin, Sergei V.,Borisevich, Albina Y. Nature Publishing Group, a division of Macmillan P 2014 NATURE MATERIALS Vol.13 No.11
The development of interface-based magnetoelectric devices necessitates an understanding of polarization-mediated electronic phenomena and atomistic polarization screening mechanisms. In this work, the LSMO/BFO interface is studied on a single unit-cell level through a combination of direct order parameter mapping by scanning transmission electron microscopy and electron energy-loss spectroscopy. We demonstrate an unexpected ~5% lattice expansion for regions with negative polarization charge, with a concurrent anomalous decrease of the Mn valence and change in oxygen K-edge intensity. We interpret this behaviour as direct evidence for screening by oxygen vacancies. The vacancies are predominantly accumulated at the second atomic layer of BFO, reflecting the difference of ionic conductivity between the components. This vacancy exclusion from the interface leads to the formation of a tail-to-tail domain wall. At the same time, purely electronic screening is realized for positive polarization charge, with insignificant changes in lattice and electronic properties. These results underline the non-trivial role of electrochemical phenomena in determining the functional properties of oxide interfaces. Furthermore, these behaviours suggest that vacancy dynamics and exclusion play major roles in determining interface functionality in oxide multilayers, providing clear implications for novel functionalities in potential electronic devices.