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Phase transition and field driven hysteresis evolution of a two-dimensional Ising grid consisting of ferroelectric–antiferroelectric
multilayers that take into account the long range dipolar interactions were simulated by a Monte–Carlo method. Simulations
were carried out for a 1 + 1 bilayer and a 5 + 5 superlattice. Phase stabilities of components comprising the structures with
an electrostatic-like coupling term were also studied. An electrostatic-like coupling, in the absence of an applied field,
can drive the ferroelectric layers toward 180° domains with very flat domain interfaces mainly due to the competition between
this term and the dipole–dipole interaction. The antiferroelectric layers do not undergo an antiferroelectric-to-ferroelectric
transition under the influence of an electrostatic-like coupling between layers as the ferroelectric layer splits into periodic
domains at the expense of the domain wall energy. The long-range interactions become significant near the interfaces. For
high periodicity structures with several interfaces, the interlayer long-range interactions substantially impact the configuration
of the ferroelectric layers while the antiferroelectric layers remain quite stable unless these layers are near the Neel temperature.
In systems investigated with several interfaces, the hysteresis loops do not exhibit a clear presence of antiferroelectricity
that could be expected in the presence of anti-parallel dipoles, i.e., the switching takes place abruptly. Some recent experimental
observations in ferroelectric–antiferroelectric multilayers are discussed where we conclude that the different electrical
properties of bilayers and superlattices are not only due to strain effects alone but also due to long-range interactions.
The latter manifests itself particularly in superlattices where layers are periodically exposed to each other at the interfaces. 相似文献
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L. F. Makarenko F. P. Korshunov S. B. Lastovskii L. I. Murin M. Moll I. Pintilie 《Semiconductors》2014,48(11):1456-1462
It is shown experimentally that, in contrast to the stable configuration of (interstitial carbon)-(interstitial oxygen) complexes (C i O i ), the corresponding metastable configuration (C i O i *) cannot be found in n-Si based structures by the method of capacitance spectroscopy. The rates of transformation C i O i * →C i O i are practically the same for both n- and p-Si with a concentration of charge carriers of no higher than 1013 cm?3. It is established that the probabilities of the simultaneous formation of stable and metastable configurations of the complex under study in the case of the addition of an atom of interstitial carbon to an atom of interstitial oxygen is close to 50%. This is caused by the orientation dependence of the interaction potential of an atom of interstitial oxygen with an interstitial carbon atom, which diffuses to this oxygen atom. 相似文献
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Laura E. Stoflea Nicoleta G. Apostol Cristina Chirila Lucian Trupina Raluca Negrea Lucian Pintilie Cristian M. Teodorescu 《Journal of Materials Science》2014,49(9):3337-3351
The band bending at Cu/PZT(001) interfaces is investigated by X-ray photoelectron spectroscopy (XPS) for a PZT(001) layer which exhibits initial outwards ferroelectric polarization. Two competitive processes are identified: (a) formation of the Schottky barrier between the ferroelectric and unconnected Cu islands, and (b) coalescence of the Cu islands, realisation of an electrical contact to the ground of the system, inducing the apparent loss of the component of the ferroelectric polarization perpendicular to the sample surface, at least as it manifests in band bending. Three mechanisms are proposed to explain this loss of band bending when a full metal layer connected to ground is formed on the surface: (i) over-compensation of depolarization field in the sub-surface region, (ii) formation of domains with in-plane orientation of the polarization vector and (iii) loss of polarization in the near-surface layers of the ferroelectric due to electrons provided by the metal. These result in a non-monotonous variation of binding energies with the amount of Cu deposited. High resolution transmission electron microscopy and piezoresponse force microscopy confirmed these hypotheses. The XPS data allowed also to derive the surface PZT composition, its evolution with the deposition of copper and the formation of surface compounds. 相似文献
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Constantin Tnase Lucia Pintilie Raluca Elena Tnase 《International journal of molecular sciences》2021,22(4)
In the total stereo-controlled synthesis of natural prostaglandins (PGs) and their structural analogs, a vast class of compounds and drugs, known as the lactones, are encountered in a few key steps to build the final molecule, as: δ-lactones, γ-lactones, and 1,9-, 1,11-, and 1,15-macrolactones. After the synthesis of 1,9-PGF2α and 1,15-PGF2α lactones, many 1,15-lactones of E2, E3, F2, F3, A2, and A3 were found in the marine mollusc Tethys fimbria and the quest for understanding their biological role stimulated the research on their synthesis. Then 1,9-, 1,11-, and 1,15-PG lactones of the drugs were synthesized as an alternative to the corresponding esters, and the first part of the paper describes the methods used for their synthesis. The efficient Corey procedure for the synthesis of prostaglandins uses the key δ-lactone and γ-lactone intermediates with three or four stereocenters on the cyclopentane fragment to link the PG side chains. The paper describes the most used procedures for the synthesis of the milestone δ-Corey-lactones and γ-Corey-lactones, their improvements, and some new promising methods, such as interesting, new stereo-controlled and catalyzed enantioselective reactions, and methods based on the chemical/enzymatic resolution of the compounds in different steps of the sequences. The many uses of δ-lactones not only for the synthesis of γ-lactones, but also for obtaining 9β-halogen-PGs and halogen-substituted cyclopentane intermediates, as synthons for new 9β-PG analogs and future applications, are also discussed. 相似文献
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Corina Lavinia Dumitriu Alexandru Savin Valeriu Sunel Otilia Pintilie Raluca Craciun 《Polymer-Plastics Technology and Engineering》2013,52(4):481-486
The paper deals with the study of some polymer-biologically active principle systems characterized by the controlled release of the bioactive component by hydrolyze followed by diffusion. The systems were obtained by coupling the 2-mercapto-benzotiazolyl-acetic acid and N-(m-nitrobenzoyl)-L-methionine on poly(vinyl alcohol) by means of esteric bonds in the presence of diciclohexylcarbodiimide as an activator. The influence of some coupling process parameters on the reaction efficiency was studied, such as the drug/support and activator/support ratios. The coupling products with a maximum content of biologically active compound were characterized by spectral measurements, also as regards the capacity of bioactive compound release under the conditions simulating those within the gastro-intestinal tract. The antibacterial activity of the conjugates against Staphylococcus aureus, Eschrichia coli, Sarcina lutea, and Bacillus subtilis was determined. 相似文献
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Photoconductive properties of some sol-gel deposited, ferroelectric thin films are investigated in the ultraviolet (UV) domain. The investigated materials are: Bi4Ti3O12 (BiT); SrBi2Ta2O9 (SBT) and Pb(Zr0.45Ti0.55)O3 (PZT). It was found that all these materials exhibit pronounced photoconductivity in the 250–500 nm domain. The best current responsivity was obtained for Bi4Ti3O12 (BiT) films. 相似文献
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M. Cernea F. Vasiliu C. Plapcianu C. Bartha I. Mercioniu I. Pasuk R. Lowndes R. Trusca G.V. Aldica L. Pintilie 《Journal of the European Ceramic Society》2013,33(13-14):2483-2490
Double perovskite Sr2FeMoO6 was prepared by two ways consisting in sol–gel technique and solid-state reaction method. The resulting powders from gel and mixed oxides precursors showed microstructures consisting of very fine grains (0.5–0.8 μm) and a crystalline perovskite structure. The structural and microstructural properties of the double perovskite Sr2FeMoO6 powders as-prepared and ceramics were compared. Tetragonal Sr2FeMoO6 pellets were prepared from the two powders by spark plasma sintering at: 1000, 1100 and 1200 °C and then annealing at 1200 °C, 2 h in 5%H2/Ar. The pellets presented different magnetic characteristics. The saturation magnetization of the samples prepared by sol–gel is close to those prepared by conventional synthesis method. 相似文献
10.
Marin Cernea Carmen Galassi Bogdan S. Vasile Claudio Capiani Ciceron Berbecaru Ioana Pintilie Lucian Pintilie 《Journal of the European Ceramic Society》2012,32(10):2389-2397
(Na1/2Bi1/2)TiO3 doped in situ with 11 mol% BaTiO3 (NBT–BT0.11) powders were synthesized by a sol–gel method, and the electrical properties of the resulting ceramics were investigated. The powders consisting of uniform and fine preliminary particles of about 50 nm were prepared by calcining the gel precursor at 700 °C. (Na1/2Bi1/2)0.89Ba0.11TiO3 ceramics, sintered at temperatures up to 1150 °C have a rhombohedral symmetry, while the ceramic sintered at 1200 °C exhibits a tetragonal crystalline structure. The ceramics show high dielectric constant (?r ~ 5456), dielectric loss of 0.02, depolarization temperature Td ~ 110 °C and temperature corresponding to the maximum value of dielectric constant Tm ~ 262 °C. The dielectric constant (?33) and the piezoelectric constant (d33) attain the maximum values of 924 and 13 pC/N, respectively, while the electromechanical coupling factor (kp) value is 0.035. The NBT–BT0.11 ceramics derived from sol–gel present high mechanical quality factor (Qm ~ 860). The dielectric and piezoelectric properties values of NBT–BT0.11 ceramics derived from sol–gel are smaller than those of samples produced by the conventional solid state reaction method, due to the grains size and oxygen vacancies that generate dipolar defects. 相似文献