| 1. |
- Canalias, Carlota, et al.
(författare)
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Periodic poling of KTiOPO4 : From micrometer to sub-micrometer domain gratings
- 2006
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 340:1, s. 27-47
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Tidskriftsartikel (refereegranskat)abstract
- Some novel techniques to do periodic poling of KTP are described. Emphasis on ways to avoid domain broadening and merging of domains is presented with reference to the original properties of flux grown KTP. For sub-Am structures E-beam lithography and deep UV-laser lithography were used to pattern the samples, and chemical process to promote selective poling to obtain high quality domain gratings in up to 1 mm thick samples.
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| 2. |
- Gallo, Katia, et al.
(författare)
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Bidimensional Hexagonal Poling of LiNbO3 for Nonlinear Photonic Crystals and Quasi-Crystals
- 2006
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 340, s. 69-74
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication of bidimensional arrays of hexagonal domains with strictly periodic and quasi-periodic patterns for the implementation of nonlinear photonic crystals and quasi-crystals in z-cut congruent LiNbO3.
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| 3. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Electrically controlled birefringent colors of Smectic C* Deformed Helix Ferroelectric Liquid
- 2008
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Ingår i: Ferroelectrics. - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 365
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Konferensbidrag (refereegranskat)abstract
- Short helix pitch (p0 = 0.45 μm) ferroelectric liquid crystal (FLC) mixture possessing high birefringenc under the action of applied voltage not more than 5 V provides four electrically switched birefringent colors: blue, green, yellow and red, while before only two [1] or three [2] colors were switched. Contrast ratio of birefringence colors were measured dependently on the driving voltage frequency. A possible application in field sequential color display where fast switching time is required has been proposed.
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| 4. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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“Inherent Continuous, Hysteretic Free and Memorized Gray Scale of FLC Display Cells Based
- 2008
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Ingår i: Ferroelectrics. - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 364
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Konferensbidrag (refereegranskat)abstract
- Ferroelectric liquid crystal (FLC) mixtures with high spontaneous polarization (Ps > 50 nC/cm2) possessing ferroelectric domains [1] exhibit a multistability effect which has been known for more than 10 years [2, 3]. Any light transmission level can be memorized in the effect after the driving voltage is switched off. The multistability effect is responsible for three new electrooptical modes with continuous, memorized and reversible gray scale. Depending on the asymmetry in boundary conditions and crystallooptical parameters of the cell, these modes differ among themselves under the shape of the gray scale curve that can be either S (double or single) or V-shaped. Origin of the phenomenon is under consideration here.
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| 5. |
- Lagerwall, J. P. F., et al.
(författare)
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Chiral smectic C subphases induced by mixing a bistereogenic antiferroelectric liquid crystal with a non-chiral liquid crystal
- 2005
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Ingår i: Ferroelectrics. - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 315, s. 221-230
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Tidskriftsartikel (refereegranskat)abstract
- By mixing a bistereogenic antiferroelectric liquid crystal (AFLC) compound, exhibiting only the SmQ* and SmC a * mesophases, with the achiral N-SmC liquid crystal HOAB we could induce all three AFLC SmC-type subphases, SmC α *, SmC β * and SmC γ *. This seems to be in contradiction with two recent postulations regarding the subphase stability, one of which suggests that the subphases appear as a result of strong chiral interactions, the other that these phases require high smectic order, something one would generally not expect in mixtures. We have studied the helical pitch, optical tilt angle, spontaneous polarization and the x-ray diffraction due to the smectic layering, as a function of mixing ratio in order to better understand the relation between phase sequence and mixture composition. The smectic layer spacing shows a strongly non-linear behavior, suggesting that the basic structure of the pure AFLC substance is retained up to a HOAB content of about 75%.
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| 6. |
- Lobov, A., et al.
(författare)
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Field induced evolution of regular and random 2D domain structures and shape of isolated domains in LiNbO3 and LiTaO3
- 2006
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 341:1, s. 109-116
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Tidskriftsartikel (refereegranskat)abstract
- The shapes of isolated domains produced by application of the uniform external electric field in different experimental conditions were investigated experimentally in single crystalline lithium niobate LiNbO3 and lithium tantalate LiTaO3. The study of the domain kinetics by computer simulation and experimentally by polarization reversal of the model structure using two-dimensional regular electrode pattern confirms applicability of the kinetic approach to explanation of the experimentally observed evolution of the domain shape and geometry of the domain structure. It has been shown that the fast domain walls strictly oriented along X directions appear after domain merging.
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| 7. |
- Nordlof, M., et al.
(författare)
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Fabrication and Characterization of Two-Dimensional Nonlinear Photonic Crystal in KTiOPO4
- 2008
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 373, s. 22-25
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Tidskriftsartikel (refereegranskat)abstract
- We present fabrication and characterization of a nonlinear photonic crystal with a rectangular domain lattice of 6.09 mu m x 6 mu m in a flux-grown KTiOPO4 crystal. The structure was used to demonstrate CW tunable second harmonic generation in the blue regime.
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| 8. |
- Petzelt, J., et al.
(författare)
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Grain boundary and size effect on the dielectric, infrared and Raman response of SrTiO3 nanograin ceramics
- 2008
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 363, s. 227-244
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Tidskriftsartikel (refereegranskat)abstract
- The recently revealed giant grain size effect on dielectric properties in undoped SrTiO3 ceramics (J. Petzelt et al., J. Phys.: Con dens. Matter 19, 196222 (2007) and references therein), was extended to smaller grains of 80 nm mean grain size. Like for previously studied ceramics with larger grain size, in addition to dielectric permittivity also the infrared and Raman responses were studied and discussed. It was shown that the reduced effective permittivity is fully accounted for by the infrared soft mode behaviour and, similar to single crystals and other ceramics studied, no dielectric dispersion appears below the THz frequency range. The rather universal (independent of the grain size and sintering process) double dead layer structure was proposed to be responsible for the observed changes in the infrared and Raman spectra, allowing the grain core to keep the single crystal dielectric function. The outer dead layer shell (obviously charged due to an oxygen deficit) is very thin (similar to 1 nm) having frequency and temperature independent low permittivity (similar to 10) and is responsible for the static permittivity suppression. The inner layer of only slightly distorted perovskite structure is polar with local polarization normal to grain boundaries gradually decreasing towards the grain centre. This polarization and/or the thickness of the polar layers, which compensate the charged grain boundaries, appear to increase on decreasing temperature, particularly below the structural phase transition. Its nature is still not fully understood. In agreement with our previous suggestions, from the Raman data it con be also concluded that in the low-temperature tetragonal phase of all SrTiO3 ceramics, the local tetragonal axes tend perpendicular to the grain boundaries and the tetragonality is strongly reduced compared to single crystals.
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| 9. |
- Sharma, P., et al.
(författare)
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Piezoelectric activity in c-axis oriented LiNbO3/ZnO bilayers grown by laser ablation technique
- 2005
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 329, s. 969-972
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Tidskriftsartikel (refereegranskat)abstract
- LiNbO3/ZnO multi-layer with a preferred c-axis orientation has been grown on glass and SiO2/Si substrates by laser ablation technique. The piezoelectric activity in as deposited films is demonstrated using a novel approach to the atomic force microscope. In the presence of an in plane low frequency (0.1 to 5 Hz) ac electric field, we monitor and image the induced piezoelectric response normal to the film plane between two electrodes.
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| 10. |
- Shur, Vladimir, et al.
(författare)
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Nanoscale Domain Effects in Ferroelectrics. Formation and Evolution of Self-Assembled Structures in LiNbO3and LiTaO3
- 2007
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 354, s. 145-157
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the most interesting nanoscale domain effects resulting in formation andevolution of self-assembled domain structures in various representatives of LiNbO3 andLiTaO3 family. Several exotic domain kinetic scenarios for complete suppression of theclassical wall motion have been revealed. It has been shown that the modification of thesurface layer allows to obtain: (1) the wall motion controlled by merging with nanoscaledomains generated in front of the moving wall and (2) the discrete switching by enlarge-ment of the web-like self-assembled ensemble of isolated domains. The formation ofnanoscale quasi-periodic and self-similar structures during cooling after pulse heatingwithout any application of external electric field was studied. It has been shown thatall experimental results can be explained, if the retardation of the bulk screening of thedepolarization field is taken into account.
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| 11. |
- Shur, Vladimir, et al.
(författare)
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Shape Evolution of Isolated Micro-Domains in Lithium Niobate
- 2007
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 360, s. 111-119
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Tidskriftsartikel (refereegranskat)abstract
- The varieties of domain shapes produced in single crystals of lithium niobate LiNbO 3 family by application of the uniform electric field have been revealed. The crucial role of predetermined nucleation effect representing the step generation at vertices of polygon domain and step growth in three Y directions was discussed. We put emphasis on formation of unusual domain shapes created by switching in non-equilibrium conditions arisen due to retardation of the screening of depolarization field. Formation of oriented fingers and dendrite self-assembled domain structures during switching with artificial surface dielectric layer and during spontaneous backswitching was considered.
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| 12. |
- Diosa, J.E. 0, et al.
(författare)
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Dielectric relaxation studies in Cs2SO4
- 2006
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Ingår i: FERROELECTRICS. - 0015-0193. ; 333, s. 253-258
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric measurements of Cs2SO4 show a distinct relaxation at low frequencies at several isotherms ( T < 651 degrees C). For example, the relaxation frequency is around 5.1 kHz at 376 degrees C and increases to approximately 1 MHz at 651 degrees C. The relaxation has an activation energy of 0.97 eV, which is in close agreement whit that of Cs+ transport. We suggest that the observed dielectric relaxation could be produced by the Cs+ jump and SO4- reorientation that cause distortion and change the local lattice polarizability inducing dipoles like CsSO4-.
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| 13. |
- Eriksson, Annika, 1975
(författare)
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Phase Transitions of the Magnetoelectric A2NiMoO6 (A = Ba, Sr) and Ca2NiWO6 by Neutron Diffraction
- 2006
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Ingår i: Ferroelectrics. - 0015-0193. ; 339, s. 1921-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic ferroelectric double perovskites A2NiMoO6 (A = Ba, Sr), and Ca2NiWO6have been characterised using neutron powder diffraction (NPD) data. The Ba2NiMoO6compound has previously been reported in cubic or hexagonal symmetry which led to investigationof polymorphism. High temperature NPD data of the Sr2NiMoO6 compoundindicates a continuous structural phase transition from tetragonal to cubic symmetry atapproximately 550 K. The reduction in symmetry is linked to spontaneous polarizationallowing the structural perturbation to be described as an improper ferroelectric phasetransition. The Ca2NiWO6 compound shows similar behaviour as Sr2NiMoO6 above700 K, possibly P21/n→(I2/m)→14/m→Fm-3m.
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| 14. |
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