National Institute Of Materials Physics - Romania

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5974 articles found

5341. Dielectric relaxation investigations of new synthetized organo-metallic liquid crystal

Authors: Beica, T; AlexeIonescu, AL; Ionescu, AT; Miraldi, E; Pucci, D; Rajteri, M

Published: 1995, MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 270, 100, DOI: 10.1080/10587259508031019

An impedance spectroscopy experimental characterization of a new synthetized Palladium complex organo-metallic liquid crystal is reported. It has been found that although organo-metallic complexes modify some of the physical properties of the liquid crystals, namely transition temperatures, values of the relaxation times and conductivity, they still have, in the nematic phase, the general behaviour of the usual liquid crystals. In particular the low frequency conductivity is very small, so one can conclude that the considered organo-metallic liquid crystal behaves like a good insulator. The temperature dependence of the static parallel and perpendicular components of the dielectric tensor are reported.

5342. ELECTRIC TWINNING IN QUARTZ BY TEMPERATURE-GRADIENT

Authors: ILIESCU, B; CHIRILA, R

Published: 1995, CRYSTAL RESEARCH AND TECHNOLOGY, 30, 235, DOI: 10.1002/crat.2170300219

This paper presents a new method for obtaining electric twins in quartz crystal: thermal treatment in a temperature gradient at about 500 degrees C, that means under phase transition point. + 5X quartz crystal plates for resonators were used; a temperature gradient of 15-25 degrees C was applied for 4-5 hours along the Y axis (the place length). For + 5X resonators, the diminution of the resonant frequency and the increase of the inductance were plotted as a function of the level of twinning.

5343. The effect of the space charge on the properties of an inhomogeneous pyroelectric ceramic

Authors: PINTILIE, L

Published: 1995, STRUCTURE AND PROPERTIES OF INTERFACES IN CERAMICS, 357, 418, DOI:

5344. EPR spectra of Cr3+ ions in LiNbO3:ZnO and LiNbO3:CaO

Authors: Bravo, D; Martin, A; Voda, M; Lopez, FJ

Published: 1995, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 134, 264, DOI: 10.1080/10420159508227227

The electron paramagnetic resonance spectra of Cr3+ in LiNbO3 co-doped with ZnO or CaO (approximate to 6%) have been studied. Both impurities give rise to the same effect as that observed in MgO-doped samples: a strong diminution of the anisotropic (axial) spectrum reported for LiNbO3:Cr and the appearance of an intense and isotropic line. The origin of this line in the co-doped samples is discussed.

5345. Fast diffusion of the off-center impurities Cu+ and Li+ in the KCl lattice

Authors: Despa, F; Topa, V

Published: 1995, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 137, 1529, DOI:

In this work, we perform a study of the off-center effect: on the diffusion coefficient and we propose a new mechanism for fast diffusion. The model assumes that the equilibrium positions of the cationic impurities are noncentral and that the diffusion proceeds by hopping across the potential barrier along the nonlinear paths with the highest probability [1]. The nonlinear paths between two consecutive positions characterize even the selfdiffusion and furthermore, in the off-center diffusion this path is appropriate. The main results is that the off-center position considerably enhances the diffusion. The theoretical diffusion coefficients have been obtained by modeling the potential barrier. Changes of the configuration entropy and the vibration spectra due to the presence of the noncentral impurity are included in the model. We emphasize the good agreement of the model with the experimental data for KCl:Cu+ and show that if the impurity is placed close to the central site, the appropriate diffusion coefficient is close to that for the cationic self-diffusion: We proceeded in the Li+ cation case as in the case of Cu+ cation.

5346. Influence of illumination on time dependence of currents in MISIM structures with ZnS:Mn active layers

Authors: OPREA, A; GOLDENBLUM, A; BOGATU, V

Published: 1995, ELECTRONIC, OPTOELECTRONIC AND MAGNETIC THIN FILMS, 1, 567, DOI:

5347. GAUSS WINDOW FOR SINGULAR SYSTEM ANALYSIS IN GRANULOMETRY

Authors: DIMOFTE, C; MIHUT, L; BALTOG, I

Published: 1995, FOURTH CONFERENCE IN OPTICS, ROMOPTO '94, 2461, 523, DOI: 10.1117/12.203471

5348. Time dependence of currents in thin films and powder electroluminescent structures with ZnS active layers

Authors: OPREA, A; GOLDENBLUM, A; BOGATU, V; KOLENTSOV, K; YOURUKOVA, L

Published: 1995, ELECTRONIC, OPTOELECTRONIC AND MAGNETIC THIN FILMS, 1, 571, DOI:

5349. NEAR INFRARED PHOTOMETRIC ANALYZER

Authors: MIHUT, L; DIMOFTE, C; BALTOG, I

Published: 1995, FOURTH CONFERENCE IN OPTICS, ROMOPTO '94, 2461, 555, DOI: 10.1117/12.203480

5350. Modified ruthenium exchanged zeolites for enantioselective hydrogenation

Authors: Parvulescu, VI; Parvulescu, V; Coman, S; Radu, C; Macovei, D; Angelescu, E; Russu, R

Published: 1995, PREPARATION OF CATALYSTS VI: SCIENTIFIC BASES FOR THE PREPARATION OF HETEROGENEOUS CATALYSTS, 91, 570, DOI:

Preparation of modified ruthenium molecular sieves has been investigated in two steps deposition of ruthenium and modifying of ruthenium molecular sieves in presence of ligands. As support sieve there were used two molecular sieves with large pore apertures and low acidity strength (zeolite L and APO-34). Correlation of in situ W-VIS ruthenium deposition measurements with catalyst characterisation revealed that ruthenium deposition takes place not only through ionic exchange but also through adsorption of ruthenium hydrolysed species. Modifying of the ruthenium molecular sieves catalysts with ligands has as effect a diminution of electronic charge on metal. The experimental data indicate that the presence of ligand favours an enantioselective hydrogenation of D-fructose to D-mannitol even if the yields are not very high.