Search results for "Optical"

Coupled rotational and translational modes in the mixed molecular crystal KBr1?x (CN) x

1980

TheE g andT 2g acoustic phonon modes of the molecular crystals KBr0.96(CN)0.04 and KBr0.86(CN)0.14 have been investigated by inelastic neutron scattering at 6, 90 and 300 K. Clear resonances due to mode-mode coupling to molecular excitations were observed. In complementary ultrasonic experiments the elastic constants were found to pass through minima as a function of temperature. The results were quantitavely explained by a model which assumes simple forms of the molecular excitation spectrum. An alternative interpretation, though being only qualitative, postulates a freezing of the CN molecules into a glass-like phase.

Crystal field splitting of some rare earth intermetallic compounds with Cu3Au structure

1980

Inelastic neutron scattering studies were performed in the paramagnetic phases of several rare earth compounds that crystallize in the cubic Cu3Au structure: ErPb3, ErTl3, ErIn3, HoPb3, HoTl3, HoIn3, PrSn3, PrPb3, PrTl3, PrIn3, CeIn3, La1−c Pr c Tl3, and Pr(In0.5Tl0.5)3. The energies, widths and intensities of the crystal field excitations are determined and discussed in terms of interactions between the rare earth ions. Variations of the crystal field parameters are observed across the series.

Peculiarity of Low Density Plasma-Assisted Charge Emission Produced at LATGS Crystal Surface

2011

Time and energy distribution measurements for a weak plasma-assisted electron and ion emission, initiated at the surface of L-α alanine doped TGS (LATGS) single crystals by a drive ac (500 Hz) electric field exceeding 5 × 103 V/cm, have been performed especially at temperatures below as well as above phase transition. Time spectra of charges obtained at temperatures below phase transition are considerably different than that detected above phase transition; total number of charges registered under switching conditions is about an order higher than that produced during mere charging of the sample; time dependent energy spectra involve charges (electrons and ions) with energies up to a few hu…

1H NMR, DSC, dielectric, and dilatometric studies of phase transitions and molecular dynamics in N (C2H5)4SbCl4

1994

The results of dielectric, dilatometric, 1H NMR, and DSC studies on N(C2H5)4SbCl4 crystals are presented. The title compound undergoes two phase transitions at Tc1 = 272 K reversible of first order and at Tc2 = 393 K irreversible. The values of transition entropies and enthalpies are compared with those of other tetraethylammonium halogenoantimonates and bismuthates (III). The spin-lattice relaxation times and the values of the second moments of the 1H NMR line for the N(C2H5)4SbCl4 crystal are measured in the temperature range of 70 to 400 K. Two minima of T1 are observed. They are attributed to CH3 group reorientations. The activation energies for the processes are determined.

Transient Optical Absorption and Luminescence in Calcium Tungstate Crystal

2001

The peculiarities of colour centre production in doped alkali halides

1996

The peculiarities of colour centre production and recombination in KBr, KI crystals doped with Tl, In are examined. The photostimulated dopant ion luminescence (PSL response) follows that of the F-centre production in the subnanosecond time range. It is concluded that the radiation defects in a doped crystal are spatially distributed in the near vicinity of the dopants. To a limited extent the photo- and thermostimulated defect recombination also takes place near the dopant.

Symmetry and Stability of the Rutile-Based TiO2 Nanowires: Models and Comparative LCAO-Plane Wave DFT Calculations

2012

The rod symmetry groups for monoperiodic (1D) nanostructures have been applied for construction of models for bulk-like titania nanowires (NWs) cut from a rutile-based 3D crystal along the direction of a chosen crystallographic symmetry axis (in this study we consider only Ti atom-centered axes). The most stable [001]-oriented TiO2 NWs with rhombic cross sections are found to display the energetically preferable {110} facets only, while the nanowires with quasi-square sections across the [110] axis are formed by the alternating {110} and {001} facets. For simulations on rutile-based nanowires possessing four different diameters for each NW type, we have performed comparative large-scale ab …

Morphotropic ceramic solid solutions of the Pb(B3+½Nb½)O3- PbTiO3binary system

2000

Abstract The structure, dielectric, ferroelectric and electromechanical properties of lead lutecium niobate-titanate (PLuNT) and lead erbium niobate-titanate (PErNT) binary systems are reported. The data of phase diagram, crystallographic symmetry and morphotropic phase boundaries (MPB) are provided. High values of the electromechanical coupling coefficients kp = 0.66, kt = 0.48, k31 = 0.36 of (1−x)PLuN − xPT ceramics are attained in compositions near the MPB at x≈0.41.

1988

Structure et proprietes thermodynamiques de polyamides rigides portant ces groupes lateraux flexibles

Asymmetric [N–I–N]+ halonium complexes

2020

The first asymmetric halogen-bonded iodonium complexes [I(py)(4-DMAP)]PF6 (2c) and [I(py)(4-Etpy)]PF6 (2e) were prepared via [N–Ag–N]+ → [N–I–N]+ cation exchange of their analogous 2-coordinate silver complexes. The complexes were characterised by 1H and 1H–15N HMBC NMR spectroscopy, and single crystal X-ray crystallography.