Changes in the structure of the Rb2NaYF6: Yb3+ crystal upon transition from the cubic to tetragonal phase

The pattern of lattice distortions occurring in the vicinity of Yb3+ ions during the transition of the Rb2NaYF6: Yb3+ crystal from the cubic to tetragonal phase has been revealed using all the parameters of the empirically found crystal fields for paramagnetic centers of the Yb3+ ions with cubic and tetragonal symmetry. It has been shown that the YbF6 octahedra are rotated about the fourfold axis through an angle approximately equal to 1.2°. Moreover, the octahedra themselves are deformed so that the F- ions symmetrically located in the plane perpendicular to the axis of rotation come close to the impurity ion at a distance of 0.0004 nm. The fluoride ions located on the axis of rotation, conversely, move away from the Yb3+ ion at a distance of 0.0005 nm. Based on the obtained results, it has been concluded that the total condensate of order parameters of the studied phase transition involves not only the critical rotations of octahedral groups but also the noncritical displacements of atoms in the rotated octahedra. © 2013 Pleiades Publishing, Ltd

An analysis of the trigonal center structure of Yb3+ ion in CsCaF3

© Springer-Verlag Wien 2014. The crystal field parameters determined from interpretation of optical spectra are used to analyze distortions of a crystal lattice in the vicinity of an impurity ion and vacancy at a Cs+ site compensating the excess positive charge in the trigonal centers of Yb3+ ions in CsCaF3 crystal. Interactions of the impurity ion with the nearest neighbors (an octahedron of F- ions) and the next nearest neighbors (a cube of Cs+ ions) are considered within the superposition model. It is established that, at formation of the trigonal center, three F- ions of the nearest octahedron, placed symmetrically along the threefold axis on the side of the vacancy, move away from the impurity ion a little and significantly deviate from this axis. The second triangle of F- ions, on the contrary, comes nearer to the impurity ion and nestles on the axis of the center a little. The three Cs+ ions, the second neighbors on the side of the vacancy, slightly come nearer to Yb3+ ion and considerably nestle on the center axis. The second triangle of Cs+ ions, from the opposite side of vacancy, also comes nearer to the paramagnetic ion and also nestles on the center axis a little. The Cs+ ion, lying on the center axis, comes considerably nearer to the impurity ion

On the Interpretation of the level structure of the Ground 3d 5 Manifold of Mn III, Fe IV, Co v and Ni VI

The level structure of the ground 3d 5 configuration of Mn 2+, Fe 3+, Co 4+ and Ni 5+ ions was theoretically interpreted by means of a least-squares fit of the energy parameters to the observed values within the framework of the single-configuration approximation. In the Hamiltonian in addition to real electrostatic, spin-orbit, and spin-spin interactions, electrostatic and spin-orbit interactions correlated by configuration mixing were included. It was shown that the correct positions of almost all the energy levels are determined when the Hamiltonian includes the terms of the lineal (two-body operators) and nonlinear (three-body operators) theory of the configuration interaction. The most correct theoretical description of the experimental spectra was obtained by taking into account relativistic interactions and correlation effects of spin-orbit interactions. Adjustable parameters of the interactions included into the Hamiltonian were found

Astrometric-spectroscopic determination of the absolute masses of the HgMn binary star Phi Herculis

The Mercury-Manganese star Phi Her is a well known spectroscopic binary that has been the subject of a recent study by Zavala et al. (2006), in which they resolved the companion using long-baseline interferometry. The total mass of the binary is now fairly well established, but the combination of the spectroscopy with the astrometry has not resulted in individual masses consistent with the spectral types of the components. The motion of the center of light of Phi Her was clearly detected by the Hipparcos satellite. Here we make use of the Hipparcos intermediate data (`abscissa residuals') and show that by combining them in an optimal fashion with the interferometry the individual masses can be obtained reliably using only astrometry. We re-examine and then incorporate existing radial-velocity measurements into the orbital solution, obtaining improved masses of 3.05 +/- 0.24 M_Sun and 1.614 +/- 0.066 M_Sun that are consistent with the theoretical mass-luminosity relation from recent stellar evolution models. These mass determinations provide important information for the understanding of the nature of this peculiar class of stars.Comment: Total of 18 pages including figures and tables, in emulateapj format. To appear in The Astronomical Journal, June 2007 issu

Analysis of the Structure of Tetragonal Oxygen Centers Associated with Yb3+ ions in the KMgF3 Crystal

The parameters of the crystal field of the tetragonal oxygen center associated with a Yb3+ ion in the KMgF3 crystal found previously in a study of optical and ESR spectra are applied to analyze lattice distortions in the vicinity of the impurity ion and the O2- ion compensating for the excess positive charge. Within the super-position model, it was ascertained that the Yb3+ ion and the neighboring ions of fluorine and oxygen on the axis of the center shift significantly along the direction from the O2- ion to the Yb3+ ion during the formation of the tetragonal oxygen center. As this takes place, the distances of both (fluorine and oxygen) ions from the impurity ion increase. The four F- ions of the nearest octahedral neighborhood of Yb3+ that are arranged symmetrically in the plane perpendicular to the axis of the center slightly recede from the axis. © 2003 MAIK "Nauka/Interperiodica"

On the interpretation of the energy levels of the 4f 3 ground configuration of the free Nd3+ ion

The positions of the energy levels of the 4f 3 ground configuration of the free Nd3+ ion is interpreted theoretically within the single-configuration approximation with a Hamiltonian involving real electrostatic, spin-orbit, and spin-spin interactions, as well as the electrostatic and spin-orbit interactions correlated by configuration mixing. The most exact theoretical description of the experimental level energies is obtained by taking into account the relativistic interactions and the correlation effects of spin-orbit coupling, which are characterized by six parameters: M 0, M 2, M 4, P 2, P 4, and P 6. For all the interactions included in the Hamiltonian, consistent sets of semiempirical parameters are found. © 2007 Pleiades Publishing, Ltd

Crystalline electric fields and the ground state of YbRh2Si2 and YbIr2Si2

We have constructed the crystalline electric field (CEF) splitting of the energy levels of Yb3+ (4f13) in the clean intermetallic compounds YbRh2Si2 and YbIr2Si2. The data of measurements using methods of inelastic neutron scattering, electron spin resonance, and Mössbauer spectroscopy, together with relevant structural, thermodynamic, and magnetic properties, were used as input to calculations of the CEF level schemes in these non-Fermi-liquid systems. The experimental data of both compounds are found to be well explained on the basis of the CEF 4f-schemes with the Γt 6 - (1) ground state symmetry. © 2007 Elsevier B.V. All rights reserved

EPR and optical spectroscopy of the Yb3+ cubic center in ß-PbF2

Optical spectroscopy and EPR are employed to study a ß-PbF2 crystal doped with Yb3+ ions. The presence of only one paramagnetic center, the Yb3+ ion with cubic symmetry, is established. Its optical lines are identified, the empirical system of energy levels is constructed, and the phenomenological crystal field potential is determined. The information on the phonon spectrum of the ß-PbF2 crystal is obtained from the electron-vibrational structure of the optical absorption and luminescence spectra. © 2001 MAIK "Nauka/Interperiodica"

DEVELOPMENT AND OPTIMIZATION OF AN ULTRA WIDEBAND MINIATURE MEDICAL ANTENNA FOR RADIOMETRIC MULTI-CHANNEL MULTI-FREQUENCY THERMAL MONITORING

The article is devoted to the development of a printed ultra-wideband miniature antenna that can be used for microwave radiometry. An antenna design with a ring-shaped radiator has been proposed, which provides reception of microwave radiation from biological tissues in the 1800–4600 MHz range. The results of mathematical modeling of the antenna electromagnetic field in biological tissues using the finite difference time domain (FDTD) method are presented. Optimization of the antenna design has been carried out to ensure acceptable matching parameters and optimal antenna functionality. The developed antenna has a height of 6 mm and a calculated mass of 5 g; it is planned to manufacture a dielectric substrate based on PDMS polymer with the addition of barium titanate. The issues of calculating the antenna parameters (measurement depth, resolution and distribution of radiation power over the volume of biological tissue, sensitivity, etc.) are considered. The research results and design parameters of the developed antenna demonstrated the effectiveness of the new antenna and the possibility of its adaptation to the object of research. Considering the presence of an ultra-wide band and miniature dimensions, the antenna can be a sensor of a multi-frequency multi-channel microwave radiothermograp

Optical Spectroscopy of Octahedral Impurity Yb3+ Ions in a CsCaF3 Crystal

Optical spectra of a CsCaF3 crystal doped with Yb3+ ions are experimentally separated into groups of lines corresponding to different impurity centers formed by the Yb3+ ions introduced to sites with the hexagonal and dodecahedral environment of ligands. In the spectra of octahedral centers, the lines related to the cubic and trigonal centers are identified. The empirical energy level diagrams are constructed for impurity centers of both types, from which parameters of the relevant crystal fields are found