Synthesis, crystal structure, and IR spectral study of Na[(UO2)(C3H7COO)3] · 0.25H2O and K[(UO2)(C3H7COO)3]

Synthesis, IR spectral study and X-ray diffraction analysis of single crystals of Na[(UO₂)(C₃H₇COO)₃] · 0.25H₂O (I) and K[(UO₂)(C₃H₇COO)₃] (II) were carried out. Compound I is monoclinic, unit cell parameters are: a = 13.5671(15) ?, b = 20.070(2) ?, c = 13.6139(15) ?, ?? = 106.839(2)°, space group P2₁, Z = 8, R = 0.0493. Compound II is orthorhombic, unit cell parameters are: a = 17.1325(9) ?, b = 19.6966(11) ?, c = 21.9686(11) ?, space group P2₁2₁2₁, Z = 16, R = 0.0563. Mononuclear groups [UO₂(C₃H₇COO)₃]^? related to the A ₃ ⁰¹ crystal-chemical group (A = UO ₂ ²⁺ , B ⁰¹ = C₃H₇COO^?) of uranyl complexes are the uranium-containing structural units of crystals I and II. The data of IR spectral study agree well with X-ray diffraction data.     

Observation of the Photoinduced Conductivity in a Regular Domain Structure with Tilted Walls in MgO:LiNbO3 at a Wavelength of 632.8 nm at Bragg Diffraction

A 632.8-nm radiation-induced change in the conductivity of a regular domain structure (RDS) formed in a 5% MgO:LiNbO₃ crystal has been detected for the first time. As a result, the relaxation rate for the Bragg diffraction efficiency on the RDS, which is observed after the application of an external electric field, increases with the intensity of a probe beam. This dependence is linear in the initial stage of relaxation caused by the screening of the external field because of the redistribution of charges over tilted conductive domain walls of the RDS. For the probe beam with an intensity of 49 mW/mm², the induced effective conductivity of the RDS, which is estimated as σ_eff = 3.5×10⁻⁹Ω⁻¹m⁻¹, is more than four orders of magnitude higher than the dark conductivity of the single-domain MgO:LiNbO₃ sample.

     

Evidence of Homogeneous Intermediate Valence Coexisting with the Long-Range Magnetic Order in EuCu2(Si,Ge)2

JETP Letters - The phase diagram of the intermediate valence system EuCu2Ge2 is investigated by measuring the temperature dependencies of the heat capacity and the electrical resistance as a...     

Stereochemistry of thorium in oxygen-containing compounds

Voronoi–Dirichlet (VD) polyhedra and the method of intersecting spheres have been used to perform analysis of coordination of 198 types of crystallographically different Th(IV) atoms in the crystal structures of oxygen-containing compounds characterized with R ≤ 0.05. The volumes of VD polyhedra have been determined for the thorium atoms forming ThO_n complexes in which the Th–O bond lengths (2.14–2.91 Å) are roughly independent of the CN (n), varying from 4 to 12. It has been found that the phase transition of thorianite ThO₂ at elevated pressure is accompanied by a considerable distortion of the thorium VD polyhedra because of the appearance of faces corresponding to Th–Th contacts in which the interatomic distances are shorter than in thorium metal. It has been demonstrated that the baric phase transitions in thorium metal and thorianite are accompanied by similar changes in characteristics of Th VD polyhedra, which are tentatively believed to be a result of appearance of bonding 5f interactions between thorium atoms.     

Relationship between the Structure and Nonlinear Optical Properties of R[UO<Subscript>2</Subscript>L<Subscript>3</Subscript>] and R<Subscript>3</Subscript>[UO<Subscript>2</Subscript>L<Subscript>3</Subscript>]<Subscript>4</Subscript> Crystals (L—Carboxylate Ion)

The nonlinear optical activity (Q) of uranyl carboxylates containing [UO₂(L)₃]^– complexes in the crystal structure, where L is the anion of aliphatic or unsaturated monocarboxylic acids, has been characterized for the first time by the second harmonic generation method. It has been shown using molecular Voronoi–Dirichlet polyhedra that specific features of the cationic sublattice of U and R atoms in carboxylate structures depend on noncovalent interactions between outer-sphere R⁺ cations and [UO₂(L)₃]^– complex anions. The existence of a relationship between Q and the magnitude of the vector characterizing the displacement of the uranium atom nucleus from the centroid of its Voronoi–Dirichlet polyhedron in the cation sublattice of U and R atoms is revealed.     

Mode-locked Kerr frequency combs

We analyze a mode-locked regime in Kerr frequency combs generated in nonlinear microresonators. Using damped driven nonlinear Schr?dinger equations we show that the combs can produce subpicosecond optical pulses when the resonators are characterized with a small enough anomalous group velocity dispersion. We provide an analytical solution of the problem for the case of small damping.     

Diffraction of Light on a Regular Domain Structure with Inclined Walls in MgO:LiNbO3

JETP Letters - Features of the Bragg diffraction of a Gaussian light beam on a regular domain structure with inclined 180° domain walls in a 5% MgO:LiNbO3 crystal have been studied...     

Fundamental limitations of sensitivity of whispering gallery mode gyroscopes

We analyze theoretically both the fundamental and the technical quantum limitations of the sensitivity of a passive resonant optical gyroscope based on a high finesse monolithic optical microcavity. We show that the quantum back action associated with the resonantly enhanced optical cross- and self-phase modulation results in the standard quantum limit of the angle random walk of the gyroscope, which reaches approximately 0.2 deg/hr^1/2 for a millimeter scale CaF₂ whispering gallery mode resonator based device.     

First evidence for a Sm<Superscript>3+</Superscript>-type contribution to the magnetic form factor in the quasielastic spectral response of intermediate valence SmB<Subscript>6</Subscript>

The momentum-transfer dependence of the magnetic form factor associated with the quasielastic spectral component in the dynamic magnetic response of intermediate valence SmB₆ has been measured using inelastic neutron scattering on a double-isotope (¹⁵⁴Sm, ¹¹B) single crystal. The experimental dependence differs qualitatively from those obtained earlier for the inelastic signals, as well as from the field-induced magnetic form factor of SmB₆ obtained by polarized neutron diffraction. This observation is interpreted by specifically considering the Curie-type contributions to the dynamic susceptibility, which arise from the mixing of 4 f⁵ and 4 f⁶J-multiplets into the intermediate valence state wavefunction.     

Ultra high Q crystalline microcavities

We report on the fabrication technique of ultra high Q optical crystalline whispering gallery mode microresonators and discuss their properties. The technique is suitable for the majority of available optical crystals and for production of resonators with small size. To validate the method, we made CaF₂ resonators with Q factors exceeding 4 × 10⁸ and a diameter smaller than 100 μm. A single mode resonator has also been fabricated. Possible utilization of these new resonators in quantum optics is discussed.