Relation between the real structure and optical inhomogeneity of lithium niobate single crystals

Crystallography Reports - A real structure of lithium niobate single crystals has been studied by the etching method. A relationship between the real structure and the optical inhomogeneity...     

Structure and properties of single crystals of tin-doped potassium titanyl phosphate

Single crystals with the compositions KTi_0.47Sn_0.53OPO₄ and KTi_0.25Sn_0.75OPO₄ were grown by spontaneous crystallization from flux in the K₂O-TiO₂-SnO₂-P₂O₅ quaternary system, and their structures were established from precision X-ray diffraction data. The incorporation of tin into the crystals lowers the asymmetry of cation positions in the (Ti,Sn)O₆ octahedra. The addition of even a small amount (x < 0.4) of tin to the K(Ti_{1 ? x} Sn_x)OPO₄ crystals causes fast symmetrization of the octahedra. The process slows down with an increase in the tin content until the attainment of the composition KSnOPO₄ and localization of tin in the centers of octahedra. It is these structural features that are responsible for a decrease in the optical nonlinearity of the crystals and in the intensity of second harmonic generation by laser radiation in these crystals.     

Growth and properties of Nb-or Sn-doped KTiOPO4 crystals

Single crystals of potassium titanyl phosphate, KTiOPO₄, doped with Nb or Sn to various doping levels are grown by crystallization from flux. Their atomic structure and physical properties are studied. It is found that both dopants greatly affect the configuration of titanium-oxygen polyhedra and, hence, the ferroelectric and nonlinear optical properties of the crystals. Superionic transitions with abrupt changes in electrical conductivity are observed in some crystals for the first time.     

Synthesis,physical properties,and atomic structure of niobium-doped RbTiOPO<Subscript>4</Subscript> crystals

Single crystals of solid solutions Rb_1?xTi_1?xNb_xOPO₄(RTP: Nb) were grown and the temperature dependences of their dielectric and nonlinear optical properties and electric conductivity were studied. The maximum possible niobium content in these crystals is close to x = 0.1. The niobium impurities decelerate growth of {100} faces, and crystals take a plate-like habit. With increasing doping level, ferroelectric phase transitions diffuse and their temperature decreases. A specific feature of the dielectric properties of RTP: Nb crystals is the appearance of a broad relaxation maximum ε₃₃ in the temperature range 200–600°C caused by the formation of vacancies in the rubidium cation sublattice. The intensity of second-harmonic generation under laser irradiation decreases with increasing niobium content. The atomic structure of a crystal with x = 0.01 is studied and it is established that niobium substitutes for titanium only in Ti(1) positions.     

Structural study of K<Subscript>0.93</Subscript>Ti<Subscript>0.93</Subscript>Nb<Subscript>0.07</Subscript>OPO<Subscript>4</Subscript> single crystals at 30 K

The structure of a K_0.93Ti_0.93Nb_0.07OPO₄ single crystal is studied at the temperature 30 K. The measurements are performed on a four-circle HUBER-5042 diffractometer with a DISPLEX DE-202 cryostat. Processing of the diffraction data and the preliminary refinement of the model are performed using the ASTRA program package. The final refinement of the structure model is made using the JANA2000 program complex. The refinement shows that the structure of a K_0.93Ti_0.93Nb_0.07OPO₄ crystal at T = 30 K is similar to its structure at room temperature. No phase transitions are revealed. Slight temperature-induced displacements of the potassium positions in the large cavities of the mixed framework are established.     

F-projectors and F-covering subgroups of finite groups

Given a nonempty set ω of primes and a nonempty class F of groups, we define the F ^ω - projector and F ^ω -covering subgroup of a finite group and study their properties (existence, invariance under certain homomorphisms, conjugacy, and embedding). We extend the results of Gasch¨utz, Schunck, Erickson, and others.     

Synthesis,molecular and crystal structure,and properties of 10‐propylthio‐5,10‐dihydrophenarsazine

10‐Propylthio‐5,10‐dihydrophenarsazine 2 was obtained by the reaction of 10‐chloro‐5,10‐dihydrophenarsazine 1 with propanethiol in the presence of triethylamine under mild conditions. The structure of 2 was established by X‐ray single crystal diffraction. The reaction of 2 with 2,4‐bis(ethylthio)‐1,3,2,4‐dithiadiphosphetane‐2,4‐disulfide 3 at room temperature affords a novel route to S‐10(5,10‐dihydrophenarsazine) S′‐ethyl‐S″‐propyltetrathiophosphate 4 . © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:287–291, 2000     

Cascade Transformations of 1-R-Ethynyl-9,10-anthraquinones with Amidines: Expanding Access to Isoaporphinoid Alkaloids

The interaction of acetamidine and phenylamidine with peri-R-ethynyl-9,10-anthraquinones in refluxing n-butanol leads to the formation of cascade transformations products: addition/elimination/cyclization―2-R-7H-dibenzo[de,h]quinolin-7-ones and(or) 2-R-3-aroyl-7H-dibenzo[de,h]quinolin-7-ones. The anti-inflammatory and antitumor properties of the new 2-R-7H-dibenzo[de,h]quinolin-7-ones were investigated in vivo, in vitro, and in silico. The synthesized compounds exhibit high anti-inflammatory activity at dose 20 mg/kg (intraperitoneal injection) in the models of exudative (histamine-induced) and immunogenic (concanavalin A-induced) inflammation. Molecular docking data demonstrate that quinolinones can potentially intercalate into DNA similarly to the antitumor drug doxorubicin.     

Synthesis and Crystal Structure of Copper(II) Trifluoroacetates,Cu2(CF3COO)4 · 2 CH3CN and Cu(CF3COO)2(H2O)4

Cu₂(CF₃COO)₄ · 2 CH₃CN ( I ) and Cu(CF₃COO)₂(H₂O)₄ ( II ) have been prepared by concentrating of acetonitrile and aqueous solutions respectively. According to X-ray data, the complex I consists of binuclear molecules with Cu–O 1.969 Å, Cu–N 2.114 Å. The Cu…Cu distance was found to be 2.766 Å, one of the longest for dimeric structures, apparently, due to the high acidity of trifluoroacetic acid. The coordination environment of Cu atom in II can be described as 4 + 2: 2 Cu–O (H₂O) 1.937 Å, 2 Cu–O (CF₃COO) 1.985 Å, 2 Cu–O (H₂O) 2.447 Å. The mononuclear structure is stabilized by formation of two intra- and six intermolecular hydrogen bonds.     

Synthesis,properties, and structure of potassium titanyl phosphate single crystals doped with hafnium

Single crystals of potassium titanyl phosphate doped with hafnium are grown by spontaneous flux crystallization. Their physical properties are studied, and the structure of three KTi_{1 − x} Hf _x OPO₄ crystals (x = 0.01, 0.03, and 0.12) is determined. In the crystals studied, hafnium mostly occupies the second titanium position. The doping of KTP crystals with hafnium results in an elongation of K-O bonds in the potassium polyhedra and, as a consequence, in a considerable (by approximately 180°C) decrease in the temperature of ferroelectric phase transition. The magnitude of anomalous permittivity substantially decreases. The electrical conduction in the specimens studied decreases by approximately half an order of magnitude in the low-temperature region but remains almost unchanged in the high-temperature region. Even at minor concentrations, the presence of a hafnium additive in the specimens considerably (by 35%) enhances the intensity of the second harmonic generation of laser radiation.