Characterization of defects generated by di-and trivalent cations in the potassium-dihydrophosphate structure and their influence on growth kinetics and face morphology

Different types of defect sites generated by the impurities of divalent (M²⁺) and trivalent (M³⁺) metals in the structure of potassium dihydrophosphate KH₂PO₄ (KDP) were revealed by crystal-chemical analysis and computer simulation. These sites cause different deformations of the crystal matrix by generating different local strains, which enhance the inhibiting effect of impurity atoms adsorbed on the surface. This fact accounts for the different influence of di-and trivalent cations on the growth kinetics and face morphology of KDP crystals. The effect of the M³⁺ ions is associated primarily with their adsorption on the face surfaces, whereas the influence of the M²⁺ ions results from their insertion into the surface layer of the crystal.     

The Effect of Fluid-Saturation on Mechanical Behavior of the Coating–Substrate System under Contact Loading

Russian Physics Journal - The influence of the fluid saturation of a porous coating on the mechanical properties of the coating and the entire coating-substrate system is addressed. An important...     

Luminescence of Zn<Subscript>2</Subscript>L<Subscript>2</Subscript>- and PVC-based organic molecular compositions under photo- and electroexcitation

Spectral and luminescent properties of Zn₂L₂ complex {mu-2-bis((3-pyridine-2-il)-5-(2-salicyldeniminophenyl)-1,2,4-triaurum(2-))dizinc(2+)solvate with ethanol} are investigated in solutions, powder, and thin polyvinylcarbazole (PVC) films. The trends in their change versus the nature, aggregate state, and excitation method are established. Electroluminescence (λ_max = 493 nm) of an ITO/PEDOT/PVC: Zn₂L₂/LiF/CaMg/Ag device is excited, and its current-voltage and brightness-voltage characteristics are investigated.     

Unconventional anisotropic superexchange in alpha'-NaV2O5

The strong line broadening observed in electron spin resonance on NaV2O5 is found to originate from an unusual type of the symmetric anisotropic exchange interaction with simultaneous spin-orbit coupling on both sites. The microscopically derived anisotropic exchange constant is almost 2 orders of magnitude larger than the one obtained from conventional estimations. Based on this result we systematically evaluate the anisotropy of the ESR linewidth in terms of the symmetric anisotropic exchange only, and we find microscopic evidence for precursor effects of the charge ordering already below 150 K.     

Uranyl orthovanadate of composition (UO2)3(VO4)2 · 4H2O: Synthesis and characterization

Uranyl orthovanadate of composition (UO₂)₃(VO₄)₂ · 4H₂O was prepared by heating uranovanadic acid HVUO₆ · 2H₂O under hydrothermal conditions at 200°C. X-ray fluorescence analysis, high-temperature X-ray diffraction, scanning calorimetry, and IR spectroscopy served to study dehydration and to determine the structure, X-ray diffraction, and spectroscopic characteristics of dehydration products.     

Crystal and molecular structures of potassium cobalt hydrogen phthalate K2[Co(H2O)6](C8H5O4)4 ⋅ 4H2O and mechanism of Co2+ impurity trapping in KAP crystals

The single-crystal X-ray diffraction analysis of K₂[Co(H₂O)₆](C₈H₅O₄)₄ ? 4H₂O has been carried out. The K₂[Co(H₂O)₆](C₈H₅O₄)₄ ? 4H₂O single crystals are obtained in attempting to grow the KAP crystals with the maximum possible content of Co²⁺ impurity cations. The crystals are isostructural to the earlier-studied similar crystals with Ni(II). The structure is formed by double layers of biphthalate anions and the Co²⁺ and K⁺ cations in between. The Co²⁺ cations are coordinated only by water molecules, whereas the coordination of the K⁺ cations involves both the biphthalate anions and water molecules. A detailed crystal chemical analysis, together with the data on the growth kinetics of KAP crystals in the presence of Co²⁺ and the mass-spectrometric data obtained earlier for the KAP crystals, leads to the conclusion that the Co²⁺ impurity cations should be located in the form of the [Co(H₂O)₆]²⁺ cationic complexes in the interblock layers of the KAP crystals.     

Luminescence of CdS:Ag Quantum Dots in a Polymethacrylate Matrix

Semiconductor quantum dots (QDs) exhibit intense luminescence and reproduce optical characteristics. Doping with metal ions has a positive effect on their properties. Introduction of QDs into polymer matrices leads to the formation of a required morphology of composites. There is a problem in synthesis of optically transparent polymer composites containing QDs of the А²В⁶ group that consists in the extremely low solubility of metal chalcogenides and most of their precursors in monomers. To solve this problem, we used colloidal synthesis. CdS QDs were synthesized by the method of appearing reagents in situ in methylmethacrylate (MMA). Doping with Ag⁺ ions was performed by adding a silver salt into the reaction mixture during the synthesis of CdS QDs. The PMMA/CdS:Ag luminescent polymer glasses were synthesized by radical block polymerization of MMA. The transparency of the composites at wavelengths exceeding 500 nm reaches 92% (5 mm). The luminescence excitation is related to the interband electron transitions in CdS crystals. Luminescence in the range of 500–600 nm is observed due to electron relaxation via a system of levels in the band gap of doped CdS crystals. The positions and intensities of the spectral bands depend on the Ag⁺ concentration, particle size, excitation wavelength, and other factors. The formation of Cd(Ag)S/Ag₂S structures at Ag⁺ concentrations higher than 5.0 × 10^–3 mol/L quenches the luminescence.