Concentration variations in the optical pseudogap and refractive index of crystals of Cu6PS5I1–xClx solid solutions

The effect of anionic substitution of halogen atoms on the spectral position and shape of the optical absorption edge and the dispersion of the refractive index of crystals of Cu₆PS₅I_1–xCl_x solid solutions are studied. The concentration dependences of the width of the optical pseudogap, refractive index, and lattice parameters are shown to be interrelated in these solid solution crystals.     

Role of exciton-phonon interactions and disordering processes in the formation of the absorption edge in Cu<Subscript>6</Subscript>P(S<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>x</Subscript>)<Subscript>5</Subscript>Br crystals

The absorption edge in Cu₆P(S_1?x Se_x)⁵Br crystals has been studied for strong absorption in the temperature range of 77–330 K. The parameters of the Urbach absorption edge and exciton-phonon interactions in Cu₆P(S_1-x Se_x)₅Br crystals are determined and their effect on the composition disorder is studied.     

Optical activity of γ<Subscript>1</Subscript>-(Ga<Subscript>x</Subscript>In<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>Se<Subscript>3</Subscript> crystals

The optical activity of uniaxial γ₁-(Ga_xIn_1?x )₂Se₃ crystals (x=0.1, 0.2, 0.3, 0.4) is studied at T=295 and 77 K in the spectral range 0.5–0.8 πm. It is found that the cationic substitution In → Ga leads to a nonlinear increase in the specific rotation of the plane of polarization ρ and the component g ₃₃ of the gyration tensor. It is shown that the gyrotropy of the crystals studied is determined by high-energy transitions whose energy exceeds the energy of the edge transitions and that the gyrotropy observed has a molecular origin.     

Investigating the mechanisms of diamond polishing using Raman spectroscopy

Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe₃O₄) and haematite (α-Fe₂O₃), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides.     

Influence of anionic substitution on phase transitions in Cu6PS5I1− x Cl x mixed crystals

Cu₆PS₅I_{1? ?} ? _x Cl _x mixed crystals were grown using chemical vapour transport. Isoabsorption studies of optical absorption edge and optical polarization measurements were performed in the temperature range 77–320?K. The influence of anionic I?→?Cl substitution on the phase transitions in Cu₆PS₅I_{1? ?} ? _x Cl _x mixed crystals is studied. Compositional dependence of the phase-transition temperatures is obtained and the x,T-diagram for Cu₆PS₅I_{1? ?} ? _x Cl _x mixed crystals is constructed.     

Spectroscopic studies of thermal treatment effect on the composition and size of CdS1−xSex nanocrystals in borosilicate glass

The effect of heat treatment parameters on the chemical composition and average size of CdS_1−xSe_x nanocrystals obtained in borosilicate glass by diffusion-limited growth is studied by optical absorption and Raman scattering spectroscopy. An increase of selenium content from 0.75 to 0.83 in the nanocrystals with the heat treatment temperature and duration is observed. Three lowest-energy optical transitions in CdS_1−xSe_x nanocrystals are assigned to corresponding electronic transitions based on the observed dependence of the confinement-related absorption maxima on the nanocrystal size.     

Urbach absorption edge and disordering processes in As2S3 thin films

The temperature studies of transmission spectra for as-deposited and annealed amorphous As₂S₃ thin films are carried out. The optical absorption spectra in the range of their exponential behaviour are analysed, and the dispersion dependences of refractive index as well as their temperature variation are investigated. The Urbach behaviour of optical absorption edge is revealed, the Urbach absorption edge parameters are determined, and their temperature dependences are studied. The effect of different type of disordering on the optical absorption processes in As₂S₃ thin films is studied. A comparative analysis of Urbach absorption edge parameters of As₂S₃ bulk glasses and thin films is performed.     

Extraction of platinum with Astrafloxin FF from aqueous-organic solutions: Separative extraction-spectrophotometric determination of platinum(II) and platinum(IV) species

The optimum conditions of the extraction of the ion associates of platinum with the thiocyanate ions and the polymethine basic dye Astrafloxin FF by aromatic hydrocarbons and acetic acid esters from aqueous and aqueous-organic solutions were studied. The introduction of water-soluble donor-active solvents (hexamethylphosphoric triamide, N,N-diethylacetamide, N,N-dimethylformamide, and N,N-diethylformamide) leads to a considerable increase in the extraction of the ion associates of platinum and the simultaneous suppression of the extraction of the simple dye salt. The molar absorption coefficients of the extracts of ion associates are as high as (8.1?C13.3) × 10⁴. 84?C96% platinum is extracted in the form of ion associates by a single extraction. The conversion of platinum into ion associates makes it possible to separate platinum from many elements, including Cu, Cd, Ni, Co, Cr, Pb, In, Ag, Pd, Ir, Rh, and Ru, by extraction. In this case, platinum(II) is extracted in the form of ion associates under standard conditions, whereas platinum(IV) is extracted only after the preliminary thermal treatment of the test sample. A new procedure was developed for the extraction-spectrophotometric determination of the trace amounts of platinum(II) and platinum(IV), in particular, in their mixtures.     

Internal friction in Cu6PS5Br superionic crystals and related composites

Mechanical properties of Cu₆PS₅Br single crystals and composites based on them have been investigated by the internal friction method. The measurements of the internal friction and the shear modulus have been performed in the temperature range of 80–300 K at deformation frequencies of 10–100 mHz in a mode of forced torsional vibrations. The maxima caused by the superionic and ferroelastic phase transitions have been found in temperature dependences of the internal friction. It has been shown that a more than two-fold decrease in the shear modulus with increasing temperature in the range of 150–230 K is caused by mobility unfreezing in the cation sublattice of the Cu₆PS₅Br single crystal during the superionic phase transition. An abrupt (more than threefold) increase in the shear modulus upon heating in the range of 260–270 K is caused by the ferroelastic phase transition of the Cu₆PS₅Br single crystal. Parameters of the internal friction of this single crystal in the course of mentioned phase transitions have been determined.