Dmitry A. Fursenko

FTIR spectroscopy of D2O and HDO molecules in the c-axis channels of synthetic beryl

Abstract This paper presents the results of Fourier transform infrared (FTIR) spectroscopy of a synthetic beryl, containing D2O molecules in its c-axis channels, which we synthesized under hydrothermal conditions at 600 °C and 1.5 kbar. The frequencies of absorbance bands in the range of the stretching vibrations and their overtones and combination modes for D2O and HDO molecules have been assigned for the first time. On the basis of our assignments, the absorbance bands observed for the natural beryl in the range of the OD stretching vibrations have been explained.

2D modeling of the regeneration surface growth on crystals

A physical model is proposed to describe the growth of regeneration surfaces (flat crystal surfaces that are not parallel to any possible faces). According to this model, the change in the growth rate of a regeneration surface during its evolution and the decrease in the number of subindividuals forming the growth front can be explained by the implementation of two types of geometric selection: within each subindividual (the absorption of rapidly growing faces by slowly growing ones) and between subindividuals (when subindividuals absorb each other). A numerical modeling of the growth of the regeneration surface (30.30.19) of potassium alum crystals showed quantitative agreement between the model proposed and the experimental data.

2D modeling of regeneration surface growth on a single-crystal sphere

This paper investigates the evolution of a sphere produced from a single crystal potassium alum in course of its regeneration, using numerical 2D-simulation in the kinematic model, which describes the growth of the regenerating surfaces.The modeling results demonstrate a qualitative agreement between the predictions of the kinematic model and real processes of sphere regeneration. It is shown that the face arising on the regenerating surface of a sphere may grow either more slowly or more rapidly than the surrounding surface. In the latter case, the face interacts with the regeneration surface and disappears from the sphere surface before intersecting in edges with neighboring faces. The influence of the input model parameters on the numerical modeling results is analyzed. It is established that the roughness parameters of the initial surface of a single-crystal sphere significantly affect the surface evolution during regeneration.

Submillimeter ESR spectra of Fe 2+ ions in synthetic and natural beryl crystals

Electron spin resonance spectra of non-Kramers bivalent iron (Fe2+) ions have been detected in synthetic and natural beryl crystals with an iron impurity. The observed ESR spectra have been attributed to resonance transitions of Fe2+ ions from the ground (singlet) state to excited (doublet) levels with the splitting Δ = 12.7 cm–1 between the levels. The experimental angular and frequency dependences of the resonance field of the ESR signal have been described by the spin Hamiltonian with the effective spin S = 1. The analysis of the ESR data and optical absorption spectra indicates that the Fe2+ ions are situated in tetrahedral positions and substitute Be2+ cations in the beryl structure.

Micro-sectoriality in hydrothermally grown ruby crystals: the internal structure of the boundaries of the growth sectors

This study explores the fine structural details of the boundaries between the growth micro-sectors in a ruby crystal grown hydrothermally on a nonsingularly oriented (01) seed. The samples were examined using IR-spectroscopy and HRTEM-analysis, demonstrating that the interfaces of the micro-sectors serve as ‘traps’ for OH-groups often observed in grown crystals. Counter to what has previously been reported, a significant proportion of these OH-groups is incorporated into ruby crystals in an orderly manner, forming diaspore-like layers growing epitaxially on the corundum (012) lattice planes. The tensions on the boundaries between the micro-sectors result in local increase of internal pressure, making the diaspore-like phase stable. The assumption is made that the mechanism discussed in the article can explain the occurrence of OH-groups in the structure of nominally anhydrous minerals, such as MgSiO3 (akimotoite) which is structurally similar to corundum.