arXiv subjects

O. M. Vovk

Publications and source records attributed to O. M. Vovk.

3 recordsLinked to original sources

arXiv2026

Influence of CaO and SiO2 additives on the sintering behavior of Cr,Ca:YAG ceramics prepared by solid-state reaction sintering

Optical ceramics of yttrium aluminum garnet (Y3-xCaxAl4.95Cr0.05O12) doped with 0.1 at.% of chromium ions and 0.5, 0.8, and 1.2 at.% of calcium ions were prepared by reactive sintering in vacuum at 1750 degrees C. The influence of SiO2 and CaO sintering aids on the optical properties and microstructure of Cr,Ca:YAG ceramics was investigated. A decrease in CaO concentration led to a reduction of Cr,Ca:YAG transparency from 81 to 0 percent at 1064 nm; moreover, ceramics with lower CaO content exhibited abnormal grains and high porosity. These features were attributed to interactions between silica and calcium oxide during vacuum sintering. Two mechanisms are proposed to explain the effect of CaO and SiO2 on the formation of Ca,Cr:YAG ceramics. The first involves the formation of a liquid phase due to the CaO-SiO2 interaction during the heating stage, resulting in abnormal grain growth. The second mechanism is the mutual consumption of Si4+ and Ca2+ ions during the isothermal stage of sintering, which leads to a decrease in Cr4+ concentration. Both mechanisms negatively affect the optical and laser properties of the ceramics.

cond-mat.mtrl-sci↗

arXiv2024

The effect of cerium doping and rate of crystallization on the microstructure of the Al2O3/YAG eutectic composite

Eutectics of Sapphire/Yttrium-Aluminum garnet and Ce-doped Sapphire/Yttrium-Aluminum garnet (Ce up to 1 at.%) with a Chinese script microstructure were obtained by the method of horizontal directional crystallization in a carbon-containing reducing atmosphere based on argon gas. The effects of the pooling rate and Ce-dopant concentration on the microstructure of the eutectic were studied by the modified chord method. The deviation of the dependence of the characteristic eutectic distance on the pooling rate from the Jackson-Hunt model has been established. A change in the pathway for restructuring the structure of the doped eutectic at a certain critical pooling rate was revealed, which may indicate that the development of morphological instability of the crystallization front is carried out as a two-stage process. The conditions for obtaining doped eutectic of high homogeneity have been established. It was shown that increasing cerium ion concentration causes an increase in the structure parameters and its value deviation. Intensive formation of the third phase occurred when the limit of cerium ion concentration was exceeded.

cond-mat.mtrl-sci↗

arXiv2021

Improved efficiency of planar light converters based on Al2O3-YAG:Ce eutectic crystals: Physical Trends and Limits

A theoretical model of a crystalline converter of white light with internal scattering medium is proposed. Obtained are the expressions for estimation of the light converter efficiency depending on its optical parameters (refractive index and coefficients of absorption at the wavelengths of the incident and re-emitted light), as well as on the geometrical dimensions and the scattering indicatrix of the optical system. The physical limits of improvement of the converter efficiency due to strong internal scattering, are established. Realized are the theoretical and experimental estimations of the efficiency of the light converter based on the crystals of Al2O3-YAG:Ce eutectic alloy which amounts to 16%. This is twice as high in comparison with the efficiency of the light converter based on YAG:Ce single crystal.

physics.optics↗