Concentration Of Cr4 Research Articles

Evaluation of the efficiency of Cr3+ → Cr4+ conversion in non-stoichiometric YAG: Cr ceramics

The aim of the work was to study the effect of the YAG: Cr ceramics' stoichiometry deviation on the optical properties and efficiency of valence conversion of Cr cations. YAG: Cr ceramic powders with deviations from stoichiometry ranging from 0.225 to −0.35 at % excess yttrium were synthesized by chemical precipitation. The optical and luminescent properties of YAG: Cr4+ ceramics, as well as the microstructure of the ceramics, were studied. It has been shown that small deviations from the stoichiometry of YAG: Cr (within 0.35 at %) do not have a significant effect on the optical transmission and microstructure of YAG: Cr3+ ceramics, but strongly affect some characteristics of YAG: Cr4+ ceramics. It was found that the presence of excess aluminum or yttrium cations in YAG: Cr4+ ceramics leads to a decrease in the concentration of Cr4+ and a deterioration in the conversion from Cr3+ to Cr4+.

Effect of the sintering temperature on the microstructure and optical properties of YAG:Cr,Mg ceramics

YAG:Cr, Mg optical ceramics were prepared by the solid-state reactive sintering method within the temperature range of 1750–1800 °C. The influence of the sintering temperature on the microstructure, phase composition, and optical properties of YAG:Cr, Mg ceramics was studied. It has been shown that optimal obtaining temperature of YAG:Cr, Mg ceramics doped with 0.5 аt.% of chromium ions and 0.5 аt.% of magnesium ions is 1765 °C. YAG:Cr, Mg ceramics sintered at T = 1765 °C possess the lowest porosity and optical losses in the visible wavelength range. They are characterized by the average grain size of about 3 μm and in-line transmittance above 80%. Thermal annealing of ceramics results in transition of a part of Cr3+ ions to Cr4+ charge state. A decrease in concentration of Cr4+ ions in tetrahedral coordination with increase the sintering temperature has been observed. This effect was attributed to different charge compensation mechanisms of Mg2+ ions taking place in YAG:Cr, Mg ceramics obtained at various temperatures. Finally, laser performance of YAG:Cr, Mg ceramics was estimated in the passive Q-switch mode.

ANALISIS STRUKTUR PASAR INDUSTRI RUMAH TANGGA SASIRANGAN DI KOMPLEK MANARAP KABUPATEN BANJAR

This study focused on market structure analysis of home industry Sasirangan in Menarap, KertakHanyar, Banjarto determine market structure type. The purpose of the study to determine marketstructure and determine conditions of competition in sasirangan home industry. The method usedis quantitative descriptive, which is research that is shown to describe the existing phenomena byusing individual or group characteristic numbers. Technique are collecting questionnaire anddocumentation data. Data analysis techniques by knowing market share, market concentration ofCR4 to know market structure. The results showed that the highest market share is Hai***Craftsmen at 11.31%, and CR4 concentration ratio indicate that structure market Sasirangan inMenarap is Monopolistic Competetion with percentage ratio of 32.58%. The results of the studyshowed that the structure market is a Monopolistic Competetion with similar products but thereis competition due to a slight differentiation in terms of quality and marketing.Keywords : 1; Market Structure 2; Condition 3; Marketing 4; Produk

Orthorhombic (Fe2TiO5)-monoclinic (Cr2TiO5) solid solution series: Synthesis by gel routes, coloring and NIR reflectivity evaluation

CrxFe2-xTiO5 compositions of the solid solutions series from pseudobrookite Fe2TiO5 to monoclinic Cr2TiO5 have been prepared by the ceramic route and gel methods. At 1400 °C, pseudobrookite crystallizes in the x = 0–0.4 range, both pseudobrookite and monoclinic Fe-Cr2TiO5 coexist at x = 0.5, while in the range x = 0.7–1.5 monoclinic Fe-Cr2TiO5 crystallizes. Powders were 5 wt% glazed within a double-firing frit and the composition with x = 0.1 fired at 1000 °C exhibits the best red color (L*a*b* = 43.2/18.8/12.5), showing an intense band at 520 nm in the UV–Vis–NIR absorption spectrum associated with Cr4+ in octahedral coordination. The unit cell volume of the pseudobrookite decreases smoothly with the chromium amount, associated with the entrance of Cr4+ replacing Ti4+, while the volume of the Fe-Cr2TiO5 unit cell increases with the entrance of Fe3+ replacing Cr3+. The use of flux agents, the compaction pressure and the gel methods increase the crystallization of pseudobrookite but do not improve the reddish color, which is associated with the concentration of Cr4+ in the pigment. The optimized pigment composition Cr0.1Fe1.9TiO5 also shows a high NIR reflectance (55% in powder, 54% in glazed sample).

Nd:YAG/Cr:YAG composite laser ceramics

This work reports the synthesis of transparent composite ceramics consisting of Nd:YAG in the central part and Cr4+:YAG in the edge cladding. The central part of ceramics was shaped like 14-mm-diameter disk or 11-mm-side square and an outer diameter of the edge cladding was 18 mm or 23 mm, respectively. The central part of ceramics had an optical transmittance of ~84% at a wavelength of 1.06 µm. The concentration of Cr4+ in Cr4+:YAG ceramics of three different compositions was estimated from the transmission spectra measured and known absorption cross sections. The optimal composition of edge cladding was estimated to be 2.5 mol % Cr + 0.5 mol % Ca + 97 mol % YAG to avoid self-excitation in Nd:YAG.

High‐Temperature Electrical Conductivity of LaCr1−xCoxO3 Ceramics

LaCr1−xCoxO3 solid‐solution ceramics (x = 0.0–0.3) were prepared by pressureless sintering of a submicrometer powder. The powder was synthesized by a modified glycine nitrate process at 800°C. The electrical conductivity of the material sintered at 1600°C was measured by AC four‐wire method from room temperature to 1200°C. While undoped (x = 0) LaCrO3 revealed semiconductivity dominated by thermally activated mobility of small polarons over a vast temperature range, substitution of Co for Cr gave rise for a pronounced enhancement of conductivity at temperatures >200°C. XPS analysis showed that the concentration of Cr4+ on the Cr‐site and Co2+ at the Co‐site increased with Co substitution suggesting a thermally activated redox reaction Cr3+ + Co3+→Cr4+ + Co2+ to create additional charge carriers. Thus, Co doping offers a high potential for designing the electrical conductivity making LaCr1−xCoxO3 an interesting resistivity material for high temperature applications.

Composite Nd:YAG/Cr4+:YAG transparent ceramics for thin disk lasers

This work reports the fabrication of composite transparent ceramics consisting of a Nd:YAG central part and a Cr4+:YAG edge cladding. The central part of ceramics was shaped into 14mm-diameter disk or 11mm-side square and an outer diameter of the edge cladding was 18mm or 23mm, respectively. The central part of ceramics exhibited an optical transmittance of ~84% at the wavelength of 1.06µm. The concentration of Cr4+ in Cr4+:YAG ceramics with three different compositions was evaluated using measured transmission spectra and reported absorption cross sections. Taking into account the infeasibility condition for self-excitation, the optimal composition of edge cladding was estimated to be 2.5at% Cr, 0.25at% Ca:YAG.

Concentration of Cr4+ impurity ions and color centers as an indicator of saturation of forsterite crystals Mg2SiO4 with oxygen

The influence of the oxygen partial pressure P O 2 in the growth atmosphere on the coefficient of chromium distribution between the crystal and the melt of forsterite, the Cr3+ and Cr4+ ion contents in crystals, and the concentration of color centers induced by irradiation has been investigated. It has been established that the crystals grown at low oxygen partial pressures P O 2 (0.01–0.05 kPa) are characterized by low concentrations of Cr4+ ions and color centers. A change in the oxygen partial pressure to P O 2 ∼ 0.85 kPa leads to an increase in the Cr4+ center concentration by a factor of ∼10 and in the color center concentration by a factor of ∼5. A further increase in the oxygen partial pressure to P O 2 to 12 kPa remains the concentration of these centers almost unchanged. A model has been proposed according to which the intrinsic defects formed under conditions of a relative excess of oxygen leads to both the self-oxidation of chromium and the formation of color centers in the forsterite crystals under irradiation.

Fluorescence mapping of oxidation states of Cr ions in YAG crystal fibers

We have demonstrated the use of laser scanning confocal microscope for mapping the refractive index as well as Cr3+ and Cr4+ fluorescence in Cr:YAG crystal fibers with 1μm spatial resolution. The corresponding sensitivities for Cr3+ and Cr4+ fluorescence intensities are 1.6×1017/cm3 and 7.5×1015/cm3, respectively. The share of Cr4+ ions in the total Cr concentration is found to be proportional to the ratio of Ca to Cr concentrations. However, only less than 1% of the Ca2+ ions become active in charge compensation. The concentration of Cr4+ ions is higher near the center of the crystal fiber when the core diameter is less than 300μm. In addition, stress-induced striations created near the fiber center disappear when the fiber diameter is smaller than 500μm.

Influence of Nd co-doping on the Cr4+ content in PWO single crystal

The formation mechanism of Cr4+ in PbWO4 (PWO) crystals is studied by optical absorption and X-ray excited luminescence (XEL) spectra. It is found that the concentration of Cr4+ depends not only on the initial amount of Cr3+ but more importantly on the coaddition of Nd3+. This material may be used as a new passive Q-switched laser in view of its high absorption coefficient in the NIR region. For Cr-containing sample, Cr3+ primarily replaces Pb2+ and results in large relaxation of lattice. In order to keep the scheelite structure, some Cr3+ ions are oxidized into Cr4+ and occupy W6+ sites. In the codoping case, Nd3+ preferentially substitute for Pb2+ and Cr is forced into W6+ sites in the form of Cr4+ to keep charge neutrality and structural integrity. This view is strongly supported by FT-IR spectra. The origin of the decrease and even extinction of XEL is also discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)