Octahedral Positions Research Articles

Unusual Manganese Luminescence Channels in Low Doped MgAl2O4

We have done the rigorous characterizing of the Mn-doped MgAl2O4 (Mn = 0, 0.02, 0.04, 0.1 wt.%) single crystals and the comprehensive analysis of their optical properties theoretically supported by the Modified Crystal Field Theory to obtain the most complete picture, to date, of the diverse absorption and luminescence behavior of MgAl2O4:Mn spinels. The study has focused on exploring the formation and coexistence of multivalent states of Mn and identifying the conditions needed for activating luminescence channels. We found that Mn takes the charge state +2, +3 and +4 and occupies both tetrahedral and octahedral positions. Six luminescence channels related to Mn ions were identified for the first time. Two channels activate the luminescence at 520 nm: intra-atomic transitions in tetrahedral coordinated Mn2+ ions under VIS-excitation and a recombination Mn3+→Mn2+→Mn3+ process involving Mn3+ in tetrahedral positions under X-ray. Mn3+ in tetrahedrons and octahedrons activate luminescence channels at 733 and 926 nm under UV-C and VIS excitations. Two distinct processes involving Mn3+ and Mn4+ ions in octahedrons result in the luminescence at 651 nm. The first is an intra-atomic transition in the Mn4+ occurring under VIS-excitation. The second appears through a charge transfer Mn3+→Mn4+→Mn3+ in the octahedrons under UV-B-excitation.

Titanium ion effects on the spectroscopic and electrical characteristics of germano silicate lead alumino tellurite glass ceramics for dielectric applications

The Glass-ceramics 10GeO2-(55-x) SiO2–29PbO–5Al2O3–1TeO2 doped with varying amounts of TiO2 (0 < x < 5 mol %) were prepared through the process of melt quenching followed by heat treatment. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA) were used to analyze these glass ceramics besides the usual spectral studies like optical absorption, Electron Paramagnetic Resonance (EPR), Fourier Transform Infrared Spectroscopy (FTIR) and Raman. These investigations demonstrated the existence of crystalline phases that comprise complexes of Ti4+ as well as Ti3+ ions that were dispersed randomly. Additionally, it is seen that Ti3+ ions, which are more prevalent as TiO2 concentration rises, take up the tetragonally deformed octahedral positions inside the network of glass ceramics. FTIR spectra of the synthesized samples provided information regarding the existence of different structural units in the glass ceramic matrix, which included SiO4, GeO4, GeO6, PbO4, PbO6, AlO6, TeO4, TeO3, TiO4, and TiO6. At 30 °C, the 3 mol % Ti-doped sample has a minimum conductivity of 1.623 × 10−9 S cm−1. Therefore, the dielectric and spectroscopic investigations suggest that glass ceramics containing 3 mol% of TiO2 are rigid and appropriate for dielectric applications.

The nephelauxetic fonction he applied to the luminescence of Mn4+ and Mn5+ ions in oxides and oxyhalides

It was shown recently that the emission energy of octahedrally-coordinated Mn4+ ions in 101 oxides and 51 fluorides can be estimated from the nephelauxetic function he. Here, we extent this concept to Mn4+ ions incorporated in oxyfluorides and in compounds that do not primarily offer octahedral positions for this dopant in their crystal structure. We show that Mn4+ tends to reconstitute a 6-fold coordinated environment in these crystal lattices and tends to reconstitute either pure [MnF6]2- or pure [MnO6]8- octahedra in oxyfluorides, depending on the O/F ratio in the virgin host lattice. We also show that the “he model” can be used to estimate the energy of the NIR emitting 1E state of tetrahedrally-coordinated Mn5+ with an accuracy of ±350 cm−1.

The effects of hydrogen on the bonding properties of SiC/Cu interface via first-principles calculations

Ceramic/metal interfaces own great importance of technology, but the weak interface bond limits their applications. In this work, the effects of doping H element on the stability and bonding properties of SiC/Cu interface are studied by first principles calculations. In order to study the stability of interface, the potential surfaces were firstly studied for the C and Si terminated SiC/Cu interfaces. The C terminated interface is more stable than the Si terminated interface, which contributes the largest work of adhesion of 3.998 J/m2. The effects of hydrogen on the interface bonding properties were further studied. The occupation properties of hydrogen atoms were then studied, the hydrogen tends to occupy the octahedral position with negative formation energy. To reveal the bonding strength of SiC/Cu interface, the tensile simulations were carried out. The hydrogen owns obvious effects on the tensile strength depends on its occupation site. The movement and diffusion properties of hydrogen atoms in the interface zone were studied combining molecular dynamics and climbing image nudged elastic band method. Finally, the bonding mechanisms were analyzed by combining charge density, state density, differential charge and bader charge. Based on the above calculation results, it is found that for SiC(001)/Cu(111) interface, the H element generally has a negative impact on the bonding properties of SiC/Cu interface.

A Novel Banana-Shaped Mixed-Metal Co/Fe Polyoxometalate Cluster.

The synthesis and characterization of a Co/Fe mixed-metal banana-shaped polyoxometalate with the formula [(Co2.5Fe0.5(H2O)PW9O34)2(PW6O26)]16- (Co5Fe) is reported. This transition-metal-substituted polyoxometalate readily assembles from its components in a one-pot reaction and crystallizes in the monoclinic space group P21/c. The structure of Co5Fe can be considered a double sandwich composed by two B-α-{Co2.5Fe0.5PW9O40} Keggin units, in which one coordinatively saturated octahedral metal position is equally occupied by Co(II) and Fe(III) ions with a 50% of site occupancy. These Keggin units are linked via a hexalacunary Keggin unit {PW6O26}. Single crystal X-ray diffraction and magnetic measurements support the proposed atom arrangement within the crystal structure. Magnetic measurements of these double trimeric unit {Co2.5Fe0.5O13}2 show a combination of antiferromagnetic interaction, the presence of spin frustration, and the first-order spin-orbit coupling Co(II) ions. Electrocatalytic water oxidation measurements show that Co5Fe displays low stability in both homogeneous and heterogeneous conditions. This is evidenced by the constant increase on the catalytic currents over time together with the appearance of polyoxometalate-derived electrode-bound species that can be responsible for the observed catalytic activity.

The dominant roles of “electron-density-mechanism” and “chemical-bonding-mechanism” for hydrogen in molybdenum and lithium

Using first-principles calculations, we have systematically studied structures and thermodynamic stability of interstitial H as well as the H-vacancy interaction in molybdenum (Mo) and lithium (Li). Single H atom prefers to occupy tetrahedral interstitial position (TIP) and octahedral interstitial position (OIP) in Mo and Li, respectively, and the solution energies are 0.87 eV and −0.66 eV, respectively. In Mo, mono-vacancy can capture as many as seven H atoms and each H atom prefers to bind onto an isosurface of valence electron density. However, H atoms detach from vacancy to occupy the OIPs outside vacancy in Li. Based on these results, we reveal that the electron-density-mechanism (EDM) and chemical-bonding-mechanism (CBM) cause different properties of H in Mo and Li, respectively. In Mo, since the valence electron density everywhere in interstitial lattice is much high, H atom has to search a place where the valence electron density must be suitable. Accordingly, vacancy can provide an optimal valence electron density region for H dissolution, and the optimal valence electron density is 0.10 electron/Å3 at vacancy. In Li, H atom exhibits the negative solution energy in the interstitial lattice, which promotes H atom to form ionic bond with neighboring Li atom. H atoms do not combine inside vacancy but stay at the OIPs outside vacancy to form ionic bonds with neighboring Li atoms. We believe that the EDM and CBM can be generalized to other transition metals and other alkali metals, respectively.

Effect of substitution of aluminium and neodymium on structural and magnetic properties of yttrium iron garnet studied using 57Fe internal field NMR

The structural and magnetic properties of non-magnetic aluminium and magnetic neodymium substituted yttrium iron garnet samples (Y3-xAlxFe5O12 and Y3-nNdnFe5O12) were investigated. Powder samples were synthesized using auto combustion route. The Rietveld refinement analysis of the samples confirmed the presence of the garnet phase and showed presence of minimal impurity phases, specifically perovskite and hematite. Substitution on Y3Fe5O12 with Al resulted in a linear decrease in saturation magnetization, while Nd substitution showed a non-linear change. In accordance with this the Internal Field Nuclear Magnetic Resonance (IFNMR) spectrum exhibited a downward shift in peak frequency when Al was substituted, and a significant reduction in intensity with Nd substitution in yttrium iron garnet samples. Aluminium ions take up either tetrahedral or octahedral positions in the lattice, apart from the dodecahedral site, because of their smaller ionic radii. This causes a decrease in the hyperfine field that originates from Fe3+ ions in tetrahedral and octahedral sites. On the other hand, neodymium ions occupy dodecahedral sites and are expected not to affect Fe ions. Concurrently, an observable peak shift was not observed in the IFNMR spectrum for Nd substitution. However, Nd substitution introduced strain in the lattice due to their larger ionic radii compared to yttrium, which they replace. This strain causes disorder in tetrahedral and octahedral sites and affects 57Fe signal intensity. The magnetic properties observed from VSM analysis is also interpreted in view of observed changes in the 57Fe IFNMR spectrum. X-ray Photoelectron spectroscopy (XPS) was employed mainly to explore spin orbit splitting of Fe 2p state in the samples.

Structural, optical, and dielectric properties of Co0.6Mn0.4GdxFe2-xO4 ferrites prepared through sonochemical method

Gadolinium-substituted cobalt manganese ferrite nanoparticles with the composition Co0.6Mn0.4GdxFe2-xO4 (where x ranges from 0.0 to 0.08, with x = 0.02) were prepared through the sonochemical method. X-ray diffraction reveals that grown samples are single-phase cubic spinel belonging to space group Fd3m, where the crystallite sizes decrease with increasing Gd3+ content. At high doping ratios (x > 0.06), there was a slight increase in crystallite size compared to that of pure Co–Mn ferrite (x = 0), while the lattice parameter (a) decreased in the low doping range of Gd (x < 0.06), resulting in a reduction in crystallite size. Bertaut's method confirms that 80 % of the tetrahedral (A) sites were occupied by Mn ions, while the remaining sites were occupied by other cations in the octahedral (B) positions. Gd3+ ions were found exclusively in the octahedral-B sites. Co2+ ions were expected to occupy the octahedral-B site, which was confirmed in this study for the x = 0.0 and 0.02 samples. Field emission scanning electron microscopy shows the samples are agglomerated and have dense structures. Fourier transform infrared and Raman spectra validated the presence of spinel ferrite modes. Dielectric investigations indicate that as the Gd3+ content exceeds x = 0.0, the dielectric constant and dielectric loss decrease at lower frequencies. The observed dielectric behavior exhibited typical dispersion patterns attributed to Maxwell-Wagner polarization. Furthermore, changes in dielectric properties were observed as the Gd3+ content in Co0.6Mn0.4GdxFe2-xO4 nanoparticles increased, which can be attributed to the presence of oxygen vacancies and variations in the distribution of Fe3+ ions at both A and B-sites.

Unveiling the impact of Fe-doping concentration on the local structure and morphological evolution of Cr2O3 nanoparticles

A series of Cr2−xFexO3 (0.0 ≤ x ≤ 0.3) nanoparticles were successfully synthesized using a sol-gel-based method. Analysis through XRD and SAED of both pure and Fe-doped Cr2O3 nanoparticles revealed a rhombohedral structure belonging to the R3‾cD3d6 space group, without the formation of secondary phases or Fe clusters. Fe ions were well integrated, as indicated by fluctuations in lattice parameters, and lattice strain. The crystallite size decreased from 38.42 to 27.54 nm with increasing doping concentration. HRTEM images depicted evenly distributed nanoparticles. At lower dopant concentrations (x = 0.1), smaller and more heterogeneous nanorod-like structures emerged, with average sizes and lengths of 36.56 and 39 nm, respectively. Increasing the doping content to x = 0.2 resulted in a morphological shift towards semi-spherical and ellipsoidal shapes, with average dimensions of 22.84 and 31 nm, respectively. At higher doping levels (x = 0.3), nanoparticles grew to 66.5 nm in size and exhibited a spherical morphology. Raman and Fourier transform infrared spectra showed red-shifting of absorption bands with increasing Fe content, attributed to variations in bond length and Cr/Fe–O–Cr/Fe structural perturbation. XPS and Mössbauer spectroscopy analyses confirmed the oxidation states of Fe3+ and ionized oxygen vacancies in the crystal lattice of Cr2O3 nanoparticles. Higher values of quadrupolar splitting Δ indicated greater structural disorder induced by Fe3+ in octahedral positions and in an oxygen-deficient environment. Atomistic simulations confirmed that Fe3+ dopants can induce the presence of vacancy-complexes, forming a stable double-defect configuration with vacant Cr sites along the c-axis, proximal to oxygen vacancies with a single positive charge. These findings offer both experimental and theoretical insights into the dynamics of structural defects in trivalent transition metal doping of Cr2O3 nanoparticles, which holds significant implications for spintronics research.

Solvent‐Less Synthesis of Compositionally Tuned Mixed Metal (Ni−Zn) Ferrites for Enhanced Electrocatalytic Water Splitting and Supercapacitance

AbstractExploring efficient, abundant, economical and stable materials for sustainable energy applications, such as electrochemical water splitting and supercapacitance, is a challenging task. Mixed transition metal spinel ferrites can rationally be customized to attain these features and deliver enhanced electrochemical activity. The catalytic performance of spinels is remarkably influenced by tuning the cationic occupancy at the tetrahedral or octahedral position. Herein, a set of spinel Ni1‐xZnxFe2O4 (0≤x≤1) nanocomposites were obtained via a scalable solventless thermolysis of metal acetylacetonate precursors at relatively mild temperatures. A suite of techniques such as powder p‐XRD, EDX, SEM, TEM, HRTEM, and SAED were employed to confirm the formation of the Ni−Zn ferrite solid solutions. It was found that small amounts of Ni at tetrahedral sites were beneficial for charge storage and hydrogen evolution. For instance, Ni0.2Zn0.8Fe2O4 nanocomposite demonstrated superior HER activity with a much lower overpotential of 87 mV compared to the pristine NiFe2O4 (213 mV) or ZnFe2O4 (164 mV) catalysts. However, Ni‐occupied tetrahedral sites were not suitable for OER, whereby the pristine ZnFe2O4 displayed high catalytic activity with an overpotential of 330 mV, outperforming other electrode compositions. The study helps to identify suitable compositions and site tuning for HER, OER and supercapacitors.

Efficiency of Cr3+ → Cr4+ conversion in YSAG:Cr ceramics

In this study, we investigated the influence of the position and quantitative content of scandium in YSAG:Cr on the efficiency of chromium cation valence conversion. YSAG:Cr ceramic powders were synthesized using the chemical precipitation method. It was determined that the microstructure of ceramics and the luminescent properties of YSAG:Cr4+ depend on the predominant position of scandium, whether it replaces octahedral or dodecahedral positions in the garnet crystal lattice. An increase in Scdod content contributed to a decrease in grain size and a shift of the emission peak of Cr4+ ions towards the short-wavelength region. Conversely, an increase in Scoct content led to an increase in grain size and a shift of the maximum of the luminescent band towards the long-wavelength region. It was found that increasing the quantitative content of scandium in the octahedral position in the garnet structure by up to 50 % enhances the efficiency of the conversion of Cr3+ to Cr4+, while an increase in the proportion of Scdod resulted in a decrease in conversion efficiency.

Study of the structure and properties of interstitial alloys TixMo1 – xCyNz

Developing the new materials with improved properties suggests study of the crystal structure and properties of multicomponent interstitial alloys. We present the results of studying the crystal structure and microhardness of TixMo1 – xCyNz interstitial alloys in massive samples with different ratios of concentrations of constituent elements. The samples obtained by self-propagating high-temperature synthesis were subjected to homogenizing annealing at 2600 K for 8 h and cooled together with the furnace. Data of neutron diffraction revealed that the alloys have a face-centered cubic crystal structure in which Ti and Mo atoms, as well as C and N, are intersubstituted and statistically located in the 4b positions and octahedral 4a positions, respectively. The Rietveld method was used to determine crystallite sizes, dislocation densities, and microstrain using X-ray diffraction patterns. The microhardness of the samples was determined by the Vickers method. It is shown that the crystallite sizes determined by the Williamson-Hall and Scherrer methods differ significantly, whereas the patterns of crystallite growth in size, as well as regularities of changes in the dislocation density and microstrains follow change in the concentration of the components in the composition. As the carbon content in the alloy increases, the crystallite sizes and microstrains decrease, and the dislocation density increases. It is revealed that the smaller the crystallite size and the higher the dislocation density, the more microhardness is displaced towards increasing the carbon content. With a change in the ratio of components in TixMo1 – xCyNz as the crystallite size and microstrains decrease and dislocation density increases, the microhardness of the alloy increases by 1.5 – 2 times compared to binary carbide and titanium nitride. The results obtained can be applied to the use of interstitial alloys in instrumental and high-temperature engineering.

ZnxFe3-xO4–ZnO heterojunction interfaced with poly(L-DOPA) electron transfer mediator layer for enhanced visible light photocatalytic activity

Z-scheme heterojunctions comprising ZnxFe3-xO4@poly(L-DOPA)@ZnO (ZF@PD@ZnO) were synthesized using solvothermal and precipitation techniques. The study aimed to investigate the impact of the poly(L-DOPA) electron transfer mediator on the photocatalytic performance of ZnxFe3-xO4@ZnO (ZF@ZnO) nanocomposites under visible light irradiation. X-ray diffraction (XRD) and HRTEM analysis confirmed the formation of heterostructures, identifying the crystalline phases of both ZnO and zinc ferrite. BFTEM images revealed a polyhedral shape for all samples, with a tendency toward mild agglomeration. The partial inversion of the zinc ferrite cubic spinel structure was evidenced by FT-IR, XPS, and VSM analyses. Zinc ferrite was found to be ferromagnetic, with cation distributions between tetrahedral (A) and octahedral (B) positions as [Zn0.62+Fe0.43+]A[Fe0.42+Fe1.63+]BO4. The samples exhibited notable photocatalytic activity against Rhodamine B, serving as a model contaminant. Furthermore, the stability and reusability of the samples were examined. Additionally, the study elucidated the photocatalytic mechanism produced by the ternary Z-scheme ZF@PD@ZnO, involving spin-polarized charge carriers. Energy band alignment was evaluated by combining ultraviolet photoelectron spectroscopy (UPS) with UV-Vis spectroscopy. The interplay between band alignment and reactive oxygen species (ROS) generation was discussed in correlation with EPR results. Enhanced ROS generation under visible light illumination, observed in the ZF@PD@ZnO nanocomposite, is mainly due to the addition of the conductive poly(L-DOPA) layer, acting as an electron transfer mediator in the Z-scheme heterojunction, ensuring enhanced charge separation.

Tyrosol removal by photo–Fenton–like process using CaAlFe mixed oxides synthesized via hydrocalumite from aluminum salt cake

Solids with potential application in tyrosol (Ty) removal by photo–Fenton processes have been synthesized using aluminum salt cake as a source. Two series of hydrocalumite layered double hydroxides (LDH) were synthesized: one containing structural Fe3+ (occupying octahedral positions in the LDH) and another containing surface impregnated Fe3+; all solids were calcined in air at 750 °C. The solids were characterized by powder X–ray diffraction, FT–infrared spectroscopy, thermal analysis, N2 adsorption–desorption isotherms at –196 °C, particle size distribution and electron microscopy. One of the main differences between the two series was that Fe3+ impregnation by the incipient wetness method and subsequent calcination at 750 °C did not lead to the formation of CaAlFe mixed oxides. The calcined solids were evaluated as photocatalysts in the photo–Fenton process for Ty removal (a typical compound found in olive oil mill wastewater), the samples containing surface Fe3+ showing better results. The solid prepared by impregnation of hydrocalumite with 20% iron and subsequently calcined at 750°C, under the optimum reaction conditions (catalyst dose = 0.5 g/L, [H2O2] = 0.468 g/L and [Ty]0 = 100 mg/L, in the presence of UV light), reached complete Ty removal with contaminant mineralization of 95% after only 60 min reaction. The cyclic study showed that this sample maintained its stability after 3 cycles of reuse without iron leaching, and a better performance than other materials reported in the literature.

First occurrence of dumortierite in Croatia: its chemical composition and appearance as an igneous mineral in leucogranite-hosted pegmatite

In this article, dumortierite from Croatia is described for the first time. Dumortierite formed in a pegmatite dyke cutting through Cretaceous two-mica leucogranite of the magmatic-metamorphic complex of Mt. Moslavačka Gora. The pegmatite dyke shows a magmatic mineral association of coarse-grained quartz, orthoclase, microcline and albite, less abundant muscovite, biotite, pinkish andalusite and blue-coloured prismatic dumortierite I crystals. Subsequent alteration by titanium-rich hydrothermal fluids led to partial replacement of dumortierite I and andalusite by secondary fibrous to acicular purple dumortierite II enriched in Mg and Ti. During temperature decrease perthite developed in feldspars and at a still later stage, sericite partially replaced not only feldspars but also andalusite and both types of dumortierite along grain boundaries and cracks. Final alteration at very low temperatures caused formation of clay minerals at the expense of feldspars. According to mineral chemical analyses, the feldspars are represented by albite and K-feldspar with a low albite component. Biotite corresponds to annite and its subhedral shape and chemical composition point to magmatic crystallisation from a peraluminous melt derived from a crustal source. Coarse muscovite flakes contain 1.31-1.48 wt.% FeO and 0.56-0.70 wt.% TiO2. Their Na/(Na+K) ratios (0.08–0.09) prove a magmatic origin, whereas lower ratios in sericite (0.04–0.06) indicate formation during retrogression. Magmatic muscovite is in textural equilibrium with andalusite, also implying an igneous origin for the latter, which belongs to the S3 textural type of andalusite in felsic igneous rocks. Electron microprobe analyses clearly show a strong positive correlation between Si tetrahedral deficiency (3-Si) and the sum of Al+Ti, (R2= 0.85) in both types of dumortierite, implying Al replacement by Ti. However, Al replacement by Ti is not restricted to Al in the octahedral position, as generally accepted, but most probably also in the tetrahedral position. Distinct pleochroic colours in dumortierite are usually explained by the [Fe/(Fe+Ti)]x100 factor, but according to this study, elevated Mg contents stabilize red to violet coloured dumortierite at higher [Fe/(Fe+Ti)] x100 factors than those previously suggested.

Thermally activated growth of ternary oxyhydroxides on perovskites for efficient water oxidation.

Perovskite oxides are promising catalysts for water oxidation. Herein, we constructed a Sr3CoFeWO9 triple perovskite with Co, Fe, and W atoms sharing octahedral positions. Thermally activated growth of an amorphous FeCoW oxyhydroxide layer on this perovskite pre-catalyst greatly enhanced the oxygen evolution reaction (OER) activities, reducing overpotential at 10 mA cm-2geo by 115 mV. This highlights the benefits of compositional design and structural reconstruction for efficient electrocatalytic materials.

First-principles study of the magnetic anisotropy of ultrathin B-, C-, and N-doped FeCo films

Iron-based layered systems are of great interest because of their ability to tune effective material parameters such as magnetic anisotropy energy (MAE). The influence of the crystallographic structure of Fe, its thickness, and the presence of other layers above and below the Fe layer on magnetic parameters, such as the MAE of the studied system, is an intriguing and important topic from an application point of view. Here, we present a density functional theory (DFT) study of the magnetic anisotropy of nine-monolayer Fe, FeCo, and FeCo films with B, C, and N dopants placed in octahedral interstitial positions. The theoretical study is based on calculations using the full-potential local-orbital code FPLO and the generalized gradient approximation. The chemical disorder in the FeCo layers was modeled using the virtual crystal approximation. The structures of the layers were subjected to optimization of the geometry of the interlayer spacings and the neighborhood of the dopant sites. We determined the local magnetic moments and the excess charge at each layer position. We also identified the influence of dopant atoms on the magnetic properties of FeCo layers, such as magnetization and magnetic anisotropy.

Luminescence and photoconversion properties of Ce-doped Ca3Sc2Si3O12 crystal

This work is dedicated to investigation of the luminescent properties of the prospective photoconversion material based on the crystal of Ce3+ doped Ca3Sc2Si3O12 (CSSG) garnet. The GSSG:Ce crystal was grown using the micro-pulling-down (μPD) method. The CSSG:Ce crystal exhibited an intensive photoluminescence (PL) emission band with two sub-bands peaked at 504 and 545 nm, corresponding to 5d-4f (2F5/2;7/2) transitions. Furthermore, we have investigated also the formation of cerium multicenters in the GSSG:Ce crystal using analyses of the structure of Ce3+ photoluminescence emission and excitation spectra under excitation of the luminescence of this crystal by synchrotron radiation. The formation of Ce3+-multicenters in CSSG:Ce garnet is caused by the local inhomogeneity of the dodecahedral sites of garnet lattice due to localization of the hetero-valent Sc3+ and Si4+ cations in the octahedral and tetrahedral positions of the garnet host. The existence of Ce3+ multicenters resulted in a significant enhancement of the Ce3+ emission band in the red range and improving the performance of conventional YAG:Ce phosphor. The next task of our work was to evaluate the possibility of application of the GSSG:Ce crystal as a light phosphor-converter (pc) for white light-emitting diodes (WLEDs). In the frame of this task, we have successfully developed a prototype of WLED by employing the CSSG:Ce crystal as a phosphor-converter (pc) with blue 450 emitting LED as well as investigated the color characteristics of this pc-WLED.

Enhancing the thermal stability and recoverability of ZrCu-based shape memory alloys via interstitial doping

ZrCu-based shape memory alloys (SMAs) are regarded as emerging smart materials with high phase transformation temperatures. However, unfavorable thermal stability and poor strain recovery rate hinder commercial applications. Herein, these issues were addressed by doping interstitial B atoms, and the impacts of B content on microstructure, martensitic transformation behavior and properties of ZrCu-based SMAs were systematically investigated. It was shown that (Zr50Cu25Ni7.5Co17.5)99.98B0.02 SMAs possessed excellent thermal stability and shape memory effect. The change of martensitic transformation temperature for this alloy was 15.7 °C after several cycles. The shape recovery rate reached 92.5 % at 8 % compressive pre-strain, which was attributed to the de-twinning of (0 0 1) compound twins and the appearance of (1 1 1) type I twins. Furthermore, it was elucidated for the first time by first-principles calculations that B atoms were covalently bonded with Zr and Cu atoms occupying the octahedral interstitial positions in the B19′ and Cm phases. This study offers an available pathway to exploit efficient and advanced products.

Mössbauer and X-ray Diffraction Spectroscopy of High-Iron Bauxites from Kazakhstan.

The bauxite ores of Kazakhstan were analyzed using Mössbauer spectroscopy, X-ray diffraction and an X-ray fluorescence analysis. Experimental data on the structural-phase composition of bauxites were obtained, and the features of the iron-bearing minerals within them were revealed. The studied bauxites were high in iron. The magnetic part of bauxite was mainly represented by aluminohematite with a concentration of CAl = 3.34-5.73 at.%, alongside goethite in small amounts. The predominant phase in the bauxite samples was the alumina-bearing mineral gibbsite with a well-crystallized monoclinic lattice. The main siliceous mineral of bauxite is kaolinite, which showed distorted octahedral positions in a number of samples. Siderite amounts were found to vary in the range of 0-15 at.% in the present iron-bearing minerals. Ilmenite was also present in the bauxite of some deposits; anatase was found in all bauxites and was the final product of ilmenite decomposition in the weathering crust.