25 research outputs found

    Comparing the magnetic and magnetoelectric properties of the SmFe3(BO3)4 ferroborate single crystals grown using different solvents

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    SmFe3(BO3)4 single crystals have been grown from the bismuth trimolybdate and lithium tungstate-based melt–solutions. Samarium ferroborate single crystals were grown first from the lithium–tungstate flux. The magnetic and magnetoelectric properties of the synthesized crystals have been compared. It is shown that the SmFe3(BO3)4 ferroborate grown from the bismuth trimolybdate-based melt–solution contains impurities of Bi3+ ions (∼5% at.), which replace Sm3+ ions, while the SmFe3(BO3)4, ferroborate grown from the lithium tungstatebased melt–solution contains minor or zero amounts of such impurities. The magnetoelectric and magnetodielectric effects with the Bi3+ admixture appeared 1.5× stronger than in SmFe3(BO3)4; this is probably due to twinning

    Ecological and radiation safety of Central Asia

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    Previous calculations showed that in the Kyrgyz Republic 7.2% of the total population are exposed to the “radiation risk”, in the Republic of Kazakhstan - about 3%, in the Republic of Tajikistan - 1.7% and in the Republic of Uzbekistan - 0.3%. The number of radiation-contaminated territories in the Republics of Central Asia is equal: the Kyrgyz Republic contains about 132 million m3 of waste, the Republic of Tajikistan contains about 180 million m3 of waste, the Republic of Uzbekistan contains 640 million m3 of waste, and the Republic of Kazakhstan contains approximately 10,000 million m3 of waste. Total: in the four Republics of Central Asia, the total amount of radioactive waste is 10952 million m3. Taking as a basis the limited liability company “Vismut GmbH” from Germany, which carried out the reclamation of uranium tailings with a volume of 160 million m3 of tailings at a cost of about 8 billion euros for about 37 years. Using a thermodynamic approach, it is shown that the costs of reclamation of uranium tailings for the four Central Asian Republics will be 548 billion euros, and the duration will be about 40 years

    Chemical disorder reinforces magnetic order in ludwigite (Ni,Mn)(3)BO5 with Mn4+ inclusion

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    Crystals of ludwigite Ni2.14Mn0.86BO5 were synthesized by flux growth technique and contain Mn3+ and Mn4+. A possible mechanism of the manganese valence states stabilization has been proposed. The structural and magnetic characterization of the synthesized samples has been carried out in detail. The cations composition and Mn valence states of the crystal were determined using X-ray diffraction and EXAFS technique. The comparative analysis was carried out between the studied crystal and Ni2MnBO5 synthesized previously. Magnetic susceptibility measurements were carried out. The magnetic transition in the studied composition occurs at the 100 K temperature that is higher than in Ni2MnBO5 although the studied composition is more disordered. The calculations of the exchange integrals in the frameworks of indirect coupling model revealed strong antiferromagnetic interactions. The several magnetic subsystems existence hypothesis was supposed. The possible magnetic structure was suggested from the energies estimation for different ordering variants

    Computational Design of Radical Recognition Assay with the Possible Application of Cyclopropyl Vinyl Sulfides as Tunable Sensors

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    The processes involving the capture of free radicals were explored by performing DFT molecular dynamics simulations and modeling of reaction energy profiles. We describe the idea of a radical recognition assay, where not only the presence of a radical but also the nature/reactivity of a radical may be assessed. The idea is to utilize a set of radical-sensitive molecules as tunable sensors, followed by insight into the studied radical species based on the observed reactivity/selectivity. We utilize this approach for selective recognition of common radicals—alkyl, phenyl, and iodine. By matching quantum chemical calculations with experimental data, we show that components of a system react differently with the studied radicals. Possible radical generation processes were studied involving model reactions under UV light and metal-catalyzed conditions

    Synthesis of NdSc3(BO3)4 single crystals and study of its structure properties

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    Using the group method, single crystals of NdSc3(BO3)4 are grown from a melt solution and X-ray structural studies are performed. It is shown that at room temperature the NdSc3(BO3)4 crystal has a huntite-type structure with space group P3121. The temperature dependence of the heat capacity shows anomalous behaviour at Т ¼ 504 ± 1 K. This anomaly corresponds to a structural phase transition from R32 to P3121. It is known that a similar transition occurs in RFe3(BO3)4 crystals; an anomaly in the specific heat is also observed. Theoretical calculations are carried out from the first principles of the lattice dynamics of the crystal under study in a high-symmetry phase with the R32 space group. An unstable (soft) mode in the boundary point of Brillouin zone was found. It was determined that this structural instability is responsible for the structural displacement-type phase transition R32 / P3121

    Magnetic structure of Cu2MnBO5 ludwigite: thermodynamic, magnetic properties and neutron diffraction study

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    Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.We report on the thermodynamic, magnetic properties and the magnetic structure of ludwigite-type Cu2MnBO5. The specific heat, low-field magnetization and paramagnetic susceptibility were studied on a single crystal and combined with powder neutron diffraction data. The temperature dependence of the specific heat and the neutron diffraction pattern reveal a single magnetic phase transition at T = 92 K, which corresponds to the magnetic ordering into a ferrimagnetic phase. The cation distribution and the values and directions of magnetic moments of ions in different crystallographic sites are established. The magnetic moments of Cu2+ and Mn3+ ions occupying different magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their directions do not coincide with the directions of the principal crystallographic axes. The small value of the magnetic moment of copper ions occupying site 2a is indicative of partial disordering of the magnetic moments on this site. The magnetization measurements show a strong temperature hysteresis of magnetization, which evidences for field-dependent transitions below the phase transition temperature

    Crystal formation of Cu-Mn-containing oxides and oxyborates in bismuth-boron fluxes diluted by MoO3 and Na2CO3

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    The high-temperature crystallizing phases of fluxes (molten solutions) based on Bi2O3:MoO3=1:3 and diluted by Na2CO3, B2O3 (under varying of Na2CO3:B2O3) and CuO and Mn2O3 (0≤Mn2O3:CuO≤5) are studied. The conditions of the stable crystallization of Mn2+1-xCuxMoO4, Mn23+O3, Mn2+Mn23+O4, Mn2+1-xCuxMn3+BO4 and Mn2+2-xCuxMn3+BO5 have been found. The influence of MoO3 and Na2CO3 to the crystallization processes of Mn2+- and Mn3+-containing Mn2+1-xCuxMoO4 and Mn2+Mn23+O4 and Mn23+O3 are clarified. The occurrence of the chemical bonds of these types at the crystallization of Mn-heterovalent Mn2+1-xCuxMn3+BO4 and Mn2+2-xCuxMn3+BO5 oxyborates is studied. Single crystal growth techniques of these oxyborates are suggested. The results of structural and magnetic characterization of some discussed compounds are presented
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