Search

A series of CuMnMO (M = Mg, Al; x = 0-0.08) samples was prepared using the low-temperature hydrothermal method. Crednerite-type materials are obtained for a low level of substitution, i.e. up to x = 0.08, and transmission electron microscopy observations indicate that the average crystallite size decreases with an increase in x. The evolution of unit cell parameters in function of x, from Rietveld refinements using X-ray powder diffraction data, presents a distinct behaviour for both series, but corresponds in both cases to a regularisation of the triangular network in the ( a, b) plane. The investigation of the structural, thermal and magnetic properties reveals that the substitution has a significant role on the magnetism in CuMnMO (M = Mg, Al). It was found that the Mg and Al substitution on the Mn site leads to a small increase in the magnetisation values at low temperature, although the particle size decreases, which can be related to a release of magnetic frustration. [ABSTRACT FROM AUTHOR]

Marine shells are a natural, cheap, abundant and renewable resource, which can be used to produce useful materials, such as for the construction industry. The present study focuses on the transformation of Mya arenaria exoskeletons from the Black Sea into calcium hydroxide by using low-temperature hydrothermal synthesis. In contrast with other methods, this energy-saving process does not involve calcination of shells prior to the hydrothermal treatment. XRD results show the formation of calcium hydroxide with preferential orientation and interesting atypical morphology, which is strongly influenced by the composition of the reaction medium. [ABSTRACT FROM AUTHOR]

In this study, we report the growth and comprehensive spectroscopic analysis of TmF 3 -doped CaF 2 crystals, grown using the vertical Bridgman method. The optical absorption and photoluminescence properties of both trivalent (Tm 3+ ) and divalent (Tm 2+ ) thulium ions were investigated. Optical absorption spectra in the UV-VIS-NIR range reveal characteristic transitions of Tm 3+ ions, as well as weaker absorption bands corresponding to Tm 2+ ions. The Judd-Ofelt (JO) formalism was applied to determine the intensity parameters Ω 2 , Ω 4 , and Ω 6 , which were used to calculate radiative transition probabilities, branching ratios, and radiative lifetimes for the Tm 3+ ions. The emission spectra showed concentration-dependent quenching effects, with significant emissions observed for the concentration of 0.1 mol% TmF 3 under excitation at 260 nm and 353 nm for Tm 3 + ions and at 305 nm for Tm 2+ ions. A new UV emission associated with divalent Thulium is reported. The results indicate that higher TmF 3 concentrations lead to increased non-radiative energy transfer, which reduces luminescence efficiency. These findings contribute to the understanding of the optical behavior of Tm-doped fluoride crystals, with implications for their application in laser technologies and radiation dosimetry.

Iron phosphate materials have attracted a lot of attention due to their potential as cathode materials for lithium-ion rechargeable batteries. It has been shown that lithium insertion or extraction depends on the Fe mixed valence and reduction or oxidation of the Fe ions' valences. In this paper, we report a new synthesis method for the Fe 3 (PO 3 OH) 4 (H 2 O) 4 mixed valence iron phosphate. In addition, we perform temperature-dependent measurements of structural and physical properties in order to obtain an understanding of electronic-structural interplay in this compound. Scanning electron microscope images show needle-like single crystals of 50 μm to 200 μm length which are stable up to approximately 200 °C, as revealed by thermogravimetric analysis. The crystal structure of Fe 3 (PO 3 OH) 4 (H 2 O) 4 single crystals has been determined in the temperature range of 90 K to 470 K. A monoclinic isostructural phase transition was found at ~213 K, with unit cell volume doubling in the low temperature phase. While the local environment of the Fe 2+ ions does not change significantly across the structural phase transition, small antiphase rotations occur for the Fe 3+ octahedra, implying some kind of electronic order. These results are corroborated by first principle calculations within density functional theory, which also point to ordering of the electronic degrees of freedom across the transition. The structural phase transition is confirmed by specific heat measurements. Moreover, hints of 3D antiferromagnetic ordering appear below ~11 K in the magnetic susceptibility measurements. Room temperature visible light absorption is consistent with the Fe 2+ /Fe 3+ mixed valence.