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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]

Branded for its potential electronic ferroelectricity, charge-ordered LuFe2O4 has a layered Fe triangular framework, whose topology is a source of degeneracy, both at the charge and spin levels. Here we present an in-depth characterization of LuFe2O4-hp, the high-pressure (hp) polymorph of LuFe2O4, using electron, x-ray, and neutron diffraction, combined with transport and magnetization measurements. We show that LuFe2O4-hp is characterized by a misfit-related monoclinic structure, accommodating a buckled triangular [Lu]∞ layer and two shifted adjacent rectangular [Fe]∞ planes belonging to a distorted rock salt-type layer. The release of the geometric frustration of the Fe magnetic lattice in the hp form leads to collinear antiferromagnetic ordering at TN=380K. Possible coexistence of charge and magnetic orders in this material opens research pathways for the design of tunable multifunctional devices using high-pressure techniques. [ABSTRACT FROM AUTHOR]

Combining functionalities in devices with high performances is a great challenge that rests on the discovery and optimization of materials. In this framework, layered oxides are attractive for numerous purposes, from energy conversion and storage to magnetic and electric properties. We demonstrate here the oxygen storage ability of ferroelectric LuFe2O4+x within a large x range (from 0 to 0.5) and its cycling possibility. The combination of thermogravimetric analyses, X-ray diffraction and transmission electron microscopy evidences a complex oxygen intercalation/de-intercalation process with several intermediate metastable states. This topotactic mechanism is mainly governed by nanoscale structures involving a shift of the cationic layers. The ferrite is highly promising because absorption begins at a low temperature (), occurs in a low oxygen pressure and the uptake of oxygen is reversible without altering the quality of the crystals. The storage/release of oxygen coupled to the transport and magnetic properties of LnFe2O4 opens the door to new tunable multifunctional applications. [ABSTRACT FROM AUTHOR]

The title compound is hydrothermally synthesized from aqueous mixtures of FePO4, Fe(NO3)3, and 2M aq. [ABSTRACT FROM AUTHOR]

Abstract: A LuFe2O4+δ sample, previously characterized by X-ray synchrotron and neutron diffraction, has been studied by electron microscopy techniques, in order to get a precise description of its micro- and nanostructures at room temperature. The X-ray synchrotron data vs. temperature show that the monoclinic distortion is associated with the charge ordering; this distortion results in elongated twinning domains, which enhance the complexity of the microstructural state at room temperature. The structural modulation associated with oxygen excess is observed in large domains inside a non modulated matrix, in contrast with the modulations associated with the charge ordering of the Fe2+ and Fe3+ species, which are mostly short-range. The investigation of the nature and density of defects in the sample shows that they are nano-scaled, preserving the regularity of the layer stacking mode, and limited to the formation of one- or two-units large stacking faults, associated with gliding mechanisms. Based on these observations, an original description of the LuFe2O4 ferrite structure, through puckered [LuO4]∞ sandwiching [Fe2]∞ layers, is proposed. [Copyright &y& Elsevier]

Apolycrystalline sample of LuFe204 has been investigated by means of powder synchrotron x-ray and neutron diffraction and transmission electron microscopy (TEM), along with Mössbauer spectroscopy and transport and magnetic properties. A monoelinic distortion is unambiguously evidenced, and the crystal structure is refined in the monoelinic C2/m space group [aM = 5.9563(1 )Å, bU = 3.4372(1)Å, cU = 8.6431(1)Å, &BGR; = 103.24(1)°]. Along with the previously reported modulations distinctive of the charge-ordering (CO) of the iron species, a new type of incommensurate order is observed, characterized by a vector q1→ = &AGR;1a→*M + &GGR;1c→ (with &AGR;1 = 0.55, &GGR;1 = 0.13). In situ heating TEM observations from 300 to 773 K confirm that the satellites associated with q{ vanish completely, only at a temperature significantly higher than the CO temperature. This incommensurate modulation has a displacive character and corresponds primarily to a transverse displacive modulation wave of the Lu cations position, as revealed by the high resolution, high angle annular dark tield scanning THM images and in agreement with synchrotron data refinements. Analyses of vacuum-annealed samples converge toward the hypothesis of a new ordering mechanism, associated with a tiny oxygen deviation from the 04 stoichiometry [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]

The magnetic properties of a polycrystalline sample of LuFe204 have been investigated by means of magnetization measurements combined with neutron scattering, between 1.5 and 300 K. Magnetic Bragg peaks appear below TN = 240 K and can be indexed in a monoclinic cell, using two propagation vectors, k1 = (0 2/3 0)m and k2 = (0 2/3 l/2)m [or k2 = (0 2/3 1/6)m], which correspond to either a ferromagnetic or an antiferromagnetic stacking of the [Fe204]oo bilayers. A modeling of possible magnetic structures evidences in addition that the coupling within a bilayer can be either ferromagnetic or antiferromagnetic. Results point out a complex magnetic ground state, which can be understood as coexisting antiferromagnetic and ferrimagnetic phases with a large axial magnetic anisotropy of about 8 meV. [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.