Precursor synthesis and properties of iron and lithium co-doped cadmium oxide

Lithium and iron co-doped cadmium oxide Cd0.9(Li1-xFex)0.1O (x = 0.1, 0.3, 0.5, 0.7) with NaCl structure has been synthesized using formate of the composition Cd0.9(Li1-xFex)0.1(HCOO)2·2H2O as a precursor. The NMR spectroscopy results demonstrate that the structure of lithium-doped cadmium oxide appears to have impurity centers only of one type. All the synthesized samples show a metal-like conductivity as indicated by the growth of their electrical resistance with temperature increasing in the interval 78–330 K. The study of the magnetic properties of the Cd0.9(Li1-xFex)0.1O samples at 5 and 300 K revealed that they are ferromagnets, whose saturation magnetization increases with the iron concentration both at low and room temperature reaching the maximal values in the samples with a Li and Fe concentration of 3 and 7 at.%, respectively. An enhancement of the iron concentration in Cd0.9(Li1-xFex)0.1O from x = 0.5 to x = 0.7 leads to an abrupt growth of the magnetization from 0.30 to 1.94 emu/g at 5 K and from 0.16 to 1.03 emu/g at 300 K. Iron doping with a simultaneous reduction of the lithium concentration also results in an increase of the band gap. The properties of these compounds are explained on the basis of first-principles calculations of their band structure.The research was carried out within the state assignment of the Ministry of Education and Science of the Russian Federation (theme “Spin”, No. AAAA-A18-118020290104-2), supported in part by “Electrical Engineering” Shanghai class 2 Plateau Discipline, the Government of the Russian Federation (Decree No. 211, Contract No. 02.A03.21.0006), “Electrical Engineering” Shanghai class 2 Plateau Discipline and the National Natural Science Foundation of China (NSFC, Nos. 12074242, 51862032). Absorption spectra were obtained using the equipment at the Center for Joint Use "Spectroscopy and Analysis of Organic Compounds" at the Postovsky Institute of Organic Synthesis, UB RAS. The optical measurements were carried out in accordance with the scientific and research plans and state assignment of the Institute of Solid State Chemistry, UB RAS (Grant No. AAAA-A19-119031890025-9). E.V.C. acknowledges funding by Saint Petersburg State University project for scientific investigations (ID No. 73028629). TPeer reviewe

Landscape science: a Russian geographical tradition

The Russian geographical tradition of landscape science (landshaftovedenie) is analyzed with particular reference to its initiator, Lev Semenovich Berg (1876-1950). The differences between prevailing Russian and Western concepts of landscape in geography are discussed, and their common origins in German geographical thought in the late nineteenth and early twentieth centuries are delineated. It is argued that the principal differences are accounted for by a number of factors, of which Russia's own distinctive tradition in environmental science deriving from the work of V. V. Dokuchaev (1846-1903), the activities of certain key individuals (such as Berg and C. O. Sauer), and the very different social and political circumstances in different parts of the world appear to be the most significant. At the same time it is noted that neither in Russia nor in the West have geographers succeeded in specifying an agreed and unproblematic understanding of landscape, or more broadly in promoting a common geographical conception of human-environment relationships. In light of such uncertainties, the latter part of the article argues for closer international links between the variant landscape traditions in geography as an important contribution to the quest for sustainability

Zinc glycolate Zn(OCH2CH2O): Synthesis and structure, spectral and optical properties, electronic structure and chemical bonding

This article presents new findings obtained from the study of formation conditions, crystal structure, thermal, spectral, optical properties and electronic band structure of zinc glycolate Zn(OCH2CH2O). This compound was synthesized by heating the solutions of zinc formate Zn(HCOO)2·2H2O in ethylene glycol (A) or in a mixture of ethylene glycol and distilled water (B). The crystal structure of Zn(OCH2CH2O) has been studied using the X-ray powder diffraction method. It is shown that the crystal structure is built via zigzag joining of [Zn4O12C8H16] tetracycles with the tetrahedrally coordinated zinc (ZnO4). Zinc atoms inside the tetracycles and the tetracycles themselves are interconnected with oxygen bridges. Complex anions OCH2CH2O2- are bonded to zinc atoms by chelation. The unit cell parameters of Zn(OCH2CH2O) are as follows: the tetragonal structure, space group I41/a (88−2), Z = 16, a = b = 11.08673(9) Å, c = 11.5902(1) Å, V = 1424.62(2) Å3. The IR and Raman spectra of Zn(OCH2CH2O) correlate fully with the results of structural analysis. Under UV excitation, the luminescence spectra of Zn(OCH2CH2O) samples synthesized following the methods (A) and (B) are characterized by emission maxima at 460 nm (blue luminescence) and 540 nm (yellow-green luminescence), respectively. Yellow-green luminescence is due to the presence of an admixture of zinc oxide nanoparticles of size 10 nm in the sample. The electron density functional method is employed to study the electronic band structure and chemical bonding in Zn(OCH2CH2O). It is shown that the 3dZn orbitals are covalently bonded to 2pO orbitals so that an octagon is formed, where the zinc atoms of four neighboring ZnO4 tetrahedrons are linked through their vertices. The feasibility of synthesizing a layered structure of Zn(OCH2CH2O) is analyzed on the basis of ab initio calculations and Voigt-Reuss-Hill theory.The X-ray study was carried out at the Multiple-Access Center for X-ray Structure Analysis at the Institute of Solid State Chemistry, UB RAS. The UV-Vis spectra were recorded using the equipment of the Multiple-Access Center for Spectroscopy and Analysis of Organic Compounds at the Postovsky Institute of Organic Synthesis, UB RAS. This work was carried out in accordance with the scientific and research plans and as defined in the state assignment for the Institute of Solid State Chemistry, UB RAS (grant No. AAAA-A19–119031890025-9). The electronic structure calculations were performed with the URAN cluster in the Institute of Mathematics and Mechanics, UB RAS. E.V.C. acknowledges support from Saint Petersburg State University (grant No. ID 90383050).Peer reviewe

Synthesis, Structure, and Properties of EuLnCuSe₃ (Ln = Nd, Sm, Gd, Er)

EuLnCuSe3 (Ln = Nd, Sm, Gd, Er), due to their complex composition, should be considered new materials with the ability to purposefully change the properties. Samples of the EuLnCuSe3 were prepared using Cu, rare earth metal, Se (99.99%) by the ampoule method. The samples were obtained by the crystallization from a melt and annealed at temperatures 1073 and 1273 K. The EuErCuSe3 crystal structure was established using the single-crystal particle. EuErCuSe3 crystallizes in the orthorhombic system, space group Cmcm, KCuZrS3 structure type, with cell parameters a = 4.0555 (3), b = 13.3570 (9), and c = 10.4602 (7) Å, V = 566.62 (6) Å3. In structure EuErCuSe3, erbium ions are coordinated by selenium ions in the octahedral polyhedron, copper ions are in the tetrahedral coordination, europium ions are between copper and erbium polyhedra layers and are coordinated by selenium ions as two-cap trigonal prisms. The optical band gap is 1.79 eV. At 4.7 K, a transition from the ferrimagnetic state to the paramagnetic state was detected in EuErCuSe3. At 85 and 293 K, the compound is in a paramagnetic state. According to XRPD data, EuLnCuSe3 (Ln = Nd, Sm, Gd) compounds have a Pnma orthorhombic space group of the Eu2CuS3 structure type. For EuSmCuSe3, a = 10.75704 (15) Å, b = 4.11120 (5) Å, c = 13.37778 (22) Å. In the series of EuLnCuSe3 compounds, the optical band gap increases 1.58 eV (Nd), 1.58 eV (Sm), 1.72 eV (Gd), 1.79 eV (Er), the microhardness of the 205 (Nd), 210 (Sm), 225 (Gd) 235 ± 4 HV (Er) phases increases, and the thermal stability of the phases increases significantly. According to the measurement data of differential scanning calorimetry, the EuNdCuSe3 decomposes, according to the solid-phase reaction T = 1296 K, ΔH = 8.2 ± 0.8 kJ/mol. EuSmCuSe3 melts incongruently T = 1449 K, ΔH = 18.8 ± 1.9 kJ/mol. For the EuGdCuSe3, two (Tα↔β = 1494 K, ΔHα↔β = 14.8 kJ/mol, Tβ↔γ = 1530 K, ΔHβ↔γ = 4.8 kJ/mol) and for EuErCuSe3 three polymorphic transitions (Tα↔β = 1561 K, ΔHα↔β = 30.3 kJ/mol, Tβ↔γ = 1579 K, ΔHβ↔γ = 4.4 kJ/mol, and Tγ↔δ = 1600 K, ΔHγ↔δ = 10.1 kJ/mol). The compounds melt incongruently at the temperature of 1588 K, ΔHmelt = 17.9 ± 1.8 kJ/mol and 1664 K, ΔHmelt = 25.6 ± 2.5 kJ/mol, respectively. Incongruent melting of the phases proceeds with the formation of a solid solution of EuSe and a liquid phase

Synthesis and characterisation of new MO(OH)2 (M = Zr, Hf) oxyhydroxides and related Li2MO3 salts

Two new solid MO(OH)2 (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P21/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling

Structural and Magnetic Transitions in CaCo3V4O12\mathrm{CaCo_{3}V_{4}O_{12}} Perovskite at Extreme Conditions

We investigated the structural, vibrational, magnetic, and electronic properties of the recently synthesized CaCo$_{3}$V$_{4}$O$_{12}$ double perovskite with the high-spin (HS) Co$^{2+}$ ions in a square-planar oxygen coordination at extreme conditions of high pressures and low temperatures. The single-crystal X-ray diffraction and Raman spectroscopy studies up to 60 GPa showed a conservation of its cubic crystal structure but indicated a crossover near 30 GPa. Above 30 GPa, we observed both an abnormally high “compressibility” of the Co–O bonds in the square-planar oxygen coordination and a huge anisotropic displacement of HS-Co$^{2+}$ ions in the direction perpendicular to the oxygen planes. Although this effect is reminiscent of a continuous HS → LS transformation of the Co$^{2+}$ ions, it did not result in the anticipated shrinkage of the cell volume because of a certain “stiffing” of the bonds of the Ca and V cations. We verified that the oxidation states of all the cations did not change across this crossover, and hence, no charge-transfer effects were involved. Consequently, we proposed that CaCo$_{3}$V$_{4}$O$_{12}$ could undergo a phase transition at which the large HS-Co$^{2+}$ ions were pushed out of the oxygen planes because of lattice compression. The antiferromagnetic transition in CaCo$_{3}$V$_{4}$O$_{12}$ at 100 K was investigated by neutron powder diffraction at ambient pressure. We established that the magnetic moments of the Co$^{2+}$ ions were aligned along one of the cubic axes, and the magnetic structure had a 2-fold periodicity along this axis, compared to the crystallographic one

New Antiferromagnetic Perovskite CaCo₃V₄O₁₂ Prepared at High-Pressure and High-Temperature Conditions

A new perovskite, CaCo²⁺₃V⁴⁺₄O₁₂, has been synthesized at high-pressure and high-temperature (HP-HT) conditions. The properties of this perovskite were examined by a range of techniques. CaCo₃V₄O₁₂ was found to adopt a double-perovskite cubic lattice [<i>a</i> = 7.3428(6) Å] with <i>Im</i>3̅ symmetry. We have established that this new perovskite is stable at ambient conditions, and its oxidation and/or decomposition at ambient pressure begins above 500 °C. It undergoes an abrupt antiferromagnetic transition around 98 K. Electrical resistivity data suggest semimetallic conductivity in the temperature range of 1.6–370 K. We have established that the Co²⁺ ions in CaCo₃V₄O₁₂ are in the high-spin state with a sizable orbital moment, even though their square-planar oxygen coordination could be more suitable for the low-spin state, which is prone to Jahn–Teller distortion. Electrical resistivity curves also exhibit a distinct steplike feature around 100 K. CaCo₃V₄O₁₂ is a first example of perovskite in which the sites A′ are fully occupied by Co²⁺ ions, and hence its synthesis opens the door to a new class of double perovskites, ACo₃B₄O₁₂, that may be derived by chemical substitution of the A sublattice by lanthanides, sodium, strontium, and bismuth and by other elements and/or of the B sublattice by some other transition metals

Structural and Vibrational Properties of the Ordered Y₂CaGe₄O₁₂ Germanate: A Periodic Ab Initio Study

DFT calculations with six LDA, GGA, and hybrid functionals have been performed using the CRYSTAL09 code to describe the crystal structure and vibrational spectra of Y₂CaGe₄O₁₂ cyclotetragermanate, a new optical host. Two space groups <i>P</i>4/<i>nbm</i> and <i>Cmme</i> have been considered. The former corresponds to a mixed (0.5 Ca + 0.5 Y) distribution at the octahedral sites found from the results of Rietveld refinement of room temperature powder XRD pattern; the latter refers to the model of crystallographically nonequivalent calcium and yttrium atomic setting in distorted oxygen octahedrons. The most accurate geometry description has been obtained with the WC1LYP and PBE (<i>n</i> = 6) hybrid functionals, while the B3LYP calculation provides the best agreement between the recorded infrared and Raman spectra and their computed counterparts. Assignments of most of the observed bands to vibrational modes are given. The comparison between calculated and experimental frequencies shows a general good agreement for the spectra below 600 cm^–1. The relationship between selected infrared bands and Raman lines, internal vibrations of the [Ge₄O₁₂] unit, and external modes is briefly discussed