New transition metal fluoride glasses isolated in the PbF2MtIIF2MtIIIF3 systems

New glasses have been prepared in the PbF₂M_t^IIF₂M_t^IIIF₃ systems (m_t^II = Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺; M_t^III = Fe³⁺, V³⁺, Cr³⁺, Ga³⁺). The extent of the vitreous area is shown in a PbF₂MnF₂FeF₃ diagram. Thermal properties have been measured for all samples. Some of these glasses are very transparent over a wide range of wavelengths (from 250–12 000 nm). The sixfold coordination of transition metal ions has been established by spectroscopic investigations. The structure of the glasses is discussed on the basis of a random corner-sharing of MF₆ octahedra.     

State of Fe3+ ion and Fe3+ −F− interaction in calcium fluorosilicate glasses

The state of Fe³⁺ ions and Fe³⁺ ?F^? interaction in calcium fluorosilicate glasses xCaF₂·(1- x)CaO·SiO₂) (0 ≤ x ≤ 0.3) containing a small amount of iron were investigated by ESR spectroscopy. Two resonances observed near g = 2.0 and g = 4.3 were assigned to dipole-dipole interacted Fe³⁺ ions and Fe³⁺ ions in a rhombic crystal field, respectively. The fraction of Fe³⁺ ions in a rhombic crystal field decreased and that of dipole-dipole interacted Fe³⁺ ions increased with increasing Fe₂O₃ content. It was found that the quantity of dipole-dipole interacted Fe³⁺ ions depends on the negative partial charge of fluorine ions and shows a maximum at 10 mol% CaF₂ (x = 0.2). The maximum is attributed to the largest difference between absolute values of the ionic potentials of ferric and fluorine ions which is caused by the smallest negative partial charge of flourine at 10 mol% CaF₂.     

Comparative characterization of defects formed by di-and trivalent metal dopants in KDP crystals and the structural mechanism of influence of impurities on face morphology

The structure of KDP crystals doped with trivalent (Al³⁺, Fe³⁺, Mn³⁺, V³⁺, and La³⁺) and divalent (Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) cations was simulated by minimizing the energy of atomic interactions. Three types of defects were revealed: isolated defect centers formed by M ³⁺ and Ni²⁺ ions, cluster chain centers formed by M ²⁺ ions with ionic radii exceeding 0.9 Å, and complex centers formed via the replacement of potassium ions by large Ba²⁺ dopants with the simultaneous replacement of some of the phosphorus atoms by silicon ones. The corresponding energies of defect formation are calculated. The surface morphology of the crystal faces is studied. The changes in morphology in the presence of M ³⁺ dopants are caused by their adsorption, whereas for M ²⁺ dopants, these changes are caused mainly by their incorporation into the crystal structure.     

Crystal structures of salicylideneguanylhydrazinium chloride and its copper(II) and cobalt(III) chloride complexes

The crystal structures of salicylideneguanylhydrazinium chloride hydrate hemiethanol solvate (I), salicylideneguanylhydrazinium trichloroaquacuprate(II) (II), and bis(salicylideneguanylhydrazino)cobalt(III) chloride trihydrate (III) are determined using X-ray diffraction. The structures of compounds I, II, and III are solved by direct methods and refined using the least-squares procedure in the anisotropic approximation for the non-hydrogen atoms to the final factors R = 0.0597, 0.0212, and 0.0283, respectively. In the structure of compound I, the monoprotonated molecules and chlorine ions linked by hydrogen bonds form layers aligned parallel to the (010) plane. In the structure of compound II, the salicylaldehyde guanylhydrazone cations and polymer chains consisting of trichloroaquacuprate(II) anions are joined by an extended three-dimensional network of hydrogen bonds. In the structure of compound III, the [Co(LH)₂]⁺ cations, chloride ions, and molecules of crystallization water are linked together by a similar network.     

Structural impact of iron ions on BaBiBO4 glasses: Spectroscopic and dielectric investigations

Transparent glasses of composition 10BaO.20Bi₂O₃.(70 ? x)B₂O₃.xFe₂O₃ (wt.%) where 0 ≤ x ≤ 2.0, were characterized by XRD and SEM. Physical, spectroscopic and dielectric properties were investigated. At higher dopant of Fe₂O₃, EPR results revealed that, the number of Fe³⁺ ions participate in the resonance is decreased by forming a new signal at g ≈ 3.015 due to increase of antiferromagnetic interaction of Fe³⁺ ions and/or formation of low spin Fe³⁺ ions in the glass matrix. With initial 0.5 wt.% doping of Fe₂O₃, less dense glass is formed with colloids of metallic Bi⁰ atoms. The absorption bands at 604 and 712 nm in F5 glass are ascribed to Bi⁰ and Bi⁺ radicals respectively. No characteristic Fe³⁺ absorption bands (spin-forbidden) are found. Fe²⁺ ions are increased at higher concentration of Fe₂O₃. Higher concentration of Fe₂O₃ is favorable for BO₂O^?, BO₃, BiO₆ and FeO₆ symmetry unit leads to low band gap and high Urbach energy. By doping of Fe₂O₃ the dielectric parameters like dielectric constant (ε′), loss (tanδ and ac electrical conductivity (σ_ac) are found to increase.     

Mössbauer spectroscopic study of gamma-ray irradiated potassium phosphate glasses

A Mössbauer spectroscopic study was performed to investigate the effect of γ-ray irradiation on the formation of non-bridging oxygens in the potassium phosphate glasses denoted by the formula x K₂O · (100 ? x)P₂O₅ · 7 Fe₂O₃ (0 ? x ? 50 mol.%). Mössbauer spectra for these glass samples consisted of two kinds of doublets due to Fe²⁺ and Fe³⁺ ions of octahedral symmetries. Only small changes occurred in the Mössbauer parameters as a result of irradiation at room temperature in a dry nitrogen atmosphere, except for the decrease in the absorption area for the Fe²⁺ ions. The decrease in the absorption area was attributed to the electron transfer from the Fe²⁺ ions to the neighboring oxygens. Thermal annealing experiments for a few non-irradiated glass samples indicated that the decrease in the absorption area was confirmed to be due to γ-rays rather than heating during the irradiation.     

Iron redox equilibrium, structure and properties of zinc iron phosphate glasses

Iron redox equilibrium, structure and properties were investigated for the 10ZnO-30Fe₂O₃-60P₂O₅ (mol%) glasses melted at different temperatures. The structure and valence states of the iron ions in these glasses were investigated using Mössbauer spectroscopy, Raman spectroscopy and differential thermal analysis. Mössbauer spectroscopy indicated that the concentration of Fe²⁺ ions increased in the 10ZnO-30Fe₂O₃-60P₂O₅ (mol%) glass with increasing melting temperature. The Fe²⁺/(Fe²⁺ + Fe³⁺) ratio increased from 0.18 to 0.38 as the melting temperature increased from 1100 to 1300 °C. The measured isomer shifts showed that both Fe²⁺ and Fe³⁺ ions are in octahedral coordination. It was shown that the dc conductivity strongly depended on Fe²⁺/(Fe²⁺ + Fe³⁺) ratio in glasses. The dc conductivity increases with the increasing Fe²⁺ ion content in these glasses. The conductivity arises from the polaron hopping between Fe²⁺ and Fe³⁺ ions which suggests that the conduction is electronic in nature in zinc iron phosphate glasses.     

Iron environment in calcium-soda-phosphate glasses and vitroceramics

The structure of calcium-soda-phosphate glasses and vitroceramics with relatively high iron content was investigated by X-ray diffraction, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. The X-ray diffraction analysis proves the vitreous state of the as prepared samples and the development of crystalline phases in the annealed samples. The ferric ions disposed in sites that give rise to the absorption line with g_ef ≈ 4.3 in the EPR spectra of vitreous samples are not more evidenced in the spectra of the annealed samples, from which only of a symmetric and narrowed line with g_ef ≈ 2 is recorded. The room temperature ⁵⁷Fe Mössbauer spectra both of glass and vitroceramic samples consist of two quadrupole doublets characteristic for octahedral sites of Fe²⁺ and Fe³⁺ ions. The isomer shift for glass samples decreases and for vitroceramic samples increases with the iron oxide content.     

Simulation of defects formed by cations of bivalent and trivalent metals in the structure of potassium dihydrogen phosphate: A computational technique

This paper reports on the results of crystal chemical analysis and computer simulation of the defect structure of potassium dihydrogen phosphate (KDP) containing impurities of bivalent and trivalent metals. It is shown that these impurities can form defect centers of different types: isolated centers formed by M ³⁺ and Ni²⁺ ions and, in part, by Co²⁺ ions at interstitial sites, chains composed of M ²⁺ impurity ions with radii from ≈0.65 to ≈1.1 Å, and centers created through the substitution of large-sized bivalent cations for potassium ions either with the formation of additional potassium vacancies or through the heterovalent isomorphism mechanism. The calculations are performed using different-type interatomic interaction potentials, and a comparative analysis of the results obtained is carried out.     

Local structure and medium range ordering of tetrahedrally coordinated Fe3+ ions in alkali–alkaline earth–silica glasses

Tetrahedral iron (III) environments in alkali–alkaline earth–silica glasses have been studied as functions of alkali and alkaline earth cation type and Fe₂O₃ content using photoluminescence and optical absorption spectroscopies. The luminescence band centered at 13 000–15,500 cm⁻¹ is attributed to the ⁴T₁(G) → ⁶A₁(S) transition of tetrahedral Fe³⁺ ions. This band has Gaussian linewidths of 1500–3000 cm⁻¹ but linewidths exhibit no clear compositional dependency. Ligand field strength, 10Dq, and the Racah parameters B and C are consistent with tetrahedral Fe³⁺ and here for the first time their linear variation with the alkali/alkaline earth ratio of ionic radii, cation field strengths or individual oxide basicities is demonstrated. This is attributed to the effects of near-neighbor cations on length and covalency of Fe³⁺–O bonds and on host glass structure. Alkali cations stabilize Fe³⁺ ions in tetrahedral coordination; stabilization increases linearly with increasing alkali ionic radius and therefore with decreasing alkali field strength. The role of alkaline earth cations in Fe³⁺ stabilization in these glasses is not clear, although their effect is the inverse of that of the alkalis. The structural behavior of Fe³⁺ is defined as selective, reflecting its strong local ordering effects.     

A new Pb<Superscript>II</Superscript>(ethylenediaminetetraacetate) coordination polymer with a two-dimensional layer structure

A new Pb^II?edta^4– coordination polymer, Pb₂(edta)(H₂O)_0.76 (edta^4– = ethylenediaminetetraacetate) was synthesized under hydrothermal condition. Single crystal X-ray analysis reveals that it represents a novel two-dimensional (2D) Pb²⁺–edta^4– layer structure with a (4,8²)-topology. Each edta^4– ligand employs its four carboxylate O and two N atoms to chelate one Pb^II atom (hexa-coordinated) and connects five Pb^II atoms (ennea-coordinated) via its four carboxylate groups to form 2D layer framework. Adjacent layers are packed into the overall structure through vander Waals interactions.     

Crystal structure and magnetic properties of the LaCo0.5Fe0.5O3 perovskite

The magnetic and crystal structures of the LaCo_0.5Fe_0.5O₃ perovskite are investigated. It is established that the unit cell of this compound at room temperature is characterized by rhombohedral distortions. As the temperature decreases, the compound undergoes a structural phase transition from the rhombohedral phase to the orthorhombic phase in the temperature range 200–300 K. The LaCo_0.5Fe_0.5O₃ perovskite has an antiferromagnetic structure with the G _z spatial orientation of the antiferromagnetic vector. The magnetic properties of the LaCo_0.5Fe_0.5O₃ perovskite are interpreted within a model according to which the ground state of Co³⁺ ions is a low-spin state and the existence of the weak ferromagnetic component is associated with the exchange interactions between the Fe³⁺ ions.     

Predicting a major role of surface spins in the magnetic properties of ferrite nanoparticles

Room‐temperature magnetization hysterisis measurements were conducted on Mn_0.5Zn_0.5Gd_xFe_(2‐x)O₄ ferrite nanoparticles, with x = 0, 0.5, 1.0, 1.5. The structure of this ferrite is normal spinel where the added of Gd³⁺ ions occupied the octahedral sites and replaces Fe³⁺ ions. The saturation magnetization was found to increase with the initial addition of the Gd³⁺ ions followed by a sharp decrease with further addition of Gd³⁺ ions. The Curie temperature was found to increase up to Gd³⁺ concentration of x = 1.0, and then decreases at x = 1.5. These results were attributed to the surface spins. Because the size of Gd³⁺ ions is larger than that of Fe³⁺ ions, the substitution of Fe³⁺ ions with the Gd³⁺ ions results in surface disorder which results in surface spins. A core‐shell magnetization model was introduced where several factors were combined to explain our results. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ikranite: Composition and structure of a new mineral of the eudialyte group

The crystal structure of a new mineral, ikranite, of the eudialyte group discovered in the Lovozero massif (the Kola Peninsula) was established by X-ray diffraction analysis. The crystals belong to the trigonal system and have the unit-cell parameters a = 14.167(2) Å, c = 30.081(2) Å, V = 5228.5 Å 3, sp. gr. R3m. Ikranite is the first purely ring mineral of the eudialyte group (other minerals of this group contain ring platforms of either tetrahedral or mixed types). It is also the first representative of the eudialyte group where Fe³⁺ prevail over Fe²⁺ ions.     

Synthesis and crystal structure of new phosphate NaFe 4 2+ Fe 3 3+ [PO4]6

New sodium iron orthophosphate NaFe ₄ ²⁺ Fe ₃ ³⁺ [PO₄]₆ was synthesized by the hydrothermal method. The crystal structure (sp. gr. $P\bar 1$ ) was established by the heavy-atom method, with the exact chemical formula of the compound being unknown; R _hkl = 0.0492, R _whkl = 0.0544, S = 0.52. The new compound is analogous to iron phosphate Fe ₃ ²⁺ Fe ₄ ³⁺ [PO₄]₆ studied earlier. However, these two compounds differ in the Fe²⁺ and Fe³⁺ contents, because Na⁺ ions in the new compound are located at the centers of symmetry not occupied earlier.     

Neutron and X-ray diffraction study of superstructure and localized magnetic moments in Cu0.5Fe0.5Cr2S4 and Cu0.5In0.5Cr2S4 compounds

The superstructure parameters for the Cu_0.5Fe_0.5Cr₂S₄ and Cu_0.5In_0.5Cr₂S₄ compounds have been determined by neutron and X-ray diffraction. The localized magnetic moments in different sublattices measured for Cu_0.5Fe_0.5Cr₂S₄ are equal to 3.06 ± 0.17 μB for Fe³⁺ ions in the A-site and 2.76 ± 0.22 μB for Cr³⁺ ions in the B-site (Cu⁺ possess no magnetic moment), which are much less than the magnetic moments for the ions in the purely ionic state.     

Cation distribution in the structure of titanium-containing ludwigite

The crystal structure of natural titanium-containing ludwigite has been refined. The unit-cell parameters are a = 9.260 ± 0.002 Å, b = 12.294± 0.002 Å, c = 3.0236± 0.0005 Å, sp. gr. Pbam, and R = 0.0288. The observed cation distribution over the M1-M4 positions corresponds to the structural formula (Mg_0.5)(Mg_1.0)(Mg_0.338Fe _0.162 ²⁺ )(Fe _0.47 ³⁺ Ti _0.21 ⁴⁺ Mg _0.15 ²⁺ Al _0.10 ³⁺ Fe _0.07 ²⁺ (BO₃)O₂. Highly charged titanium ions in the M4 position are balanced mainly with magnesium and not with divalent iron ions.     

Mössbauer spectra in the xNa2O·(1 − x − y)B2O3·yFe2O3 glass system

A Mössbauer spectroscopic study is made on xNa₂O·(1 ? x ? 7)B₂O₃·yFe₂O₃; 0.045 ? x ? 0.405 and y = 0.05, 0.10 and 0.15 samples quenched from the melt. The presence of two quadrupole doublets indicates that an amphoteric cation like Fe³⁺ occupies both the tetrahedral “network forming” and the octahedral “network modifying” sites in the glass structure. The observed variations of isomer shift and quadrupole splitting with the values of x are similar to the ones found earlier in lead borates but different from those observed earlier in soda borates and other alkali alumino borates. In samples with smaller values of x, an additional devitrified magnetic phase of Fe₂O₃ is seen. The distribution of Fe³⁺ ions in different sites and phases is also discussed.     

The Fe<Superscript>2+</Superscript>/Fe<Superscript>3+</Superscript> ratio in natural and heat-treated iron-rich eudialytes

The structures of natural iron-rich eudialyte (specimen 3458 from the Khibiny massif, the Kola Peninsula) and two heat-treated samples of this mineral calcined at 700 and 800°C were determined by X-ray diffraction. The trigonal unit-cell parameters (sp. gr. R3m) are as follows: a = 14.2645(1) Å, c = 29.9635(5) Å; a = 14.1307(1) Å, c = 30.1229(3) Å; a = 14.1921(2) Å, c = 30.2417(5) Å, respectively. It was found that Fe³⁺ ions in the calcined eudialytes, as well as impurities in the starting specimen, occupy the square-pyramidal Fe³⁺(V) sites, whereas Fe²⁺ ions are in the planar-tetragonal Fe²⁺(IV) sites.     

Specific features of the substitution of Fe<Superscript>3+</Superscript> impurity ions for Zr<Superscript>4+</Superscript> in NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The EPR spectra of Fe³⁺ impurity ions in NaZr₂(PO₄)₃ single crystals at 300 K are investigated, and the spin Hamiltonian of these ions is determined. A comparative analysis of the spin-Hamiltonian and crystal-field tensors is performed using the maximum invariant component method. It is demonstrated that Fe³⁺ impurity ions substitute for Zr⁴⁺ ions with local compensator ions located in cavities of the B type. It is revealed that the invariant of the spin-Hamiltonian tensor B₄ and the crystal-field tensor V ₄ ⁴⁴ depend substantially on the mutual arrangement of ions in the first and second coordination spheres. The corresponding dependences are analyzed.