New La/Zn substituted strontium ferrites Sr(2 −x)La x [Fe(2 − x)Zn x ]O5, (0 ≤ x ≤ 0.3) with brownmillerite- type structure are obtained and studied via X-ray phase analysis and Mössbauer spectroscopy. Depending on the conditions of synthesis, substituting Zn2+ cations can either mainly occupy tetrahedral positions in a brownmillerite structure, or be uniformly distributed between the tetrahedral and octahedral positions. It is shown that they are reversibly oxidized by atmospheric oxygen at elevated temperatures.

Highly homogeneous mullite-type solid solutions Bi2Fe(4-x)CrxO9 (x = 0.5, 1, 1.2) were synthesized using a soft chemistry technique followed by a solid-state reaction in Ar. The crystal structure of Bi2Fe3CrO9 was investigated using X-ray and neutron powder diffraction, transmission electron microscopy and (57)Fe Mössbauer spectroscopy (S.G. Pbam, a = 7.95579(9) Å, b = 8.39145(9) Å, c = 5.98242(7) Å, RF(X-ray) = 0.022, RF(neutron) = 0.057). The ab planes in the structure are tessellated with distorted pentagonal loops built up by three tetrahedrally coordinated Fe sites and two octahedrally coordinated Fe/Cr sites, linked together in the ab plane by corner-sharing forming a pentagonal Cairo lattice. Magnetic susceptibility measurements and powder neutron diffraction show that the compounds order antiferromagnetically (AFM) with the Néel temperatures decreasing upon increasing the Cr content from TN ∼ 250 K for x = 0 to TN ∼ 155 K for x = 1.2. The magnetic structure of Bi2Fe3CrO9 at T = 30 K is characterized by a propagation vector k = (1/2,1/2,1/2). The tetrahedrally coordinated Fe cations form singlet pairs within dimers of corner-sharing tetrahedra, but spins on the neighboring dimers are nearly orthogonal. The octahedrally coordinated (Fe,Cr) cations form antiferromagnetic up-up-down-down chains along c, while the spin arrangement in the ab plane is nearly orthogonal between nearest neighbors and collinear between second neighbors. The resulting magnetic structure is remarkably different from the one in pure Bi2Fe4O9 and features several types of spin correlations even on crystallographically equivalent exchange that may be caused by the simultaneous presence of Fe and Cr on the octahedral site.

Composite electrode materials based on LiFeBO3 are synthesized under different conditions and studied as the cathodic materials for lithiumion batteries. Composites with different degrees of iron oxidation are synthesized by annealing in a closed system with the use of metal-oxide getters. Based on the results of cyclic voltammetry and galvanostatic cycling of samples with different Fe(II) contents, it is concluded that the surface composition is the determining factor for applicability of materials to reversible processes of inter-calation-deintercalation.

A novel anion-deficient perovskite-based compound, Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13), was synthesized via the citrate-based route. This compound is an n = 5 member of the AnBnO(3n-2) homologous series with unit-cell parameters related to the perovskite subcell a(p)≈ 4.0 Å as a(p)√2 ×a(p)× 5a(p)√2. The crystal structure of Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13) consists of quasi-2D perovskite blocks with a thickness of three octahedral layers separated by the 1/2[110](1[combining macron]01)(p) crystallographic shear (CS) planes, which are parallel to the {110} plane of the perovskite subcell. The CS planes transform the corner-sharing octahedra into chains of edge-sharing distorted tetragonal pyramids. Using a combination of neutron powder diffraction, (57)Fe Mössbauer spectroscopy and atomic resolution electron energy-loss spectroscopy we demonstrate that the B-cations in Pb(2.4)Ba(2.6)Fe(2)Sc(2)TiO(13) are ordered along the {110} perovskite layers with Fe(3+) in distorted tetragonal pyramids along the CS planes, Ti(4+) preferentially in the central octahedra of the perovskite blocks and Sc(3+) in the outer octahedra of the perovskite blocks. Magnetic susceptibility and Mössbauer spectroscopy indicate a broadened magnetic transition around T(N)∼ 45 K and the onset of local magnetic fields at low temperatures. The magnetic order is probably reminiscent of that in other AnBnO(3n-2) homologues, where G-type AFM order within the perovskite blocks has been observed.

Novel anion-deficient perovskite-based ferrites Pb2Ba2BiFe5O13 and Pb(1.5)Ba(2.5)Bi2Fe6O16 were synthesized by solid-state reaction in air. Pb2Ba2BiFe5O13 and Pb(1.5)Ba(2.5)Bi2Fe6O16 belong to the perovskite-based A(n)B(n)O(3n-2) homologous series with n = 5 and 6, respectively, with a unit cell related to the perovskite subcell a(p) as a(p)√2 × a(p) × na(p)√2. Their structures are derived from the perovskite one by slicing it with 1/2[110]p(101)p crystallographic shear (CS) planes. The CS operation results in (101)p-shaped perovskite blocks with a thickness of (n - 2) FeO6 octahedra connected to each other through double chains of edge-sharing FeO5 distorted tetragonal pyramids which can adopt two distinct mirror-related configurations. Ordering of chains with a different configuration provides an extra level of structure complexity. Above T ≈ 750 K for Pb2Ba2BiFe5O13 and T ≈ 400 K for Pb(1.5)Ba(2.5)Bi2Fe6O16 the chains have a disordered arrangement. On cooling, a second-order structural phase transition to the ordered state occurs in both compounds. Symmetry changes upon phase transition are analyzed using a combination of superspace crystallography and group theory approach. Correlations between the chain ordering pattern and octahedral tilting in the perovskite blocks are discussed. Pb2Ba2BiFe5O13 and Pb(1.5)Ba(2.5)Bi2Fe6O16 undergo a transition into an antiferromagnetically (AFM) ordered state, which is characterized by a G-type AFM ordering of the Fe magnetic moments within the perovskite blocks. The AFM perovskite blocks are stacked along the CS planes producing alternating FM and AFM-aligned Fe-Fe pairs. In spite of the apparent frustration of the magnetic coupling between the perovskite blocks, all n = 4, 5, 6 A(n)Fe(n)O(3n-2) (A = Pb, Bi, Ba) feature robust antiferromagnetism with similar Néel temperatures of 623-632 K.

Samples of solid solutions of the series Sr(Fe1 − x Co x )0.9Ga0.1O2.5 with brownmillerite structure are produced from appropriate amounts of oxides Fe, Co, Ga, and SrCO3 in different gaseous media and temperature conditions using solid-phase synthesis. Features of the distribution of cations over nonequivalent positions of the crystalline structure of the obtained samples are studied using the 57Fe Mössbauer absorption and emission spectroscopy.

We report the formation of ternary graphite intercalation compounds (GICs) with FeCl 3 and PtCl 4 via reaction between hexachloroplatinic acid and a binary GIC with iron(III) chloride. Mössbauer spectroscopy and X-ray microanalysis results show that ternary GICs form only when the interlayer spaces in the parent binary GIC are incompletely occupied (stage III or lower). The coexistence of different chloride molecules in the ternary GIC leads to the formation of intermetallic nanoparticles when the material is reduced. The yield of the intermetallic phase increases with decreasing graphite particle size.

By physicochemical methods (XRD, SEM, TEM, TGA, Mössbauer spectroscopy, magnetization measurements), the conditions (temperature, pO 2 , structure) of oxidation and reduction by the internal solid-phase mechanism in the spinel composite oxides Ni x Mn 1 − x Fe 2 O 4 and Zn x Mn 1 − x Fe 2 O 4 are established; the correlation between reactions kinetics (and mechanism) and the distribution of cations of different charges by structural positions is shown.

High-temperature electrical conductivity measurements, structural data from powder X-ray diffraction and 57Fe Mössbauer spectroscopy were combined to study the interrelationship of oxygen ion transport and p- and n-type transport in Sr2(Fe1−xGax)2O5, where x=0, 0.1 and 0.2. Although gallium substitution generally decreases the total ion-electron transport, the transition of the orthorhombic brownmillerite structure to a cubic phase on heating results in the recurrence of the conductivity to the same high level as in the parent ferrite (x=0). The changes of the partial contributions to the total conductivity as a function of x are shown to reflect a complicated interplay of the disordering processes that develop in the oxygen sublattice on heating in response to replacement of iron with gallium.

Fe-57 Mossbauer spectroscopy is used to study anion-deficient perovskite-related scandium-doped ferrites SrFe1-xScxO3-gamma (0.00 less than or equal to x less than or equal to 0.20) over a wide range of temperatures. The Sc3+ cations substituting for iron interrupt the rapid electron exchange Fe3+ +Fe4+ = Fe4+ + Fe-3, which occurs in the ferrite lattice at room temperature. The tetravalent iron Fe-p(4+), which is excluded from the exchange, is stabilized in the five-coordinate oxygen surrounding. At temperatures above a phase transition (T > 350degreesC), the Sc3+ cations induce anisotropy in the oxygen vacancy distribution in the nearest-neighboring average iron cations.

CuCr 2 S 4 -based solid solutions containing solute atoms on the Cu or Cr site were studied with the aim of changing the band structure of the spinel to semiconducting, while maintaining a high magnetic ordering temperature. Cu 1 − x M x Cr 2 S 4 and CuCr 2 − x M x S 4 (M = Al, Ga, In, Fe, Co, As) quaternary phases were synthesized, and CuCr 2 S 4 , Cu 0.3 Co 0.7 Cr 2 S 4 , and Cu 0.5 Fe 0.5 Cr 2 S 4 single crystals were prepared using high-temperature solution growth and chemical vapor transport. The magnetic materials were characterized by a variety of techniques.

A universal equation was derived which relates the enthalpy of preference of cations for alternative systems of interstices in the close packing of any anions to characteristic interatomic distances. A self-consistent system of the enthalpies of preference of cations for octahedral or tetrahedral coordination was first proposed for sulfides and selenides, and an analogous system for oxides was substantially extended. The calculation results were shown to agree with experimental data, including those for some halides and hydrides.

Heterovalent substitution of As5+, Sb5+, V5+, and Sn4+ diamagnetic ions in CuCr2S4 was studied. The results show that, similar to other 3d10 diamagnetic ions, the As5+ ions occupy only tetrahedral interstices in the close packing of sulfur ions, while the Sb5+ and Sn4+ 4d10 ions, as well as the Sc3+, Ti4+, and V5+ 3d0 ions occupy only octahedral sites. A new compound of composition Cu3AsCr8S16 was synthesized and characterized. It crystallizes in an orthorhombic (sp. gr.Pmm2) spinel-derived structure containing ordered Cu and As ions in tetrahedral sites(a = 13.942 ± 0.004 Å,b = 6.878 ± 0.002 Å,c = 19.692 ± 0.006 Å, Z = 4, V = 1888.43 ± 0.92 Å). The CuCr1.5Sb0.5S4 spinel phase is found to crystallize in sp. gr.Fd3m (a = 10.009 ± 0.002 Å,u = 0.3815 ± 0.0004 Å) with partial ordering on octahedral sites.