Low-temperature heat capacity and thermodynamic functions of compounds with the composition Ba(A<Stack><Subscript>2/3</Subscript><Superscript>III</Superscript></Stack>U<Subscript>1/3</Subscript>)O<Subscript>3</Subscript> (A<Superscript>III</Superscript> = Sc,Y)

The heat capacity of crystalline Ba(Sc_2/3U_1/3)O₃ and Ba(Y_2/3U_1/3)O₃ in the range 80–350 K was studied by adiabatic vacuum calorimetry, and the thermodynamic characteristics of these compounds were evaluated. Their standard entropies of formation at 298.15 K were calculated.     

A physicochemical study of compounds formed in the systems A<Superscript>III</Superscript>(HSiUO<Subscript>6</Subscript>)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O (A<Superscript>III</Superscript> = Y,La-Lu)

Compounds in the systems A^III(HSiUO₆)₃-H₂O (A^III = Y, La-Lu) were prepared by stepwise dehydration of uranosilicate A^III(HSiUO₆)₃ decahydrates (A^III = Y, La-Lu), and their structural transformations were studied by high-temperature X-ray diffraction technique and IR spectroscopy.     

X-ray diffraction study of the Tm<Subscript>2</Subscript>M<Stack><Subscript>3</Subscript><Superscript>I</Superscript></Stack>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> (M<Superscript>I</Superscript> = Li,Na, K) ferrites

The Tm₂M₃^IFe₅O₁₂ (M_I = Li, Na, K) compounds have been prepared for the first time by solid-state reactions between thulium(III) oxide, iron(III) oxide, and alkali metal carbonates, and their symmetry class and unit-cell parameters have been determined by X-ray diffraction.     

Crystal structure of the perovskites Ba<Subscript>2</Subscript>A<Superscript>II</Superscript>UO<Subscript>6</Subscript> (A<Superscript>II</Superscript> = Zn,Cd, Pb)

The compounds Ba₂ZnUO₆, Ba₂CdUO₆, and Ba₂PbUO₆ were prepared by high-temperature solidphase reactions. Their structures (space group Fm \(\bar 3\) m) were refined by the Rietveld method. In the morphotropic series Ba₂A^IIUO₆, correlations were found between the A^II-O, U-O, and Ba-O bond lengths and the crystal-chemical radius of A^II.     

New ferromagnetics based on manganese-alloyed chalcopyrites A<Superscript>II</Superscript>B<Superscript>IV</Superscript>C<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>

This review describes the principles of semiconductor spintronics, represents the physicochemical properties of materials based on manganese-alloyed A^IIB^IVC₂^V compounds, considers the results from theoretical simulation of magnetic properties of A^IIB^IVC₂^V alloyed with 3d metals, summarizes the basic approaches to explanation of ferromagnetism with Curie points above room temperature arising in A^IIB^IVC₂^V:Mn, and indicates promising ways to synthesize and study magnetic semiconductors based on chalcopyrites A^IIB^IVC₂^V in order to produce a suitable material for spintronic devices.     

Magnetic properties of LaInO<Subscript>3</Subscript>-based perovskite-structure photoluminescent materials doped with Nd<Superscript>3+</Superscript>, Cr<Superscript>3+</Superscript>, and Mn<Superscript>3+</Superscript> ions

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.     

Dy<Superscript>3+</Superscript>-activated M<Subscript>2</Subscript>SiO<Subscript>4</Subscript> (M = Ba,Mg, Sr)-type phosphors

The alkaline orthosilicates of M₂SiO₄ (M = Ba, Mg, Sr) activated with Dy³⁺ and co-doped with Ho³⁺ are prepared through conventional solid-state method, i.e., mixing and grinding of solid form precursors followed by high-temperature heat treatments of several hours in furnaces, generally under open atmosphere and investigated by X-ray diffraction (XRD) to get phase properties and photoluminescence (PL) analysis to get luminescence properties. The thermal behaviours of well-mixed samples were determined by differential thermal analysis (DTA)/thermogravimetry (TG). The PL spectra show that the 478 and 572 nm maximum emission bands are attributed, respectively, to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions.     

Heat Capacity and thermodynamic functions of DyMe<Superscript>II</Superscript>Cr<Subscript>2</Subscript>O<Subscript>5.5</Subscript>(Me<Superscript>II</Superscript>-Mg,Ca) in the range from 298.15 to 673 K

The calorimetric method is used to investigate the heat capacity of DyMe^IICr₂O_5.5(Me^II-Mg, Ca) chromites in the range from 298.15 to 673 K. The C _p ⁰ ～ f(T) curves exhibit λ-like effects at 348 and 548 K for DyMgCr₂O_5.5 and at 473 K for DyCaCr₂O_5.5, which apparently relate to second-order phase transitions. The temperature dependences are calculated for thermodynamic functions C _p ⁰ (T), H ⁰(T)-H ⁰(298.15), S ⁰(T), and Φ**(T).     

Novel perovskites M2IILnIIIRuVO6 as emission control catalysts

New perovskites, M₂^IILn^IIIRu^VO₆, where M^II = Ba and Sr, Ln^III = rare earths, Y and Bi, were prepared. The Ba series exhibits cubic cells for Ln^III = La to Dy and hexagonal cells for Ln^III = Yb and Y. The Sr series exhibits superlattices for Ln = La through Nd and orthorhombic distortions for Ln = Sm through Yb. Ba₂LaRuO₆ showed catalytic activity and thermal stability for the reactions: 2NO + 2CO → N₂ + 2CO₂ and 2CO + O₂ → 2CO₂. The combination of three basic cations per Ru and the perovskite structure stabilizes Ru in these catalysts.     

Phase transitions and thermal expansion of apatite-structured compounds

The phase transitions and thermal expansion of apatite-structured compounds with the general formula M₅^II(A^VO₄)₃L (M^II = Ca, Sr, Cd, Ba, Pb; A^V = P, V; L = F, Cl) have been studied by high-temperature X-ray diffraction and differential thermal analysis. The Pb-containing apatites are shown to undergo phase transitions involving a reduction in unit-cell symmetry from hexagonal to monoclinic. The thermal expansion anisotropy in the hexagonal phases increases in the order Ca < Sr < Ba < Pb < Cd, and the monoclinic phases are less anisotropic but have larger thermal expansion coefficients in comparison with the hexagonal phases.     

Doping of the perovskite M<Superscript>I</Superscript>M<Superscript>II</Superscript>O<Subscript>3</Subscript> with weighable amounts of Pu and Am

Matrices of the compositions 0.2La₂O₃·Al₂O₃ and 0.4La₂O₃·Fe₂O₃, containing weighable amounts of Pu (13 mg g^?1) and Am (0.336 mg g^?1), were prepared, and their leaching rates were studied. The leaching rates calculated from the surface area determined by low-temperature nitrogen adsorption (BET method) virtually coincide with those found previously for the matrices with tracer amounts of the radionuclides, which indicates that these parameters are intrinsic characteristics of the matrices. The leaching rates calculated from the geometric surface areas are considerably higher and depend on the material porosity and hence on the procedure of its synthesis. The rates of the matrix corrosion were calculated from the ¹⁴⁷Pm leaching rates. They show that the matrix will not disintegrate into small fragments for 100 thousand years even under the emergency conditions of repository flooding with water.     

Crystallization from high-temperature solutions in the Na<Subscript>2</Subscript>O-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-M<Superscript>VI</Superscript>O<Subscript>3</Subscript> (M = Mo,W) systems

We have studied the crystallization behavior of Na₂O-NaPO₃-M^VIO₃(M^VI = Mo, W) high-temperature solutions containing 15 mol % Bi₂O₃ in the pseudoquaternary systems Na₂O-Bi₂O₃-P₂O₅-M^VIO₃ and have established the conditions for the formation of Na₃Bi(PO₄)₂, high-temperature BiPO₄, NaBi(MoO₄)₂, Bi₂WO₆, and NaMoO₂PO₄. The compounds identified have been characterized by powder x-ray diffraction and IR spectroscopy.     

Synthesis,structure, and thermal expansion of M<Subscript>2</Subscript>Fe<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>16</Subscript> and MFeTiO<Subscript>4</Subscript> compounds

Compounds that crystallize in four structure types in M₂O-Fe₂O₃-TiO₂ systems have been prepared by solid-state reactions. The M₂Fe₂Ti₆O₁₆ (M = Rb, Cs) compounds have been prepared for the first time. The thermal expansion coefficients of the MFeTiO₄ (M = Li, Na) and M₂Fe₂Ti₆O₁₆ (M = Na, K, Rb, Cs) compounds have been determined by high-temperature X-ray diffraction.     

Perovskite M<Superscript>I</Superscript>M<Superscript>II</Superscript>O<Subscript>3</Subscript> as a matrix for incorporation of the actinide fraction of HLW

Perovskites of the compositions xLa₂O₃·Al₂O₃ and xLa₂O₃·Fe₂O₃ were prepared by cold pressing and sintering at temperatures of up to 1500°C, and their properties were studied. Perovskites based on lanthanum aluminate are more porous than those based on lanthanum ferrite, whereas the rate of radionuclide leaching from the former compounds is lower than from the latter compounds. The parameter x varied in a relatively wide range does not affect the leaching rate.     

X-ray diffraction study of the Cu<Subscript>2</Subscript>Se-In<Subscript>2</Subscript>Se<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>Se<Subscript>3</Subscript> system near CuInCr<Subscript>2</Subscript>Se<Subscript>5</Subscript>

The structure of three compounds in the Cu₂Se-In₂Se₃-Cr₂Se₃ system near CuInCr₂Se₅ is determined by single-crystal x-ray diffraction: CuInCr₄Se₈ (I), Cu₂In₂Se₄ (II), and Cu_0.5In_0.5Se (III). I has a cubic (spinel type) structure: a = 10.606(4) Å, Z = 4, sp. gr. F43m. II has a pseudotetragonal (sphalerite type) structure: a = 5.774(2) Å, c = 11.617(6) Å. The structure of II was solved in a reduced unit cell with a = 5.774(2) Å, b = 5.774(2) Å, c = 7.095(6) Å, = 113.95(5)°, = 113.95(5)°, = 90.00(4)°, Z = 1, sp. gr. P1. III has a triclinic cell (disordered structure of II): a = 4.088(1) Å, b = 4.091(2) Å, c = 4.101(1) Å, = 60.05(1)°, = 60.08(1)°, = 89.98(4)°, Z = 1, sp. gr. P1. The Cu and In atoms in I sit in inequivalent tetrahedral sites, and the Cr atoms reside in octahedral interstices of the close packing of Se atoms. The bond lengths are In–Se = 2.538(6), Cr(1)–Se(1) = 2.514(7), Cr(1)–Se(2) = 2.576(8), and Cu–Se = 2.437(5) Å. In II, all of the atoms sit in tetrahedral sites; the mean bond lengths are In–Se = 2.578(6) and Cu–Se = 2.44(1) Å. In III, the Cu and In atoms are fully disordered in the same tetrahedral site; the mean Cu(In)–Se bond length is 2.508(6) Å.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1435–1439.Original Russian Text Copyright © 2004 by Antsyshkina, Sadikov, Koneshova, Sergienko.     

Synthesis and characterization of M<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> (M = Ca,Sr and Ba) by a solid-state metathesis approach

A solid-state metathesis approach initiated by microwave energy has been successfully applied for the synthesis of orthovanadates, M₃V₂O₈ (M = Ca, Sr, and Ba). The structural, vibrational, thermal, optical and chemical properties of synthesized powders are determined by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, magnetic property measurements and diffused reflectance spectra in the UV-VIS range. The direct bandgap of the synthesized materials was found to be 3·55 ± 0·2 eV, 3·75 ± 0·2 eV and 3·57 ± 0·2 eV for Ca₃V₂O₈, Sr₃V₂O₈ and Ba₃V₂O₈, respectively.     

Structural,optical and magnetic properties of Cr doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> powders and thin films

The (In_1?xCr_x)₂O₃ powders as well as thin films of x = 0.03, 0.05 and 0.07 were synthesized using a solid state reaction and an electron beam evaporation technique (on glass substrate), respectively. The influence of Cr doping concentration on structural, optical and magnetic properties of the In₂O₃ samples was systematically studied. The X-ray diffraction results confirmed that all the Cr doped In₂O₃ samples exist cubic structure of In₂O₃ without any secondary phases presence. The chemical composition analyses showed that all the Cr doped In₂O₃ compounds were nearly stoichiometric. The X-ray photoelectron spectroscopy analysis of the Cr doped In₂O₃ thin films showed an increase of oxygen vacancies with Cr concentration and the existence of Cr as Cr³⁺ state in the host In₂O₃ lattice. A small blue shift in the optical band gap was observed in the powder compounds, when the dopant concentration increased from x = 0.03 to x = 0.07. In thin films, the band gap found to increase from 3.63 to 3.74 eV, with an increase of Cr concentration. The magnetic measurements show that the undoped In₂O₃ bulk powder sample has the diamagnetic property at room temperature. And a trace of paramagnetism was observed in Cr doped In₂O₃ powders. However (In_1?xCr_x)₂O₃ thin films (x = 0.00, 0.03, 0.05 and 0.07) samples shows soft ferromagnetism. The observed ferromagnetism in thin films are attributed to oxygen vacancies created during film prepared in vacuum conditions. The ferromagnetic exchange interactions are established between metal cations via free electrons trapped in oxygen vacancies (F-centers).     

Large enhancement of upconversion luminescence in Er<Superscript>3+</Superscript>/In<Superscript>3+</Superscript>:Ba<Subscript>0.85</Subscript>Ca<Subscript>0.15</Subscript>TiO<Subscript>3</Subscript> lead-free piezoelectric ceramics

A series of In³⁺-doped Ba_0.85Ca_0.15TiO₃:0.75%Er³⁺/xIn³⁺ (BCT:Er/xIn) lead-free piezoelectric ceramics with excellent upconversion luminescence were synthesized by the solid state reaction method. The effects of In³⁺ content on the crystal structure, ferroelectric, dielectric, piezoelectric, and upconversion luminescence properties were systematically studied. Under 980 nm excitation, a giant enhancement of the green emission (550 nm) by 10 times is achieved upon 2.5% mol In³⁺ doping, which is rarely observed in rare-earth ions-doped perovskite ferroelectric materials. The ultraviolet-visible-near infrared absorption measurements show that the In³⁺ doping may improve the dissolution of Er³⁺ ions and modify the isolate-/clustered-Er³⁺ ratio for x?≤?2.5%, resulting in the enhancement of the absorption cross-section, thereby contributing to the enhancement of green luminescence. Unfortunately, the In³⁺ doping suppresses the ferroelectric and piezoelectric properties of the BCT:Er/xIn ceramics. This problem can be resolved by adding a small amount (1 mol%) of Yb³⁺ to the BCT:Er/xIn ceramics to restore their good ferroelectric and piezoelectric properties. Such In³⁺ and rare-earth ions co-doped ceramics with greatly enhanced upconversion luminescence and good ferroelectricity and piezoelectricity may have potential applications in electro-optical devices.     

Synthesis of nanocomposites based on MO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> (M = Ca,Sr, Ba) glasses

This work examines the effect of KBF₄ additions on the crystallization behavior of glasses based on the multicomponent systems MO-Bi₂O₃-B₂O₃ with M = Ca, Sr, and Ba. The glass-ceramic composites obtained contain a δ-Bi₂O₃-based crystalline phase with a crystallite size of ≃7 nm, evenly distributed over the glass matrix. The 400°C electrical conductivity of the nanocomposites reaches 2 × 10⁻⁴ S/cm, and the activation energy is 1.1 eV, typical of anion conduction. These values are comparable to those reported for δ-Bi₂O₃ ceramics.     

Preparation and characterization of Eu<Superscript>3+</Superscript> activated CaSiO<Subscript>3</Subscript>, (CaA)SiO<Subscript>3</Subscript> [A = Ba or Sr] phosphors

Eu³⁺ activated CaSiO₃, (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ have been prepared by sol-gel technique. Residual solvent and organic contents in the gel were removed by firing at 100°C for 3–4 h at 300 and 600°C for 2 h. Small exothermic shoulder around 850 to 875°C, as observed in DTA curve, corresponds to crystallization temperature of the doped calcium silicate. Influence of firing temperature on the luminescence of Eu³⁺ shows the maximum emission intensity in gel fired at 850°C. Photoluminescence emission peak is observed at 614 nm due to⁵D₀ →⁷F₂ transition of Eu³⁺ ion in (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ phosphors, when excited by 254 nm. The (Ca, Ba) SiO₃ material is proposed as an efficient red phosphor.