Defect Solid Solution Research Articles

Hydrogen storage properties of Mg 1− xCa xNi 2− y defect solid solutions

Ternary Mg 1− x Ca x Ni 2− y solid solutions were synthesized by powder sintering. The phase structures and hydrogen storage properties of the sintered samples were investigated. In a certain range of x and y values, the samples are a single C15 Laves phase with various types of defects. The reduction of Ni content leads to the formation of omission solid solution with vacancies on the sites of Ni. These vacancies increase the hydrogen storage capacity, but decrease the reversibility of hydrogen absorption and desorption.

Study on Dy 2O 3-Doped Medium Temperature Sintering (Ba,Sr)TiO 3 Series Capacitor Ceramics

The influence of Dy 2O 3 doping on the properties of medium temperature sintering (Ba, Sr)TiO 3 series capacitor ceramics was studied by single factor various amount method, and the law of the influence on the medium temperature sintering (Ba, Sr)TiO 3 series capacitor ceramics was obtained. The dielectric materials used for multilayer ceramic capacitor was obtained, of which the dielectric constant was 1375, the dielectric loss was 0.0060, the density was 5.92 g·cm −3, the sintering temperature was less than 1150 °C, the capacitance temperature changing rate (Δ C/C) was less than ± 15%, the voltage withstand strength was more than 9.3 kV·mm −1, and the crystal grain size was about 1 μm. The surface morphology of the sample doped with various amount Dy 2O 3 was analyzed by scanning electron microscope (SEM). The results showed that doping Dy 2O 3 could form defect solid solution, stop grain growth, fine crystal grain, widen curie peak, obtaining high dielectric constant and low dielectric loss, capacitance temperature property was suited for X7R character, in the (Ba,Sr)TiO 3 series ceramics. At the same time, the voltage withstand strength was enhanced greatly.

Influence on the structural characteristic of defect solid solution Gd xZr 1− xO 2− x/2 with 0.18 ⩽ x ⩽ 0.62 under longer term annealing studied by 155Gd Mössbauer spectroscopy

Three kinds of defect solid solution Gd x Zr 1− x O 2− x/2 with 0.18 ⩽ x ⩽ 0.62, including the three single crystal samples with x = 0.21, 0.26 and 0.30, were investigated by 155Gd Mössbauer spectroscopy at 12 K. Difference in the structural characteristic under longer term annealing were confirmed by comparing the 155Gd Mössbauer parameters of the polycrystalline samples sintered one time and twice at 1773 K for 16 h in air, respectively. The results indicated that the polycrystalline samples sintered twice have relatively equilibrated structure by comparing with the three single crystal samples. After being sintered twice, basically the local structure around the Gd 3+ ions does not change, but the degree of the displacements of the six 48f oxygen ions from positions of cubic symmetry becomes slightly smaller, and distribution of the Gd 3+ ions in the system becomes more homogeneous.

Aluminum in magnesium silicate perovskite: Formation, structure, and energetics of magnesium‐rich defect solid solutions

MgSiO3‐rich perovskite is expected to dominate Earth's lower mantle (pressures >25 GPa) with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms: MgA + SiB = MA + MB and SiB = AlB + 0.5 (vacancy)O. Phase synthesis studies show that both substitutions do occur and the nonstoichiometric or defect substitution is prevalent along the MgSiO3‐MgAlO2.5 join. Lattice parameters associated with the first substitution (stoichiometric) show more rapid increases with increasing Al content than those for the second substitution (nonstoichiometric), consistent with the differences in size of substituting ions. Oxide melt solution calorimetry has been used to compare the energetics of both substitutions. The stoichiometric substitution, represented by the reaction 0.95 MgSiO3 (perovskite) + 0.05 Al2O3 (corundum) = Mg0.95Al0.10Si0.95O3 (perovskite), has an enthalpy of −0.8 ± 2.2 kJ/mol. The nonstoichiometric reaction, 0.90 MgSiO3 (perovskite) + 0.10 MgO (rocksalt) + 0.05 Al2O3 (corundum) = MgSi0.9Al0.1O2.95 (perovskite) has a small positive enthalpy of 8.5 ± 4.6 kJ/mol. Configurational T ΔS terms play a role in both substitutions. The defect substitution is not prohibitive in enthalpy, entropy, or volume, is favored in perovskite coexisting with magnesiowüstite and may significantly affect the elasticity, rheology, and water retention of silicate perovskite in Earth.

Synthesis, Structure and Electrophysical Properties of Cation-Deficient Lanthanum-Calcium Manganites

Two series of defect solid solutions based on La 0.6 Ca 0.4 MnO 3-z : La x Ca 0.4 MnO 3-z (0 < x < 0.4) and La 0.6 Ca x MnO 3-z (0 < x < 0.15), deficient in La- and Ca-ions, respectively, have been investigated. X-ray diffraction studies show that in all cases solid solutions are formed with structure close to ideal cubic perovskite lattice. The lattice parameter monotonically changes with the defect concentration. The oxygen content also decreases monotonically with increase in the cation deficiency. Thus, the introduction of defects in A-cation sublattice of the perovskites under study results in removal of oxygen ions, which enables the charge compensation.

Aluminum in Magnesium Silicate Perovskite: Synthesis and Energetics of Defect Solid Solutions

AbstractMgSiO3 - rich perovskite is expected to dominate the Earth's lower mantle (pressures &gt; 25 GPa), with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms: MgA+ SiB = MA + MB and SiB = AlB + 0.5 VO. Phase synthesis studies show that both substitutions do occur, and the nonstoichiometric or defect substitution is prevalent along the MgSiO3 - MgAlO2.5 join. Oxide melt solution calorimetry has been used to compare the energetics of both substitutions. The stoichiometric substitution, represented by the reaction 0.95 MgSiO3 (perovskite) + 0.05 Al2O3 (corundum) = Mg0.95Al0.10Si0.95O3 (perovskite), has an enthalpy of -0.8±2.2 kJ/mol. The nonstoichiometric reaction, 0.90 MgSiO3 (perovskite) + 0.10 MgO (rocksalt) + 0.05 Al2O3 (corundum) = MgSi0.9Al0.1O2.95 (perovskite) has a small positive enthalpy of 8.5±4.6 kJ/mol. The defect substitution is not prohibitive in enthalpy, entropy, or volume, is favored in perovskite coexisting with magnesiowüstite, and may significantly affect the elasticity, rheology and water retention of silicate perovskite in the Earth.

Synthesis of stoichiometric cadmium substituted magnetites and formation by oxidation of solid solutions of cadmium ferrite and γ-iron oxide

Stoichiometric cadmium-substituted magnetites Cd x Fe 3 − x O 4 ( x = 0, 0.25, 0.50, 0.75 and 1) were prepared by a standard ceramic method. It has been found that, after grinding, these Cd-ferrites can be oxidized under prolonged isothermal conditions at low temperature (<300°C) whilst retaining the single spinel phase. The oxidation and the resulting non-stoichiometric solid solutions between CdFe 2O 4 and γ-Fe 2O 3 have been investigated by X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and infrared spectroscopy. A cation distribution for defect solid solutions of maghemite, γ-Fe 2O 3, and cadmium ferrite has been proposed.

Topotactic Oxidation of the Quadruple-Rutile-Type Chain Structure Na0.875Fe0.875Ti1.125O4

Sodium removal from Na0.875Fe0.875Ti1.125O4by means of oxidizing agents leads to the formation of the defect solid solution Na0.875−δFe0.875−δTi1.125O4(0≤δ≤0.44). A systematic increase in theaparameter of the orthorhombic unit cell is observed as the sodium content is reduced, while thebparameter decreases only slightly. The cell volume remains almost constant as a consequence of the irregular change in thecparameter and the different behavior of both theaandbparameters. Structural changes have been followed by Rietveld powder diffraction analysis. Room- and low-temperature Mössbauer studies confirm the increase in the Fe4+state with decreased sodium content in the less extracted samples withδ=0.10 and 0.15, whereas a maximum Fe4+content (about 21%) is reached in a sample withδ=0.25. Surprisingly, the amount of Fe4+does not increase with further sodium extraction. This is thought to be related to the greater oxidative power of the more oxidized materials, which facilitates a subsequent partial backreduction of Fe4+formed during the oxidation procedure. Results of both Mössbauer spectroscopy and structure refinements indicate that the Fe4+cations randomly occupy both octahedral metal positions,M(1) andM(2), of each quadruple rutile unit.

Influence of structural order on the luminescence of oxide spinels: Manganese activated spinels

Phosphor performance is often limited by preparation conditions which determine the degree of crystallinity and structural order. The influence of vacancy disorder was investigated using magnesium aluminate and magnesium gallate spinels as test cases. Spinels of composition Mg 1−xAl 2O 4−x:Mn 2+ and Mg 1−xGa 2O 4−x:Mn 2+ where 0 < x < 0.2 form defect solid solutions in which the loss of the divalent cation is compensated by the formation of both anion and cation vacancies. Defect and normal/inverse disorder was probed by comparing the emission and excitation spectra of Mn 2+. MgAl 2O 4:Mn 2+ emits at 650 nm. When x = 0.05, emission bands appear at 517 and 744 nm. These increase intensity and the 650 nm band disappears as x increases. The emission of the magnesium gallate phosphors was a single band at 507 nm for all compositions. Overall, the emission spectra were determined more by the distribution of Mn 2+ over the available sites than by either normal/inverse disorder or defect disorder.

Macroscopic ferrimagnets as magneto-optic media (abstract)

We have discovered a class of phase separated materials in which the two phases couple antiferromagnetically across the phase boundary. A prototypical example is cobalt containing ≂100-Å-diam precipitate particles of EuS with the NaCl structure. These materials show many of the properties of ferrimagnets such as compensation points so we have adopted the term ‘‘macroscopic ferrimagnet’’ to distinguish them from ferrimagnets in which the antiferromagnetic exchange couples individual atoms. As a result of the ferrimagnetic exchange between the Co and the EuS the net magnetization of the composite is low in the vicinity of compensation so the anisotropy field is high. Electron beam evaporated thin films have a perpendicular easy axis as a result of growth induced anisotropy. Another effect of the exchange between the Co and EuS is to order the EuS well above its normal Curie point of 16 K. A film with 80 mole % Co and 20 mole % EuS has a compensation point of 55 K showing that the Eu2+ has essentially its full moment of 7μB at this temperature in order to compensate the 1.65μB of Co. The EuS even shows evidence of magnetic order at room temperature. The wavelength dependence of the sign of the magneto-optic Kerr effect can only be explained if the EuS has sufficient rotation at high photon energies to be larger than the rotation of the Co. We have prepared more complex alloys that show square loop properties at room temperature, for example, Tb-Co-EuS and Tb-FeCo-EuO. X-ray diffraction analysis shows that these films consist of an amorphous matrix (Tb-Co or Tb-FeCo) with precipitates of a NaCl structure phase (e.g., defect solid solutions like Eu1−xTbxS1−x⧠x). Both atomic and macroscopic ferrimagnetism are operating in these compositions. Films with high remanence and coercivities over 4 kOe at room temperature have been obtained. Some of these compositions may be useful as magneto-optic storage media.

The defect solid solution [formula omitted]: Evidence of Na I mobility in the tunnels of a quadruple rutile-chain structure

A new defect solid solution, the series Na 7 8 (Fe III 7 8 +x Ti IV 9 8 −2x Sb V x) O 4 , was synthesized. Its homogeneity range is rather wide: 0 <- x ≤ 0.33. The incorporation of Sb V gives rise to a progressive increase of the parameters of the orthorhombic unit cell. X-ray powder structure calculations point to a partial occupancy of the large double tunnels in a quadruple rutile-chain structure. A significant ordering of cations over the octahedral framework is observed, owing to a Ti IVSb V segregation. Electrical measurements emphasize a cationic conductivity, mainly related to a 1D motion of Na I cations. A transition from a low activation energy process— E A ≤ 0.20 eV—to a high activation energy one— E A ≈ 0.75 eV—systematically occurs at T ≈ 440°C, independent of the Sb V concentration. A possible skew motion from a half tunnel to another one is proposed as a tentative explanation of the high-temperature conductivity mechanism.

Characterization of vacancy disorder in SrNd 2S 4Nd 2S 3 solid solutions by Raman spectroscopy

Raman spectra and precision X-ray diffraction patterns have been measured along the solid solution series between SrNd 2S 4 and γ-Nd 2S 3. Breaks in the values of unit cell edge and Raman linewidths are interpreted to indicate different disorder structures in this defect solid solution series.

Point Defects and Extended Defects in Niobium Oxides

THE part played by true point defects—isolated vacancies and interstitial atoms—in defect solid solutions and in mixed valence non-stoichiometric phases is not clear. In many ionic or quasi-ionic structures there is some structural reorganization and at least incipient ordering of defect clusters. In some oxides—notably those of titanium, vanadium, molybdenum and tungsten, in which the covalent component of the bonding is probably strong—slight reduction, with a change in the ratio of oxygen to metal, is accommodated largely by crystallographic shear. A complete sheet of anion sites is eliminated from the structure, forming an extended defect and greatly diminishing the extent to which a deficit of oxygen must be compensated by anion vacancies or interstitial cations. Thus Hyde and Bursill1 found that, in slightly reduced rutile, TiO1.9986, the point defect concentration could hardly exceed 10−4. In more extensively reduced rutile, changes in stoichiometry involve only changes in the spacing between crystallographic shear planes, without detectable concentrations of localized defects.

Resonance Raman Spectra of Semiconducting CdF2:In3+Crystals

Raman spectra of single-crystal Cd${\mathrm{F}}_{2}$-In${\mathrm{F}}_{3}$ solid solutions in the semiconducting state exhibit complex multiphonon scattering due to resonance coupling with a 4000-\AA{} electronic band. The 262-${\mathrm{cm}}^{\ensuremath{-}1}$ local mode becomes more intense than the normal lattice mode. Two new defect modes and five new combination modes are observed. These results are compared with the present models for semiconducting behavior in Cd${\mathrm{F}}_{2}$ defect solid solutions.

The Electrical Properties of Lanthanum Oxide‐Calcium Oxide Solid Electrolytes

Electrical conductivity measurements have been made in the system as a function of composition, temperature, and oxygen pressure. At 1600°C, can dissolve about 16 m/o which leads to the creation of anion vacancies. These defect solid solutions behave as oxygen anion conductors below an oxygen pressure of 10−7 atm. Above this pressure, the appearance of p‐type conductivity, proportional to , produces a region of mixed conduction. No evidence of n‐type conductivity was observed. Even exhibits predominantly ionic conduction at intermediate oxygen pressures. Several transport numbers were verified by emf measurements. The results of this investigation are compared with those obtained previously for other oxide electrolyte systems.

Diffusive impregnation of iron and steel with tin and antimony

1. Iron and steel may be impregnated by vaporization of tin or antimony in a vacuum. Tin impregnation turns the diffusion layer into a substitutional solid solution of tin in iron. Antimony impregnation causes the formation of a defect solid solution with a composition that approximately equals the FeSb phase. 2. Impregnation of iron and steel with tin or antimony gives rise to an increase in volume which is rather insignificant in impregnating with tin and considerable with antimony. 3. The impregnation with tin or antimony increases the corrosion resistance of steel and iron in aqueous solutions of certain acids and salts by several times. 4. Impregnation with tin should be conducted at 1050 to 1150° C for two hours; the optimal temperature for the impregnation with antimony lies around 550° C with a holding time of about three hours. In both cases a 1 mm Hg vacuum is sufficient.

The constitution of the mantle—III Consequences of the olivine-spinel transition

Evidence on the chemical composition of the mantle is reviewed. Based upon studies of the inclusions in kimberlite pipes, intrusion of peridotites in orogenic regions, and the compositions of stony meteorites and kimberlite, it is suggested that the average composition of the mantle may approximate that of a garnet peridotite. However, the upper mantle immediately below the M-discontinuity may be poorer in sialic material and close to normal dunite-peridotite in composition. When garnet peridotite is subjected to high temperatures and pressures a series of transitions dominated by the olivine—spinel transition occurs. Besides the olivine-spinel transition, pyroxene may invert to spinel plus coesite, whilst garnet and coesite may dissolve in the spinel at higher temperatures to form a highly disordered defect solid solution. The data in Parts I and II show that these changes should occur under the P- T conditions present in the upper 1000 km of the mantle and take place over an appreciable depth range. The position and extent of this transition range depends upon the assumed temperature distribution in the upper mantle. By choosing a suitable temperature distribution, the transition region can be made coincident with region C (Bullen) in which phase changes and inhomogeneity have been inferred on other grounds. It is found that the proposed transition phenomena are capable of explaining the known data on seismic velocity distribution, elasticity and density in the mantle. The temperature distribution required to make the phase transition region coincident with region C is supported by recent studies of the temperature dependence of electrical conductivity in the mantle. Both convection and conduction mechanisms of heat transfer may give rise to this temperature distribution. A specific model for the mantle is proposed.