Chemical Control of Underdoped and Overdoped States in Y(Ba2 ? ySry)Cu3O6 + δ

The chemical control of underdoped and overdoped states in the Y(Ba_{2 – y} Sr _y )Cu₃O_{6 +} (0.1 and 0.9) compounds has been observed by high-resolution O K-edge X-ray-absorption near-edge-structure spectra. The chemical substitution of Sr for Ba in the fully-oxygenated Y(Ba_2–y Sr _y )Cu₃O_{6 +} (0.9) compounds gives rise to high hole concentrations within both the CuO₂ planes and the out-of-plane sites, leading to the overdoped state and the decrease in the superconducting transition temperature from 92 K for y=0 to 84 K for y=0.8. In contrast, an increase in the Sr content in the oxygen-deficient Y(Ba_{2 – y} Sr _y )Cu₃O_{6 +} (0.1) compounds did not indicate superconductivity. The oxygen-deficient compounds exhibit the underdoped state due to the low hole concentration.     

Phase Relations in the SrO–Bi2O3–Fe2O3 System

The phase relations in the composition region SrFeO_{3 –} –Fe₂O₃–BiFeO₃ are studied in air by x-ray diffraction and electron microscopy. The 1000°C phase compatibility diagram is constructed. Sr_{1 – x} Bi _x FeO_{3 –} solid solutions are prepared in the range 0 < x 0.8. Their lattice parameter is found to vary nonlinearly with x. Two new phases were identified: (Sr,Bi)₃Fe₄O _y (tetragonal lattice, a= 3.907(2) Å, c= 27.30(2) Å) and Sr_0.6Bi_0.4FeO_{3 –} (tetragonal lattice,a = 5.555(2) Å, c= 11.848(5) Å).     

Synthesis of Sr- and Fe-doped LaGaO3 perovskites by the modified citrate method

Fine particle strontium and iron substituted lanthanum gallates La_1–x Sr _x Ga_1–y Fe _y O_3–, where x = 0.2, 0.4, and 0.6; y = 0.2, 0.4, 0.6, and 0.8, have been synthesized by a modified citrate method. The formation of these powders was confirmed by the X-ray powder diffraction (XRD) and the fine particle of La_0.6Sr_0.4Ga_0.2Fe_0.8O_3– was investigated by scanning electron microscopy (SEM), and particle size analysis. The single phase of La_0.8Sr_0.2Ga_0.4Fe_0.6O_3–, La_0.6Sr_0.4Ga_0.2Fe_0.8O_3–, and La_0.4Sr_0.6Ga_0.2Fe_0.8O_3– powders could be obtained both with and without calcination. The amount of the secondary phase increased when the amount of Sr in La_1–x Sr _x Fe_0.6Ga_0.4O_3– was more than 0.2 (x > 0.2) and the amount of Fe in La_0.6Sr_0.4Ga_1–y Fe _y O_3– and La_0.4Sr_0.6Ga_0.2Fe_0.8O_3– was less than 0.8 (y < 0.8). The results indicated that in the pH range of 1.36–9.27, the single phase of La_0.6Sr_0.4Ga_0.2Fe_0.8O_3– was formed without calcination and the pH had negligible effects on the structure and lattice parameter. The fine particle of these calcined powders (<4 m) was obtained with the average particle size 1.70 m at pH = 1.36 and with the average particle size between 0.56–0.60 m at pH range between 3.39–9.27, and with a lattice parameter about 3.9 Å.     

Phase Relations in the Systems Ln1 – x Ba x CoO3 – δ(0 < x ≤ 0.66; Ln = Nd, Sm)

Data are presented on the structural and magnetic properties of Ln_{1 – x} Ba _x CoO_{3 –} (Ln = Nd, Sm; 0 < x 0.66) samples slowly cooled in air after synthesis. The composition stability limits of the intermediate phases Ln_{1 – y} Ba_{1 + y} Co₂O_{5 +} and solid solutions are determined. The magnetic phase diagram of the Nd_{1 – x} Ba _x CoO_{3 –} system is constructed.     

Phase equilibria at 1100°C in air and crystal structure of solid solutions in the system LaCoO<Subscript>3</Subscript>—SrCoO<Subscript>2.5</Subscript>—“SrNiO<Subscript>3</Subscript>”—“LaNiO<Subscript>3</Subscript>”

Phase equilibria in the LaCoO₃—SrCoO_2.5—SrNiO₃—LaNiO₃ system are studied at 1100°C in air using samples prepared by standard solid-state reactions and by the citrate route. The composition region and structure of La_{1 – x}Sr_xCo_{1 – y}Ni_yO_{3 –} solid solutions are determined by x-ray powder diffraction. The structure is refined by the Rietveld profile analysis method with Fullprof 2002. The solid solutions with 0< x 0.5 have a rhombohedrally distorted perovskite structure (sp. gr.R c). The rhombohedral distortion decreases with increasing Sr content, and the solid solutions with x > 0.5 have an ideal cubic structure (sp. gr. Pm3m). The composition dependences of lattice parameters for the La_{1 – x}Sr_xCo_{1 – y}Ni_yO_{3 –} solid solutions are presented.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1520–1525.Original Russian Text Copyright © 2004 by Aksenova, Gavrilova, Cherepanov.     

On the nano-size intergrowth of Sr4Fe6O13±δ and (Sr1?xLax)FeO3?δ phases in the mixed conductor Sr3.6La0.4Fe6Oz

The microstructures of mixed-conducting Sr₄Fe₆O_13±, and Sr_3.6La_0.4Fe₆O _z (nominal composition) have been studied by electron microscopy. The lanthanum free material shows a microstructure containing mainly Sr₄Fe₆O_13±, with some 5 vol% Sr_1–y La _y Fe₁₂O₁₉embedded as micron-size inclusions. The lanthanum-containing material revealed a significantly different microstructure consisting of 20 vol% micron-size Sr_1–y La _y Fe₁₂O₁₉embedded in 40 vol% (Sr_0.85La_0.15)FeO_3–tetragonal perovskite, and 40 vol% of plate-shaped nano-scale intergrowths between (Sr_1–x La _x )FeO_3–and Sr₄Fe₆O_13±phases. Domains with dimensions of 20–50 nm are observed in the tetragonal perovskite when viewed along its fourfold axis. From compositional analysis it is concluded that there is little or no solubility of La in the Sr₄Fe₆O_13±phase. The observed microstructure is important input in explaining the significant effect of La addition on the transport properties of Sr₄Fe₆O_13±materials.     

Influence of Soaking in the Molten (Li0.62K0.38)2CO3Eutectic on the Structure and Conductivity of LiMnxFe1 – xO2and Li1 – yMnyFeO2 + δ

The phase composition, structure, and 920-K electrical conductivity of LiMn _x Fe_{1 – x} O₂(0 < x 1) and Li_{1 – y} Mn _y FeO_{2 +} (0 < y 1) materials prepared by solid-state reactions in air at 1270 K were studied before and after soaking in molten (Li_0.62K_0.38)₂CO₃. The highest conductivity of 32 S/m was found in the spinel solid solution Li_0.2Mn_0.8FeO_{2 +} ( = 2/3). Soaking in the carbonate melt converted all Li_{1 – y} Mn _y FeO_{2 +} samples into rocksalt solid solutions and reduced their conductivity.     

Doping of calcium titanate with chromium and indium

The lattice parameters and composition range of orthorhombic CaTi_{1 – x} Cr_xO_{3 –} solid solutions were determined by x-ray powder diffraction. Samples with the nominal compositions CaTi_{1 – y} In_yO_{3 –} , synthesized in the range y=0.05–0.3, consisted of two phases: CaTiO_{3 –} and a CaIn₂O₄-based phase. The compositions of the synthesized phases were checked by x-ray microanalysis. The electrical conductivity of the CaTi_{1 – x} Cr_xO_{3 –} (0 < × 0.2)solid solutions was measured as a function of oxygen partial pressure (0.21 × 10⁴ to 1.0 × 10^–11 Pa) at 900 and 1000°C. Cr doping of calcium titanate was shown to increase its conductivity. A mechanism of defect formation in doped calcium titanate was inferred from conductivity versus data.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 475–478.Original Russian Text Copyright © 2005 by Murashkina, Demina.     

Influence of Argon on the Phase Behavior and Vibrational Properties of Solid Nitrogen at High Pressure

The mixed solid N ₂–Ar has been studied at high pressure at the nitrogen–rich side of the phase diagram by Raman spectroscopy. The argon atoms dissolve into some of the nitrogen structures. Within the *–phase the Ar–-atoms are mainly located at the sphere–like disordered sites in agreement with computer simulations. The second order transition of pure N ₂ is still present in the mixed solid at 25 mole% Ar. The * – * and *–fluid transitions in the mixed solid are shifted compared to the pure system. The phase diagram of the mixture for x[N ₂]0.75 has been studied.     

Piezoelectric and mechanical properties of ceria-doped lead zirconate titanate ceramics

Phases, microstructures and properties of lead-zirconate-titanate (PZT) ceramics with the compositions Pb(Zr_0.535– Ce Ti_0.465) O₃ where =0.0, 0.001, 0.01, 0.02 and 0.05 were studied. Rhombohedral and tetragonal phases were present at =0.0. The amount of the rhombohedral phase increased with increasing , and only the tetragonal phase was present for >0.001. Thec/a ratio of the tetragonal phase also increases with increasing . Particles of CeO₂ were found to be present in compositions with >0.01, indicating that the solubility of CeO₂ is less than 1a/o on the metals basis. The piezoelectric and electromechanical constants achieved maximum values for =0.001. The hardness increased monotonically with increasing . The modulus of rupture and the fracture toughness, however, went through a minimum and both stayed lower than their values for =0.     

Transport Properties of Ca1 – x MnO3 – δ + xCeO2(0 < x ≤ 0.15) Mixtures

Data are presented on the temperature-dependent electrical conductivity and thermoelectric power of Ca_{1 – x} MnO_{3 –} + xCeO₂ (0 < x 0.15) mixtures obtained as intermediate products in the synthesis of Ca_{1 – x} Ce _x MnO_{3 –} solid solutions. The electrical properties of the mixtures are shown to be dominated by those of the perovskite-like phase Ca_{1 – x} MnO_{3 –} and to depend on Ca concentration. All of the samples with 0 x 0.15 exhibit n-type conductivity. The charge transport in CaMnO_{3 –} below 930 K is attributable to small-polaron hopping. At higher temperatures, conduction through delocalized states seems to prevail. In the Ca_{1 – x} MnO_{3 –} + xCeO₂ mixtures with 0.05 x 0.15, small-polaron hopping is observed between 160 and 920 K. Below 160 K, the temperature variation of conductivity in the samples with x = 0.1 and 0.15 follows Mott's law.     

Mixtures of (N2)1−x : (O2) x at High Pressures and Low Temperatures

We performed Raman measurements at 18 K and pressures up to 25 GPa in order to construct a tentative phase diagram of the (N ₂)_1–x :(O ₂)_x –system at low temperatures. We varied the composition of the mixed system over the whole concentration range. Here we focused on the systems with high nitrogen concentration and pressures above 2 GPa. It is known that at room temperature oxygen is highly solvable in the –phase of N ₂. The experimental results show that oxygen suppresses the disorder–order transition –N ₂.     

Superconductivity of (Y1−xREx)Ba2Cu3O7#x2212;δ system

Polycrystalline samples of the superconducting oxides (Y_1–x RE _x )Ba₂Cu₃O_7– (RE = Er and Dy) withx=0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared. From the X-ray diffraction and the electrical resistivity measurements, it was found thatT _c and the unit cell volume have common peaks nearx0.4. Close examination of previously published data on the (Y_1–xRE _x )Ba₂Cu₃O_7– system also indicate that an anomaly exists nearx–0.4. This anomaly is ascribed to an anomalous change of in oxygen nearx0.4.     

Phase Equilibria and Structure of Solid Solutions in the La–Co–Fe–O System at 1100°C

Phase equilibria in the La–Co–Fe–O system are studied at 1100°C in air using samples prepared by the citrate, nitrate, and conventional ceramic routes. The stability regions and structures of solid solutions in the La–Co–Fe–O system are determined by x-ray powder diffraction: LaCo_{1 – y} Fe _y O_{3 –} (0 < y 0.25, sp. gr. R c; 0.775 y< 1, sp. gr. Pbnm), Co_{1 – y} Fe _y O (0 < y 0.13, NaCl-type structure, sp. gr. Fm3m), and Fe_{3 – x} Co _x O₄ (0.84 x 1.38, sp. gr. Fd3m). The structural parameters of phase-pure solid solutions are determined by the Rietveld method. The composition dependences of lattice parameters are presented for LaCo_{1 – y} Fe _y O_{3 –} (0 < y 0.25) and Fe_{3 – x} Co _x O₄ (0.84 x 1.38). The 1100°C isotherm of the pseudoternary system La₂O₃–CoO–Fe₂O₃ in air is constructed.     

Synthesis, Structure, Microstructure, and Electrical Conductivity of (La,Sr)(Ga,Mg)O3 – δOxide-Ion-Conducting Ceramics

Oxide-ion-conducting perovskite ceramics (La_{1 – y} Sr _y )(Ga_{1 – x} Mg _x )O_{3 –} were prepared using hydrated Mg and La salts as starting reagents. X-ray diffraction and IR spectroscopy data demonstrate that the symmetry of the solid solutions changes in the sequence orthorhombic–rhombohedral–cubic with increasing Sr + Mg content.     

Anomalous High-Temperature Properties of BaPbO3-Based Solid Solutions

The thermal expansion, thermal stability, and electrical resistivity of the Ba_{1 – x} M _x Pb_{1 + y} O_{3 +} (M = Sr, Ca; 0 x 1.0, 0 y 0.2) and Ba_{1 – x} M" _x Pb_{1 – y} M" _y O_{3 +} (M" = K, La; M" = Sc, Sb; x, y= 0.01) ceramic materials were studied between 293 and 1073 K in air. The linear thermal expansion coefficient of the ceramics was found to increase abruptly at 700 K, from (10–14) × 10^–6K^–1in the range 300–600 K to (13–18) × 10^–6K^–1in the range 800–1000 K. The electrical resistivity of the ceramics passes through a sharp maximum near 750 K, with the largest jump in resistivity at the compositions Ba_0.6Sr_0.4PbO₃and Ba_0.9Ca_0.1PbO₃. The anomaly in thermal expansion is likely associated with the rearrangement of the lead–oxygen polyhedra in the structure of the solid solutions, and the jump in resistivity is attributable to changes in the average oxidation state of Pb ions in the surface layer of the ceramics.     

Piecewise polynomials and the partition method for nonlinear ordinary differential equations

Summary An efficient numerical method, used previously for linear differential equations [1], is here extended to systems of nonlinear ordinary differential equations. Spline functions are used as the basic approximations. Residuals are liquidated by setting their integrals equal to zero over specified subintervals of the intervals of analyticity. Several diverse examples are given.Notation a Radius of circular membrane - [C _j ] An unsymmetrical 4×4 matrix, defined by Eq. (6) - [C _j ] An unsymmetrical 6×6 matrix, defined by Eq. (8) - E Young's modulus - F _i Algebraic or transcendental functions - L Differential operator - R Closed interval - T Dimensionless radius stress for the circular membrane - [Y _j ] The transpose of the row matrix [y _j –1,y _j –1,y _j ,y _j ] - [Y _j ] The transpose of the row matrix [y _j –1,y _j –1,y _j–1 ,y _j ,y _j ,y _j ] - Residual - Poisson's ratio Formerly with Department of Theoretical and Applied Mechanics, University of Illinois, Urbana, Illinois, USA.