Phase Relations in the Cu–Sb–O System

The Cu–Sb–O system was studied by x-ray diffraction and thermal analysis between 700 and 1000°C. The compositions of copper antimonates were refined. Sb₂O₄ was found to exist in two polymorphs above 800°C: -Sb₂O₄ (dominant phase) and -Sb₂O₄. The evolution of phase equilibria with increasing temperature was examined. The isothermal sections of the Cu–Sb–O phase diagram were mapped out using new and earlier reported results.     

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).     

Phase Relations in the NaVO3–Ca(VO3)2 System

The phase diagram of the NaVO₃–Ca(VO₃)₂ system is mapped out. The system is shown to contain NaVO₃-based solid solutions (0–5 mol % Ca(VO₃)₂), Ca(VO₃)₂-based solid solutions (0–17 mol % NaVO₃), and the double metavanadate Na₂Ca(VO₃)₄. The results on the sequence of phase changes during heat treatment of an Na₂CO₃ + CaCO₃ + 2V₂O₅ mixture and on the direction of diffusion flows (studied by the Tubandt method) indicate that the phase formation in the NaVO₃–Ca(VO₃)₂ system is mainly due to the diffusion of Na⁺ ions.     

Phase Relations in the SiC–LaB6 System

The T–x phase diagram of the SiC–LaB₆ join in the quaternary system La–B–C–Si is mapped out. The join is shown to be pseudobinary, with simple eutectic phase relations. The eutectic is located at 74 mol % SiC and 26 mol % LaB₆, with a melting point of 2110 ± 20°C.     

Phase evolution and gas-phase particle size distributions during spray pyrolysis of (Bi,Pb)SrCaCuO and Ag(Bi,Pb)SrCaCuO powders

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)SrCaCuO powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi_1.8Pb_0.44Sr₂Ca_2.2Cu₃O_x composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)SrCaCuO powders were (Bi,Pb)₂Sr₂CuO_x (2201), Ca₂PbO₄ (plumbate), (Bi,Pb)₂Sr₂CaCu₂O_x(2212), and (Bi,Pb)₃Sr₂Ca₂Cu₁O_x(3221). For T≥800°C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900°C, a large number of ultrafine particles (<30 nm) were formed, probably from the PbO vapor released from the reactor walls. Using spray pyrolysis, it is easy to control stoichiometry and limit the phase segregation at the nanometer-scale so that homogeneous and phase-pure materials can be obtained rapidly during subsequent processing.     

Phase Relations in the Reduction of Solid Solutions in the Co–Mn–Ti–O System

The hydrogen reduction of spinel solid solutions in the Co–Mn–Ti–O system was investigated by a static method. Six phase regions were identified in which the gas phase is in equilibrium with various combinations of -Co, TiO₂ (rutile), and solid solutions of variable composition: Co _A Mn _B Ti_{3 – A – B} O₄ (spinel), Co _m Mn_{2 – m} TiO₄ (spinel), Co _N Mn_{1 – N} TiO₃ (ilmenite), and Co _n Mn_{1 – n} O (NaCl). The equilibrium compositions of the solid solutions and the corresponding oxygen partial pressures were determined, and the general trends of the reduction of spinel solid solutions in the Co–Mn–Ti–O system were established.     

Phase Relations in the NiFe2O4–NiCr2O4–CuCr2O4System

The phase relations in the NiFe₂O₄–NiCr₂O₄–CuCr₂O₄system were investigated experimentally and theoretically. X-ray diffraction data were used to construct the phase diagram of the system and elucidate the structural mechanisms of the transitions from the cubic spinel structure to the tetragonal (I42d, c/a< 1 and I4₁/amd, c/a> 1) and orthorhombic (Fdd2) structures.     

Effect of Cd Substitution for Bi on Superconductivity of the Bi-2201 Phase in the Bi—La—Ca—Cu—O System

A series of the Bi-2201 samples with the nominal composition of (Bi_2–x Cd _x )La_0.7Ca_1.3CuO _z has been synthesized and effect of Cd substitution for Bi on the superconductivity has been investigated. As a result, it is found that almost single phase samples are obtained for a considerable wide composition of 0.0 x 0.8, their crystal structures have a tetragonal or a pseudotetragonal symmetry in the whole composition range, and the sample unexpectedly changes from superconductor to semiconductor by little Cd-substitution of about 0.1. The semiconducting samples show a temperature dependence of the resistivity suggesting that the transport process is followed by a three-dimensional variable range hopping conduction.     

The Effect of Sn Substitution of Pb on Microstructure and Superconducting Properties of Bi–Pb–Sr–Ca–Cu–O Superconductor

The effect of substitution of Pb by Sn in Bi_1.6Pb_0.4?x Sn _x Sr₂Ca₂Cu₃ O _δ samples at x = 0.0, 0.1, 0.2, and 0.3 on the critical transition temperature and structural properties was investigated in this work. All the samples were prepared by the solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), resistance–temperature curve (R–T), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The Sn ⁴⁺ substitution of Pb ²⁺ caused significant changes in the properties of the samples. The formation of the (Bi, Pb)-2212 phase was stabilized and the T _c (onset) was improved at the x = 0.2 level of Sn ⁴⁺ substitution. The SEM micrographs have shown that the structure of the sample with x = 0.2 became more dense. However, samples with x = 0.1 and 0.3 have not shown zero resistance by EDS analysis because of oxygen deficiency.     

Stable and Metastable Phase Equilibria in the Bi2O3–BiPO4 System

The stable and metastable phase equilibria in the Bi₂O₃–P₂O₅ system were studied in the range 0–50 mol % P₂O₅ by differential thermal analysis and x-ray diffraction. The results were used to construct the corresponding phase diagrams. In the equilibrium state, the system contains one sillenite phase with Bi₂O₃ : P₂O₅ = 12 : 1 and four other bismuth phosphates (2 : 1, 3 : 1, 5 : 1, and 1 : 1). In a metastable state, resulting from solidification of metastable melts, there exist * solid solutions (0–25 mol % P₂O₅) based on the high-temperature form of Bi₂O₃. At lower temperatures, the * phase transforms eutectoidally into the metastable phase, which has the same structural basis as the high-temperature solid solutions. At room temperature, the phase exists in a narrow composition range around 15 mol % P₂O₅. At lower P₂O₅ contents, the * phase decomposes at 868 K by a monotectoid reaction to form a mixture of the metastable and phases. The phases 3Bi₂O₃ · P₂O₅ () and 2Bi₂O₃ · P₂O₅ (), melting incongruently at 1193 and 1223 K, respectively, appear in both the equilibrium and metastable phase diagrams.     

Phase Transformations in the Y2Cu2O5–BaCuO2 System

The sequence of phase transformations in the Y₂Cu₂O₅–BaCuO₂ pseudobinary system was studied during heating and cooling in the range 1170–1310 K. The results demonstrate that the reaction zone in BaCuO₂/Y₂Cu₂O₅ diffusion couples consists of BaCuO₂/YBa₂Cu₃O_{7 –} /Y₂BaCuO₅/Y₂O₃/Y₂Cu₂O₅ layers, corresponding to the sequence of chemical changes during YBa₂Cu₃O_{7 –} crystallization between 1170 and 1220 K. In the range 1260–1310 K, BaCu₂O₂ is formed. During cooling of a Y₂Cu₂O₅ + 4.3BaCuO₂ mixture, YBa₂Cu₃O_{7 –} crystallizes in a wide temperature range, between 1240 and 1190 K. The process depends on the presence of BaCu₂O₂ on the surface of Y₂BaCuO₅ grains in the high-temperature solution and the oxygen supply from the gas phase.     

Phase Relations in the SnSe2–Er2Se3 System

The phase diagram of the SnSe₂–Er₂Se₃ system is studied using differential thermal analysis, x-ray diffraction, microstructural analysis, and microhardness and density measurements. The SnSe₂–Er₂Se₃ system is pseudobinary and contains two eutectics and two intermediate phases, Er₂Sn₃Se₉ and Er₂SnSe₅. At room temperature, the SnSe₂-based solid solution extends to 4.5 mol % Er₂Se₃, and the SnSe₂ solubility in Er₂Se₃ is 2 mol %.     

Phase Equilibria in the Li–W–Mn–O System

An isothermal compositional subsolidus phase equilibrium diagram of the Li–W–Mn–O system is constructed. Possible solid-state transformations in the system at a variable pressure and constant temperature are presented and phase transformations involving melt in temperature and pressure ranges of interest are analyzed.     

Phase Relations in the Li–V2O5–Cu System at 600°C and Cathodic Properties of Cu x V2O5

The phase relations in the Li–V₂O₅–Cu system at 600°C are studied by x-ray diffraction. The existence of the known vanadium bronzes M _x V₂O₅ (M = Li, Cu) is confirmed, and the composition ranges of the related solid solutions are determined. -Li _x V₂O₅ (0.22 x 0.49) and -Li _x V₂O₅ (0.88 x 1.0) are shown to dissolve Cu, forming Li _x Cu _y V₂O₅ solid solutions with y = 0.72 – 1.48x and y = 0.58 – 0.18x, respectively. Cu _x Li _y V₂O₅ solid solutions (y= 0.51 – 0.76 x) are only obtained from -Cu _x V₂O₅ (0.24 x 0.67). -Li _x V₂O₅ and -Cu _x V₂O₅ form a continuous series of solid solutions. The cathodic properties of Li–V₂O₅–Cu materials in high-temperature pulsed lithium batteries are investigated.     

Phase Relations in TiAl+Nb System

The microstructures and phases of ternary TiAl+Nb alloys containing 50-60 at.-%Al, 0-21 at.-%Nb have been studied using transmission electron microscopy (TEM) and X-ray powder diffraction. The phases present in the alloys and their distribution were found to be a sensitive function of composition. The phase relations between γ-TiAl and γ1 (a new ordered ternary intermetallic compound based on γ-TiAl) were determined. Essentially single γ phase was determined for alloys with relativety low Nb content (≤10 at.-%Nb). the γ1 phase was determined to exist in the composition range containing higher Nb contents (15-21 at.-%Nb). Between γ and γ1 phases, with intermediate Nb contents there is a transitional phase γ1 (a superstructure of γ-TiAl). As for the influence of Al concentration on the phase relations. the γ1 phase was inclined to form in the alloys with relatively high Al contents. The ordering transformation of γ, to γ1 is a continuous ordering process and the transition may be second order.     

Effect of silver addition on superconductivity in the Bi1.6Pb0.4Sr1.6Ca2Cu3O10−y system

Silver/superconductor composites containing 0 to 80 vol% silver have been prepared and their properties determined. Optimum heat treatment at sintering temperatures ( 800° C) under low oxygen pressures produces material with high critical current density and improves physical properties. Magnetic susceptibility measurements have been found to be consistent with resistivity results. In order to retain a single high-T _c phase with increasing silver content, decreased oxygen partial pressures are required. Using the normal-state resistivity of these composites, a percolation threshold at a silver volume fraction of 43% was observed, while zero resistivity measurements show that a continuous superconducting network can be obtained with up to 80 vol% silver. The critical current density of 21 vol% silver-doped samples was found to be 1520 A cm^–2 at 77.3 K, compared to 260 A cm^–2 for an undoped sample.     

Observation of the Energy Gap above T c in (Bi,Pb)2Sr2Ca2Cu3O10+δ using Break-Junction Tunneling

Tunneling measurements of (Bi,Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀₊ have been carried out with break junction to study the gap feature above T _c = 106 K. The decreasing gap magnitude with increasing the temperature does not disappear at T _c for the most significant data. The gap-closing temperature is found to be T* 160 K.