Effect of Nd2O3 Concentration on the Defect Structure of CeO2–Nd2O3 Solid Solution

An extensive X-ray study of CeO₂–Nd₂O₃ solid solutions was performed, and the densities of solid solutions containing various concentrations of NdO_1.5 were measured using several techniques. Solid solutions containing 0–80 mol% NdO_1.5 were synthesized by coprecipitation from Ce(NO₃)₃ and Nd(NO₃)₃ aqueous solutions, and the coprecipitated samples were sintered at 1400°C. A fluorite structure was observed for CeO₂–NdO_1.5 solid solutions with 0–40 mol% NdO_1.5, which changed to a rare earth C-type structure at 45–75 mol% NdO_1.5. The change in the lattice parameters of CeO₂–NdO_1.5 solid solutions, when plotted with respect to the NdO_1.5 concentration, showed that the lattice parameters followed Vegard's law in both the fluorite and rare earth C-type regions. The maximum solubility limit for NdO_1.5 in CeO₂ solid solution was approximately 75 mol%. The relationship between the density and the Nd concentration indicated that the defect structure followed the anion vacancy model over the entire range (0–70 mol% NdO_1.5) of solid solution.     

Orthophosphates and Diphosphates Containing Zinc and Copper and Zinc and Cobalt

Solid solutions of diphosphates of zinc and copper and of zinc and cobalt were synthesized from mixtures of pure diphosphates at temperatures up to 1000°C. Their X-ray diffractometry patterns varied continuously from one end member to the other. Solid solutions of orthophosphates of composition Zn_3−xCox(PO₄)2, with x = 0.4–1.6, were formed at temperatures up to 950°C; all exhibited the structure of γ-Zn₃(PO₄)2. Solid solutions of orthophosphates of composition Zn_3−xCu_x(PO₄)2 exhibited more-complex behavior. At 1000°C and copper contents of 20–80 mol%, a phase that is related to Cu₃(PO₄)2, termed here the "ε-phase," predominated. At 850°–950°C and in the region from 20 mol% to ∼33 mol% of copper, the solid solutions (the "η-phase") adopted the structure of graftonite. At 800°–900°C and 10–15 mol% of copper, the solid solutions exhibited a new structure (the "δ-phase"), which we found to be related to the mineral sarcopside. At temperatures 950°C, the solutions that contained 5–15 mol% of copper (the "β-phase") had the structure of β-Zn₃(PO₄)2, whereas at 800°–850°C, solutions with 5 mol% of copper (the "-phase") exhibited the structure of γ-Zn₃(PO₄)2. Attempts to synthesize Cu⁺ZnPO₄ and Cu⁺Cu²⁺Zn₃(PO₄)3 were unsuccessful.     

Scandium-Doped Anatase (TiO2) Nanoparticles Directly Formed by Hydrothermal Crystallization

Anatase-type TiO₂ solid solutions doped with 0–10 mol% scandium were formed by hydrothermal crystallization under weak basic conditions above 180°C for 5 h from amorphous co-precipitates that were obtained from the aqueous precursor solutions of TiOSO₄ and Sc(NO₃)₃ using aqueous ammonia. The anatase particles were spindle-like and consisted of nanosized-crystallites (23–25 nm). The lattice parameter c ₀ of anatase and the length and width of the spindle-like anatase gradually increased when the scandium content was increased. The diffuse reflectance spectra of the as-prepared TiO₂ doped with scandium showed that the onset of absorption slightly shifted to longer wavelengths with increasing scandium content. The band gap of anatase was slightly increased by making solid solutions with scandium oxide.     

Phase Relations and Ordering in the System Erbia-Hafnia

The system erbia-hafnia was investigated using thermal expansion measurements and room-temperature X-ray diffraction of quenched and annealed samples. The range of existence of the solid solutions based on HfO₂ and Er₂O₃ was determined by the precision lattice parameter method. Three compounds with hexagonal structure are reported: the first is an ordered fluorite-related phase with the ideal formula Er₄Hf₃O₁₂ and decomposes with increasing temperature at ∼1500°C into a solid solution of the fluorite type; the second is formed at ∼55 mol% Er₂O₃, corresponding closely to the formula Er₅Hf₂O_11.5, and undergoes a transformation at ∼1650°C into cubic solid solutions to fluorite and C type. The third compound is formed within the concentration range between 60 and 90 mol% Er₂O₃. This compound, Er₆HfO₁₁, decomposes at ∼1700°C into a cubic solid solution of the C type. A proposed phase diagram for the system erbia-hafnia is presented.     

Formation, Characterization, and Hot Isostatic Pressing of Cr2O3-Doped ZrO2 (0,3 mol% Y2O3) Prepared by Hydrazine Method

In the ZrO₂-Cr₂O₃ system, metastable t -ZrO₂ solid solutions containing up to 11 mol% Cr₂O₃ crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter c decreases linearly from 0.5149 to 0.5077 nm with increased Cr₂O₃ content, whereas the lattice parameter a is a constant value ( a = 0.5077 nm) regardless of the starting composition. At higher temperatures, transformation (decomposition) of the solid solutions proceeds in the following way: t (ss)→ t (ss) + m + Cr₂O₃→ m + Cr₂O₃. Above 11 mol% Cr₂O₃ addition, c-ZrO₂ phases are formed in the presence of Cr₂O₃. The t -ZrO₂ solid solution powders have been characterized for particle size, shape, and surface area. They consist of very fine particles (15–30 nm) showing thin platelike morphology. Dense ZrO₂(3Y)-Cr₂O₃ composite ceramics (∼99.7% of theoretical) with an average grain size of 0.3 μm have been fabricated by hot isostatic pressing for 2 h at 1400°C and 196 MPa. Their fracture toughness increases with increased Cr₂O₃ content. The highest K _Ic value of 9.5 MPa·;m^1/2 is achieved in the composite ceramics containing 10 mol% Cr₂O₃.     

Formation of Metastable Fluorite Phase by Rapid Quenching of Melts in the Y2O3-Ta2O5 System

Melts of x mol% Ta₂O₅–Y₂O₃ (x = 0–32.5) were rapidly quenched to investigate the formation of metastable fluorite solid solutions. C-type Y₂O₃, fluorite, and fergusonite phases existed in the compositional regions of 0 x 16, 8 x 32.5, and 27.5 x 32.5, respectively. Their lattice parameters were precisely measured through either Rietveld analysis or a least-squares fit of the individual X-ray diffraction peak positions. The lattice parameter of the fluorite phase decreased linearly with increasing Ta₂O₅ content, strongly suggesting the formation of compositionally homogeneous metastable solid solutions. Ta₂O₅ was almost insoluble into Y₂O₃ at 1700°C in the equilibrium state.     

Effect of Ni and Co Additives on Phase Decomposition in TiB2–WB2 Solid Solutions Formed by Induction Field Activated Combustion Synthesis

Solid solutions of TiB₂–WB₂ were densified and annealed simultaneously to cause the decomposition into the phases (Ti,W)B₂ and (W,Ti)B₂. Ni and Co were added to solid solutions formed by induction field activated combustion synthesis. The presence of these metals as additives markedly enhanced the kinetics of the subsequent decomposition process. With these additives, decomposition to the two phases occurred within minutes (360 s) in contrast to hours when the solutions did not include the additives. The phases resulting from decomposition, (Ti,W)B₂ and (W,Ti)B₂, were identified by X-ray to have the hexagonal AlB₂ and W₂B₅ structures, respectively. The precipitated phase, (W,Ti)B₂, occurred as elongated grains with aspect ratios of as high as about 10 in samples containing Ni as the additive.     

Formation of Alumina/Zirconia (3 mol% Yttria) Composite Powders Prepared by the Hydrazine Methods

Alumina/3 mol% yttria-doped zirconia composite powders have been prepared by the hydrazine method. As-prepared powders are AlO(OH) gel solid solutions and the mixtures of this and amorphous ZrO₂ below and above 10 mol% ZrO₂, respectively. The formation process leading to α–Al₂O₃– t -ZrO₂ composite powders is examined.     

Formation and Transformation of Cubic ZrO2 Solid Solutions in the System ZrO2—Al2O3

In the system ZrO₂-Al₂O₃, cubic ZrO₂ solid solutions containing up to 40 mol% Al₂O₃ crystallize at low temperatures from amorphous materials prepared by the simultaneous hydrolysis of zirconium and aluminum alkoxides. The values of the lattice parameter, a, increase linearly from 0.5095 to 0.5129 nm with increasing Al₂O₃ content. At higher temperatures, the solid solutions transform into tetragonal ZrO₂ and α-Al₂O₃. Pure ZrO₂ crystallizes in the tetragonal form at 415° to 440°C.     

Metastable Phase Selection and Partitioning for Zr(1−x)AlxO(2−x/2) Materials Synthesized with Liquid Precursors

Aqueous solutions of zirconium acetate and aluminum nitrate were spray pyrolyzed at 250°C and upquenched to different temperatures to yield metastable solid solutions of composition Zr_{(1− x )}Al_xO_{(2− x /2)}. An amorphous oxide forms first during pyrolysis which subsequently crystallizes as a single phase for x ≤ 0.57 (≤40 mol% Al₂O₃). The crystallization temperature increased with Al₂O₃ content. Electron diffraction, supported by Raman spectroscopy, indicates that the initial phase is tetragonal. At higher temperatures, the initial solid solation partitions to other metastable phases, viz., t -ZrO₂+γ-Al₂O₃, prior to achieving their equilibrium phase assemblage, m -ZrO₂+α-Al₂O₃. Partitioning yields a nanocomposite microstructure with grain sizes of 20–100 nm, compared to the 3 to 5 nm in the initial, single phase. Compositions containing 45 to 50 mol% Al₂O₃ concurrently crystallize and partition. The structure selected during crystallization and the partitioning phenomena are discussed in terms of diffusional constraints during crystallization, which are conceptually similar to those operating during rapid solidification.     

Stoichiometry of Fluorotopaz and of Mullite Made from Fluorotopaz

Mixtures of alumina and silica containing 68–78 wt% alumina react above 600°C with 0.5 mol of SiF₄ per mole of alumina to form fluorotopaz. High-resolution X-ray powder diffraction data were used to determine very accurate cell parameters of fluorotopaz as a function of 1 wt% compositional increments. The samples containing 69–76 wt% A1₂O₃ were found to have a linear cell parameter relationship. Compositions outside that range show discontinuities in the cell parameters, indicating solid solution behavior between 69 and 76 wt% alumina. Within this range the composition of fluorotopaz may be written 2A1₂O₃·_xSiO₂· SiF₄ where 1.07 x 1.53. Pyrolysis of all compositions of fluorotopaz solid solution yields mullite whiskers containing 76.1 wt% alumina (65.2 mol%).     

Density, Surface Tension, and Viscosity of PbO-B2O3-SiO2 Glass Melts

The density, surface tension, and viscosity of the melts from the PbO-B₂O₃-SiO₂ system have been measured at temperatures in the range 1073–1473 K. The effect of composition on these properties was also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO₂/B₂O₃ ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ∼60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B₂O₃ content in the range of the PbO content between 30–60 mol%, and mainly by the PbO content in the range of the PbO content >60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B₂O₃ was half that of SiO₂ (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction.     

Formation of Zirconia Solid Solutions Containing Alumina Prepared by New Preparation Method

In the system ZrO₂–Al₂O₃, a new method for preparing ZrO₂ solid solutions from ZrCl₄ and AlCl₃ using hydrazine monohydrate is investigated. c -ZrO₂ solid solutions containing up to ∼40 mol% Al₂O₃ crystallize at low temperatures from amorphous materials. The formation mechanism is discussed from IR spectral data. The values of the lattice parameter α increase linearly from 0.5072 to 0.5105 nm with increasing Al₂O₃ content. At higher temperatures, transformation of the solid solutions proceeds as follows: c ( SS ) → t ( ss ) → t ( ss ) +α-Al₂O₃→ m +α-Al₂O₃. m -ZrO₂–α-Al₂O₃ composite ceramics are fabricated by hot isostatic pressing for 2 h at 1250°C and 196 MPa. Microstructures and mechanical properties are examined, in connection with increasing Al₂O₃ content.     

Synthesis of Gadolinium-Doped Ceria Powders by Electrolysis of Aqueous Solutions

A gadolinium-doped ceria powder was produced by electrolysis of an aqueous solution containing Ce³⁺ and Gd³⁺ ions using direct and alternating current at 4–10 V of applied voltage between two platinum wire electrodes (anode and cathode). The powders produced were identified as a gadolinium-doped ceria solid solution by X-ray diffraction and chemical analysis. Large porous particles 60–70 μm in size were produced under a direct current field for 15 min. On the other hand, nanoparticles 40–250 nm in size were produced for 6–12 h of electrolysis using alternating current below 20 Hz of frequency. No particles were formed in the high frequency range from 100 Hz to 1 MHz. The nucleation and growth rates of the particles depended on the frequency of the alternating current and electrolysis time applied. The Gd₂O₃/CeO₂ ratio of the particles formed with alternating current was lower than that of the starting solution.     

Synthesis of High-Tc Dual-Phase Ag–YBa2Cu3O7–x Superconductor Composite Powders by Sol–Gel Process

Fine, homogeneous, dual-phase Ag–YBa₂Cu₃O_{7– x} composite powders were prepared by a simple colloidal sol–gel coprecipitation technique that was previously used for synthesis of single-phase YBa₂Cu₃O_{7– x} . Samples containing up to 60 wt% silver were synthesized. Silver neither reacted with nor degraded the YBa₂Cu₃O_{7– x} . The presence of silver was found to aid the oxygenation of the precursor during calcination to form orthorhombic YBa₂Cu₃O_{7– x} . Measurements made by ac magnetic susceptibility showed no significant degradation in transition temperature for samples containing up to 40 wt% silver.     

Direct Formation and Photocatalytic Performance of Anatase (TiO2)/Silica (SiO2) Composite Nanoparticles

Anatase (TiO₂)/silica (SiO₂: 23.9–27.7 mol%) composite nanoparticles were directly synthesized from (i) the reaction of titanyl sulfate (TiOSO₄) and sodium metasilicate (Na₂SiO₃) under mild hydrothermal conditions, (ii) the acidic precursor solutions of TiOSO₄ and tetraethylorthosilicate (TEOS) by thermal hydrolysis, and (iii) the metal alkoxides, i.e., tetraisopropoxide (TTIP) and TEOS, by the sol–gel method. Their photocatalytic activities were evaluated by measurements of the relative concentration of methylene blue after UV irradiation. The as-prepared TiO₂/SiO₂ composite nanoparticles showed far more improved photocatalytic activity than the pure anatase-type TiO₂. The composite nanoparticles formed from (i) TiOSO₄ and Na₂SiO₃ as well as those from (ii) TiOSO₄ and TEOS showed fairly good photocatalytic activity, and it was better than that of those synthesized from (iii) the metal alkoxides, which was suggested to be due to the difference in crystallinity of the anatase.     

Solid Solubility of GeO2 in SnO2

Subsolidus equilibrium relations were reexamined in the SnO₂-rich portion of the system GeO₂-SnO₂ (60 to 98 mol% SnO₂). A limited solid solution based on SnO₂ was confirmed; 4mol% GeO₂ dissolved in SnO₂ at 1250 C, and glass was formed on quenching over the compositional range above 4mol% GeO₂. Phase relutions in the system are discussed with reference to the polymorphism of GeO₂ and its glass-forming ability, and a possible phase diagram is given .     

Revised Phase Diagram of the System ZrO2-CeO2 Below 1400°C

The phase diagram of the system ZrO₂-CeO₂ was rein-vestigated using hydrothermal techniques. Cubic, tetragonal, and monoclinic solid solutions are present in this system. The tetragonal solid solution decomposes to monoclinic and cubic solid solutions by a eutectoid reaction at 1050°50°C. The solubility limits of the tetragonal and cubic solid solutions are about 18 and 70 mol% CeO₂, respectively, at 1400°C, and about 16 and 80 mol% CeO₂, respectively, at 1200°C. Solubility limits of the monoclinic and cubic solid solutions are about 1.5 and 88 mol% CeO₂ at 1000°C, and 1.5 and 98 mol% CeO₂ at 800°C, respectively. The compound Ce₂Zr₃O₁₀ is not found in this system.     

Formation and Transformation of TiO2 (Anatase) Solid Solution in the System TiO2—Al2O3

In the system TiO₂—Al₂O₃, TiO₂ (anatase, tetragonal) solid solutions crystallize at low temperatures (with up to ∼ 22 mol% Al₂O₃) from amorphous materials prepared by the simultaneous hydrolysis of titanium and aluminum alkoxides. The lattice parameter a is relatively constant regardless of composition, whereas parameter c decreases linearly with increasing Al₂O₃. At higher temperatures, anatase solid solutions transform into TiO₂ (rutile) with the formation of α-Al₂O₃. Powder characterization is studied. Pure anatase crystallizes at 220° to 360°C, and the anatase-to-rutile phase transformation occurs at 770° to 850°C.     

Direct Formation of Iron(III)-Doped Titanium Oxide (Anatase) by Thermal Hydrolysis and Its Structural Property

Anatase-type TiO₂ (titania) doped with iron up to 19.8 mol% was directly formed as nanometer-sized particles from acidic precursor solutions of TiOSO₄ and Fe(NO₃)₃ by simultaneous hydrolysis, under mild hydrothermal conditions at 180°3C. Iron content in the anatase-type TiO₂ was much less than that of the starting composition of the precursor solutions because of slower hydrolysis rate of Fe(NO₃)₃ than that of TiOSO₄ at 180°3C. The XRD data, TEM selected-area diffraction patterns, and Mössbauer effect measurement showed that iron(III) formed a solid solution in the anatase-type TiO₂ precipitates and that there was no iron oxide precipitated as secondary phase without making a solid solution with TiO₂ present in the precipitates. Doping of Fe₂O₃ into TiO₂ shifted the phase transformation from anatase-type to rutile-type structure to a low temperature. On the phase transformation from anatase to rutile, iron oxide was precipitated as Fe₂TiO₅ (pseudobrookite) phase. When the iron content was increased in the anatase phase, onset of optical absorption shifted to longer wavelengths, and absorption in the UV-light region and in the visible-light region over 400–600 nm clearly appeared in the diffuse reflectance spectra of the as-prepared Fe(III)-doped TiO₂.