Stannous-Stannic Equilibrium in Molten Binary Alkali Silicate and Ternary Silicate Glasses

The stannous-stannic equilibrium in binary alkali silicate and ternary silicate glasses was studied by equilibrating glassmelts with air at 1400°C. The Sn²⁺-Sn⁴⁺ equilibrium shifts more toward the oxidized state with increasing ionic radii of the alkali ions or with increasing concentration of the alkali ions in the same series of glasses. The slope of the straight lines obtained on plotting log (Sn⁴⁺)/(Sn²⁺)( pO₂ )^n/2 vs mol% R₂O increased in the order Li→Na→K. In ternary silicate glasses having the base glass composition 20Na₂O·10RO·70SiO₂, the Sn²⁺-Sn⁴⁺ equilibrium shifts more toward the reduced state, with increasing bond strength between the divalent cations and the nonbridging oxygens. With increasing temperature, the equilibrium shifts more toward the reduced state.     

Subsolidus Phase Relations and Transparent Conductors in the Cadmium-Indium-Tin Oxide System

Subsolidus phase relations have been determined in the CdO–InO_1.5–SnO₂ system at 1175°C. A cubic-bixbyite solution In_{2−2 x} (Cd,Sn)_{2 x} O₃ (0 < x < 0.34), a cubic spinel solution (1− x )CdIn₂O₄– x Cd₂SnO₄ (0 < x < 0.75), and an orthorhombic-perovskite solution Cd_{1− x} Sn_{1− x} In_{2 x} O₃ (0 < x < 0.045) having the GdFeO₃ structure have been discovered. The CdO phase field exists over a small range of InO_1.5 (<3%) and SnO₂ (<1%). Orthorhombic Cd₂SnO₄ (Sr₂PbO₄ structure) and rutile SnO₂ appear to be point compounds with negligible solubility. The vertical section between spinel CdIn₂O₄ and orthorhombic Cd₂SnO₄ was determined between 900° and 1175°C. The spinel phase field (1− x )CdIn₂O₄– x Cd₂SnO₄ was found to extend between x = 0 and x = 0.75 at 1175°C or x = 0.78 at 900°C. All of the phases in this system appear to allow small excess quantities of the donors In and/or Sn (vs cation stoichiometry) which may be the source of the electrons that give these oxides their n-type character. The electrical and optical properties of bulk and thin-film specimens in this system are compared and contrasted with each other and the relative merits of each are assessed.     

Reduction of Ions in Glass by Hydrogen

The reduction by hydrogen of Fe³⁺, Ce⁴⁺, and Sn⁴⁺ in soda-lime-silica glass was found to be diffusion-limited in the glass transition temperature range (500°C). The reduction was studied in fibers by chemical analysis and in bulk samples by optical absorption. Reduction to Fe²⁺, Ce³⁺, and Sn²⁺ proceeds by a reaction of the type H₂+2(ɛSi-O)^-+2Fe³⁺→2Fe²⁺+2(ɛSi–OH). Since the rate of reduction by hydrogen is quite similar for these systems and since reduction cannot be accomplished with CO, it is concluded that hydrogen is the diffusing species. A mechanism is developed in which hydrogen diffuses through the glass until it is trapped by a reducible ion.     

Internal Oxidation of Ce3+-BaTiO3 Solid Solutions

The reoxidation process in highly Ce³⁺-doped BaTiO₃ ceramics was studied using TEM. Samples of two different types of solid solutions, Ba_1−XCe³⁺ _X Ti_1−X/4( V _Ti) X/4 O₃ and Ba_1−XCe³⁺ _X Ti⁴⁺_{1− X} Ti³⁺ _X O₃, were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. The solid solutions were reoxidized by annealing in air at high temperatures (1000°—1100°C). As a result of internal oxidation of Ce³⁺ and Ti³⁺, fluorite CeO₂ and monoclinic Ba₆Ti₁₇O₄₀ phases were precipitated in the perovskite matrix. In Ba_1−XCe³⁺ _X Ti_1−X/4( V _Ti)X/4O3 solid solution precipitates nucleate heterogeneously at grain boundaries and at extended defects inside the grains, whereas in Ba_1−XCe³⁺_XTi⁴⁺_1−XTi³⁺_XO₃ solid solution precipitates are nucleated mainly homogeneously inside reoxidized perovskite grains. The form of the precipitates and their orientational relationship with the matrix, as well as the mechanism of internal oxidation, are discussed.     

Electroless Copper Coating of Zirconia Utilizing Palladium Catalyst

Electroless Cu coating of zirconia particles using a Pd⁰ catalyst is investigated in this paper. Uncoated and Cu-coated ZrO₂ particles are characterized by various analytical techniques to understand the mechanism of electroless Cu coating of ZrO₂ particles, which involves reduction of Pd²⁺ on ZrO₂ particle surfaces by Sn²⁺ to produce pure metallic Pd⁰ clusters, which provide catalytic sites for Cu deposition. The concept of XPS core-level binding energy shift due to small cluster size is utilized to predict the size of pure Pd⁰ clusters. The electroless Cu-coating process can be utilized in the future to produce Cu-doped ZrO₂ particles required for various potential applications.     

Mechanical Properties of Magnesia-Doped Lanthanum Chromite versus Temperature

Magnesia-doped lanthanum chromite is a potential material for use in solid oxide fuel cells as an interconnector due to its resistance to oxidation and reduction. The strength and toughness of La(Cr _0.9 Mg _0.1 )O₃ were measured from 25° to 1000^deg;C in the as-fired reduced state and after oxidation. The as-fired samples showed a peak in toughness of approximately 3.9 MPa.m^1/2 at 125^deg;C which decreased to approximately 1.4 MPa.m^1/2 at 600^deg;C and 2.8 MPa.m^1/2 at room temperature. This peak in toughness is hypothesized to be due to the rhombohedral-to-orthorhombic phase transition by a toughening mechanism that is currently being investigated. The strength was also affected by the phase transition for both the as-fired reduced and the oxidized samples.     

Parallel Solution-Based Synthesis Approach for Search of Lanthanoid-Activated Ca2SnO4 Phosphor Materials

In the search for new fluorescent materials among lanthanoid-activated Ca₂SnO₄ compounds, a parallel solution-based synthesis approach was applied and a new blue-emission Ca₂SnO₄:Ce phosphor was discovered; its emission intensity reaches 80% of the intensity of one of the best commercial Y₃Al₅O₁₂:Ce³⁺ phosphors. Among 14 lanthanoid-activated materials, three categories could be distinguished with respect to the effect of the dopant ion on the excitation and emission properties of the phosphor. In addition, potential phosphors in the A–Sn–O (A=Mg, Ca, Sr, and Ba) systems were investigated and Ca₂SnO₄ was found to be the most suitable host compound for the lanthanoid-activated phosphors.     

Cassiterite Solubility in High-Silica K2O-Al2O3-SiO2 Liquids

The saturation surface of cassiterite, SnO₂, was determined for liquids in the system K₂O–Al₂O₃–SiO₂ as a function of bulk composition and temperature. At fixed K₂O/Al₂O₃ cassiterite solubility varies weakly with SiO₂ concentration (76 to 84 mol%), temperature (1350° to 1550°C), and log ( f _O2) (−0.7 to −5.3). Cassiterite solubility is also approximately independent of composition in liquids with molar ratios of K₂O/Al₂O₃ lessthan equal to 1 (peraluminous liquids). As K₂O/Al₂O₃ increases from 1 (peralkaline liquids), however, cassiterite solubility increases steeply and approximately linearly with K₂O in excess of Al₂O₃. It is proposed that potassium in excess of aluminum combines with Sn⁴⁺ to form quasi-molecular complexes with an effective stoichiometry of K₄SnO₄.     

Crystal Chemistry and Phase Equilibria in the System CdO-PbO-O

The subsolidus portion of the system CdO-PbO-O was investigated at high temperatures and oxygen pressures in cold-seal pressure vessels. Specially prepared cadmium hydroxide precipitate was used to achieve reaction equilibria. Two ternary oxide phases exist in the system: Cd₂PbO₄ is stable under all conditions investigated; CdPb₂O₅ dissociates (2CdPb₂O₅⇋ Cd₂PbO4+Pb₃O₄+O₂). The P-T univariant curve was mapped. Compatibility triangles illustrate the phase equilibria of the system. Cell constants for Cd₂PbO₄ are: a ₀=5.671, b ₀=9.902, C ₀= 3.139, all ±0.001 Å. The space group was determined as Pbam ( Pba2 ); Cd₂PbO₄ is isostructural with the Sr₂PbO₄ structure type. Derived average metal-oxygen distances are: Cd–O 2.35 and Pb–O 2.08 Å. The structure of CdPb₂O₅ is not known.     

Effect of Impurity Cations on the Growth and Habits of SnO2 Crystals in the SnO2-Cu2O Flux System

The effects of a small amount of cations with valence states ranging from mono- to hexavalent on the growth and habits of SnO₂ crystals growing in the SnO₂-Cu₂O flux system were systematically investigated. Trivalent cations having ionic radii closer to that of Sn⁴⁺ had a conspicuous effect upon the size and habits of SnO₂. Pentavalent cations with ionic radii similar to those of Sn⁴⁺ had some effect, whereas cations of other valence states showed no effect at all.     

Microwave Characteristics of (Pb,Ca)(Fe,Nb,Sn)O3 Dielectric Materials

The dielectric properties of (Pb_{1− x} Ca _x ){(Fe_1/2Nb_1/2)_{1– y} Sn _y }O₃ solid solutions, where 0.4 lessthan equal tox ≤ 0.6, y = 0.05, 0.1, have been investigated at microwave frequencies. The replacement of Fe³⁺/Nb⁵⁺ by Sn⁴⁺ at the B–site of the perov-skite structure considerably improves the loss quality factor Q and does not remarkably affect the dielectric constant epsilon_r and the temperature coefficient of resonant frequency tau_f. The tau_f value of nearly 0 ppm/°C can be realized for x= 0.55. New high-quality dielectric ceramics having epsilon_r of 85.3-89.9,Qf values of 7510-8600 GHz, and τ_f of 0-9 ppm/°C were obtained at 1150°C for 3 h sintering in air. The influence of the sintering atmosphere on dielectric properties was also investigated.     

X-Ray Study of Phase Transitions in Ferroelectric PbNb2O6 and Related Materials

The phase transitions in PbNb₂O₆ and in compositions of the type Pb_1+x (B_xNb_1-x)O₆, where B = Ti⁴⁺, Zr⁴⁺, or Sn⁴⁺, have been investigated between 25° and 650°C. using X-ray and dilatometric techniques. The modified PbNb₂o₆ compositions possess orthorhombic PbNb₂O₆-type structure, with the additional Pb²⁺ ions occupying vacant lattice sites. The lattice parameters a and c expand and b contracts during heating until, at the ferroelectric Curie temperature, a and b suddenly coincide and c expands slightly. Besides this phase change at the Curie temperature, the nonstoichiometric compounds show an additional phase transition in the range 450° to 300°C. depending on composition. The intermediate phase of Pb_l+x(Ti₂Nb_1-z)₂O₆ appears to possess orthorhombic symmetry.     

Synthesis and Stability of Nanocrystalline Lead Stannate

Nano-crystalline PbSnO₃ was synthesized by a sol–gel route. It was an anion-deficient pyrochlore ( a = b = c = 1.0677 nm) with space group Fd3m. TEM images confirmed the nano-size of particles as ∼10 nm, aggregated into larger clusters up to 1 μm. DSC-TGA investigation revealed that the PbSnO₃ was unstable >800°C with 2.95% weight loss. The products of the reactions, Pb₂SnO₄ and SnO₂, were identified by in situ high-temperature XRD. The complex decomposition reactions were deduced as (2 + x )PbSnO₃= Pb₂SnO₄+ (1 + x )SnO₂+ x PbO ( x = 0.104). The lattice parameters of PbSnO₃ were determined by high-temperature XRD. The cell volume of PbSnO₃ increased with increasing temperatures. The average volumetric thermal expansion of PbSnO₃ was calculated as (β= 3.35 × 10⁻⁵/°C).     

Effect of Tetravalent Dopants on Raman Spectra of Tetragonal Zirconia

Tetragonal zirconia solid solutions were prepared by the additions of ceria, titania, germania, and cassiterite into 2-mol%-Y₂O₃-stabilized t -ZrO₂ (2Y-TZP), and the effect of the dopant size on the changes in the Raman spectra of t -ZrO₂ was investigated. The frequencies of the Raman modes that were associated with Zr-O bond stretching decreased as doping with the oversized cation (Ce⁴⁺) increased and increased linearly as doping with the undersized dopants (Ti⁴⁺, Ge⁴⁺, Sn⁴⁺) increased within the solubility limits of the dopants in 2Y-TZP. The frequency of the 640 cm⁻¹ Raman band decreased as the square root of the unit-cell volume increased, suggesting that the ionic size of dopants governs the Raman mode that is related to the short ZrO bond between two ZrO bonds in t -ZrO₂ solid solutions. Although there was no consistent relationship between the change in the tetragonality of t -ZrO₂ solid solutions and the tetravalent cation size, the intensity ratio of the Raman modes at 609 and 640 cm⁻¹ ( I ₆₀₉/ I ₆₄₀) decreased as the ionic size decreased.     

Phase Separation in 12 mol% Ceria-Doped Zirconia Induced by Heat Treatment in H2 and Ar

The phase separation in 12 mol% CeO₂─ZrO₂ ceramic heattreated in a mixture of H₂ and Ar was investigated by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and Raman scattering. After heat treatment at temperatures above 1200°C, the tetragonal solid-solution phase separated into Zr₂Ce₂O₇ and the monoclinic phase. Raman scattering measurements also provided supplementary evidence for the phase separation. XPS showed that the valence change from Ce⁴⁺ to Ce³⁺ predominantly occurred, whereas the reduction from Zr⁴⁺ to Zr³⁺ took place above 1200°C. It is concluded, that in the highly reduced sample, where the valence changes from Ce⁴⁺ (Zr⁴⁺) to Ce³⁺ (Zr³⁺), the phase separation is noticeably promoted. Below 1000°C the phase separation was suppressed because of no appreciable valence change to trigger the phase separation, and the single tetragonal phase was retained.     

Positive Temperature Coefficient of Resistivity Effect in Highly Donor–Doped Barium Titanate

BaTiO₃ ceramics doped with different La concentrations (0–12 mol%) were prepared by sintering under the reducing conditions of a nitrogen atmosphere containing 1% hydrogen. The critical donor concentration that causes blocking of the exaggerated grain growth was observed to be ∼10 mol% La. The samples, which were semiconducting after sintering under reducing conditions, were subsequently reoxidized by annealing in air to induce the positive temperature coefficient of resistivity (PTCR) effect. After reoxidation at 1150°C a noticeable PTCR effect was observed in the samples doped with La concentrations as high as 2.5 mol%. The room-temperature resistivity after reoxidation was found to increase with increasing donor concentration due to an increase in the thickness of the insulating layers at the grain boundaries. TEM analysis showed that reoxidation of the samples caused precipitation of the Ti-rich compound Ba₆Ti₁₇O₄₀ inside the doped BaTiO₃-matrix grains.     

Development of an Open-Ended Coaxial Line Probe for Measurement of Dielectric Properties of Inorganic Materials at High Temperature

An open-ended coaxial line probe for dielectric measurements at high temperatures was developed. The probe, which was fabricated using stainless steel as the center and outer conductors and quartz wool as an insulator, can function well up to 800°C. The dielectric properties of the raw materials and resultant materials were measured using a network analyzer that was equipped with the open-ended coaxial line probe at high temperatures to clarify the formation reaction process of YVO₄:Eu³⁺ and Mg₂SnO₄:Mn²⁺ phosphors using a microwave heating method. The developed probe was confirmed to be effective for reaction-process analyses at high temperatures.     

Effect of Reoxidation on the Grain-Boundary Acceptor-State Density of Reduced BaTiO3 Ceramics

To investigate the effect of reoxidation on the grain-boundary acceptor-state density of reduced barium titanate, n -doped BaTiO₃ ceramics are sintered in a reducing atmosphere (2% H₂+ 98% N₂) and then annealed in oxygen. After annealing at 1150°C for different times, the experimental results show a relationship between temperature-averaged acceptor-state density and annealing time as N _s= N _so Bt ^1/n with n between 2 and 3. An inherent acceptorstate density N _so= 4.25 × 10¹² cm⁻² is obtained with an increase rate B = 4.8 × 10¹² cm⁻². min^−1/3, when n reaches 3. The inherent grain-boundary acceptor states in the reduced n -doped BaTiO₃ ceramics are believed not due to adsorbed oxygen ions.     

Oxidation-Reduction Equilibria in Molten Na2O.2SiO2 Glass

The oxidation-reduction equilibria in molten glasses having a soda/silica ratio of 1/2 and containing small amounts of variable-valence ions of the transition elements titanium, vanadium, iron, cobalt, and nickel, the post-transition elements tin and antimony, and the rare-earth element cerium were obtained by equilibrating the melts with various atmospheres. The simple mass expression
was always applicable. In the expression, n is the number of electrons involved in the valence change of the metal M. The value of n is 1 for all systems except for the ions of antimony and tin where n is 2. The ions found are those generally accepted as existing in glass melts which are Ti³⁺, Ti⁴⁺; Fez+, Fe³⁺; Ce³⁺, Ce⁴⁺; Mn²⁺, Mn³; Co²⁺, Co³⁺; Ni²⁺, Ni³; Sb³⁺, Sb⁵⁺; and Sn²⁺, Sn⁴⁺. Two mass action expressions were needed for vanadium-containing glasses to describe the equilibria between 5+, 4+, and 3 f species.     

Photoluminescent Properties of ABaPO4:Eu (A=Na, K) Phosphors Prepared by the Combustion-Assisted Synthesis Method

Blue-emitting phosphors A BaPO₄:Eu ( A =Na, K) are synthesized by the combustion-assisted synthesis method. The formation of single A BaPO₄ ( A =Na, K) phases has been confirmed by X-ray powder diffraction (XRD). X-ray photoelectron spectroscopy (XPS) is used to investigate europium valence in the A BaPO₄:Eu ( A =Na, K) samples. Evidence is found that the A BaPO₄:Eu ( A =Na, K) samples prepared in this paper exhibit a mixed-valence europium state (Eu³⁺ and Eu²⁺). Photoluminescence (PL) results show that the NaBaPO₄:Eu and KaBaPO₄:Eu phosphors emit a strong blue light under UV excitation.