Stable and metastable phase equilibria in the GeSe2-Se system

Stable and metastable phase equilibria in the binary system GeSe₂-Se have been investigated by means of optical and electron microscopy, electron probe microanalysis (EPMA), x-ray diffraction (XRD), thermal analysis, and adiabatic calorimetry. A revised equilibrium phase diagram is presented. A not previously observed λ-type phase transition was observed near ∼420 K (147 °C) for GeSe₂. The intermediate phase, φ, which earlier had been considered as metastable, is shown to be stable through extensive annealing experiments and by adiabatic calorimetry. The φ phase, with composition near Ge₃Se₇, melts incongruently at 658±5 K (385±5 °C) to GeSe₂ and a liquid with 85±2 at.% Se. The liquidus of GeSe₂ and φ was determined by EPMA of annealed-and-quenched samples. Both a stable (φ-Se-liquid) and a metastable (GeSe₂-Se-liquid) eutectic point were observed. The stable one was observed at 480±2 K (207±2 °C) and 92.5±1.0 at.% Se, whereas the temperature of the metastable eutectic (GeSe₂-Se-liquid) was observed to be ∼10 K lower. Metastable phase equilibria, obtained on thermal evolution of glasses with different compositions, are described and discussed.     

Stable and metastable phase equilibria in the GeSe2-Se system

Stable and metastable phase equilibria in the binary system GeSe₂-Se have been investigated by means of optical and electron microscopy, electron probe microanalysis (EPMA), x-ray diffraction (XRD), thermal analysis, and adiabatic calorimetry. A revised equilibrium phase diagram is presented. A not previously observed λ-type phase transition was observed near ∼420 K (147 °C) for GeSe₂. The intermediate phase, φ, which earlier had been considered as metastable, is shown to be stable through extensive annealing experiments and by adiabatic calorimetry. The φ phase, with composition near Ge₃Se₇, melts incongruently at 658±5 K (385±5 °C) to GeSe₂ and a liquid with 85±2 at.% Se. The liquidus of GeSe₂ and φ was determined by EPMA of annealed-and-quenched samples. Both a stable (φ-Se-liquid) and a metastable (GeSe₂-Se-liquid) eutectic point were observed. The stable one was observed at 480±2 K (207±2 °C) and 92.5±1.0 at.% Se, whereas the temperature of the metastable eutectic (GeSe₂-Se-liquid) was observed to be ∼10 K lower. Metastable phase equilibria, obtained on thermal evolution of glasses with different compositions, are described and discussed.     

Re-investigation of the phase constitution of the system Pt-Te

The phase relations of the system Pt-Te have been investigated using the conventional sealed-capsule technique. The identification of phases present in the reaction products was made by reflected light microscopy, X-ray diffraction, and electron probe microanalysis. Four binary phases were confirmed to exist in the system: PtTe., Pt₃Te₄, Pt₂Te₃ and PtTe₂. The composition of all these appears to be constant without showing any appreciable compositional range. The Pt₂Te phase was not found in this study. The Te content in platinum and the Pt in tellurium in solid solution are negligible, less than 0.5 at.% up to 1000°C. The eutectic point between Pt and PtTe is near at 40 at.% Te and at 870°C. The Pt₂Te₃ phase is stable up to about 675°C, whereas the melting point of the Pt₃Te₄ phase is apparently above 1000°C. The most part of liquidus curve between PtTe₂ and Te exists above 1000°C. Physico-chemical properties of Pt-Te phases obtained in this study are given. The revised phase diagram of the Pt-Te system is proposed from this study.     

Stable and metastable phase equilibria of the In-Se system

The In-Se phase diagram was redetermined using DTA, x-ray analysis, optical microscopy, TEM, and scanning electron microscopy. In₉Se₁₁ and In₅Se₇ are stable phases at stoichiometric composition and βIn₂Se₃ was observed at 59.6 at % Se. ΒIn₂Se₃ decomposes at 198 °C into γIn₂Se₃ and In₅Se₇. Alloy melts between 33 and 54 at.% Se exhibit a strong tendency for undercooling. Between 50 and 60 at. % Se, the InSe, In₆Se₇, or In₂Se₃ phases solidify directly from the undercooled melt, and the formation of In₅Se₇ and In₉Se₁₁ is suppressed while applying cooling rates between 2 to 10 K/min. The respective undercooled states and metastable phase equilibria are provided.     

The antimony-niobium (Sb-Nb) system

A constitutional diagram was established for the Nb-Sb system in the region with more than 30 at. % Sb and below 1450 °C. Investigation of the phase relations was based on differential thermal analysis (DTA), light optical microscopy, electron probe microanalysis, and X-ray diffraction experiments on argon arc melted bulk alloys, which were annealed at 600 °C in vacuum-sealed silica capsules up to 1400 h. Differential thermal analysis runs (5 to 20 K/min, T _max=1450 °C) were performed on alloys vacuum sealed in Ta crucibles with an inner lining of W. In contrast to earlier claims for the existence of five binary phases, Nb₃Sb, Nb₃Sb₂, NbSb, Nb₅Sb₄ (or Nb₄Sb₃), and NbSb₂, the authors observed only three binary compounds: Nb₃Sb, Nb₅Sb₄, and NbSb₂. These compounds are essentially line compounds at their stoichiometric composition and without a significant homogeneity region at 600 °C. All compounds are formed by peritectic reactions: L+(Nb)↔Nb₃Sb (1750±25 °C, (L℞55 at.% Sb), L+Nb₃Sb↔Nb₅Sb₄ (1320±10 °C, L℞71 at.% Sb), and L+Nb₅Sb₄↔NbSb₂ (1180±10 °C, L℞88 at.% Sb). The system is characterized by a depleted eutectic reaction L↔(Sb)+NbSb₂ at 618±8 °C and L℞99 at.% Sb.     

Solutions of aluminum in liquid lithium: contribution to the Li-Al phase diagram

The Li-rich (up to 15.8 at.% Al) region of the Li-Al phase diagram has been determined by resistivity-temperature and thermal analytical methods. The eutectic lies at 180.5 ± 0.4 °C (453 ± 0.4 K) and 0.57 ± 0.04 at.% Al. The hypereutectic liquidus rises smoothly from the eutectic in two sections corresponding to the crystallization of Li₉Al₄ and Li₃Al₂, respectively. The peritectic decomposition of Li₉Al₄ into Li₃Al₂ and a liquid of composition of 9.2 ± 0.3 at. % Al occurs at 347 ± 4 °C. The hypoeutectic liquidus could not be differentiated from the eutectic horizontal. The depression of the freezing point of Li on adding Al is extremely small, suggesting significant positive deviations from ideality. The calculated γ_Li value at the eutectic composition is 1.0051.     

Preparation and characterization of nanostructured Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> and Sn<Subscript>0.5</Subscript>-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Nanostructured Bi₂Se₃ and Sn_0.5-Bi₂Se₃ were successfully synthesized by hydrothermal coreduction from SnCl₂·H₂O and the oxides of Bi and Se. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscope (FESEM). Bi₂Se₃ powders obtained at 180°C and 150°C consist of hexagonal flakes of 50–150 nm in side length and nanorods of 30–100 nm in diameter and more than 1 μm in length. The product obtained at 120°C is composed of thin irregular nanosheets with a size of 100–200 nm and several nanometers in thickness. The major phase of Sn_0.5-Bi₂Se₃ synthesized at 180°C is similar to that of Bi₂Se₃. Sn_0.5-Bi₂Se₃ powders are primarily nanorod structures, but small amount of powders demonstrate irregular morphologies.     

The Pr-rich portion of the Ni-Pr system

The Ni-Pr phase diagram on the Pr-rich side was revised using differential thermal analysis, differential scanning calorimetry, and scanning electron microscopy. The existence of four stoichiometric compounds, Ni₂Pr, NiPr, Ni₃Pr₇, and NiPr₃, was confirmed; however, the melting temperatures of 766 °C (NiPr), 566 °C (Ni₃Pr₇), and 562 °C (NiPr₃) are considerably different from the previously reported values. The same was true for the four eutectic reactions, which were determined to be as follows: liquid (L) (45±1 at.% Pr) ↔ Ni₂Pr+NiPr at a mean temperature of 732±5 °C; L (65±1 at.% Pr) ↔ NiPr+Ni₃Pr₇ at a mean temperature of 550±2 °C; L (72±2 at.% Pr) ↔ Ni₃Pr₇+NiPr₃ at a mean temperature of 557±2 °C; and L (77±1 at.% Pr) ↔ NiPr₃+Pr.     

The Ho-Sn (Holmium-Tin) system

The Ho-Sn phase diagram was established by means of differential thermal, x-ray, and microscopic analyses of 23 as-cast alloys. Seven intermetallics were found to form in the system. Ho₅Sn₃ melts congruently at 1915°C. The intermetallics Ho₅Sn₄, Ho₁₁Sn₁₀, Ho₄Sn₅, HoSn₂, Ho₂Sn₅, HoSn₃ form in peritectic reactions at 1720 ±13,1592 ±11,1144 ±11,1114 ±15,509 ±12, and 420 °C, respectively. Compounds Ho₅Sn₄ and Ho₄Sn₅ were observed for the first time. The Ho-rich eutectic crystallizes at 1252 ±11°C and contains ≅13 at. % tin. The solid solubility of Sn in Ho is about 2.5 at. % and that of Ho in Sn is negligible. The enthalpy of mixing of liquid Ho-Sn alloys was studied by calorimetric method. The limit enthalpy of dissolution of Ho in Sn was calculated to be-78.4 kJ/mol.     

Microfibrous entrapment of small catalyst particulates for high contacting efficiency removal of trace CO from practical reformates for PEM H2-O2 fuel cells

Preferential oxidation (PROX) of CO in H₂ is the most efficient way to remove CO from a practical reformate stream for PEM H₂-O₂ fuel cells. Pt/Al₂O₃ has long been known as a suitable catalyst for this purpose. Over the conventional Pt/Al₂O₃ catalyst, however, PROX of CO in H₂ has been known to occur at temperatures above 150°C, and the maximum CO conversion usually takes place at about 200°C. In this study, the promotion of Pt/Al₂O₃ with a transition metal results in significantly enhanced catalytic performance in the temperature range of 25 to 150°C. The active reaction temperature window is enlarged to 25 to 200°C compared with a narrow window at about 200°C over the conventional Pt/Al₂O₃. A high void and a tailorable sintered microfibrous carrier consisting of 5 vol.% of 4 and 8 μm diameter Ni fibers is used to entrap 15 vol.% 150 to 250 μm diameter Al₂O₃ particulates. The alumina support particulates are uniformly entrapped into a sinter-locked, three-dimensional network of 4 and 8 μm Ni fibers. Promoter and Pt are then dispersed onto the microfibrous entrapped alumina support particles by the incipient-wetness impregnation method. The composite catalysts possess 80 vol.% voidage. At equivalent bed volumes, microfibrous entrapped catalysts achieve complete CO reduction (GC detection limit ∼40 ppm CO) at five times the higher gas hourly space velocity value compared with packed beds of 1 to 2 mm catalyst particles demonstrating ultrahigh contacting efficiency provided by the microfibrous entrapped catalysts. This paper was presented at the ASM Materials Solutions Conference & Show held October 18–21, 2004 in Columbus, OH.     

The Hafnium-Platinum Phase Diagram

Phase relationships were determined in the Hf-Pt system at temperatures up to 1690 °C using both metallographic and neutron Rietveld refinement techniques. An unusual displacive transformation is observed below 200 °C in the rhombohedral compound Hf₃Pt₄, similar to that recently discovered in the compound Zr₃Pt₄. Crystallographic data are presented for the compounds HfPt₄, HfPt₃, Hf₂Pt₃, Hf₃Pt₄, HfPt, and Hf₂Pt. A complete phase diagram is presented for the Hf-Pt binary system.     

Preparation of ultra-fine FeNiMnO<Subscript>4</Subscript> powders and ceramics by a solid-state coordination reaction

A mixed oxalate FeNiMn(C₂O₄)₃·nH₂O, a coordination compound, was synthesized by milling a mixture of ferrous iron chloride, nickel acetate, manganese acetate, and oxalic acid at room temperature. A spinel-structured FeNiMnO₄ powder with high sintering activity and chemical homogeneity was obtained by calcining the mixed oxalate in air at 800°C for 2 h. Dense FeNiMnO₄ ceramics with a relative density of ∼98% were achieved by sintering powder compacts at a lower temperature of 1100°C for 5 h. The specific resistivityρ _25°C and the thermal constant B_25/85°C were 4382 Ω·cm and 3373 K, respectively. The aging coefficient ΔR/R(%) of the ceramics after annealing at 150°C for 500 h was 0.6%.     

Magnesium-rare earth phase diagrams: Experimental investigation of the Ho-Mg system

The Ho-Mg phase diagram was determined in the range 0 to 100 at.% Mg by differential thermal analysis (DIA), X-ray powder diffraction, optical and scanning electron microscopy, and electron probe microanalysis (EPMA). Four intermediate phases were found to exist, and their crystal structures were confirmed or determined as the following: (1) β phase, Ho₂Mg, cubic,cI2, W type, peritectic formation 1170 °C; (2) HoMg, cubic,cP2, CsCl type, peritectic formation 845 °C; (3) HoMg2, hexagonal,hP12, MgZn₂ type, peritectic formation 695 °C; and (4) Ho₅Mg₂₄, cubic, cI58, α Mn-type, peritectic formation 600 °C. The β phase undergoes a eutectoidal decomposition at 685 °C and 29.0 at.% Mg. A eutectic reaction was observed to occur at 555 °C and 90.0 at.% Mg. The data obtained in this study are compared with those of other previously studied RE-Mg phases and briefly discussed. “Mischmetal” is the tradename of an inter-rare earth alloy ideally containing: 27 at.% La, 48 at.% Ce, 5 at.% Pr, 16 at.% Nd, and 4 at.% other rare earths. This composition is close to that of a typical rareearth ore.     

Interfacial phase formation during growth of ferromagnetic CdCr2Se4 on AlGaAs and ZnSe/AlGaAs

Microstructure and interfacial phase formation of CdCr₂Se₄ thin films deposited by molecular beam epitaxy on GaAs, Al_0.1Ga_0.9As and ZnSe/Al_0.1Ga_0.9As have been investigated with high-resolution transmission electron microscopy, fine-probe energy-dispersive spectroscopy and Z-contrast imaging. For CdCr₂Se₄ grown epitaxially on GaAs and/or Al_0.1Ga_0.9As, Cr tends to segregate to the interface forming either a layer enriched with Cr or trapezoidal-shaped Cr-rich precipitates. On ZnSe, CdCr₂Se₄ grows epitaxially at temperatures >300 °C, but when grown at 350 °C, the interface is quite rough or wavy. When the CdCr₂Se₄ is grown at 300 °C, the CdCr₂Se₄/ZnSe interface is more planar, but the CdCr₂Se₄ film is only epitaxial up to a thickness of about 5 nm, and then becomes polycrystalline as the thickness of the film increases. An interfacial phase, Cd_xZn_1−xSe, forms at the CdCr₂Se₄/ZnSe interface, the thickness of which is determined by specific growth conditions.     

Isothermal section of the Pt–Sb–Te system at 1000 °C

The phase relations in the system Pt–Sb–Te have been investigated at 1000 °C, using sealed glass capsule techniques. The reaction products have been studied by reflected light microscopy, X-ray diffraction, and electron probe microanalysis. At 1000 °C, Pt, PtSb, PtSb₂, Pt₃Te₄, and PtTe₂ are the stable solid phases. There are two liquid phase fields: a large field extends across the ternary system from the Pt–Sb join to the Pt–Te join, the other as a thin strip near the Sb–Te join. PtSb becomes Pt-poor up to 3 at.% from stoichiometry as substitution of Te for Sb and Pt increases. PtSb₂ and PtTe₂ exhibit the largest solid solution range among the solid phases present.     

Experimental investigation of the Tb-Mg phase diagram

The Tb-Mg alloys were studied in the range 0 to 100 at.% Mg, by using X-ray powder diffraction, optical and scanning electron microscopy, electron probe microanalysis (EPMA), and differential thermal analysis (DTA). The following intermediate phases were identified and their crystal structures confirmed: TbMg (cubic,cP2 CsCl type), TbMg₂ (hexagonal,hP12-MgZn₂ type), and TbMg₃ (cubic,cF16-BiF₃ type). Two phases, moreover, were confirmed or identified in a composition range very close to 83 at.% Mg: χ₁ phase (cubic,cF440-GdMg₅ type) and χ₂ phase (cubic,cI58-αMn type). All the phases show peritectic formation with the possible exception of the χ₂ phase. The following phase equilibria were also determined: a eutectic reaction at 530 °C and 90.5 at.% Mg and a eutectoidal decomposition of the (βTb) phase at 670 °C and ∼28 at.% Mg.     

Electrodeposition of platinum metal and platinum-rhodium alloy on titanium substrates

A method for application of an adherent platinum (Pt) and platinum-rhodium (Pt-Rh) alloy plate to a titanium (Ti) substrate includes steps of surface pretreatment, anodization, and electrodeposition of Pt and Pt-Rh alloy from their electrolytic baths consisting of H₂Pt₂Cl₆·6H₂O (20 gL⁻¹), and HCl (300 gL⁻¹) for a Pt bath. The Pt-Rh bath consists of H₂Pt₂Cl₆·6H₂O (20 gL⁻¹), and HCl (300 gL⁻¹) and Rh₂ (SO₄)₃ (2 gL⁻¹). At the optimum conditions of electroplating, the Pt and Pt-Rh deposits were formed over the anodized Ti substrates with high adhesion, brightness, and high current efficiency (35.33% for Pt and 70.38% for the Pt-Rh alloy).     

Dispersion strengthening for dimensional stability in low-melting-point solders

An improved solder structure with an ultrafine grain size of ∼200–500 nm and significantly enhanced mechanical properties has been created by incorporating nanosized, nonreacting, noncoarsening oxide dispersoids into solder alloys. These solders display up to three orders of magnitude reduction in the steady-state creep rate, 4–5 times higher tensile strength at low strain rates, and improved ductility under highstrain-rate deformation. With a dispersion of TiO₂ particles, the Pb-Sn eutectic solder with a low-melting point of 183°C can be made more creep resistant than the Au-20Sn eutectic solder with a much higher melting point of 278°C. This technique can be extended to other solder systems, such as the emerging lead-free solder alloys, and used to achieve enhanced dimensional stability. For more information, contact H. Mavoori, Bell Laboratories, Lucent Technologies, 1A-102 Bell Labs, 600 Mountain Avenue, Murray Hill, New Jersey 07974; e-mail hareesh@lucent.com.     

Phase Equilibria at 1173 K in the Ternary Fe-Pt-Tb System

The solid-state phase equilibria in the ternary Fe-Pt-Tb system in the compositional region below 75 at.%Tb at 1173 K have been studied by using x-ray diffraction, scanning electron microscopy and energy dispersion spectroscopy techniques. The 1173 K isothermal section consists of 18 single-phase regions, 33 two-phase regions, and 16 three-phase regions. At 1173 K, the maximum solid solubility of Pt in α-(Fe, Tb) is less than 2 at.%Pt and that of Pt in Fe₂Tb, Fe₃Tb, Fe₂₃Tb₆, Fe₁₇Tb₂ is below 1 at.%Pt; the compounds Pt₅Tb, Pt₃Tb, Pt₂Tb, Pt₄Tb₃, PtTb, Pt₄Tb₅, Pt₃Tb₅, PtTb₂, and PtTb₃ are confirmed to exist at 1173 K and the highest solid solubility of Fe in them is below 1 at.% Fe; the maximum solid solubility of Tb in α-(Fe, Pt), γ-(Fe, Pt), FePt, FePt₃, and (Pt, Fe) (namely, the solid solution of Fe in Pt) is about 1, 2, 1.9, 1.5, and 1.5 at.%Tb, respectively. No ternary compound was found to exist in this section at 1173 K.