Phase Relations in the System Fe2O3–Fe3O4–YFeO3 in Air

Measurements were made of temperature and ternary composition for coexisting liquid and crystalline phases on the air isobar in the system Fe₂O₃-Fe₃O₄-YFeO₃ with particular regard to the stability range and compositional limits of yttrium iron garnet. Phase equilibrium relations were determined by conventional quenching techniques combined with measurements of loss in weight at the reaction temperature to locate true ternary compositions. The intersection of the air isobar with the ternary univariant boundary curve for coexisting magnetite, garnet, and liquid phases results in a eutectic-type situation at the composition Y_0.27Fe_1.73 O_2.87 and 1469°± 2°C. A similar intersection of the isobar with the boundary curve for coexisting garnet, orthoferrite, and liquid phases gives rise to a peritectic-type reaction at 1555° 3°C. and Y_0.44Fe_1.56 O_2.89 The yttrium iron garnet crystallizing from liquids within these temperature and composition limits contains up to 0.5 mole % iron oxide in excess of the stoichiometric formula in terms of the starting composition 37.5 mole % Y₂O₃, 62.5 mole % Fe₂O₃. At 1470° C. the garnet phase in equilibrium with oxide liquid contains 2 mole % FeO in solid solution. The small solubility of excess of iron oxide and partial reduction of the garnet phase in air are unavoidable during equilibrium growth from the melt.     

Phase Relations in the Garnet Region of the System Y2O3–Fe2O3–FeO–Al2O3

Liquidus equilibrium relations for the air isobaric section of the system Y₂O₃–Fe₂O₃–FeO–Al₂O₃ are presented. A Complete solid-solution series is found between yttrium iron garnet and yttrium aluminum garnet as well as extensive solid solutions in the spinel, hematite, orthoferrite, and corundum phases. Minimum melting temperatures are raised progressively with the addition of alumina from 1469°C in the system Y–Fe–O to a quaternary isobaric peritectic at 1547°C and composition Y _0.22 Fe _1.08 Al _0.70 O _2.83* Liquidus temperatures increase rapidly with alumina substitutions beyond this point. The thermal stability of the garnet phase is increased with alumina substitution to the extent that above composition Y _0.75 Fe _0.65 Al _0.60 O ₃ garnet melts directly to oxide liquid without the intrusion of the orthoferrite phase. Garnet solid solutions between Y _0.75 Fe _1.25 O ₃ and Y _0.75 Fe _0.32- Al _0.93 O ₃ can be crystallized from oxide liquids at minimum temperatures ranging from 1469° to 1547°C, respectively. During equilibrium crystallization of the garnet phase, large changes in composition occur through reaction with the liquid. Unless care is taken to minimize temperature fluctuations and unless growth proceeds very slowly, the crystals may show extensive compositional variation from core to exterior.     

Thermal Stability of Gallium Orthoferrite in the System Fe2O3-FeO-Ga2O3

Gallium orthoferrite (Ga_{2- x} Fe _x O₃) has a maximum thermal stability which coincides roughly with liquidus temperatures at oxygen pressures near atmospheric. As a result, changes in ambient oxygen pressure between 0.2 and 10 atm have a pronounced effect on equilibria. The compound exhibits a wide range in Ga:Fe ratio on both sides of the stoichiometric GaFeO₃ but is essentially invariant in oxygen content to 1500°C in air. The orthoferrite bears many similarities to the corresponding aluminum compound Al₂- _x Fe _x O₃.     

Phase Relations in the Ternary System Fe2O3—FeO—YFeO3

Equilibrium data are presented for the ternary system Fe₂O₃–FeO–YFeO₃ in ambient atmospheres of air, oxygen, and carbon dioxide at melting temperatures. The temperature range for the coexistence of yttrium-iron garnet and oxide liquid decreases with decreasing oxygen partial pressure from 127°C in oxygen to 86° C in air to 28° C in carbon dioxide. In addition, the composition of the garnet phase crystallizing from these melts changes with variations of temperature and oxygen pressure. The experimental data are discussed in terms of a polythermal-polybaric model of the system. Some conclusions are drawn as to the limiting conditions in different atmospheres for the growth and the resulting composition of yttrium-iron garnet crystals in equilibrium with ternary oxide liquids.     

Phase Equilibrium Studies in the System Iron Oxide-Y2O3–Gd2O3

Equilibrium data at liquidus temperatures are presented for compositions in the quaternary system Y-Gd-Fe-O in ambient atmospheres of oxygen gas (p_O2, = 760 mm Hg), air (P_O2, = 159 mm Hg), and CO₂ (p_O2 variable). Incongruent melting occurred in yttrium-iron and gadolinium-iron garnet phases and in all intermediate garnet solid solutions in the three oxygen pressure sections studied. Fractionation in the yttrium/gadolinium ratio between oxide liquid and crystalline garnet phases in the quaternary system was not observed experimentally, indicating that unzoned (Y,Gd)₃Fe₅O₁₂ crystals may be grown from a melt without special precautions to maintain a fixed Y/Gd ratio.     

A series of flexible design adaptations to the Nikon E‐C1 and E‐C2 confocal microscope systems for UV,multiphoton and FLIM imaging

Multiphoton microscopy is widely employed in the life sciences using extrinsic fluorescence of low‐ and high‐molecular weight labels with excitation and emission spectra in the visible and near infrared regions. For imaging of intrinsic and extrinsic fluorophores with excitation spectra in the ultraviolet region, multiphoton excitation with one‐ or two‐colour lasers avoids the need for ultraviolet‐transmitting excitation optics and has advantages in terms of optical penetration in the sample and reduced phototoxicity. Excitation and detection of ultraviolet emission around 300 nm and below in a typical inverted confocal microscope is more difficult and requires the use of expensive quartz optics including the objective. In this technical note we describe the adaptation of a commercial confocal microscope (Nikon, Japan E‐C1 or E‐C2) for versatile use with Ti‐sapphire and OPO laser sources and the addition of a second detection channel that enables detection of ultraviolet fluorescence and increases detection sensitivity in a typical fluorescence lifetime imaging microscopy experiment. Results from some experiments with this setup illustrate the resulting capabilities.     

Thermal Stability of Barium Ferrite (BaFe12O19)

Compositions in the system Fe₂O3-FeO-BaO in the vicinity of the compound BaFe₁₂O₁₉ were studied at temperatures from 1300° to 1550°C and oxygen pressures from 10⁻² to 10² atm. Equilibrium relations involving several barium ferrous ferrites are described. Barium ferrite can be crystallized congruently from the melt at 40 atm oxygen pressure and 15400°C.