E.D. Kolb

Hydrothermal synthesis of aluminum orthophosphate

Abstract We have investigated extensions and modifications of previous AlPO 4 growth techniques, designed to overcome the difficulties posed by the negative temperature coefficient of solubility. On the assumption that solubility could be improved even at higher temperatures provided pressure was kept high, we investigated crystal growth in the range 150–325°C at 1000–10,000 psi. The preparation of nutrient material of large enough particle size that it would not be convected in the hydrothermal fluid and become included in the crystal posed a problem. Successful techniques for the recrystallization of small particle AlPO 4 by slowly raising the temperature of a hydrothermal vessel are described. Processes for growth by slowly increasing the temperature of a saturated solution and for growth in a negative temperature gradient where the large particle nutrient is contained in a basket in the upper cooler region of the autoclave are described. The fact that growth in a positive temperature gradient is possible has been established and growth on seeds where nutrient was contained in the hotter bottom region of the autoclave and seeds were held in the upper cooler region was carried out. The processes have been used to prepare crystals grown on seeds at rates up to 0.41 mm/day (16 mil/day).

Dislocation-free and low-dislocation quartz prepared by hydrothermal crystallization

Abstract A reproducible technique for the hydrothermal crystallization of low dislocation-density and dislocation-free α-quartz on (0001) and (01 1 1) seeds is described. Dislocations are shown to propagate from pre-existing dislocations in seeds and from particulate inclusions (lithium sodium iron silicate) grown into the crystal. To prepare dislocation-free material in high yields dislocation free seeds which are carefully etched to remove damage and growth in noble-metal-lined autoclaves to reduce iron containing inclusions are necessary. Etching studies showed that shallow etch pits are probably associated with ordinary dislocations while etch pipes are associated with dislocations found under growth conditions were iron decoration is probable. Growth rate had no obvious effect on perfection over a growth rate range of 2–4X. Problems associated with a unique Burgers vector determination are outlined. The relationship of dislocations and strain to cracking previously observed in growth on (01 1 1) seeds is discussed.

The growth of high acoustic Q quartz at high growth rates

Abstract A technique for the hydrothermal growth of high acoustic Q (>106) quartz at rates above 100 mil/day (2.5 mm/day) is reported. This technique hinges upon the fact that the solid solubility in quartz of the proton which causes loss is decreased as the growth temperature increases. Typical conditions for high Q-high rate growth are: 374 °C, crystallization temperature; 23°, temperature difference (ΔT) between dissolving and growth zones; 88% fill; 40000 psi (2759 bar) and 103 mil/day growth rate on a surface within 5° of a basal (0001) plane. The Q is 1.4 × 106. The concept of effective distribution constant developed to describe impurity segregation in melt growth is shown to be applicable to solution growth with appropriate modifications. A new quantity, the effective equilibrium constant for the segregation of (M+3) ions and (H+) in quartz is shown at constant temperature to depend on rate (where rate changes are brought about by fill and ΔT changes) in a manner analogous to the dependence of the effective distribution constant in melt growth. It is suggested that the concept of effective equilibrium constant can be extended to polycomponent growth in general.

Phase equilibria of Y3Al5O12, hydrothermal growth of Gd3Ga5O12 and hydrothermal epitaxy of magnetic garnets☆

Abstract Nonmagnetic garnets are important as laser hosts and as substrates for thin magnetic garnet films for bubble memory and related studies. Hydrothermal growth presents the advantages of perfection and easy scale-up for these materials. The complete Y 2 O 3 -Al 2 O 3 -H 2 O phase diagram was determined at conditions previously used for YAG growth in (CO 3 ) = and (OH) - . Y 3 Al 5 O 12 was found to be congruently saturating, while YA1O 3 was never the primary phase. These results are correlated with growth studies and used to deduce conditions for Gd 3 Ga 5 O 12 growth. Gd 3 Ga 5 O 12 was found to be incongruently saturating and grew easily from (OH) - solutions containing more than 1 M (molar) excess Ga 2 O 3 . Optimum conditions for growth and some data on perfection are reported. Techniques for the hydrothermal epitaxial growth of magnetic garnets on Gd 3 Ga 5 O 12 were studied and compared: (1) growth in a thermal gradient from Gd 3 Ga 5 O 12 , (2) reaction of the oxides and hydroxides, and (3) hydrothermal tipping. Macroscopically good films were prepared by all these methods and the conditions required for each are reported. The advantages and disadvantages of the techniques are reported and the quality of the films produced is discussed.

Optical Spectra of Rare‐Earth Orthoferrites

The rare‐earth orthoferrites form a class of optical materials having intrinsically good transmission in the infrared between about 1.3 and about 8 μ. In thin sections they have enough transparency to be useful in the visible region. Optical absorption loss can be less than α=0.5 cm‐−1 in the infrared, but Fe valence changes can reduce the transparency drastically. Doping experiments with Sn, Bi, Sb, Mg, and H+ are reported and their effect on optical transparency is given.

Production and perfection of “z-face” quartz

Abstract Synthetic quartz grown on minor rhombohedral seed plates is most economical for the fabrication of resonators for certain monolithic crystal filters. Laboratory studies leading to the choice of commercial growth conditions are reviewed. Conditions for growth in large autoclaves are described. The role of fill, temperature, temperature difference and mineralizer is discussed. The growth rate under present conditions in (OH) - solutions is 32–38 mil/day and acoustic Q s adequate for applications (>10 6 ) are routinely obtained at rates of 35 mil/day. OH concentration in minor rhombohedral growth depends on growth rate in a manner similar to that reported for basal plane growth. New evidence for the inclusion of non-charge compensated OH, probably in the form of H 2 O inclusions, is advanced. Statistical data on a number of runs are presented showing the uniformity of growth rate throughout the growth vessel. As a means for improving seed quality and the yield and perfection of grown material, a new polariscope designed for use in this work is described. It is shown that as much as a 20% increase in yield can be obtained by choosing low strain seeds. Defects in seed plates are usually propagated into grown quartz and strain was found to increase with growth rate.

Hydrothermal growth of hematite and magnetite

Hematite and magnetite have been crystallized on seeds under hydrothermal conditions. Optimum conditions for hematite growth were found to be: 5 M NaOH; crystallization temperature, 385–445 °C; percent fill, 71–77%; δT, 5 °C, and seed orientation (1012) and (0001). Magnetite can be crystallized from systems containing metallic Fe at generally similar conditions. The implications for hydrothermal corrosion are discussed.

Hydrothermal Growth of Bubble‐Domain Memory Materials

Tm and Y orthoferrite crystals with areas on the (001) face larger than 1 in.2 were grown. Optimum conditions were 20M (molal) KOH, 89% fill, 5% baffle opening, 385°C crystallization temperature, temperature differential 25°, and seeds {001} hydrothermally grown Y and TmFeO3 plates. Growth rates were about 1–4 mil/day. Bubble size, mobility, and other properties compared favorably with flux‐grown crystals. Magnetically uniaxial garnets were crystallized from starting materials including (Gd, Tb)3Fe5O12, (Gd, Tb, Er)3(Al, Fe)2[(Fe, Al)O4]3, (Eu, Er)3(Ga, Fe)2[(Fe, Ga)O4]3 and (Y, Gd)3(Al, Fe)2[(Fe, Al)O4]3. Seeds were flux‐grown crystals of similar composition. Orientation of the easy magnetic axis was usually similar to that observed in flux growth and properties compared favorably. Heteroepitaxial growth of (Eu, Er)3(Ga, Fe)5O12 on (Nd0.2Gd0.8)3Ga5O12 was achieved. Optimum conditions for homoepitaxial garnet growth were generally similar to those for orthoferrite. In garnet growth most experiments were c...

Narrow Linewidth and High Infrared Transmission in Hydrothermally Grown Yttrium Iron Garnet

The properties of yttrium iron garnet (YIG) grown from high‐temperature—high‐pressure aqueous (hydrothermal) solvents have been studied. YIG with a room‐temperature ferromagnetic linewidth as low as 0.3 Oe and with an infrared extinction coefficient at 1.14 μ as low as 0.5 has been prepared. Such YIG should be useful for lasers, laser optical devices, and microwave devices, and the hydrothermal technique is shown to have advantages over conventional flux growth for the reproducible production of large garnets. Linewidth is shown to correlate with proton content which is affected by the concentration of Ca2+ ions in the lattice. Absorbtion at 1.14 μ is uniformly low in hydrothermal YIG, and this fact is discussed. The role of impurities, dopants, and conditions of growth are discussed.

Pressure-volume-temperature behavior in the system H2O-H3PO4-AlPO4 and its relationship to the hydrothermal growth of AlPO4

Abstract Pressure-volume-temperature relationships in the systems H 2 O - H 3 PO 4 and 2 O - H 3 PO 4 - AlPO 4 are determined in 7.58 m H 3 PO 4 , at percent fills from 70–93% and over the temperature range 150–500°C. The technique used for pressure measurement is described, is relatively simple and should be of interest for the measurement of pressures in other hydrothermal systems. The slope of p - T curves at constant percent fill, (δ p /δ T ) %f (equivalent to constant density and constant specific volume), is foun d to be independent of temperature at temperatures above the coexistence curve. Thus, data may be extrapolated to higher temperatures and pressures without significant error. Pressures in H 3 PO 4 are substantially depressed from pure water and pressures in the system H 2 O - H 3 PO 4 - AlPO 4 are slightly depressed from H 3 PO 4 . The pressure data are used to convert AlPO 4 solubility data at constant pressure to data at constant percent fill and show that in general the temperature coefficient of solubility at constant percent fill (δ s /δ T ) %f is negative. The physical chemical implications of the results with respect to the nature of species present and to a generalized phase diagram are briefly discussed and comparisons with other systems are made.