W. Van Erk

A solubility model for rare-earth iron garnets in a PbO/B2O3 solution

It is shown that the solubility of non-substituted rare-earth iron garnets in a PbO/B2O3 solution can be well described if it is assumed that the different garnet components are dissolved separately. Two descriptions for the liquid are used, a molecular fluid consisting of molecules of PbO, B2O3, Y2O3 and Fe2O3 and an ionic fluid consisting of Pb2+, B3+, Y3+, F e3+ and O2- (Temkin model). The latter description gives good agreement between the measured heat of solution and the enthaply of solution obtained from solubility data. If it is assumed that both the liquid and the solid are ideal mixtures of the end-member components, the solubility of substituted garnets like LaxY3-xGayFe5-yO12 can also be described. From experimental data it may be concluded that the degree of La substitution x is influenced by the degree of Ga substitution y, and vice versa. In addition a relation is obtained for the equilibrium distribution of Ga on tetrahedral and octahedral sites.

The effect of substrate orientation on the growth kinetics of garnet liquid phase epitaxy

Abstract The growth kinetics of liquid-phase epitaxy of Y 3 Fe 5 O 12 on Gd 3 Ga 5 O 12 substrates having (110), (211), (321), (100) or (111) orientation has been studied and the results are discussed in terms of simple theoretical growth models. The (111) face is a rough face on an atomic scale, but the other faces are more or less singular faces. Growth hillocks are observed on the surfaces of films grown on (110), (211) and (321) substrates. The epitaxial layer in between the hillocks grows via the nucleus-above-nucleus mechanism. Due to the occurrence of two-dimensional nucleation on the steps of the growth spiral, the slope of the hillocks is not a simple function of the supersaturation. The mean distance for surface diffusion is estimated to be twenty times the step height. Based on the growth rate data the order of decreasing α-factor is (110), (211), (321), (100), …. The results for growth on (111) substrates have been used to estimate the effect of volume diffusion on the supersaturation.

The growth kinetics of garnet liquid phase epitaxy using horizontal dipping

Abstract The system for the growth of rare-earth iron garnets from a supersaturated flux is treated as a three-component system: solvent (PbO and B 2 O 3 ), and solvated iron and rare-earth (or yttrium). It is assumed that the different components are solvated separately and that the solubility of garnet can be described with a solubility product. The enthalpy of solution appears to be about 86 kcal mol -1 . The model given by Ghez and Giess to describe the kinetics of this process is improved by using a different definition of supersaturation. It is shown that the interface kinetics are first order at high supercooling and become of higher order for low supercooling. The rate-determining steps in the process are both the diffusion through the boundary layer and the incorporation in the solid phase of the rare-earth species. At high growth temperature the process is diffusion-limited whereas at lower temperatures the interface process becomes slowest. With this scheme several phenomena are discussed and it is argued that the diffusion coefficient must be of the order of 10 -6 cm 2 sec -1 .

Transport processes in metal halide gas discharge lamps

An overview is given of transport reactions and corrosion phenomena in metal halide gas discharge lamps filled with a mixture of alkali halides with scandium or rare-earth iodides. The phenomena that are discussed are: (a) pressures of light-emitting species above the molten salt mixture, (b) interaction of the metal halides with the vessel wall, quartz glass as well as polycrystalline alumina, (c) transport processes along the vessel wall giving rise to wall corrosion, and (d) transport to and from the electrodes (i.e., electrode corrosion and wall blackening).

Growth of a mixed crystal from an ideal dilute solution

Abstract A description is given of the growth of the mixed crystal A x B 1− x from an ideal dilute solution of A and B in F. Two steps are distinguished in the growth process: diffusion of A and B to the crystal-fluid interface and the process occuring at the interface. The situation of equilibrium is described using classical thermodynamics, whereas for the growth process the thermodynamics of irreversible process is used. This results in a description of the rate of the process in terms of six phenomenological coefficients, three for diffusion and three for the surface process. For the case of stationary growth, formulae are given for the growth rate and the segregation coefficient as functions of the growth conditions.

Segregation of Ca and Ge in LPE growth of magnetic YSmCaFeGe garnet films

Abstract A study is made of the segregation behaviour of Ge in LPE melts for the growth of GaGe-substituted garnet films for magnetic bubble applications. The effect of changes in melt compositon are investigated for the atomic melt ratios R1 = Fe/ΣLn, f > R4 = garnet concentration and R5 = Ca/(Ca + Ge). The influence of the supercooling (growth rate) on the segregation of Ge is also determined for all these melt compositions. An empirical relation can be derived which gives the film magnetization (obtained from the Ge-content) as a function of the melt parameters and the supercooling. A model is presented, which is based on anionic formulation of the liquid and which describes the (equilibrium) solubility of these CaGe-substituted garnets at the saturation temperature. In the first place it results in an equation for the garnet solubility product, which is defined as the product of ionic concentrations c3 [Y] X c5 [Fe], as a function of saturation temperature. Another result of the model is a relation describing the segregation of Ge as a function of melt composition and saturation temperature. These equations give a reasonable fit with the presented data.

Bubble device materials with orthorhombic anisotropy

The growth characteristics and the magnetic properties of Mn‐substituted garnet films grown on (110) oriented substrates are reported. On perfectly oriented substrates hillocks are observed which occur due to the fact that (110) is a habit face. By the introduction of a slight misorientation of the substrates, the hillocks disappear and the surfaces are perfectly flat. Mn is substituted in the garnet to obtain the right magneto‐elastic properties. It is shown that the temperature dependence of the magnetic parameters can be adjusted such as required to provide a device material.

Solutal convection in garnet liquid-phase epitaxy using vertical dipping

In the vertical dipping procedure for the LPE of garnets, the growth process will cause a horizontal concentration gradient and with that a density gradient in the fluid near the growing interface. This results in a downward flow along the wafer, making the garnet film thicker at the upper part of the wafer than near the lower part. A mathematical description of this type of flow and its effect on the growth kinetics is given. Comparison with experimental data shows that the observed phenomena can be explained on the basis of this type of convection. Because this flow arises due to the growth process itself, it cannot be avoided and vertical dipping seems therefore less suitable for the production of films of uniform thickness.

The interfacial and volume transport processes during LPE growth of garnets

An analysis on the kinetical processes during the epitaxial growth of garnet films is presented. On the rough {111} garnet faces the transport process consists of the diffusion of growth units through the mass transfer boundary layer and the interfacial process; both processes have about the same mass transfer resistance. On the flat {110} faces the model of Gilmer, Ghez and Cabrera (GGC) was applicable. With help of growth rate measurements on garnet films grown on spherically shaped gandolinium garnet substrates, we were able to estimate the parameters which determine the growth process. The values of the transport process parameters of the GGC model were Λ = 80 μm, λ = 70 nm and Λs = 225 nm. For low misorientations, misorientation angle ζ 0.6°), the step interaction increases and also the volume diffusion becomes important. The volume-surface incorporation resistance is about two times higher for {110} than for {111}rcub; faces.

Segregation in liquid phase epitaxy of garnets

Abstract Experimental results on the incorporation of rare-earth ions into Y 3 Al 5 O 12 and Y 3 Fe 5 O 12 grown by liquid phase epitaxy on 〈111〉 substrates are presented. It is shown that a plot of [RE]/[Y] ratio in the solid versus [RE]/[Y] ratio in the solution on a log-log scale results in straight lines with a slope near to unity. These data can be qualitatively explained with the segregation model derived previously by one of us.