LPE growth kinetics of CaGe-Substituted EuTm₂Fe₅O₁₂ garnet films

Abstract

The diffusion-reaction growth melts fluxed with PbO-B2O3-Fe2O3, has been extended to include a thermally-activated diffusion term. The fluxed melt had a lower PbO : B2O3 ratio (11 : 1) than that generally used (≈16 : 1) for garnet LPE films. Measured growth rates for LPE films, produced from melts with four different concentrations of CaGe-Substituted EuTm2Fe5O2 garnet, fit the model with: diffusivity, D (cm2/s) = 0.06 exp( -1.0 eV kT); reactivity, K (cm/s) = 8000 exp( -1.61 eV kT); viscosity, v ( cm2 s) = 0.01; and concentration, ce ( g cm3) = 4220 exp - 1.0678 eV kT for rotation rates ω (rpm) = 36 to 196 in the growth temperature range 890 to 965°C. It is shown that the garnet melt concentration terms are the most critical ones in determining the growth rate, hence the activation energy (heat of solution) for the equilibruim concentration is reported to five significant figures. Evaluating the D and the K effects by both a numerical (results given above) and an analytic method demonstrates that these parameters are least critical in determining the growth rate in this case. © 1977.