Experimental determination of the growth rate anisotropy of garnets

Abstract

The orientational dependence of the growth rate of a typical bubble garnet system is measured in the whole solid angle range of 4x for the case of low undercooling. There are found deep singular minima a t (110) and (211) and shallow nonsingular minima a t (321) and (100). The maximum rate is attained near (111). Conclusions are drawn t o the equilibrium form of garnets and the results are djscussed in terms of thermal roughening of the garnet F-faces. The sequence of the faces in the order of decreasing roughening temperature is {llO}, {211). {321}, {loo}. The displacement velocity of misorientation steps on {211) faces is found to be 0.18 p n / s for 18 K undercooling. Die Orientierungsabhangigkeit der Wachstumsrate eines typischen ,,bubble"-Granat-Systems wird im gesamten Raumwinkelbereich von 4ic fur den Fall geringer Unterkuhlimg gernessen. Es werden fur (110) und (21 1) tiefe singulare Minima und fur (321) und (100) flache nichtsingulare Minima gefunden. Die maximale Rate wird in der Nahe von (111) erreicht. Es werden Schlusse auf die Gleichgewichtsform der Granate gezogen und die Ergebnisse im Rahmen der thermischen Aufrauhung von F-Flachen diskutiert. Die Reihenfolge der Flachen mit abnehmender Aufrauhungstemperatiir ist { 1 lo}, {211), {321}, {IOO}. Die Verschiebnngsgeschwindigkeit von Wachstumsstufen auf {211}-Flachen wird zu 0,18 pm/s bei 18 I< Unterkuhlung bestimmt.

Morphology of flux-grown vanadate garnets

“…The dominant form of the yttrium iron garnet (YIG) single crystal at higher growth temperatures (low viscosity) or at higher rotation speeds is {1 1 0} [3,14]. This may be explained by the fact that as the relative growth rate increases, the predominance of {1 1 0} faces increases because the {2 1 1} faces have a much faster growth rate than the {1 1 0} faces.…”

“…3) may be explained as follows. Table 2 shows that for Ca 3 Table 2 Ionic radii a , cation ratio, bond length, coordination ratio and the first rank F-face transition temperature from 1 1 0 to 1 1 with increasing temperature for vanadate and siliacte garnets Formula R [8] (Å ) b R [6] (Å ) c R [8] /R [6] X Fig. 5, the morphology change from {1 1 0} to {2 1 1} with increasing temperature can be ascribed to a decrease in the X-O/M-O ratio with increasing temperature.…”

“…Therefore, it can be predicted that {2 1 1} and {1 1 0} faces will dominate the habit of garnet crystals at lower temperatures. In the light of these contradictory conclusions that have been described in the literature, we propose to experimentally determine the relative importance of the temperature dependence of {1 1 0} and {2 1 1} faces in vanadate garnets [3]. By measuring 133 garnets from Fort Wrangell and Alaska, Pabst [5] concluded that there was excellent correlation between morphology and size.…”

“…Regarding the rank order of faces {1 1 0} and {2 1 1}, Hergt and Go¨rnert [3] found that the predominance of the {1 1 0} face significantly increased with increasing growth temperature for flux-grown Y 3 Ga 5 O 12 and Y 3 Fe 5 O 12 garnets. Based on experimental determination of growth rate anisotropy, they concluded that the {1 1 0} face roughens at an even higher temperature than the {2 1 1} face.…”

“…In order to clarify and solve unclear points or contradictions for the morphology of the garnets, it is very important to determine the rank order of the {1 1 0} and {2 1 1} faces [3]. To determine the rank order, vanadate garnet single crystals NaCa 2 M 2 V 3 O 12 (M ¼ Ni, Mg or Co) grown at low supersaturation levels using a NaVO 3 flux were examined.…”