THE MORPHOLOGICAL DIAGRAM OF SPINELS

Spinels exposing {100}, {110}, and {111} faces have been considered an d their Curie-Wulff plots have been drawn, admitting that the relative G{hkl} surface free energies may change in a wide range as a function of composition, inversion, and segregation degree. The normalized fre e surface energies are defined as A = G{100}/G{111}, B = G{110}/G{111} , and C = G{111}/G{111} = 1 = const. This made it possible to construc t bidimensional morphological diagrams (morphology = f(A,B) at C = con st) in the exposed-face-type, solid-type, and exposure-percentage vers ions. Eleven morphological habits of grains have been identified, incl uding {100}-cube, {110}-dodecahedron, {111}-octahedron, 14-hedron bord ered with six {100}-squares and eight {111}-hexagons, 18-hedron, 20-he dron, and up to 26-hedra bordered with (i) 6 {100}-octagons, 12 {110}- rectangles, and 8 {111}-hexagons, (ii) 6 {100}-squares, 12 {110}-recta ngles, and 8 {111}-triangles, or (iii) 6 {100}-squares, 12 {110}-octag ons, and 8 {100}-triangles. The analysis is valid for all compounds cr ystallizing in the cubic system and preferentially exposing the three enumerated faces. (C) 1996 Academic Press, Inc.