The polymorphic transformation of Tb 24O 44 to Tb 48O 88 via a partly ordered incommensurate structure
The polymorphic transformation of Tb 24O 44, β(2), to Tb 48O 88, β(3), and the probable reduction to lower oxides in the thinnest regions of a crystal is followed by high-resolution electron microscopy. The mechanism by which β(2) is observed to transform to β(3) is via a partially disordered intermediate characterized by wavy fringes into which nuclei of the transformed polymorph, β(3), grow. Wavy fringes of narrower spacing persist at the thin crystal edge, suggesting further reaction of this thin edge to more reduced compositions. Alternative explanations of the origin of the wavy fringes observed are considered.