Plan-View CBED Studies of Nio-Zro 2 (CaO) Interfaces
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PLAN-VIEW CBED STUDIES OF NiO-ZrO 2 (CaO) INTERFACES V.P. Dravid*, M.R. Notis*, C.E. Lyman* and A. Revcolevschi*" * Department of Materials Science & Engg., Lehigh University, Bethlehem, PA 18015 USA ** Laboratoire de Chimie des Solides, Universite de Paris-Sud, 91405 Orsay Cedex, FRANCE ABSTRACT Low energy lamellar interfaces in the directionally solidified eutectic (DSE) NiO-ZrO 2 (CaO) have been investigated using transmission electron diffraction and imaging. The symmetry of this bicrystal and an aspect of interfacial relaxations in the form of symmetry lowering in-plane rigid body translation (RBT) have been explored by performing convergent beam electron diffraction (CBED) experiments of plan-view bicrystals. Edge-on interfaces have also been studied by conventional and high resolution transmission electron microscopy (CTEM and HRTEM respectively), and electron diffraction fine structure analysis. Despite certain experimental difficulties due to interfacial defects and strain, plan-view CBED patterns offered valuable information concerning bicrystal symmetry and indicated no symmetry lowering RBT in this bicrystal. The suitability of plan-view CBED is briefly discussed in view of its potential as a technique to determine bicrystal symmetry and RBT. INTRODUCTION Interphase interfaces form a special class of general crystalline interfaces. Unlike grain boundaries, interphase interfaces can be equilibrium defects in a crystalline solid. Low energy interphase interfaces, in particular, have a marked influence on nucleation and growth processes in solid-state phase transformations. The structure of crystalline interfaces is an intensely pursued subject because it is believed that the generic structure-property relation can be extended to bicrystal and polycrystal interfaces. Among the available geometric approaches [1] to describe a given bicrystal and interface, Bicrystallography [2] has recently emerged as an important and useful approach. Unlike the CSL and O-lattice type concepts [3], which utilize only the translational symmetry of the crystals, bicrystallography embodies complete symmetries (translational, point and combination, i.e. space group symmetries) of the adjoining crystals. For given orientation of the two crystals and the interface plane (for planar interfaces), it is always possible to assign a point group and space group (if there is at least one dimensional translation symmetry) to the bicrystal. If the interface in question is a grain boundary, additional symmetry elements such as color reversing operations may also arise. There are many advantages in describing crystalline interfaces in the framework of bicrystallography. It can be anticipated that just as single crystal properties are expected to follow crystal symmetry, bicrystal properties should also conform to bicrystal symmetry. However, more importantly, bicrystallography provides a unique framework for analyzing interfacial defects in a rigorous and unified manner. Symmetry breaking while creating the bicrystal may lead to interfacial
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