Low-energy interfaces in NiO-ZrO 2 (CaO) eutectic
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INTRODUCTION
INTERPHASE interfaces form a special class of general interfaces, which, unlike grain boundaries, can be equilibrium interfaces in a crystalline solid. Low-energy interphasc interfaces, in particular, have a marked influence on nucleation and solid-state phase transformation phenomena. Very few attempts have been made conccrning the identification of low-energy interfaces, their structure, and microchemistry. There is especially a notable paucity of such work in oxide systems. Modeling of interfaces based on geometry or crystallography has been shown not to have any predictive power concerning low-energy interfaces. [1] The atomistic simulation of interfaces is a very powerful technique, but its application to interphase interfaces, particularly in oxides, is in its developmental stage. [2] In light of the above, it appears that characterization of model interphase interfaces in oxide systems may provide a good data base for subsequent theoretical work. This study is part of a research program concerning the characterization of interfaces in directionally solidified eutectics (DSEs) of oxide systems. [3] In this paper, we present physical arguments and experimental results concerning identification and characterization of low-energy interfaces in the DSE system, NiO-ZrO2(CaO) (hereafter referred to as NZ). We believe that the DSEs of binary or pseudo-binary oxide components represent excellent model systems for the study of interphase interfaces. The important features of a well-grown DSE are (1) parallel growth of the two phases; (2) well-defined orientation relationship (OR), (3) large number of crystallographically identical interfaces; (4) except for the influence of unidirectional heat flow,
VINAYAK P. DRAVID, Graduate Student, C.E. LYMAN, Professor, and M.R. NOTIS, Professor, are with the Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015-3195. A. REVCOLEVSCHI, Professor, is with the Laboratoire de Chimie des Solides, Universite de Paris-Sud, Orsay, France. This paper is based on a presentation made in the symposium "Interface Science and Engineering" presented during the 1988 World Materials Congress and the TMS Fall Meeting, Chicago, IL, September 26--29, 1988, under the auspices of the ASM-MSD Surfaces and Interfaces Committee and the TMS Electronic Device Materials Committee. METALLURGICAL TRANSACTIONS A
there is no external constraint on the choice of the interface plane; actually, even with directional heat flow, the interface has enough opportunity to rotate to minimum energy configuration during the growth period; and (5) no segregation or precipitation of a third phase. If a DSE exhibits the above features, it is likely that the interfaces involved are low-energy interfaces. However, it must be cautioned that there are notable exceptions to this in metallic DSEs, t4,5] and any conclusions regarding low-energy interfaces must be supplemented by additional experiments or by theoretical simulation methods which, unfortunately, are only in their develo
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