In Pursuit of the Lattice Vacancy
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Materials Research Society and hâve been privileged to witness the phénoménal growth of MRS at first hand. The stature of the Von Hippel Award must be increasing at least in proportion to this growth. I, therefore, feel very honored and grateful indeed! I would also like to add that much of my work has been done in collaboration with valued colleagues and studenfs. They deserve a substantial share of this award. Over the years, my research has been devoted mainly to the expérimental study of crystal defects and their behavior. Thèse defects can be classified according to their dimensionality as shown in the accompanying table, and they are involved in one way, or another, with a host of phenomena in crystalline mate-
rials. Since I address a rather diverse audience, it might be appropriate to discuss some of the history of lattice vacancy research and some of the détails of my personal contribution to it. This is the defect which I first began to pursue some 40 years ago and which still remains elusive in certain respects. The 1950s In 1950, when I had just obtained my ScD in physical metallurgy at MIT with the help of the GI Bill after returning from the war in Europe, the state of knowledge of lattice defects of ail types was relatively rudimentary. Fortunately for me, however, I came on the scène at a time when more and more powerful techniques were rapidly becoming available for the effective study of thèse defects. For vacancies in metals, Huntington and Seitz2 had already calculated the formation energy of a vacancy in copper to be —1 eV and that of an interstitial to be considerably larger. Also, the Kirkendall Effect, which had been observed3 just three years earlier, had demonstrated that the différent substitutional atoms in a crystalline solid solution diffuse at unequal rates and that this causes a mass flow to occur in the diffusion zone. This was a direct proof that the diffusion occurred by a defect exchange meçhanism. However, the defects could hâve been either vacancies or interstitials. It was widely suspected that they were vacancies, and that the unequal diffusion rates were due to unequal exchange rates between the différent atoms and the available vacancies, but
Professor R.W. Balluffi The Von Hippel Award, the Materials Research Society's most crystal defects (point, line, and planar), and the more complex prestigious honor, was presented to Prof. R.W. Balluffi during phenomena in which they are involved, such as diffusion, radicérémonies held at the 1990 Fall Meeting in Boston. The award ation damage, phase transformations, and plastic déformation. honors his leadership in materials science research as well as his His most récent work focuses on the structure and properties of rôle as an outstanding expérimental investigator. The award grain boundaries. He is the author of approximately 200 papers also recognizes his accomplishments for their depth, diversity, on thèse topics. and innovation, which exemplify the goals of interdisciplinary A former MRS councillor, Balluffi is a Fellow of the
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