Solid krypton in MgO
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Solid krypton in MgO M. Grant Norton Department of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164
C. Barry Carter Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455
Elizabeth L. Fleischer The Materials Research Society, Pittsburgh, Pennsylvania 15237
James W. Mayer Center for Solid State Science, Arizona State University, Tempe, Arizona 85287 (Received 29 May 1992; accepted 6 August 1992)
Recent work by the authors has been extended to demonstrate the formation of solid krypton in single-crystal magnesium oxide. The solid inclusions, which were formed by ion implantation at room temperature, have been identified by electron diffraction. The formation of solid noble gas inclusions at room temperature indicates that they were under a high pressure. This pressure was determined, based on the measured lattice parameter, to be 1.7 GPa.
Ion implantation of ceramic materials has been investigated as a means of improving the hardness and wear resistance of such materials.1 Although the majority of previous studies have used transition metal ions as the implanted species,2 implantation of noble gas ions is of interest in studying some of the fundamental aspects of the ion implantation process. Noble gas ions are immiscible with the ceramic matrix and therefore chemical effects of ion implantation such as intermixing are unlikely. It has been demonstrated that implantation of noble gas ions into metals resulted in the formation of solid, three-dimensional inclusions of the implanted species.3'4 More recently, similar observations have been made on ceramic materials implanted with noble gas ions.5"7 Comparison of the results obtained from the two materials systems (metals and ceramics) indicates that there are a number of similarities. In either material, very high pressures are necessary in order to confine solid noble gases at room temperature.8 Results from both systems clearly indicate that remarkably high pressures are generated during the growth of these inclusions.5'9 The other similarity is that the solid inclusions have an epitactic relationship with the matrix. 510 For metal matrices, solid inclusions have been observed following implantation of Ar, Kr, and Xe ions. 3 ' 1112 For ceramics, only solid Xe inclusions have been reported following J. Mater. Res., Vol. 7, No. 12, Dec 1992
implantation of Xe into single crystals of MgO and yttria-stabilized zirconia (YSZ).5'5 In this communication, the identification of solid Kr inclusions in a MgO matrix following implantation of Kr + ions is reported. Based on the calculated lattice parameter of the inclusions, a value for the pressure of these inclusions was estimated. Transmission electron microscopy (TEM) has been a widely used technique to study the nature of lattice defects formed by ion implantation. Examination of materials by TEM requires the preparation of electron transparent specimens. For metals, electron transparent samples can be readily obtained
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