Electronic structure calculations of vacancies and their influence on materials properties

Abstract

August 1997This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. PREPRINTThis paper was prepared for submittal to the DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.

Density changes in plutonium observed from accelerated aging using Pu-238 enrichment

“…It is therefore important to examine void swelling mechanisms for any significant future density changes. While this ratio is corroborated by the observation from TEM and positron annihilation measurements [5][6][7], a significant variation exists between specimens, see Table 3. Even 2 and 3 cm length specimens at 35°C, which represent bulk changes, show different values of 2.66 and 1.83.…”

“…The helium that accumulates in plutonium immediately finds an unfilled vacancy and forms bubbles inside the crystalline matrix and along grain boundaries [5][6][7]. The dilatometry shows volume expansion at a steady rate with time primarily induced by a constant helium in-growth rate of ~41.1 appm per year, whereas the data of Chebotarev and Utkina do not [4].…”

“…The X-ray diffraction study by Chebotarev and Utkina on Pu alloys aged at room temperature for 2.5 years showed lattice expansion and the lattice parameter reached essentially a constant value in 2 to 3 years [4]. Positron annihilation measurements indicate that helium-filled vacancies are present in significant numbers in aged plutonium samples [5,6]. Recent transmission electron microscopy investigation of aged Pu-Ga alloys revealed the presence of nanometer-sized helium bubbles formed from helium in-growth [7].…”

Volume changes in δ-plutonium from helium and other decay products

“…The second determination of the helium density in bubbles was obtained by Sterne et al [20] with positron annihilation lifetime measurements on old plutonium samples and with first-principles calculations of annihilation rates of positrons trapped in vacancy clusters, voids and helium bubbles. These calculations have shown that calculated positron lifetimes in old plutonium samples agree with the measured values of 180-200 ps if the He/Vac.…”

Vacancy interactions in cluster expansion formalism

“…Electronic structure calculations contribute to our understanding of vacancies and their role in determining materials properties [1]. Diffusion is known to depend strongly on vacancies.…”