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Positron Annihilation Studies of Vacancy Formation in Tungsten, Chromium, and Niobium**

  • L. C. Smedskjaer (a1), G. D. Loper (a1), M. K. Chason (a1) and R. W. Siegel (a1)

Abstract

Vacancy formation was studied in the refractory bcc metals, tungsten, chromium, and niobium, using the positron annihilation spectroscopy Doppler broadening technique, between room temperature and the respective melting temperatures, under ultra-high vacuum conditions. Temperatures were measured by optical and infrared pyrometry, a W(Rh) thermocouple, and the power delivered to the sample, with calibrations against known melting temperatures. For W, a trapping-model analysis of the data from the temperature range 300–3633 K yielded a vacancy formation enthalpy of 3.76 ± 0.39 eV. For Cr, a similar fit to the data from 296–2049 K yielded a vacancy formation enthalpy of 2.0 ± 0.2 eV. The results are discussed in relation to previous vacancy formation and self-diffusion studies. Measurements on Nb as a function of temperature and oxygen content are also presented.

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Corresponding author

Now at: Motorola Corporation, Schaumburg, Illinois 60196, USA

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Permanent address: Physics Department, Wichita State University, Kansas 67208, USA

**

This work was supported by the U.S. Department of Energy.

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References

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** This work was supported by the U.S. Department of Energy.
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