2000
DOI: 10.1103/physrevb.62.12021
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High-temperature studies of grain boundaries in ultrafine grained alloys by means of positron lifetime

Abstract: Atomic free volumes and vacancies in the ultrafine grained alloys Pd 84 Zr 16 , Cu 0.1 wt % ZrO 2 , and Fe 91 Zr 9 were studied by means of positron lifetime. The thermally stable microstructures serve as a novel type of model system for studying positron trapping and annihilation as well as the thermal behavior of vacancy-sized free volumes over a wide temperature range up to ca. 1200 K by making use of a metallic 58 Co positron source. In ultrafine grained Cu the thermal formation of lattice vacancies could … Show more

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Cited by 28 publications
(17 citation statements)
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“…Linear reversible increases of the mean positron lifetime occur after annealing at 713 and 813 K. These changes in lifetime are caused by an increase of the specific positron trapping rate, void , of nanovoids, as was found recently 6 for n-Pd 84 Zr 16 ͑see below͒. Upon further annealing at 1023 K, a decrease of occurs above about 820 K. This change in is fully reversible as shown by the sequence of data points in Fig.…”
Section: B Thermal Vacancy Formationsupporting
confidence: 74%
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“…Linear reversible increases of the mean positron lifetime occur after annealing at 713 and 813 K. These changes in lifetime are caused by an increase of the specific positron trapping rate, void , of nanovoids, as was found recently 6 for n-Pd 84 Zr 16 ͑see below͒. Upon further annealing at 1023 K, a decrease of occurs above about 820 K. This change in is fully reversible as shown by the sequence of data points in Fig.…”
Section: B Thermal Vacancy Formationsupporting
confidence: 74%
“…We conclude that the variation of at high temperatures can be quantitatively understood on the basis of thermal formation of lattice vacancies. As for Pd 84 Zr 16 , 6 no indication of additional thermal defect formation in the grain boundaries is found. In both alloys a strong segregation of Zr or Nb at grain boundaries occurs, stabilizing the nanostructure.…”
Section: B Thermal Vacancy Formationmentioning
confidence: 86%
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“…The question arises as to whether the high oxygen diffusivities of ZrO 2 ⅐Y 2 O 3 upon doping can be further enhanced by the introduction of a large number of crystallite interfaces. A reason for an enhanced oxygen diffusion could be a loosely packed grain boundary structure, which is well established for pure metals (4), or easy formation of vacancy-type free volumes within the grain boundaries (5). On the other hand, there are reports that oxygen transport across grain boundaries could be impeded by a blocking effect due to space charge layers in the grain boundary region (6) or silica-containing grain boundary phases (7).…”
mentioning
confidence: 99%