Positron annihilation study of aluminum-copper-iron FCI quasicrystals.
Date
1993
Authors
Lawther, Derek William.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
Three positron annihilation techniques have been employed for the study of defect formation and behavior in Al-Cu-Fe face centered icosahedral (FCI) quasicrystals. Room temperature Doppler broadening and positron lifetime techniques were used to study the samples as a function of thermal treatment. An in situ Doppler broadening technique was used to study the samples at elevated temperatures.
Results from measurements on sample stoichiometries of $\rm Al\sb{63}Cu\sb{25}Fe\sb , Al\sb{62.5}Cu\sb{25}Fe\sb{12.5}, Al\sb{62}Cu\sb{25.5}Fe\sb{12.5}\ and\ Al\sb{62}Cu\sb{22.5}Fe\sb{15.2}$ are reported.
Quenched-in disorder has been observed in the samples. Reversion to the equilibrium behavior occurs after annealing the samples at 200$\sp\circ$C.
Equilibrium vacancy formation and behavior has been observed and correlated with results from a variety of other techniques which have been reported in the literature.
A quasicrystal-to-microcrystal phase transition has been observed in two of the samples ($\rm Al\sb{63}Cu\sb{25}Fe\sb \ and\ Al\sb{62}Cu\sb{22.5}Fe\sb{15.2}$), indicating an instability of the FCI phase at low temperatures. The FCI phase in the other two samples ($\rm Al\sb{62.5}Cu\sb{25}Fe\sb{12.5}\ and\ Al\sb{62}Cu\sb{25.5}Fe\sb{12.5}$) has been found to be stable over the entire temperature range investigated.
It is shown that intrinsic structural vacancies exist in both the microcrystal and FCI phases. The structural vacancy is interpreted in terms of an atomic structural unit in which an inner close-packed icosahedral shell of Al atoms surrounds a vacant central site.
Thermal activation of dynamic phason hopping has been observed in the FCI phase. At $\sim$200$\sp\circ$C, distortion of the intrinsic structural vacancies occurs as Al atoms of the inner icosahedral shell begin to hop within their double well potential. At higher temperatures (525$\sp\circ$C-750$\sp\circ$C depending upon the sample stoichiometry) Cu atom phason hopping is activated and is found to coincide with the onset of plasticity in the FCI phase.
Thesis (Ph.D.)--Dalhousie University (Canada), 1993.
Results from measurements on sample stoichiometries of $\rm Al\sb{63}Cu\sb{25}Fe\sb , Al\sb{62.5}Cu\sb{25}Fe\sb{12.5}, Al\sb{62}Cu\sb{25.5}Fe\sb{12.5}\ and\ Al\sb{62}Cu\sb{22.5}Fe\sb{15.2}$ are reported.
Quenched-in disorder has been observed in the samples. Reversion to the equilibrium behavior occurs after annealing the samples at 200$\sp\circ$C.
Equilibrium vacancy formation and behavior has been observed and correlated with results from a variety of other techniques which have been reported in the literature.
A quasicrystal-to-microcrystal phase transition has been observed in two of the samples ($\rm Al\sb{63}Cu\sb{25}Fe\sb \ and\ Al\sb{62}Cu\sb{22.5}Fe\sb{15.2}$), indicating an instability of the FCI phase at low temperatures. The FCI phase in the other two samples ($\rm Al\sb{62.5}Cu\sb{25}Fe\sb{12.5}\ and\ Al\sb{62}Cu\sb{25.5}Fe\sb{12.5}$) has been found to be stable over the entire temperature range investigated.
It is shown that intrinsic structural vacancies exist in both the microcrystal and FCI phases. The structural vacancy is interpreted in terms of an atomic structural unit in which an inner close-packed icosahedral shell of Al atoms surrounds a vacant central site.
Thermal activation of dynamic phason hopping has been observed in the FCI phase. At $\sim$200$\sp\circ$C, distortion of the intrinsic structural vacancies occurs as Al atoms of the inner icosahedral shell begin to hop within their double well potential. At higher temperatures (525$\sp\circ$C-750$\sp\circ$C depending upon the sample stoichiometry) Cu atom phason hopping is activated and is found to coincide with the onset of plasticity in the FCI phase.
Thesis (Ph.D.)--Dalhousie University (Canada), 1993.
Keywords
Physics, Condensed Matter.