| dc.contributor.author | Lawther, Derek William. | en_US |
| dc.date.accessioned | 2014-10-21T12:36:22Z | |
| dc.date.available | 1993 | |
| dc.date.issued | 1993 | en_US |
| dc.identifier.other | AAINN93784 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55417 | |
| dc.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. | en_US |
| dc.description | 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. | en_US |
| dc.description | Quenched-in disorder has been observed in the samples. Reversion to the equilibrium behavior occurs after annealing the samples at 200$\sp\circ$C. | en_US |
| dc.description | 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. | en_US |
| dc.description | 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. | en_US |
| dc.description | 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. | en_US |
| dc.description | 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. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1993. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Physics, Condensed Matter. | en_US |
| dc.title | Positron annihilation study of aluminum-copper-iron FCI quasicrystals. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
