Positron-annihilation study of equilibrium defects in Al-Cu-Fe face-centered-icosahedral quasicrystals

In situ Doppler-broadening temperature scans and room temperature positron-lifetime measurements are reported for Al63CU25Fe12, Al62.5CU25Fe12.5, Al62CU25.5Fe12.5, and Al62Cu22.8Fe15.2 face-centered-icosahedral (FCI) quasicrystalline samples. Quenched-in disorder has been observed and found to anneal out of the samples above 200 degrees C. A quasicrystal-to-microcrystal phase transition has been observed in two of the samples (Al63Cu25Fe12 and Al62Cu22.8Fe15.2), indicating an instability of the FCI phase at low temperatures. No such transition is observed in the other two samples (Al62.5CU25Fe12.5 and Al62Cu25.5Fe12.5). It is shown that intrinsic structural vacancies, possessing only Al-atom nearest neighbors, exist in both the microcrystal and FCI phases and act as saturation traps for the positrons. At similar to 200 degrees C, thermal activation of dynamic Al-atom phasons in the FCI phase results in distortions of the intrinsic structural vacancies as the nearest neighbor Al atoms begin to hop within double-well potentials. At higher temperatures (525-750 degrees C depending upon the sample stoichiometry) dynamic Cu-atom phasons are activated and observed to coincide with the onset of plasticity in the FCI phase.PT: J; CR: AUDIER M, 1986, PHILOS MAG B, V54, L105 AUDIER M, 1991, PHILOS MAG B, V63, P1375 AUDIER M, 1993, J NON-CRYST SOLIDS, V153, P591 BELIN E, 1993, J NONCRYST SOLIDS, V153, P298 BELLISSENT R, 1993, J NON-CRYST SOLIDS, V153, P1 BESSIERE M, 1991, J PHYS I, V1, P1823 BRESSON L, 1993, J NONCRYST SOLIDS, V153, P468 BURKOV SE, 1992, J PHYS-CONDENS MAT, V4, P9447 CALVAYRAC Y, 1990, J PHYS-PARIS, V51, P417 CHIDAMBARAM R, 1990, B AM PHYS SOC, V35, P331 CHIDAMBARAM R, 1990, J PHYS-CONDENS MAT, V2, P251 CHIDAMBARAM R, 1990, J PHYS-CONDENS MAT, V2, P9941 CHIDAMBARAM R, 1993, PHYS REV B, V48, P3030 CODDENS G, 1991, EUROPHYS LETT, V16, P271 CODDENS G, 1993, EUROPHYS LETT, V154, P557 CODDENS G, 1993, EUROPHYS LETT, V23, P33 CORNIERQUIQUAND.M, 1993, J NONCRYST SOLIDS, V154, P10 DENOYER F, 1990, J PHYS-PARIS, V51, P651 DENOYER F, 1993, J NON-CRYST SOLIDS, V153, P595 DIVINCENZO DP, 1993, J NONCRYST SOL, V153, P145 DUNLAP RA, 1987, J PHYS F MET PHYS, V17, L39 ELSER V, 1985, PHYS REV LETT, V55, P2883 HABERKERN R, 1993, J NON-CRYST SOLIDS, V153, P303 HAUTOJARVI P, 1977, PHILOS MAG, V35, P973 HOWELL RH, 1992, MATER SCI FORUM, V105, P651 ISHIMASA T, 1990, PHIL MAG LETT, V62, P357 JANOT C, 1991, EUROPHYS LETT, V14, P355 KAN XB, 1993, J NON-CRYST SOLIDS, V153, P33 KANAZAWA I, 1990, J NON-CRYST SOLIDS, V117, P793 KANAZAWA I, 1992, MATER SCI FORUM, V105, P1093 KANG SS, 1992, PHILOS MAG A, V66, P151 KATZ A, 1991, PHYS REV B, V44, P2071 KIRKEGAARD P, 1974, COMPUT PHYS COMMUN, V7, P401 KIZUKA T, 1989, PHYS REV B, V40, P796 KLEIN T, 1991, PHYS REV LETT, V66, P2907 KLEIN T, 1993, J NON-CRYST SOLIDS, V153, P312 KLEIN T, 1993, J NON-CRYST SOLIDS, V153, P562 KOSTER U, 1993, J NONCRYST SOLIDS, V153, P446 KRISTIAKOVA K, 1992, MATER SCI FORUM, V105, P1113 LAWTHER DW, 1990, J PHYS-CONDENS MAT, V2, P6239 LAWTHER DW, 1993, J NONCRYST SOLIDS, V154, P611 LAWTHER DW, 1993, KEY ENG MATER, V81, P95 LINDQVIST P, 1993, PHYS REV B, V48, P630 MOTSCH T, 1992, J PHYS I, V2, P861 NIEMINEN RM, 1983, POSITRON SOLID STATE, P359 OHATA T, 1990, PHYS REV B, V42, P6730 PAULING L, 1938, PHYS REV, V54, P899 PIERCE FS, 1993, PHYS REV B, V47, P5670 POON SJ, 1992, ADV PHYS, V41, P303 QUILICHINI M, 1993, J NONCRYST SOLIDS, V153, P568 QUIVY A, 1993, J NONCRYST SOLIDS, V153, P482 SADOC A, 1993, J NONCRYST SOLIDS, V153, P338 SAHNOUNE A, 1993, J NONCRYST SOLIDS, V153, P343 SANYAL MK, 1989, J PHYS-CONDENS MATT, V1, P3733 SEEGER A, 1987, PHYS STATUS SOLIDI A, V102, P171 SEEGER A, 1989, POSITRON ANNIHILATIO, P275 SHASTRI A, 1993, J NON-CRYST SOLIDS, V153, P347 SHI D, 1992, MATER SCI FORUM, V110, P829 SHIELD JE, 1992, PHYSICS CHEM FINITE, V1, P125 STEPHENS PW, 1986, PHYS REV LETT, V56, P1168 TSAI AP, 1987, J MATER SCI LETT, V6, P1403 TSAI AP, 1990, PHIL MAG LETT, V61, P9 WANG K, 1993, J NONCRYST SOLIDS, V153, P357 WASEDA A, 1993, J NON-CRYST SOLIDS, V153, P635; NR: 64; TC: 17; J9: PHYS REV B; PG: 7; GA: MW349Source type: Electronic(1