The Effect of Swift Heavy Ion Irradiation on Quasicrystals
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The Effect of Swift Heavy Ion Irradiation on Quasicrystals Ratnamala Chatterjee1, Aloke Kanjilal1 & A.Dunlop2 Department of Physics, Indian Institute of Technology, New Delhi, India 2 Laboratoire des Solides Irradies, Ecole Polytechnique, Palaiseau, France 1
Abstract The effect of pure electronic excitations (by ~ 835 MeV Kr irradiation) on a stable icosahedral quasicrystal is compared with the effect of electronic excitations combined with the nuclear collisions (by 100 MeV Ni irradiation) occurring in a similar quasicrystal. The critical stopping power was kept at 1300 eV/Å for both the experiments. Under the pure electronic excitations, the R(φ)/R(0) [ratio of resistance at fluence φ and the resistance on the same piece with zero fluence) of quasicrystal goes through oscillatory changes, until at ~ 1 x 1012 ions/cm2 where this ratio drops considerably. The ex-situ XRD on the irradiated sample does show the evidence of degradation of the structure. In contrast, the Ni- irradiated sample shows an increase in resistivity after a critical fluence of 2.5 x 1013 ions/cm2 , which remains constant for higher fluences. Corresponding defect annihilation effects are observed in the XRD of Ni- irradiated samples.
Introduction When any target material is irradiated, the slowing down of ions occur mainly via two methods- (i) inelastic collisions of ions with the electrons of the target material or (ii) elastic collisions with the atoms of the target material. The former is predominant for swift heavy ions with high energies (greater than 100 MeV), whereas the latter is important for the low energy ions. In the former, electronic stopping power (electronic excitations in the target material) corresponding to the inelastic collisions, is the dominant mechanism by which swift heavy ions (SHI) lose their energy. Quasicrystals are metallic compositions that have no periodicity but have long range order. Electronic structure of quasicrystals is still not very well understood [1]. Various models exist in literature, which attempt to give possible description of electrons in quasicrystals. For this very reason, SHI irradiation seems to be an attractive tool to excite the electronic structure of quasicrystals and investigate the corresponding effects on them. Until recently, inelastic collisions were considered as inefficient to create any damage in the metallic targets. Due to the large mean free-paths of the metallic electrons, the samples are expected to get heated as a whole. From literature, it is known that such inelastic collisions could create or annihilate defects only in certain metals/ metallic alloys above an electric stopping power threshold [2]. Previous reports of irradiation on quasicrystals have been on low energy irradiation (~ 1 MeV), where the energy loss is mainly via nuclear collision. Various effects like amorphization [3] or quasicrystal to amorphous reversible transition[4] have been reported. Here, we would discuss the effect of SHI (≥ 100 MeV) on stable icosahedral quasicrystals K6.3.1
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