Investigations Of Strucutral Damage And Modification Of Muscovite Mica Caused By Energitic Heavy Ion Irradiation

Muscovite mica with layered structure is widely used in geology archaeology and solid track detector due to its excellent physical property. Moreover, muscovite mica has a remarkable performace in capacitor because of its high dielectric constant. The mica capacitor is applied in aerospace, navigation and rocket that required high accuracy, stability and reliability. Study of irradiation effects of mica has a great guidance to other materials.In this experiment, muscovite mica sheets with a thickness of 12 μm were irradiated by swift heavy ions(SHIs: 209 Bi, 114 Xe, 112 Sn and 86Kr) with energy as high as 2.0 Ge V accelerated by the Heavy Ion Research Facility in Lanzhou(HIRFL) and highly charged ions(HCIs: Xeq+ and Krq+) with an energy of 1.4 Me V offered by 320 k V high-voltage plat form of IMP. The ion fluences of SHIs range from 1×1010-1×1013 ions/cm2, and the ion fluences of HCIs range from 5×1011-1×1016 ions/cm2. The mica samples were irradiated at room temperature with different irradiation parameters, such as electrical energy loss(d E/dx)e, ion fluence and charging state. In order to investigate the effects induced by energetic heavy ion irradiation, the samples before and after irradiation were investigated by X-ray diffraction(XRD), atomic force microscopy(AFM), transmission electron microscope(TEM), ultraviolet-visible light detector(UV-Vis) and fourier transform infrared spectrometer(FTIR Spectrometer). The longitudinal sections of the tracks introduced by SHI irradiation were observed. The defective tracks caused by HCIs were also analyzed in this experiment.XRD was applied to investigate the crystal structure transition in SHI irradiated muscovite mica. According to the XRD patterns, the FWHM values of the main diffraction peaks of mica increased with the ion fluences. It is also observed that the diffraction peaks shifted to the high angles, and the interplanar distance decreased after the ion irradiation. It is indicated the appearance of the dilated phase and amorphous structure. The damage section and the dilated phase formation section were fitted according to the XRD spectrum. Compressive stress with the value increasing with the ion fluences was aslo introduced by SHI irradiation. The surface morphology of irradiated mica was observed by AFM. It is found that the flat surface of mica became rough and with nano-craters on it. Shapes of the nano-craters vary with the values of(d E/dx)e. The incidence of ion reaches the surface has a certain influence on the morphology of the defects.Latent tracks induced by energetic heavy ion irradiation were investigated according to the TEM patterns. a) Tracks with nearly circular cross-section were uniformly distributed on the TEM images. The longitudinal section of the track shows like a continuous strip. The track core represents an amorphous zone with a sharp boundary. The structure around the core remains crystalline. The mean diameter of the track is increased with the values of(d E/dx)e. b) The average diameter of the tracks induced by SHI irradiation enlarged as the samples exposed to the thousands of electrons from TEM. It is suggested that point defects introduced by the electron bombardments were gathered around the track core, which caused the enlarger of the track. c) Tracks with defective crystal structure in the core were found in the HCI irradiated mica. There was no continuous latent track found in the HCI irradiated mica.The optical properties of the irradiated mica are investigated by UV-vis spectrum. a) The band gaps became narrow and the Urbach energy increased as large amount of defects were caused by SHI irradiation. The proportion of defects and amorphous structure was increased in mica irradiated with increasing(d E/dx)e and fluences. b) The similar phenomenon was found in the HCI irradiated mica. The crystal structure in the irradiated mica was disordered and thus the band gaps of HCI irradiated mica narrowed down and Urbach energy increased with increasing ion fluence and charging state. c) More defects were introduced in mica by SHI than by HCI irradiation under the same ion fluence.The infrared spectrum shows that motions from all the atom types in the muscovite mica structure could be found in modes for all vibrations. No new peaks appeared after SHI and HCI irradiation. It is suggested that there is no new chemical bonding formation during irradiation. The intensity of all vibrational modes in mica decreased with the increasing ion fluence and(d E/dx)e. It is indicated that defects and structural modifications generated during the ion irradiation. The coordination number of Si in the tetrahedron increased, while the bond length and angle of OH are not changed after irradiation.