Opto-structural and dielectric properties of 80 MeV oxygen ion irradiated natural phlogopite mica

Abstract

Ion beams of MeV energies produce latent tracks in most dielectrics. These ion tracks in turn produce various modifications in their structural, optical and dielectric properties. These modifications are monitored using various techniques such as Ultraviolet–visible spectrometry, X-ray Diffraction, LCR meter and Fourier Transform Infra red spectroscopy in natural phlogopite mica. Thin sheets (∼20μm) of phlogopite mica were exposed to 80MeV oxygen ions. A systematic decrease of the optical band gap with ion fluence was observed. An increase in the Urbach energy indicates an increase in the disorder in phlogopite mica. The dielectric constant was found to decrease with increasing fluence while measurements of tanδ, a.c. conductivity and dielectric loss show an increase. The measured data revealed that the value of a.c. conductivity depends linearly on the frequency, with slope n ranging between 0.62 and 0.77. X-ray Diffraction analysis of pristine and irradiated phlogopite mica demonstrated that the crystallite size decreases while strain and dislocation density increases with increasing fluence. Fourier Transform Infra red spectra showed the shifting of the OH stretching band and the disappearance of Si–H bands due to irradiation. Different causes of these modifications are discussed here.