Effect of swift heavy ion beam irradiation on the dielectric and ferroelectric properties of pure and cobalt doped TGS crystals

摘要

Effect of swift heavy ion (100 MeV O~(7+) ion) beam irradiation on the temperature and frequency dependence of real (ε') and imaginary (ε″) parts of dielectric permittivity in pure and Co~(2+) doped TGS crystals are analyzed. Irradiation with swift heavy ion beam changes the dielectric response considerably. Observed dielectric peak in irradiated crystals shifts towards lower temperature and broadens up; the reduction in peak value, shift in temperature and broadening changes systematically with fluence. The most interesting results of SHI irradiation are (i) the dielectric loss peak value (e″_(max)) in all crystals is invariably less in comparison to the value in unirradiated crystals (ii) the minimum value of dielectric loss peak (e″_(max)) occurs at different fluence in different crystals, and (iii) a second loss peak is observed below T_c in CTGS10 especially at higher fluence. It seems that irradiation creates/strengthens internal field in the crystals by orienting the domains through some mechanism that is not clear at present. The observed results could be explained if one presumes that irradiation annihilate the defects already present in the crystals by creating local charges and thermal gradient resulting into internal bias field. Ferroelectric hysteresis loops demonstrate the internal bias field developing in the SHI irradiated crystals. It is argued that SHI irradiation is a better alternate in comparison to cobalt doping in inhibiting dipolar switching in TGS crystal.