Study of SmFeAso1-xfx by positron annihilation technique

SmFeAsO1-xFx superconductor was first studied by Positron lifetime spectra at room temperature and temperature dependent of Doppler-broadening spectra, meanwhile, surperposed-Neutral-Atom model and Finite-Difference method (SNA-FD) are used to calculate the positron lifetime of single crystal SmFeAsO and SmFeAsF samples with different types of vacancies. The calculated positron bulk lifetime in polycrystalline SmFeAsOxF1-x agrees well with the experimental results. The temperature dependence of S parameter of the parent sample is well fitted with two straight lines separated at about 150 K indicates that a phase transition occurred, while, the temperature dependence of S parameter of the superconductor sample shows two different slopes before and after superconductivity transition. The linearity S-T plot shows one-type of defects appears in the superconductor sample through the superconductivity transition. (authors)