Some applications of perturbed angular correlation and positron annihilation to materials science

The perturbed angular correlation (PAC) and positron annihilation spectroscopy (PAS) that use nuclear probes to characterize the micro-structure of materials are briefly described. Three examples are given to show their partial applications. The first example is the study of radiation damage in Si irradiated by fast neutrons of 1.45·10²⁰ cm⁻² and ¹⁷⁸W heavy ions of 5·10¹¹ cm⁻², respectively. The PAC and PAS measurements all show that the monovacancy-oxygen complexes and divacancies and divacancy-oxygen complexes were produced by the irradiations, and quadrivacancies and quadrivacancy-oxygen complexes were formed during thermal annealing. The second one illustrates the investigation of high T _c superconductivity for YBaCuO. The PAS experiment found the charge transfer during the superconducting trasition. The PAC measurement suggested a transition of two-to one-dimensional Cu-O-Cu chain structure at the superconducting trasition temperature T _c , which favors the charge transfer from the CuO layer to the CuO chain in YBaCuO. The third one is for investigating the hydrogen behavior in Pd_0.75Ag_0.25-H _x as functions of temperature from 77 K to RT and hydrogen concentration (x) from 0 to 35 at.%. The PAC and PAS results exhibit that hydrogen atoms are congregated into the hydrogen bubbles and the hydrogen bubbles grow with the increasing of the hydrogen concentration in Pd_0.75Ag_0.25-H _x . These examples demonstrate that the PAC and PAS techniques are very sensitive and powerful tools in materials science, which can well investigate phenomena in materials on atomic scale.