Detection of surface (approx. 1. mu. m) impurity phases in high T/sub c/ superconductors

We show that thermally stimulated luminescence is an important method for detecting insulating impurity phases that commonly occur in high T/sub c/ superconductors. The technique is sensitive to impurity phases at <1% level with a probe depth of approx. 1 ..mu..m, which is the region of interest for many superconductor applications. Samples of Y/sub 2/O/sub 3/, Y/sub 2/BaCuO/sub 5/, YBa/sub 2/Cu/sub 3/O/sub 6.2/, BaCO/sub 3/, Ba/sub 3/CuO/sub 4/, BaCuO/sub 2/, and YBa/sub 2/Cu/sub 3/O/sub x/ (xapprox. =7) were investigated. All but the high quality sintered pellets of YBa/sub 2/Cu/sub 3/O/sub x/ exhibited relatively intense luminescence. The absence of luminescence, and thus of insulating phases, is correlated with low values of rf surface resistance.