IMPURITY PHASE RECOGNITION IN YBCO HIGH T(C) SUPERCONDUCTORS BY CATHODOLUMINESCENCE SPECTROSCOPY

Cathodoluminescence (CL) microscopy of YBa2Cu3O7-x using scanning elec tron microscopy (SEM) and light microscopy revealed the presence of im purity grains with a strong CL contrast. The impurities, present withi n internal pores of the material, were characterized by wavelength-res olved CL spectroscopy and by energy dispersive X-ray (EDX) analysis. C onsideration of electron-beam conditions in the SEM resulted in a full correlation of microstructural features between the CL and electron e missive modes. Yellow CL emissions were generated from yttria-rich pha ses, and blue emissions were generated from copper-rich-barium-cuprate phases. EDX also demonstrated the presence of silicon within the pore s. It is suggested that a glassy silicate phase is present, which may wet the impurity-phase grains. In identifying and characterizing these impurities, the CL technique proved to be a powerful tool in the dete rmination of the quality of the pellet sample and hence its suitabilit y as a target material for the laser-ablation deposition of thin films .