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

Cathodoluminescence (CL) microscopy of YBa2Cu3O7-x using scanning electron microscopy (SEM) and light microscopy revealed the presence of impurity grains with a strong CL contrast. The impurities, present within internal pores of the material, were characterized by wavelength-resolved CL spectroscopy and by energy dispersive X-ray (EDX) analysis. Consideration of electron-beam conditions in the SEM resulted in a full correlation of microstructural features between the CL and electron emissive modes. Yellow CL emissions were generated from yttria-rich phases, and blue emissions were generated from copper-rich-barium-cuprate phases. EDX also demonstrated the presence of silicon within the pores. 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 determination of the quality of the pellet sample and hence its suitability as a target material for the laser-ablation deposition of thin films.