D e t a i l e d XPS s t u d i e s with emphasis on s p e c i a l c h a r a c t e r i s t i c s 3f t h e 01s and Cu2p3il-c o r el e v e l s , thermogravinietry. X-ray d i f f r a c t i o n , i n f r a r e d spectroscopy and scanning e l e c t r o i l microscopy have been used t o study t h e degradation of t h e superconducting phase YBa,Cu 0, i n c o n t a c t w i t h water under various c o n d i t i o n s . It is shown t h a t t h e superconducting YBa,Cu307-x phase i n c o n t a c t w i t h water o r humid a i r decomposes i n t o CuO, Ba(OlI)?, Y,BaCu05 and oxygen and a l s o y i e l d s BaC03 by r e a c t i o n w i t h atmospheric CO treatment may y i e l d a p a s s i v a t i o n l a y e r i n h i b i t i n g f u r t h e r decomposition.
YBa2Cu307-6 superconductors thus have been shown to be especially sensitive to moisture. This necessitates prevention of environmental degradation of the superconductor surface if we want to use these materials in practical applications. After the superconducting pellet was treated during 15 minutes with a 1% Br2-ethanol solution, the sample was immersed in de-ionized water for 12 hours. We could not detect significant changes in the Ba-XPS spectra nor is the superconductor surface visibly affected. In the survey scan we find a trace amount of Br. consistent with the formation of BaBr2 as suggested by R.P. Vasquez et all1.
CONCLUSION
The formation of a BaC03 coating on YBa2Cu307-x superconductors when exposed to water or humid air was substantiated by XPS, SEM, TGA and DTA. The superconducting phase is believed to decompose to CuO. Ba(05)2 and Y BaCuO in contact with water. The Ba(OH)* phase which is highly soluble in water reacts with C02 in the atmosphere to form the thermodynamically very stable BaC03. The high reactivity of a superconductor with water can be attributed to the high hydratation energy of the Ba2+ ions and the existence of extremely reactive 0 ' -species.
We ate extending this to study other aspects. such as surface morphology and rate of decomposition of the superconductor in humid atmosphere. Our study leads to the final conclusion that protection of ceramic material from humidity must be provided. In this respect, the Br2-etching technique seems promising for achieving passivation of the superconductor surface.
ACKNOWLEDGMENT
state physics, University of Ghent) for S W and XRD work. Furthermore the authors wish to thank the Research Commission of the R.U.G., for the purchase of a TG/DTA equipment and the NFWOJFNRS for the computing facilities in XPS. We also thank K.D. Bomben from Perkin Elmer Physical Electronics in Minnesota (USA) and T. Haemers providing the XPS measurements.