The remarkable difference in water wettability of YBa2Cu3O7−x and Y2BaCuO5 powders

The irreversible deterioration in superconducting performance caused by the reactions with air moisture is a severe obstacle for the applications of Y-Ba-Cu-O (YBCO) superconductors. However, the detailed water adsorption mechanism and the crack growth behaviors in superconductors are still not very clear. In this study, YBa2Cu3O7−x (Y123) and Y2BaCuO5 (Y211) powders are fabricated by chemical coprecipitation method for experiments. An optical contact angle measuring device is used to analyze the water wettability of powders. The results demonstrate that Y123 powders are super hydrophilic while Y211 powders are hydrophobic. The concomitant difference in surface energy of powders results in a large number of crystal spaces between Y211 particles and Y123 grain domain after crystal growth. Such crystal spaces are the vulnerable parts for air moisture. A deterioration and crack-growth mechanism of YBCO superconductors under air moisture is proposed and discussed accordingly.