Oxygen isotope effect inYBa2Cu3O7prepared by burningYBa2Cu3inO16andO18

We prepared ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ powder by ball milling a 2:1 molar mixture of the intermetallics BaCu and CuY. We synthesized ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${(}^{16}$O${)}_{7\mathrm{-}\mathrm{x}}$ and ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${(}^{18}$O${)}_{7\mathrm{-}\mathrm{x}}$ by oxidizing the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ powder in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$. The ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ${/}^{18}$O ratios were determined by laser-ionization and sputtering-ionization mass spectroscopy. The ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${(}^{16}$0${)}_{7\mathrm{-}\mathrm{x}}$ sample had 99.8 at. ${\mathrm{\%}}^{16}$O, and the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${(}^{18}$O${)}_{7\mathrm{-}\mathrm{x}}$ sample had 96.5 at. ${\mathrm{\%}}^{18}$O. Susceptibility measurements of the superconducting transition temperature ($T_c$=91.7 K for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$; half-point transition at 84 K show an isotope effect of 0.4±0.1 K.