YBa2Cu3O7 samples were prepared by a citrate synthesis technique. Powder X-ray diffraction and resistance measurements were performed for sample characterization. This single-phase material has a Tc(R=0) of 91.2 K. Electron spin resonance experiments indicate the presence of 10 to 15% of Cu3+.
Blank, D. H. A., Flokstra, J., Gerritsma, G. J., van de Klundert, L. J. M., & Velders, G. J. M. (1987). X-ray and electron spin resonance on YBa2Cu3O7 prepared by citrate synthesis. Physica B+C, 145(2), 222-226. https://doi.org/10.1016/0378-4363(87)90087-8