Zargaryan, Y. M., et al. “THE EFFECT OF DOPING ON THE SUPERCONDUCTIVITY OF THE YBa$_2$Cu$_3$O$_y$”. Proceedings of the YSU A: Physical and Mathematical Sciences, vol. 39, no. 2 (207), June 2005, pp. 46-51, doi:10.46991/PYSU:A/2005.39.2.046.