Phase formation and lattice strain in superconducting compound ${\mathrm{Y}}_{1-x}{\mathrm{La}}_x{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ $(0\mathrm{}<~x<~1)$

We study the formation and evolution of phases in the La substituted ${\mathrm{Y}}_{1-x}{\mathrm{La}}_x{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ [(Y–La)123] superconductors from XRD and Raman measurements. We find characteristic modifications in the interatomic distances, bond valence sum (BVS) values and crystallite microstrains, which correlate with corresponding features of the micro-Raman spectra at nominal La compositions $x=0.2,$ 0.5, and 0.8. Based on the Raman spectra we conclude that two phases appear, an intermediate of chemical formula ${\mathrm{Y}}_{1-x}{\mathrm{La}}_x{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ with x values less than nominal, and another phase of pure La123 with partial substitution of La for Ba and reduced $T_c.$ The crystallographic changes and the reduction of $T_c$ can be interpreted based on the formation of this pure La123 subphase upon La doping.