A study of structural and electrical properties of YBa_2-xLa_xCu₃O_7+δ

The structural and superconducting properties of the 1:2:3 system YBa_2-xLa_xCu₃O_{7+ delta} (0<or=x<or=0.6) have been investigated employing X-ray and neutron powder diffraction, thermogravimetric analysis and resistivity measurements. It has been observed that the structure undergoes a transition from orthorhombic to tetragonal symmetry at x=0.3, with normal state (T>T_c=81 K) conductivity remaining metallic, while semiconductivity is exhibited for x>or=0.35. The neutron profile analysis shows that La goes into the Ba sites, as expected, with an indication of a small but significant fraction of vacancies at the Y sites.