A neutron diffraction study of LaBa2Cu3O7−δ

The correlation between structure and oxygen content in the LaBa2Cu3O7+δ was investigated by neutron powder diffraction. It is shown that the structure is orthorhombic (Pmmm) when δ = −0.04 and tetragonal ( P4 mmm ) when δ = −0.06. Such a change in structure accompanying a very small variation in oxygen stoichiometry is remarkable. In the orthorhombic structure of the δ = −0.04 sample, there is 70% oxygen occupancy for the linear chain site (0, 1 2 , 0) and 34% for the ( 1 2 , 0, 0) site. The La sites have 13.6% Ba when δ = −0.04 and 11.2% Ba when δ = −0.06; the Ba sites have 10% La in both cases.