We report the crystal chemical properties of solid solutions obtained by substitution of lanthanum for barium in the high-Tc superconductor Ba2YCu3O7. An orthorhombic-to-tetragonal symmetry change occurs at x=0.4 in Ba2-xLaxYCu3O7±δ with the tripled perovskite supercell maintained. Charge compensation is achieved through reduction of the formal copper valence (δ=0) in the orthorhombic phase and by a mixture of excess oxygen accommodation (δ>0) and formal valence reduction in the tetragonal phase. The resistivity increases by several orders of magnitude, even though the average formal copper valence changes very little.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics