Observation of twin boundary layers in pure and alloyed YBa2Cu3O7−δ

Using an electron diffraction technique, the thicknesses of the (nonorthorhombic) twin boundary layers were measured for pure and alloyed YBa2(Cu1−xMx)3O7−δ. Boundary thickness varied from ∼0.7 nm for M=Ni, x=0.02, and δ≂0 to ∼2.6 nm for M=Al, x=0.02, and δ≂0, while it was ∼1.0 nm for a pure YBa2Cu3O7. High-resolution transmission electron imaging of similar specimens supports the existence of such twin boundary layers.