Origin of the phi approximate to+/-9 degrees peaks in YBa2Cu3O7-delta films grown on cubic zirconia substrates

The c-axis oriented UBa2Cu3O7-delta films grown on (001) yttria-stabilized cubic zirconia (YSZ) substrates often contain domains whose in-plane alignment is rotated approximately 9 degrees from the cube-on-cube epitaxial relationship: in addition to the more commonly observed 0 degrees and 45 degrees in-plane rotations. We have investigated the origin of this similar to 9 degrees orientation using in situ electron diffraction during growth and es situ 4-circle x-ray diffraction. Our results indicate that the similar to 9 degrees orientation provides the most favorable lattice match between the interfacial (110)-oriented BaZrO3 epitaxial reaction layer, which forms between YBa2Cu3O7-delta and the YSZ substrate. If epitaxy occurs directly between YBa2Cu3O7-delta and the YSZ substrate, i.e., before tile BaZrO3 epitaxial reaction layer is formed, the 0 degrees and 45 degrees domains have the most favorable lattice match. However, growth conditions that favor the formation of the BaZrO3 reaction layer prior to the nucleation of YBa2Cu3O7-delta lead to an increase in similar to 9 degrees domains. The observed phenomenon, which results from epitaxial alignment between the diagonal of a square surface net and the diagonal of a rectangular surface net, is a general method for producing in-plane misorientations, and has also been observed for the heteroepitaxial growth of other materials, including (Ba,K)BiO3/LaAlO3. The YBa2Cu3O7-delta/YSZ case involves epitaxial alignment between [<(1)over bar 11>](BaZrO3) and [110](YSZ), resulting in an expected in-plane rotation of 11.3 degrees to 9.7 degrees for fully commensurate and for fully relaxed (110)(BaZrO3) on (001)(YSZ), respectively.