Crystal distortion associated with ortho-tetra transition of REBa ₂Cu₃O_x films

Microstructure deformation has been investigated for EuBa ₂Cu₃O_x films associated with orthorhombic-tetragonal transition during cooling in an oxygen atmosphere. EuBa₂Cu₃O_x films have been grown by a pulsed laser deposition technique under 1000 mTorr oxygen pressure and 800 °C substrate temperature. After the growth, the films are cooled to 400 °C and annealed in one atom oxygen pressure for 0-110 h. The preferred orientation of the films is characterized by X-ray diffraction and φ-scan X-ray diffraction. Microstructures and lattice images of the EuBa₂Cu ₃O_x films are observed by a transmission electron microscope. All of the obtained EuBa₂Cu₃O_x films are c-axis oriented. The φ-scan X-ray diffraction revealed that films without any 500 °C annealing have a tetragonal structure. However, more than 3 h annealed films are partly orthorhombic from the peak separation in the φ-scan. The angle between the two peaks is about 0.8°. We estimate the a-axis length/b-axis length ratio (orthorhombicity) from the angle between the separated peaks to be 0.866°. It agrees with the a-axis length/b-axis length ratio of well oxidized EuBa₂Cu₃O_x bulk materials.