Quality of Inward Curved MgB2 Films Prepared by HPCVD

Arising from the superconductivity at ~39 K, magnesium diboride (MgB₂) films have great prospect in the field of superconducting radio-frequency (SRF) cavities. To match the geometrical shape of the inner surface of the SRF cavities, the deposition techniques for inward curved MgB₂ superconducting films are explored. By using pre-bent metallic substrates, curved MgB₂ films were deposited in situ. These curved films show properties comparable with those of the films deposited on a plane surface. Even when the curvature radius (CR) of the films is as small as ~2 mm, the superconducting transition temperature T_C(R = 0) of the films reaches ~36 K. The in situ-grown films were also compared with the films prepared by postdeposition bending. In the bending of CR ~ 2 mm, T_C(R = 0) of the films falls off to 25 K, much lower than that of the in situ-grown films with the same CR. The scanning results of electron microscope indicate that the wrinkles and cracks appearing in the bending are the main reason for the degradation of transition temperature.