Tailoring In-plane Crystallographic Orientation Of Epitaxial YBa2Cu₃O₇-δ Thin Films Having Perpendicular C-axes Texture

It has been known that YBa₂Cu₃O_7-δ (YBCO) crystallizes with a defected perovskite structure which is highly anisotropic and confines conductivity within the CuO planes (i.e. a-b plane) where the critial current density is substantially larger than that along the c-axis. Such features are of great importance to the superconducting properties of YBCO films deposited on various substrates, e.g., MgO, SrTiO₃, LaAlO₃, etc. MgO (100) crystal substrates are attractive substrates for the growth of YBCO films since they are widely used in the electronics and microwave industry to provide epitaxial growth of many oxide film systems. More importantly, c-axis oriented YBCO thin films can be easily grown on (100) MgO substrates over a wide range of deposition conditions, leading to the potential to transfer technology to industry.In addition to the crystallographic c-axis out-of-plane orientation, the orientation of the a-b or basal plane of YBCO crystallites within the film plane, strongly influences the superconducting properties of YBCO films due to the extremely small coherence length along the a-b plane. Our works indicate that the in-plane misorientation results in Jc values of c-axis textured YBCO films much lower than that of YBCO single crystals. As a result, the manipilation of in-plane orientation for YBCO films having perpendicular c-axis texture is valuable for real applications but challenging due to a large lattice misfit between MgO and YBCO.In present work, in-plane crystallographic orientation of perpendicular c-axis textured YBCO films grown on (100) MgO substrates are tailored by optimization of PLD deposition conditions in combination with the use of a YSZ buffer layer. An in-plane 0o oriented YBCO film can be achieved by elevating substrate temperature to 810oC, deposited directly on a (100) MgO substrate, whereas an in-plane 45o oriented YBCO film is successfully produced by employing a 20 nm thick YSZ buffer layer. Either of 0o or 45o in-plane oriented YBCO films with perpendicular c-axes is of great application value, such as transporting large current in many electronic devices, and servicing as seed layers that tolerate high superheating temperatures enabling the growth of large diameter YBCO bulk crystals. This work provides a new pathway to realizing YBCO films with controllable in-plane crystallographic orientations.