Fabrication Of Oxide Buffer Layers For High Temperature Superconducting Coated Conductors Via PVD Methods

The development of high temperature superconducting (HTS) coated conductorshas advanced the application of HTS materials. A coated conductor consists of a metalsubstrate, a superconducting layer and the buffer layers inbetween them. The textureand morphology of buffer layers would directly influence the final performance ofcoated conductors. Therefore the study on buffer layer fabrication process is importantfor high-quality HTS coated conductor manufacturing, as well as for the understandingof fundamental problems in thin film deposition. In this work oxide buffer layers werefabricated using physical vapor deposition (PVD) method, and their properties wereinvestigated. By using the optimized process of buffer layer deposition, we tried tofabricate a complete architecture of HTS coated conductor.CeO2films were magnetron sputtering deposited on single crystal YSZ substrates.Deposition parameters such as substrate temperature, sputtering pressure, RF power,deposition time, O2/Ar ratio were adjusted and the film properties were investigated byXRD, AFM, SEM, etc. It is revealed that distinct CeO2morpholgy evolution wasinduced by these parameters. Depending on the detailed deposition condition the filmpresented either a smooth, granular surface, or an “interwoven”-like surface,constructed by island structures elongating along CeO2<110> directions. Themorphological characteristics of CeO2/YSZ(001) films were correlated with the filmstrain status. Influence of different parameters on the film strain was explained to be dueto variation of energetic bombardment (i.e. the "atomic peening" effect). Based on thisexplanation, CeO2film morphology could be manipulated by controlling the strength ofenergetic bombardment.YBCO films were then deposited onto the as-grown CeO2buffer layers withdifferent morphologies, via the cost-effective method of TFA-MOD. Despite that all thebuffer layers were biaxially textured with high degrees, the critical current density (Jc)properties of the YBCO layers varied greatly, due to the difference in CeO2morphology.Surface roughness and grains size were two important factors determining Jcofsuperconducting layers. Fully structed coated conductor with metal substrate wasfabricated by adopting the optimized depostion parameters for CeO2cap layer and theIBAD-YSZ/Hastelloy C276substrate. Finally, CeO2and MgO films were deposited onto amorphous glass substrates. Thepreferred out-of-plane orientation of these films evoluted with the variations ofsputtering parameters. Mechanism for this texture evoultion was discussed. Bycombining magnetron sputtering deposition and assistantting ion-beam technique,MgO/glass films with both out-of-plane and in-plane alignments were preliminarilyrealized. This study paves the way for the searching of cost-effective method of biaxialtexture template fabrication.