Preparation And Microstructure Characterization Of Y₂(Zr_1-xTi_x)₂O₇ And Ce_1-xY_xO_2-yThin Films

Serving as important interlayers to transfer the texture of the substrate and obstruct element diffusion between the substrate and YBCO superconducting layer,superconducting buffer layers have become the necessory part of coated conductors.The present buffer layer materials include CeO2,Y2O3,La2Zr2OI7,YSZ(Yttria-Stabilized Zirconia),and so on.But these buffer layer materials still have the shortcomings,for example,the ability of blocking element diffusion is poor;the multi-layer buffer architecture is too complex,and so on.It is still necessary to develop new buffer layer materials with more excellent comprehensive performances.Therefore,the feasibility of Y2(Zr1-xTix)2O7 and Ce1-xYxO2-y thin films as buffer layers of coated conductor was discussed by studying the structural phase transition and high-temperature oxygen diffusion behavior of the films with different cation ratios in this thesis.Firstly,the stable titanium-doped zirconate yttrium Y2(Zr1-xTix)2O7(YZTO)sol was prepared by using yttrium nitrate,hexahydrate(Y(NO3)3·6H2O(AR)),zirconium octahydrate chloride(ZrOC12·8H2O(AR))and tetrazyl titanate(C16H36O4Ti(AR))as solutes.YZTO films of pure phase and solid solution were prepared on silicon substrates by sol-gel method,and epitaxial YZTO films with(001)orientation were successfully prepared on YSZ single crystal substrates.It was found that as the added ratio of Ti4+in Y2Zr2O7 gradually increased,until Ti4+ completely replaced Zr4+,YZTO films gradually changed from completely defective fluorite structure to complete pyrochlore structure;meanwhile,oxygen vacancies in the films also changed from random alignment to ordered alignment;and the ability of YZTO films to block oxygen element diffusion became stronger and stronger.Secondly,yttrium-doped ceria Ce1-xYxO2-y(CYO)sol with stable performance was synthesized by yttrium nitrate hexahydrate(Y(NO3)3·6H2O(AR)),and cerium nitrate hexahydrate(Ce(NO3)3·6H2O(AR)).Furthermore,CYO films of pure phase and solid solution were prepared on silicon substrates by sol-gel method,and CYO films with(001)epitaxial orientation were successfully prepared on YSZ single crystal substrates.The results showed that the oxygen vacancies with random distribution were introduced into CYO films due to the addition of Y3+with small ratios,and the crystal structure changed from fluorite structure to defective fluorite structure(disordered alignment of oxygen vacancies).As the ratio of Y3+added,the number of oxygen vacancies in CYO films increased and tend to be ordered from disorder,moreover,the crystal structure of the films changed from defective fluorite structure to rare earth C-type structure(ordered alignment of oxygen vacancies).At the same time,it was found that with the increasing of Y3+,the ability of CYO films to block oxygen element diffusion was firstly weakened and then enhanced.The above research results show that the higher the order degree of oxygen vacancy alignment in YZTO and CYO films is,the stronger their ability of blocking oxygen diffusion is.For example,both Y2(Zr1-xTix)2O7(x?0.9)and Ce1-xYxO2-y(x?0.7)films have strong abilities to block oxygen diffusion,and are expected to become new buffer layer materials for the preparation of high-performance YBCO coated conductors.