| The second generation high temperature superconductor REBa2Cu3O7-??REBCO?has high irreversible field,strong current capacity and good mechanical properties.SmBa2Cu3O7-??SmBCO?was a kind of REBCO high temperature superconducting film.Compared with traditional YBCO material,SmBCO has a very broad application prospect in the fields of electric power transmission,electric energy storage,strong magnetic field,etc.However,there are still a lot of problem that need to be solved in the process of thin film preparation,such as the uncontrollable composition in the film,low deposition rate,the formation of non-c-axis oriented grains and other impurity particles in the film,poor crystallization of bufferlayer on Hastelloy tape.Therefore,the study of SmBCO superconducting tapes mainly concentrated in improving the performance and reducing the cost of preparation.Laser chemical vapor deposition?Laser CVD?is a kind of novel method for preparing films,which can deposit high crystalline quality oxide film at high deposition rate.It has great practical prospect in the development of second generation high temperature superconducting tapes.The home-made Laser CVD system induced a continuous laser in a traditional MOCVD system.Laser CVD uses its optical and electrical synergistic effect to promote chemical reactions in films thereby increasing deposition rate.Epitaxial SmBCO thin films and SmBCO/Sm2O3 bilayers were deposited by Laser CVD on LAO single crystal substrates and Hastelloy tapes in this paper.The effect of process parameters on thin film phase,internal and external orientation,epitaxial mode,microstructure and deposition rate have been studied.The epitaxial SmBCO thin films were prepared on LAO single crystal substrates using MOCVD system without laser.Sm?DPM?3,Ba?DPM/TMOD?2 and Cu?DPM?2used as precursors,the influence of volatilization molar ratio,deposition temperature and deposition pressure of precursor on the element composition,phase composition and microstructure of SmBCO thin films were investigated.At the precursors'volatilization molar ratio of 1:5.12-5.54:2.16-2.82,c-axis SmBCO film without impurity phase was prepared.The a-axis oriented grains were obtained in SmBCO films at low deposition temperature and high deposition pressure.At the deposition temperature of 1075 oC and total deposition pressure of 600 Pa,the FWHM of?-scan was only 1.2o,which implied that the in-plane orientation of SmBCO thin films was good.The deposition rate was 6.6?m·h-1.The results was theoretical foundation for the preparation of SmBCO by laser CVD.In order to improve the deposition rate and crystalline quality,Laser CVD was used to deposite SmBCO film on LAO single crystal substrate.The effect of deposition temperature,oxygen partial pressure and film thickness on epitaxial growth of SmBCO films was investigated.The results showed that high deposition temperature and low oxygen partial pressure are conducive to the deposition of c-axis SmBCO thin film.At the deposition temperature and oxygen partial pressure of 740 oC and 250 Pa,the orientation of SmBCO film was c-axis,which has 1.1o of FWHM value.Compared with MOCVD,the deposition rate of laser CVD was improved,which was 8.7?m·h-1.When the thickness increased from 0.47?m to 2.72?m,the growth orientation of SmBCO thin film changed from complete c-axis orientation to a-axis and c-axis co-existent.The FWHM of?-scan of SmBCO film with d=1.06?m was 1.07o.The relationship between c-axis SmBCO thin film and LAO substrates in-plane epitaxial growth is as follows:SmBCO[100]//LAO[010]and SmBCO[010]//LAO[001].Meanwhile,the interrelation among crystal structure,micromorphology and superconducting property of SmBCO demonstrated.The SmBCO film with d=1.06?m had no a-axis and impurity grains,which had the highest Tc of 89.5 K and Jc of1.92 MA/cm2?77 K,self-field?.Compared with the structure of SmBCO film deposited by MOCVD,the SmBCO film deposited by Laser CVD had better structure at higher deposition rate and low depostion cost.So the Laser CVD technology provides technical commercial application of REBCO thin films.Furthermore,epitaxial SmBCO film was deposited on LaMnO3/MgO/Gd2Zr2O7-Hastelloy tape by Laser CVD.The effects of deposition temperature on SmBCO films were investigated.Epitaxial growth orientation transformed from a-axis and c-axis co-orientation to c-axis orientation with the increase of deposition temperature.The optimum deposition temperature range was740-760°C.The minimum FWHM of?-scan of c-axis oriented SmBCO thin film was 5.1o.Compared with FWHM of the SmBCO deposited on LAO single crystal substrate?1.07o?,its FWHM was higher,implying the in-plane orientation was poor.The poor in-plane orientation of SmBCO film was resulted from the worse crystallization of buffer layer on Hastelloy tape.Comparison to LAO single crystal substrate,the heating rate of LaMnO3/MgO/Gd2Zr2O7-Hastelloy tapes was higher at lower laser power,which is beneficial to realize practical fabrication of superconducting films.When PO2=100-250 Pa,c-axis SmBCO film was obtained.When PO2 up to 300 Pa,a-axis orientation grains appeared in SmBCO films.At PO2=200 Pa,Tc and Jc of 89.5 K and 1.92 MA/cm2?77 K,self-field?,respectively.Through analyzing laser heating principle of LAO single crystal substrate and LaMnO3/MgO/Gd2Zr2O7-Hastelloy tapes,we concluded that the SmBCO deposited on Hastelloy tapes required lower laser power and its heating rate is faster.In order to improve the crystalline quality of SmBCO on LaMnO3/MgO/Gd2Zr2O7-Hastelloy tapes,Sm2O3 was selected as buffer layer.Sm2O3/SmBCO bilayer thin films were prepared on Hastelloy tape using Laser CVD.At first,the Sm2O3 buffer layer was deposited on Hastelloy tape by Laser CVD.Next,the superconducting layer deposition was deposited on Sm2O3 film.At 740-760 oC,the orientation of buffer layer is c-axis,and its crystallization was good,and grain sizewas uniform.The temperature of Sm2O3 film was similar to deposition temperature range of SmBCO film.It provides an important precondition for preparing bi-layer thin films by one-step process.The FWHM values of SmBCO films prepared on the Sm2O3 buffer layer decreased significantly,which indicated that the orientation uniformity of SmBCO films was improved.The deposition rate of SmBCO film was up to 11.0?m·h-1. |
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