Ion Beam Induced Growth Structure of Fluorite Type Oxide Films for Biaxially Textured HYSC Coated Conductors
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fluorite type (Zro.85Yo.15Oi. 93(YSZ),
Hf 0 .74Yb0 .26 0 1 .87 , CeO 2),
pyrochlore type
(Zr 2 Sm 20 7),
and
rare-earth C type (Y 20 3, Sm 20 3) oxides on polycrystalline Ni-based alloy substrates. Cubetextured (all axes aligned with a axis substrate normal) films were obtained for fluorite and pyrochlore ones by low energy (10435* >10117*
>3192* >3094*
PrO 2 CeO 2
fluorite fluorite
0.539 0.541
0.381 0.383
10606 10500
2813 2754
Zr 2Sm20 7 Zr2 La 2O 7
pyrochlore pyrochlore
1.059 1.079
0.374 0.381
>35341* >34847*
>2472* >2304*
Zr085Y01501.93 Hf 0 .74 Yb0 2 6O1 87
Y2 0 3
rare-earth C 1.060 0.375 13428 rare-earth C 1.093 0.386 13181 *estimation from data for HfO2 , ZrO 2, Yb 20 3 , Y20 3, La 20 3, Sm20 7. Sm 2 0
3
1873 1677
300 fluorite
50
pyrochlore
z 2
X
HfC -i
2 7
X CeO
2
YSZ YS
2
Fig. 15. The relationship between lattice energy and optimized assisting Ar+ beam energy.
Sn2O not textured P-11I
1000
I2I
1500 2000
I
2500
3000
3500 4000
Lattice energy density (eV/nm3)
At high temperature near 500 degrees it collapsed because the stable alignment of normal axis vanished. The optimal temperatures for cube-textured orientation were around 100200 TC for fluorite or pyrochlore, where it was quite narrow at 300 TC for Y20 3, and no window was found for Sm20 3. The alignment axes of CeO 2 films dramatically changed between Ar+ and Kr+ assisting ions. It revealed that axis of CeO 2 could be another alignment axis to assisting ions under proper conditions, in addition to axis. By using mixed assisting ion element of Ar- and Kr+, the crystalline alignment was improved preserving cube-textured structure. In-plane azimuthal distribution of 24.5 degree was obtained.
53
The assisting ion energy dependence was discussed in connection with lattice energies for these oxide crystals. For fluorite or pyrochlore, the optimized energy was 200-250 eV, where low energy (150eV) ion bombardment with narrow window was required for crystallization of Y2 0 3 films. The calculated lattice energy suggests that rare-earth C type oxides (Y20 3 , Sm 20 3) are so sensitive to ion radiation damage because of insufficient bonding energy. Explicitly aligned pyrochlore type oxide (Zr 2Sm2O7 ) films are obtained with azimuthal FWHM of 17.1 degrees, in the condition nearly equal to the one for YSZ. It is encouraging to improve IBAD process for Y-123 conductors by better lattice matching of pyrochlore oxides, where other candidates as CeO 2 or Y2 0 3 films have yet difficulties to optimize conditions of IBAD.
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