Buffer layer materials for growing YBa
2Cu
3O
7−δ thin films on MgO substrates are examined from the viewpoint of YBa
2Cu
3O
7−δ thin-film crystallinity. The buffer layers were grown using an excimer laser. Crystallinity of the buffer layers grown on MgO substrates and the YBa
2Cu
3O
7−δ thin films on the buffer layers were evaluated by X-ray diffraction, X-ray rocking curves and X-ray φ-scan methods. One of key points to obtain YBa
2Cu
3O
7−δ thin films of the highest quality on the MgO substrates is the usage of BaZrO
3 buffer layers that are lattice matched to the MgO substrates. However, every buffer layer examined here showed the result of high-quality YBa
2Cu
3O
7−δ thin films with a
Tc of around 89 K and low surface resistance.
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