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Growth of Laser Ablated YBa_{2}Cu_{3}O_{7} Thin Films Epitaxied on (100)MgO: Influence of In-Plane Misorientations on Low and High Frequency Properties

100%

Perrin A., Guilloux-Viry M., Castel X.

Acta Physica Polonica A

1997

vol. 92

issue 1

115-125

The graphoepitaxial growth of c-axis YBa_{2}Cu_{3}O_{7} laser ablated thin films on (100)MgO induces a competition between two main in-plane orientations due to the large lattice mismatch: ⟨100⟩ YBa_{2}Cu_{3}O_{7} ∥ ⟨100⟩ MgO, c_{⊥ 0} notation or ⟨110⟩ YBa_{2}Cu_{3}O_{7} ∥ ⟨100⟩ MgO, c_{⊥ 45} notation. The ratio of c_{⊥ 45}/c_{⊥ 0} in-plane orientations (η), measured by X-ray diffraction φ scans, is ranging from 0.2% to 49.7% for the films reported here. Their crystalline qualities were compared on the basis of rocking curves (Δθ), electron channeling patterns and reflection high energy electron diffraction diagrams. The coexistence of c_{⊥ 0} and c_{⊥ 45} domains creates high angle grain boundaries. No degradation of T_{c}, residual resistance ratio (RRR) or ΔT_{c} is observed when η increases. In contrast, a strong correlation between microwave losses characterized by surface resistance (R_{S} at 10 GHz and 77 K), inductive losses S(χ") (surface of the χ" peak obtained in a.c. susceptibility at 119 Hz) and η was clearly evidenced. A minimum of losses was found for η between 3 and 6% suggesting the necessity of a low quantity of high angle grain boundaries for films optimization. Finally, some specific processes carried out recently in order to try to efficiently control η, then R_{S} are discussed.

Fluorination Under NF_{3} Flow of Oxygen Deficient YBa_{2}Cu_{3}O_{x} Thin Films Deposited on Various Types of Substrate

88%

Massiot P., Perrin C., Guilloux-Viry M., Perrin A., Sergent M.

Acta Physica Polonica A

1997

vol. 92

issue 1

221-225

Oxygen deficient YBaCuO thin films, c-epitaxially grown by laser ablation on different substrates such as (100)MgO, (100)SrTiO_{3} and (100)LaAlO_{3}, were fluorinated by an ex situ solid/gas reaction with NF_{3} (3% NF_{3} diluted in N_{2}) at 280°C. The kinetics of the reaction depends on the type of the substrate. After reaction the superconducting behaviour of the films is improved without degradation of their crystallinity, whatever the nature of the substrate. The stability of the fluorinated films under oxygen or nitrogen gas was studied. All these results will be compared with those previously obtained for fluorination of oxygen deficient YBaCuO ceramics.

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2 Acta Physica Polonica A

2 1997

2 Guilloux-Viry M.

2 Perrin A.

1 Castel X.

1 Massiot P.

1 Perrin C.

1 Sergent M.

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Growth of Laser Ablated YBa_{2}Cu_{3}O_{7} Thin Films Epitaxied on (100)MgO: Influence of In-Plane Misorientations on Low and High Frequency Properties

Fluorination Under NF_{3} Flow of Oxygen Deficient YBa_{2}Cu_{3}O_{x} Thin Films Deposited on Various Types of Substrate