PURPOSE: To obtain a superconducting material having high purity and high critical temperature and useful as a raw material for various electronic elements requiring uniform and accurate characteristic, by restricting the atomic valence of Cu for forming a specific compound oxide to divalent or trivalent.
CONSTITUTION: A substrate holder 3 having built-in heater 4 and capable of controlling the substrate temperature is disposed in a vacuum chamber 1. A substrate 2 (e.g. MgO single crystal substrate) having a thermal expansion coefficient, lattice constants, etc., close to those of the thin film to be formed is fixed on the substrate holder 3. A prescribed number of electron beam gun pairs 5, 6 are placed opposite to the substrate and the substrate is irradiated with ion beams of a group IIa element (e.g. Ba) α, group IIIa element (e.g. Y) β, Cu and oxygen at prescribed doses from the beam guns 5, 6 to form a thin crystal film on the substrate 2. Separately, the surface state of the thin film is analyzed with an X-ray source 7 and a photo-detector 8 and the atomic valence of the Cu atom constituting the thin film is monitored. The growth condition of the thin film is controlled in such a manner as to keep the atomic valence of Cu at a prescribed divalence/trivalence ratio to obtain the objective compound oxide superconducting material of formula (x is atomic ratio β/α+β and is 0.1≤x≤0.9; y and z are 0.4≤y≤3.0 and 1≤z≤5 when α1-xβx=1).
FUJITA NOBUHIKO
TANAKA SABURO
YATSU SHUJI
JODAI TETSUJI
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