Raman Spectroscopic Study of YBa_2Cu_4O_8 Thin Film Grown from Amorphous Precursor

概要

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Raman spectroscopic study was performed on YBa_2Cu_4O_8 (Y124) thin films prepared by in situ annealing of sputtered precursor. The amorphous precursors were deposited at 450℃ in 50 mTorr. The films are a-axis oriented. The ratio of the vibrational intensity of oxygen in double Cu-O chain to that of apical oxygen (I_<:O_d>/I_<:O_a>) corresponded well to the volume fraction of the Y124 phase in the films. With decrease in the composition Cu/Y, depending on oxygen pressure during deposition, the double Cu-O chain is suffered by the oxygen defects, which was confirmed by observing decreases in I_<O_d>/I_<O_a> and the appearance of the 537 cm^<-1> mode. The Y124 growth around the boundary of the stability region (1 ≤ P_<O_2> ≤ 200 Torr, 625 ≤ T ≤ 820℃) between Y124 and Y123 indicates that higher temperature and higher oxygen pressure during in situ annealing is preferable for the growth of Y124 films. The Y124 films annealed at 820℃ under 200 Torr O_2 showed I_<O_d>/I_<O_a> of 1.00, which is the same as the result for Y124 bulk prepared by a high-pressure technique.
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1996-01-15