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Change in the defect structure of composition controlled single-phase YbFe2O4 epitaxial thin films

A new type of ferroelectricity, originating from charge order and coupled to magnetism, occurs in YbFe2O4 containing triangular Fe/O double layers, which has recently generated great interest in this material. YbFe2O4 tolerates more than 10% iron deficiency even in bulk single crystals with space group R 3 ¯ m. Even though a large number of Fe deficiencies are introduced in the thin film form due to vaporization of Fe ions during deposition at high temperatures, the crystal structure with the space group of R 3 ¯ m in the films never changes within the Fe/Yb composition ratio from 1.3 to 2.2. In the previous research, the effects of the Fe/Yb composition ratio—especially in the large Fe deficient area (1.31–1.86)—on the lattice distortion and chemical bonding state of non-stoichiometric (0001)-oriented YbFe2O4 epitaxial thin films on (111) YSZ and (0001) sapphire substrates were examined. The variation of the lattice constant, Raman spectra, and optical absorption coefficient indicated that the existence of the stacking fault and the antisite Yb play an important role in the significant iron deficiency without changing the crystal structure of non-stoichiometric YbFe2O4 thin films.