Structure and electrical and transport properties of cation-deficient samples of perovskite ferrocuprates RBaCuFeO5 + δ (R = Y, La)

Abstract

The structure, thermal expansion, and electrical properties of cation-deficient ferrocuprates RBaCuFeO5 + δ (R = Y, La), which are p-type semiconductors, are investigated. The linear thermal expansion coefficient of the yttrium-barium ferrocuprate decreases upon formation of vacancies in the A sublattice (Y, Ba), while the unit cell parameters remain practically unchanged upon the formation of vacancies in different sublattices (Y, Ba, Cu/Fe) of the crystal structure. From analyzing the results of the thermopower measurements, it is assumed that the YBaCuFeO5 + δ ferrocuprate is actually a “nanocomposite” consisting of nanoregions of the Y2Cu2O5 and BaFeO3 − δ phases. The lanthanum deficiency brings about an increase in the LaBaCuFeO5 + δ unit cell while leaving very nearly unaffected its linear thermal expansion coefficient and electrical properties. The formation of cation vacancies in extended [Ba(Cu,Fe)2O5] blocks of the LaBaCuFeO5 + δ phase gives rise to tetragonal distortion of its cubic structure, a decrease in the linear thermal expansion coefficient, and an increase in the electrical resistivity of the samples, the latter resulting primarily from an increase in the carrier transport energy in (Cu,Fe)O2 layers of LaBaCuFeO5 + δ.