Structure and Electrophysical Properties of Ferrocobaltites LnBaFeCoO5 + d (Ln = Tb, Dy, Ho, Y)

Abstract

The ferrocobaltites LnBaFeCoO5 + δ (Ln = Tb, Dy, Ho, Y) have been synthesized, and the parameters of their crystal structure have been determined. The thermal expansion, electrical resistivity ρ, and thermopower S of the synthesized compounds have been investigated in air at temperatures in the range from 300 to 1100 K. The compounds have a tetragonal structure (symmetry space group P4/mmm) with the unit cell parameters a = 3.9000 Å and c = 7.5922 Å (Ln = Tb, δ = 0.31), a = 3.8973 Å and c = 7.5679 Å (Ln = Dy, δ = 0.34), a = 3.8970 Å and c = 7.5507 Å (Ln = Ho, δ = 0.28), and a = 3.9029 Å and c = 7.5538 Å (Ln = Y, δ = 0.25). The ferrocobaltites under investigation are p-type semiconductors, and their electrical resistivity ρ and thermopower S decrease in the sequence Tb Ho Y Dy (at room temperature). The linear thermal expansion coefficient of the LnBaFeCoO5 + δ phases in the vicinity of the temperatures ranging from 465 to 535 K increases from (1.15–1.23) × 10–5 to (1.73–1.93) × 10–5 K–1. The parameters of charge transfer in these ferrocobaltites have been determined. It has been found that an increase in the temperature leads to an increase in the excitation energy of charge carriers and a decrease in the activation energy of charge carrier transfer.