Structure and charge-transport properties of LnBaCuCoO5 + δ (Ln = Y, Dy) cuprocobaltites

Abstract

LnBaCuCoO5 + δ (Ln = Y, Dy) cuprocobaltites were prepared. Their unit cell parameters were determined and their thermal expansion, electrical conductivity (σ), and Seebeck coefficient (S) were studied in air in the range 300–1100 K. The compounds have tetragonal structures (space group P4/mmm). Their unit cell parameters are a = 0.3867(2) nm, c = 0.7550(7) nm, V = 112.9(2) × 10−3 nm3 for YBaCuCoO4.98; and a = 0.3872(2) nm, c = 0.7562(7) nm, V = 113.4(2) × 10−3 nm3 for DyBaCuCoO5.01. They are p-type semiconductors. The electrical conductivity of DyBaCuCoO5 + δ is slightly lower and its Seebeck coefficient is 1.5–2 times higher than the respective values for YBaCuCoO5 + δ apparently because of different electronic configurations of the rare-earth cations in LnBaCuCoO5 + δ (4d0 for Y3+ and 4f9 for Dy3+). Dilatometric measurements show that the LnBaCuCoO5 + δ phases in the range 300–1100 K do not experience structural phase transitions, and their linear thermal expansion coefficients (LTEC) are 14.3 × 10−6 K−1 for Ln = Y and 14.7 × 10−6 K−1 for Ln = Dy.