RBaCuCoO5 + δ (R = Nd, Sm, Gd) layered cuprocobaltites: Synthesis, structure, and properties

Abstract

Cuprocobaltites RBaCuCoO5 + gd(R = Nd, Sm, Gd) were prepared. Their unit cell parameters were determined, and 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, Z = 1). Their unit cell parameters are a = 0.3906(2) nm, c= 0.7648(7) nm for NdBaCuCoO5.21; a = 0.3904(2) nm, c = 0.7609(6) nm for SmBaCuCoO5.06; and a = 0.3891(2), c = 0.7592(6) nm for GdBaCuCoO5.02. The RBaCuCoO5 + δ cuprocobaltites at room temperature are p-type semiconductors, whose electrical conductivity and linear thermal expansion coefficient (LTEC) increase with increasing R3+ ionic radius, whereas the Seebeck coefficient decreases. The LTECs of RBaCuCoO5 + δ phases in the range 500–575 K increase by a factor of 1.2–1.5 because of the elimination of weakly bound oxygen. S = f(T) curves for RBaCuCoO5 + δ (R = Nd, Sm, Gd) feature maxima at 510 K for R = Sm and 365 K for R = Gd, probably, due to the change in the spin state of cobalt cations in these phases.