Structural, thermal and electrical properties of the ceramics in the NdBaFe2/3Co2/3Cu2/3O6–δ–NdSrFe2/3Co2/3Cu2/3O6–δ system

Abstract

Using ceramic method, the continuous serie of NdBa_1–xSr_xFe_2/3Co_2/3Cu_2/3O_6–δ (0.0 ≤ x ≤ 1.0) (NBS) solid solutions was prepared, their crystal structure, microstructure, oxygen nonstoichiometry, thermal expansion, electrical conductivity, and Seebeck coefficient were studied. It was found, that NBS compounds possessed perovskite-like structure and were p-type semiconductors, which lattice constants, oxygen nonstoichiometry index (δ), and Seebeck coefficient decreased, but electrical conductivity increased at substitution of barium by strontium. Near x ≈ 0.5 the phase transition from tetragonal phase into cubic one took place. The complex oxides with composition near this point (x = 0.4, 0.6) were possessed the lowest sinterability, had maximal microstrains, and minimal microhardness and values of grain sizes among the samples studied. Thermal and chemical expansion coefficients of NBS samples varied within (15.3–17.2)·10⁻⁶ K⁻¹ and (0.94–17.0)·10⁻³ respectively, and, all in all, increased by x rising. The largest value of electrical conductivity (σ₈₀₀ ≈ 290 S·cm⁻¹) was fixed for the NdBa_0.2Sr_0.8Fe_2/3Co_2/3Cu_2/3O_6–δ solid solution.