Phase Diagram of the BaO(BaCO₃)‐CaO‐CuO System

Abstract

The phase diagram of the BaO(BaCO 3 )-CaO-CuO system, especially in the barium-rich region at 900°C in air, was studied. Two new different oxycarbonates were observed: Ba 8 Ca 16/15 Cu 64/15 O 11.20 (CO 3 ) 2.66 and a solid-solution series with a chemical composition of Ba 2 Ca x+y Cu 1+(x/2)−y O 2+␦ (CO 3 ) 1−z (where 0 ≤ x ≤ 2/39 and 0 ≤ y ≤ 16 x/5). The oxycarbonate solid solution was formed in a region of the compositional triangle Ba:Ca:Cu (in moles) = (2:0:1)-(39:1:20) -(65:7:28). The solid-solution structure had P4/mmm symmetry, with lattice parameters a ≈ a p and c ≈ 2 a p , where a p represents the perovskite cell. The Ba 8 Ca 16/15 Cu 64/15 O 11.20 (CO 3 ) 2.66 compound, which had Pm3m symmetry with a lattice parameter a = 0.8116(2) nm, had no chemical-solubility range.

On the ternary compounds of the BaO-CaO-CuO system

“…About 100 hours at high temperature with intermediate grindings were necessary to obtain pure 413 and 85% pure 613 in both flowing oxygen or nitrogen. Because of the existence of many oxy-carbonates with Ca, Ba and Cu as metal atoms [5,6], infrared spectroscopy was used to detect the possible presence of CO 3 groups. None of our samples was found contaminated.…”