Synthesis and thermal stability of the new copper oxide carbonate Ba4ScCu2O7−xCO3 and other members of the series Ba4ScxCu2Oy(CO3)2−x

We report the synthesis of a new perovskite-type oxide carbonate, Ba 4 ScCu 2 O 7–x CO 3 . This phase has a tetragonal cell (a=b≈7.99 Å, c≈4.10 Å) based on a doubling of the basic perovskite subcell in the a and b directions. A possible structural model based on an ordering of Sc, Cu and C in the small cation sites is proposed. Experiments on the thermal stability of this phase have shown that raising the synthesis temperature from 940 to 1000 °C results in partial carbonate loss and a change in cell to a √2a p ×√2a p ×2c p cell as previously observed for Ba 4 YCu 2.27 O 7.08 (CO 3 ) 0.53 . In addition we show that Ba 4 ScCu 2 O 7–x CO 3 may be classed as the x=1 member of the series, Ba 4 Sc x Cu 2 O y (CO 3 ) 2–x and we also report the synthesis of other new phases in this series.