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, Ba4ScCu2O7-xCO3. This phase has a tetragonal cell (a = b approximate to 7.99 Angstrom, c approximate to 4.10 Angstrom) 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 949 to 1000 degrees C results in partial carbonate loss and a change in cell to a root 2a(p) x root 2a(p) x 2c(p) cell as previously observed for Ba4YCu2.27O7.08(CO3)(0.53). In addition we show that Ba4ScCu2O7-xCO3 may be classed as the x = 1 member of the series, Ba4ScxCu2Oy(CO3)(2-x) and we also report the synthesis of other new phases in this series.