Phase Equilibria of the System SrO‐CaO‐CuO

Abstract

A new phase, probably CaCuO 2 , is stable only below ∼740°C and has an orthorhombic average subcell: Cmca, a = 10.588 (1) × 10 −1 nm, b = 2.8122(4) × 10 −1 nm, and c= 6.3245(6)×10 −1 nm. Very weak superstructure reflections indicate two distinct supercells: an orthorhombic cell with the b axis multiplied by 10, and a monoclinic cell, C2/c or equivalent, with a mon = 10.946 × 10 −1 nm∼a o−rh , b mon = 6.345 × 10 −1 nm∼c o−rh , c mon = 2.8100 × 12 × 10 −1 nm = 33.72 × 10 −1 nm∼12[120] o−rh , and β= 105.5°. At 950°C, the ternary system SrO‐CaO‐CuO has extensive regions of solid solution. Complete solution is observed for the 2:1 series (Sr,Ca) 2 /CuO 3 ; the 1:1 series (Sr,Ca)CuO 2 accepts Ca up to ∼Sr 0.25 Ca 0.75 O 2 ; and the 14:24 series “Sr 14 Cu 24 O 41 ’extends to at least “Sr 7 Ca 7 Cu 24 O 41 .” A new ternary phase with a very narrow homogeneity range is reported: (Sr x Ca 1−x )CuO 2 , where x∼0.15 ± 0.02. The composition (Sr 0.16 Ca 0.84 )/CuO 2 has a primitive tetragonal unit cell with a =3.867(2)×10 −1 nm and c =3.2195(2)×10 −1 nm.