Subsolidus phase relations in Na2O–CuO–Sb2On system and crystal structure of new sodium copper antimonate Na3Cu2SbO6

Subsolidus phase relation studies in the NaSb3O7–Na3SbO4–CuO–CuSb2O6 quadrangle of Na2O–CuO–Sb2On system at 1123–1173 K revealed the formation of one new compound Na3Cu2SbO6. It is a superstructure derived from α-NaFeO2 type, space group C2/m, lattice constants: a=5.6759(1) Å, b=8.8659(1) Å, c=5.8379(1) Å, β=113.289(1)°. All ions are in octahedral environment, but CuO6 polyhedron exhibits strong elongation due to Jahn–Teller effect (Cu–O: 2.000(2) Å×2, 2.021(2) Å×2, 2.494(3) Å×2), whereas SbO6 octahedron is almost regular. The relationship to other similar superlattices is discussed.