Subsolidus phase relations in Na 2O–CuO–Sb 2O n system and crystal structure of new sodium copper antimonate Na 3Cu 2SbO 6

Abstract

Subsolidus phase relation studies in the NaSb 3O 7–Na 3SbO 4–CuO–CuSb 2O 6 quadrangle of Na 2O–CuO–Sb 2O n system at 1123–1173 K revealed the formation of one new compound Na 3Cu 2SbO 6. It is a superstructure derived from α-NaFeO 2 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 CuO 6 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 SbO 6 octahedron is almost regular. The relationship to other similar superlattices is discussed.