Synthesis and crystal structure of the new vanadate AgCaVO₄. Comparison with the arcanite structure

We report the synthesis and the crystal structure of the new vanadate AgCaVO₄ from laboratory powder X-ray data. Contrary to the previously reported AgBVO₄ (B=Mg, Cd), AgCaVO₄ exhibits the arcanite structure (β-K₂SO₄). Although it exhibits the same structure than arcanite, significant differences are observed. These differences are explained by deriving the atomic displacement field. The change of connectivity within the structure between β-K₂SO₄ and AgCaVO₄ results from a rotation of the VO₄ tetrahedra giving rise to a change from a face sharing to an edge sharing octahedral chains. Additionally, the thermal expansion of AgCaVO₄ has been investigated up to 800 C.