Co-substitution design: a new glaserite-type rare-earth phosphate K₂RbSc(PO₄)₂ with high structural tolerance

An alkali rare-earth phosphate K₂RbSc(PO₄)₂ was successfully obtained as a derivative of glaserite-type K₃Na(SO₄)₂ by co-substitution of K(1)O₁₂ → RbO₁₂, K(2)O₁₀ → KO₇, NaO₆ → ScO₆ and SO₄ → PO₄, while maintaining the original anionic framework. K₂RbSc(PO₄)₂ exhibits a layered [Sc(PO₄)₂]_∞ framework built from ScO₆ octahedra and PO₄ tetrahedra, with K and Rb residing in the interlayers. Its isostructural lanthanide analogues K₂RbEr(PO₄)₂ and K₂RbLu(PO₄)₂, inspired by an elemental substitution strategy, were also prepared by a high-temperature solid state reaction. The successful substitution indicates that the skeleton of K₂RbSc(PO₄)₂ is stable with high structural tolerance, which can provide a possibility for substitution of resident ions to obtain diverse structural types and applications.