Sol-gel synthesis and structure of MZr2(AsO4)3 arsenates and MZr2(AsO4) x (PO4)3 − x arsenate phosphates (M = K, Rb, Cs)

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MZr2(AsO4)3 arsenates and MZr2(AsO4) x (PO4)3 − x arsenate phosphates (M = K, Rb, Cs) have been obtained by sol-gel synthesis followed by heat treatment and have been characterized by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Continuous series of substitutional solid solutions form in the MZr2(AsO4) x (PO4)3 − x systems (0 ≤ x ≤ 3). The solid solutions have a kosnarite structure (KZr2(PO4)3, space group R 3c ). The crystal structures of MZr2(AsO4)3 and MZr2(AsO4)1.5(PO4)1.5 have been refined by full-profile analysis. The structural frameworks of these phases are built from ZrO6 octahedra and AsO4 tetrahedra or (As,P)O4 tetrahedra statistically populated by arsenic and phosphorus atoms. The alkali metal atoms occupy extraframework sites. The effect of the crystal chemical properties of alkali metals on the formation of the structures of MZr2(AsO4)3 arsenates (M = Li-Cs) and MZr2(AsO4) x (PO4)3 − x solid solutions is discussed.