Synthesis and crystal structure of three silver indium double phosphates

Three new silver indium double phosphates Ag3In(PO4)2 (I), β-(II) and α-Ag3In2(PO4)3 (III) were synthesized by solid state method (I and II—700 °C, III—900 °C). Compounds I and II crystallize into a monoclinic system (I—sp. gr. C2/m, image, image, image, image, image; II—sp. gr. C2/c, image, image, image, image, image), and compound III crystallize into a hexagonal system (sp. gr. R-3c, image, image, image). Their crystal structures were determined by the Rietveld analysis (I—image, image; II—image, image; III—image, image). Structure of Ag3In(PO4)2 is related to the sodium chromate structure type and is isotypic to α-Na3In(PO4)2. The polymorphous modifications of β- and α-Ag3In2(PO4)3 are isostructural to sodium analogs (β- and α-Na3In2(PO4)3) and are related to alluaudite (II) and NASICON (III) structure types. Compounds I and II are not stable at temperature above 850 °C. Ag3In(PO4)2 is decomposed providing silver orthophosphate Ag3PO4 and α-Ag3In2(PO4)2. β-Ag3In2(PO4)3 is transformed to α-Ag3In2(PO4)3.