Joint crystallization of KCuAl[PO₄]₂ and K(Al,Zn)₂[(P,Si)O₄]₂: crystal chemistry and mechanism of formation of phosphate-silicate epitaxial heterostructure

Abstract

Two novel phases, potassium copper aluminium bis(phosphate), KCuAl [PO 4 ] 2 (I), and potassium zinc aluminium bis(phosphate-silicate), K(Al,Zn) 2 [(P,Si)O 4 ] 2 (II), were obtained in one hydrothermal synthesis experiment at 553 K. Their crystal structures have been studied using single-crystal X-ray diffraction. (I) is a new member of the A + M 2+ M 3+ [PO 4 ] 2 family. Its open 3D framework built by AlO 5 and PO 4 polyhedra includes small channels populated by columns of CuO 6 octahedra sharing edges, and large channels where K + ions are deposited. It is assumed that the stability of this structure type is due to the pair substitution of Cu/Al with Ni/Fe, Co/Fe or Mg/Fe in different representatives of the series. From the KCuAl[PO 4 ] 2 structural features, one may suppose it is a potentially electrochemically active material and/or possible low-temperature antiferromagnet. In accordance with results obtained from X-ray diffraction data, using scanning electron microscopy, microprobe analysis and detailed crystal chemical observation, (II) is considered as a product of epitaxial intergrowth of phosphate KAlZn[PO 4 ] 2 and silicate KAlSi[SiO 4 ] 2 components having closely similar crystal structures. The assembly of 'coherent intergrowth' is described in the framework of a single diffraction pattern.

Synthesis and characterization of a novel alkali mixed magnesium-aluminum phosphate with a layered structure–KMgAl(PO4)2

“…They are classified depending on their structural type based on the metal coordination (six or four). The KCuAl(PO4)2 [15] and RbCuAl(PO4)2 [16] compounds exhibit 3D structures formed by CuO6 octahedrons sharing a common edge to form zigzag chains connected to a AlO5 polyhedron and PO4 tetrahedrons through corners and an edge. The compounds KCoAl(PO4)2 [17], NH4(Al,Co)2(PO4)2 [18], KZnAl(PO4)2 and β-NaZnAl(PO4)2 [19], (NH4)0,83(Zn0,83Al1,17)(PO4)2 [20] and α-NaZnAl(PO4)2 [21] adopted a 3D structural framework formed entirely by tetrahedrons.…”