Structural study and physical properties of a new phosphate KCuFe(PO4)2

Single crystals of a new phosphate KCuFe(PO4)2 have been prepared by the flux method and its structural and physical properties have been investigated. This compound crystallizes in the monoclinic system with the space group P21/n and its parameters are: a=7.958(3) Å, b=9.931(2) Å, c=9.039(2) Å, β=115.59(3)° and Z=4. Its structure consists of FeO6 octahedra sharing corners with Cu2O8 units of edge-sharing CuO5 polyhedra to form undulating chains extending infinitely along the b-axis. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the K+ ions are located. The Mössbauer spectroscopy results confirm the exclusive presence of octahedral Fe3+ ions. The magnetic measurements show the compound to be antiferromagnetic with Cm=5.71 emu K/mol and θ=−156.5 K. The derived experimental effective moment μex=6.76μB is somewhat higher than the theoretical one of μth=6.16μB, calculated taking only into account the spin contribution for Fe3+ and Cu2+ cations. Electrical measurements allow us to obtain the activation energy (1.22 eV) and the conductivity measurements suggest that the charge carriers through the structure are the potassium cations.

A projection along the [101] direction of the structure showing the six-edged tunnels, occupied by the K+ ions.Figure optionsDownload as PowerPoint slideHighlights
► The reported structure is of a new type.
► The structural model is supported by a Mössbauer spectroscopy study.
► The magnetic susceptibility results are reported.
► The electrical properties are discussed.