The iron potassium diarsenate KFeAs2O7 structural, electric and magnetic behaviors

Crystals of a new potassium iron (III) diarsenate (KFeAs2O7) have been grown and characterized by single crystal X-ray diffraction. It crystallizes in the triclinic space group P1-bar, with a=7.662(1) A, b=8.402(2) A, c=10.100(3) A, α=90.42(3)o, β=89.74(2)o, γ=106.39(2)o, V=623.8(3) A3 and Z=4. The final agreement factors are R=0.0342, wR=0.0889, S(F2)=1.01; the structural model is validated by bond valence sum (BVS) and charge distribution (CD) methods. The structure consists of corner-sharing FeO6 octahedra and As2O7 diarsenate groups, the three-dimensional framework delimits tunnels running along [0 1 0] direction where the potassium ions reside. The crystal structure of the title compound is different from that of the monoclinic KAlP2O7 type but structural relationships exist between the frameworks. Impedance measurements (frequency/temperature ranges: 5-13,000 Hz/526-668 K) show KFeAs2O7 an ionic conductor being the conductivity 2.76x10-7 S cm-1 at 568 K and Ea is 0.47 eV. The BVS model suggests that the most probable potassium conduction pathway is along b-direction. Magnetic measurements reveal the Curie-Weiss type paramagnetic behavior over the range 30-300 K and ferromagnetic below 29.3 K. - Graphical abstract: Optimized trajectory for K1-K2-K1 jump as determined by BVS analysis