The iron potassium diarsenate KFeAs{sub 2}O{sub 7} structural, electric and magnetic behaviors

Crystals of a new potassium iron (III) diarsenate (KFeAs{sub 2}O{sub 7}) 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, {alpha}=90.42(3){sup o}, {beta}=89.74(2){sup o}, {gamma}=106.39(2){sup o}, V=623.8(3) A{sup 3} and Z=4. The final agreement factors are R=0.0342, wR=0.0889, S(F{sup 2})=1.01; the structural model is validated by bond valence sum (BVS) and charge distribution (CD) methods. The structure consists of corner-sharing FeO{sub 6} octahedra and As{sub 2}O{sub 7} 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 KAlP{sub 2}O{sub 7} type but structural relationships exist between the frameworks. Impedance measurements (frequency/temperature ranges: 5-13,000 Hz/526-668 K) show KFeAs{sub 2}O{sub 7} an ionic conductor being the conductivity 2.76x10{sup -7} S cm{sup -1} at 568 K and E{sub a} 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.