Abstract
Crystals of a new potassium iron (III) diarsenate (KFeAs
2O
7) have been grown and characterized by single crystal X-ray diffraction. It crystallizes in the triclinic space group
P
1
¯
, with
a=7.662(1)
Å,
b=8.402(2)
Å,
c=10.100(3)
Å,
α=90.42(3)°,
β=89.74(2)°,
γ=106.39(2)°,
V=623.8(3)
Å
3 and
Z=4. The final agreement factors are
R=0.0342, w
R=0.0889,
S(
F
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
6 octahedra and As
2O
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
2O
7 type but structural relationships exist between the frameworks. Impedance measurements (frequency/temperature ranges: 5–13,000
Hz/526–668
K) show KFeAs
2O
7 an ionic conductor being the conductivity 2.76×10
−7
S
cm
−1 at 568
K and
E
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.
Optimized trajectory for K1–K2–K1 jump as determined by BVS analysis.