Mossbauer spectroscopy of langbeinite-type K2Fe2(SO4)(3)

The langbeinite-type K2Fe2(SO4)(3) was synthesized. The temperature dependence of the dielectric constant shows a clear anomaly at about 130 K. Mossbauer spectrum of Fe-57 was recorded in the temperature range from 15 to 290 K. The spectrum at all temperatures consists of two doublets which are analyzed with isomer shifts and quadrupole couplings. The quadrupole splitting of one site is 3.00 mm/s at 290 K and shows only 10% increase down to 15 K. The other one is 0.82 mm/s at 290 K and shows a drastic increase, resulting at 15 K in 2.5 times that at 290 K. The two Fe-57 sites for the electric field gradient were assigned to the two crystallographically inequivalent iron sites compairing the two octahedral oxygen environments of the iron ions. The broad background spectrum is interpreted as the distribution of the electric field gradient due to the multi-positional distribution in SO4 groups proposed by Itoh et al.