Ferrimagnetic spinels in hydrothermal and thermal treatment of MnxFe2−2x(OH)6−4x

Abstract

Products of hydrothermal treatment of the initial amorphous system MnxFe2−2x(OH)6−4x for 0≤x1 in 0.1x intervals, and products of their further thermal treatment, were examined by chemical analysis, X-ray, IR, and DTA techniques supported by magnetic measurements. After hydrothermal growth for lowx, hematite and goethite phases occurred. Although the goethite phase was still identifiable atx=0.6, formation of a solid solution with the isostructural groutite was not found. The ferrimagnetic spinel phase, which resists heating up to 400‡C, was present at 0.5≤x≤0.9. At higher temperatures, it transformed into the rhombohedral hematite type phase or into the cubic bixbyite phase. AtT≥900‡C, a ferrimagnetic spinel structure reappeared up tox=0.8. For x=0.9, the low- and high-temperature forms of the hausmannite phase occurred, forx= 1 passing from one form into another through Mn5O8 and partritgeite.For a primary mixture Mn0.5Fe(OH)4, corresponding to the manganese ferrite structure, the lattice parameter of which passes from 8.43 å through 8.33 å to 8.50 å, the probable crystallochemical formula was suggested.