W. Wolski

Defect structures in cadmium-nickel ferrites

Abstract The cation-deficient solid solutions of cadmium ferrite (CdFe 2 O 4 ) and nickel ferrite (NiFe 2 O 4 ) obtained by prolonged thermal treatment from stoichiometric samples have been investigated by X-ray powder diffraction, magnetic measurements and chemical analysis. The stoichiometric Cd x Ni 1−x Fe 2 O 4 samples were prepared from coprecipitated x Cd(OH) 2 ·(1− x )Ni(OH) 2 ·2Fe(OH) 3 -hydroxides, sintered at 1000°C during one hour. It has been found that because of the CdO volatility, stoichiometric preparations with x = 0.9 and x = 1.0 should be synthesized with the excess of 8% and 10% Cd(OH) 2 respectively. The linear increase of spinel lattice constant with increasing Cd-content and the observed X-ray reflection intensities confirm the stoichiometry and the tetrahedral coordination of Cd 2+ -ions. Thermal treatment above 1000°C leads to the defect spinel structures with the Cd 2+ -deficiency, composed from solid solutions with the general formula Cd 2+ x−α Fe 3+ 1−x+α [Ni 2+ 1−x Fe 3+ 1+x−α/3 □ α/3 ]O 4 , corresponding to a solid solution of stoichiometric (Cd, Ni)-ferrite with the maghemite, γFe 2 O 3 .

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

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.

Nonstoichiometric solid solutions during formation of Cd/Ni ferrites

Abstract Cadmium-nickel ferrites prepared by different procedures from coprecipitated amorphous x Cd(OH) 2 ·(1− x )Ni(OH) 2 ·2Fe(OH) 3 mixtures have been investigated by X-ray, magnetic and thermogravimetry techniques. In the preparations obtained by hydrothermal methods at 100 and 150°C there is a marked tendency to form solid solutions between the nickel and cadmium ferrites for lower values of x , but for higher x the lattice parameters suddenly decrease, indicating the formation of solid solutions between CdFe 2 O 4 and maghemite, γ-Fe 2 O 3 . It has been found that during a gradual heating of dried, initially amorphous mixtures of hydroxides, several distinct nonstoichiometric intermediate phases of Cd/Ni ferrites arose before the final product, corresponding to the nominal composition was formed. Prolonged thermal treatment at T ⩾1000°C, because of the Cd volatility, leads again to the defect structure solid solutions between the cadmium-nickel ferrites and maghemite.

Characterization of ferrimagnetic phases from hydrothermal storage of Cd/Ni/Fe/Al-hydroxides

Abstract Ferrimagnetic phases formed from amorphous CdxNi1−xFe2−yAly(OH)8 hydroxides with y = 0, 0.2 and 0.4 in 0.2 steps for x, coprecipitated at pH 10 with NaOH from corresponding nitrates and stored one month at 150 °C in mother solution, were studied by XRD, IR, TG and magnetic measurements. The hydrothermally obtained spinel phases displayed the same magnetic properties as the series sintered at 1000 °C only for y = 0.0 and 0.2. It is assumed that the highest incorporation of Cd2+ ions into nickel ferrite occurs for x = 0.6–0.8. The comparison of the unit cell parameters with a standard straight a = f(x) line for the CdFe2O4-NiFe2O4 solid solutions sintered at 1000 °C, indicates that the isomorphous incorporation of cadmium reaches about 0.4 mol. For the products obtained from precursors with nominal x = 1.0, the formation of a solid solution between cadmium ferrite and maghemite has been assumed to justify the ferrimagnetism of samples. The first member of the solid solution series, NiFe2O4 (x = 0.0, y = 0.0) was used to prove that the hydrothermally obtained ferrites contain OH− groups substituting O2− ions in the spinel lattice.