M. Ristić

Chemical and structural properties of the system Fe2O3-Nd2O3

Chemical and structural properties of the system (1−x)Fe2O3 + xNd2O3, 0≤x≤1, were investigated using X-ray diffraction, 57Fe Mössbauer spectroscopy and Fourier transform-infrared (FT-IR) spectroscopy. The samples were prepared by the chemical coprecipitation and thermal treatment of Fe(OH)3/Nd(OH)3 coprecipitates. X-ray diffraction showed the presence of oxide phases α-Fe2O3 + NdFeO3 in the Fe2O3-rich region, and the oxide phases Nd2O3 + NdFeO3 in the Nd2O3-rich region. 57Fe Mössbauer spectra were characterized with one sextet of spectral lines at room temperature. Mathematical evaluation of the Mössbauer spectra showed distinct regularities in the changes of Mössbauer parameters, thus indicating the presence of two subspectra with very similar spectral behaviour. High sensitivity of the Nd2O3 phase to the moisture and atmosphere CO2 was demonstrated by FT-IR spectroscopy.

Formation of nanocrystalline magnetite by thermal decomposition of iron choline citrate

Abstract Thermal decomposition of iron choline citrate (C 33 H 57 Fe 2 N 3 O 24 ) has been investigated using X-ray powder diffraction, Fourier transform infrared and 57 Fe Mossbauer spectroscopies. The starting compound was heated in a furnace at selected temperatures between room temperature and 460°C, and cooled down afterwards either by quenching in bidistilled water or by cooling in air. Final decomposition products were iron oxides Fe 3 O 4 (magnetite) and α-Fe 2 O 3 (hematite). In all samples quenched in bidistilled water magnetite was found to be a dominant crystalline phase. Self-propagating burning of iron choline citrate in air was observed. The unit-cell parameter of the obtained magnetite decreased gradually with the increase in temperature of thermal treatment of the starting compound regardless of the cooling procedure. Crystallite size of magnetite varied from 10(1) to 21(2) nm, whereas the crystallite size of hematite varied between 25(2) and 39(3) nm. FT–IR spectra showed a significant amount of organic fraction in the samples containing magnetite as a dominant crystalline phase. In absence (or presence of a small quantity) of organic phase, a transformation of magnetite to hematite occurred. The Mossbauer spectrum of iron choline citrate at RT showed a single line with pronounced broadening. On heating the starting compound at 270°C and quenching in bidistilled water a quadrupole doublet was recorded at RT. This quadrupole doublet was ascribed to amorphous iron(III)-(hydrous) oxide. For samples thermally treated at higher temperatures Mossbauer spectroscopy showed magnetite and hematite. Mossbauer spectra also showed substoichiometric magnetite, Fe 3− x O 4 , which was very pronounced in samples produced at the highest temperatures, and this was in agreement with XRD investigations.

X-ray diffraction and57Fe Mössbauer spectra of the system Fe2O3−Ga2O3

The influence of gallium substitution on the chemical and structural properties of haematite, α-Fe2O3, has been studied using X-ray diffraction and57Fe Mössbauer spectroscopy. The presence of only α-(GaxFe1−x)2O3 phase is detected for the compositions withx between 0.01 and 0.90. A gradual decrease of the unit-cell parameters of α-(GaxFe1−x)2O3 with the increase of gallium substitution is measured.57Fe Mössbauer spectra showed that the value of the magnetic hyperfine field of pure α-Fe2O3 decreases with increasing gallium for iron substitution. The hyperfine magnetic structure, which is observed for α-(GaxFe1−x)2O3 at room temperature, collapsed for the composition withx≃0.50. The changes in the57Fe Mössbauer spectra of the α-(GaxFe1−x)2O3 phase are discussed in the sense of the electronic relaxation and the superparamagnetic effects.

Ferritization of copper ions in the Cu–Fe–O system

Abstract Ferrite ceramics were prepared utilizing solid state reactions between CuO and Fe 3 O 4 or α-Fe 2 O 3 . The samples were analyzed with X-ray diffraction, 57 Fe Mossbauer and FT-IR spectroscopies. For the solid state reaction between CuO and Fe 3 O 4 , the initial atomic ratios of Cu:Fe varied between 1:299 and 1:2. With an increase in the amount of CuO in the initial reaction mixture, there was a corresponding increase in cuprospinel (cubic CuFe 2 O 4 ) in the final products of the synthesis. For the initial molar ratio of Cu:Fe=1:2, cuprospinel phase (0.85) and CuFeO 2 phase (0.15) were found by XRD, as the result of solid state reaction between CuO and Fe 3 O 4 . In this sample, a small amount of CuO was also detected. For the solid state reaction between CuO and α-Fe 2 O 3 , the initial molar ratio of 1:1 was used. The samples prepared at a maximum temperature of 800°C, contained similar fractions of tetragonal and cubic CuFe 2 O 4 phases, and also minor phases of CuO and α-Fe 2 O 3 as found by XRD. In the samples prepared at between 1000 and 1350°C, the cubic CuFe 2 O 4 phase was found together with small amounts of CuFeO 2 and CuO. Mossbauer spectra showed hyperfine field distributions and on the basis of these spectra, calculated parameters, the possible presence of Cu + and Fe 2+ ions in the samples was discussed. For the samples prepared at 1350°C the FT-IR spectrum suggested a significant increase in Fe 2+ ions, whereas the Mossbauer spectrum and calculated parameters were similar to those for the compound Cu 0.7 Fe 2.3 O 4 .

Formation of solid solutions in the system Al2O3-Fe2O3

Abstract Formation of solid solutions in the system α-(Al x Fe 1 − x ) 2 O 3 , 0 ⩽ x ⩽ 1, was investigated using X-ray diffraction. A series of samples were prepared using traditional ceramic methods, with γ-AlOOH and α-Fe 2 O 3 as starting chemicals. The terminal solid solubility limits, 27.0 ± 0.5 mol% of α-Al 2 O 3 in α-Fe 2 O 3 and 9.0 ± 0.5 mol% of α-Fe 2 O 3 in α-Al 2 O 3 , were calculated.

Structural properties of the system Al2O3Cr2O3

Abstract Structural properties of the system (1−x)Al2O3+xCr2O3 were investigated in the whole concentration range. The samples were prepared by mechano-chemical activation of γ-AlOOH and Cr2O3, sintering the resulting powder up to 1300°C. The formation of solid solutions (Al1−xCrx)2O3 was observed in the whole concentration range. The replacement of Al3+ with Cr3+ resulted in a gradual increase of the unit-cell parameter with x. For the molar fraction of Cr2O3, x⩾0.5, a phase closely related to Cr2O3 was also found. The unit-cell parameters of this phase also increased with x, although the rate of increase was much smaller. The samples of (1−x))Al2O3+xCr2O3 showed gradual changes in the FT IR spectra with x.

Ferritization of Y3+ and Nd3+ ions in the solid state

Abstract The ferritization of Y3+ and Nd3+ ions in the solid state was investigated by X-ray powder diffraction, 57Fe Mossbauer and FT-IR spectroscopies. Magnetization measurements were performed with selected samples between 4.2 and 300 K in magnetic fields up to 20 kOe. Incorporation of Nd3+ ions into a garnet-type structure and the formation of solid solutions of Y3−xNdxFe5O12 were shown. The unit-cell parameter measured for Y3Fe5O12 was 12.359(3) A, whereas for the initial molar ratio Fe2O3:Y2O3:Nd2O3=5:1:2 a value of a unit-cell parameter of 12.512(3) A was measured for the garnet-type solid solution. Hyperfine magnetic fields (HMF) of 487 and 394 kOe at the a- and d-sites, respectively, were measured at 300 K for Y3Fe5O12, while HMF of 509 kOe was measured at 300 K for NdFeO3. The formation of solid solutions of Y3−xNdxFe5O12, caused a gradual shift to lower wave numbers of IR bands defined for Y3Fe5O12. The magnetization measurements of the compounds with nominal composition (Y2Nd)Fe5O12 and (YNd2)Fe5O12 showed that the magnetic moments were higher than in Y3Fe5O12. The magnetic moments at 20 kOe, corrected for presence of some orthoferrite impurity, were 5.75 μB and 6.45 μB, respectively, whereas the moment of Y3Fe5O12 was 4.81 μB, and even in saturation it is only 5 μB. This proves that the Nd sublattice magnetization is coupled ferromagnetically to the total iron magnetization, in agreement with theoretical expectations for light rare earth garnets. The increase in magnetic moment of (YNd2)Fe5O12 relative to Y3Fe5O12 is less than twice of the increase for (Y2Nd)Fe5O12. This result is probably due to the magnetic anisotropy in the Nd-rich compound. (Y2Nd)Fe5O12 seems to exhibit a spin reorientation transition around 60 K, previously not noticed.

Formation and characterization of oxide phases in the Fe2O3-Eu2O3 system

Abstract X-ray diffraction and Mossbauer spectroscopy were used to investigate samples, prepared by chemical coprecipitation, in the system (1 − x)Fe2O3 + xEu2O3, 0 ≤ x ≤ 1. The samples obtained at 600 °C contained poorly crystallized p an amorphous fraction. When the temperature of heating was increased to 900 °C, the amorphous fraction disappeared and all samples were well crystallized. The temperature of formation of Eu3Fe5O12 was significantly lower when chemical coprecipitation was used to prepare the starting material than when the solid state reaction was applied. The formation of α-Fe2O3, EuFeO3, Eu3Fe5O12, Eu2O3 and of an amorphous phase was dependent on x. The complex nature of the samples was reflected in their Mossbauer spectra.

Thermal decomposition of pyrite

Thermal decomposition of natural pyrite (cubic, FeS2) has been investigated using X-ray diffraction and57Fe Mössbauer spectroscopy. X-ray diffraction analysis of pyrite ore from different sources showed the presence of associated minerals, such as quartz, szomolnokite, stilbite or stellerite, micas and hematite. Hematite, maghemite and pyrrhotite were detected as thermal decomposition products of natural pyrite. The phase composition of the thermal decomposition products depends on the temperature, time of heating and starting size of pyrite crystals. Hematite is the end product of the thermal decomposition of natural pyrite.

Mössbauer spectroscopic and X-ray diffraction study of the thermal decomposition of Fe(CH3COO)2 and FeOH(CH3COO)2

Thermal decomposition of iron(II) acetate, Fe(CH3COO)2, and iron(III) acetate hydroxide, FeOH(CH3COO)2, has been studied using57Fe Mössbauer spectroscopy and X-ray diffraction. Samples were thermally treated in air atmosphere between 150°C and 1000°C. The formation of maghemite γ-Fe2O3, and hematite, α-Fe2O3, is discussed. Hematite appears as the final decomposition product.