1 Introduction
2 Materials
2.1 Synthesis of ZnxFe3−xO4 NPs via Co-precipitation Method
2.2 Synthesis of ZnxFe3−xO4 NPs via the Thermal Method in Non-aqueous Solvent
3 Characterization Methods
-
X-ray photoelectron spectroscopy (XPS) PHI 5000 VersaProbe II spectrometer with an Al Ka monochromatic x-ray beam. The spectra were recorded using a PHI 5000 VersaProbe II (ULVAC-PHI, Chigasaki, Japan) spectrometer with a Al Kα monochromatic X-ray beam (E = 1486.6 eV). The operating pressure in the analytical chamber was < 3 × 10–7 Pa. The X-ray source was operated at 25 W and 15 kV beam voltage. Spectra were collected from three points each of 100 μm diameter for each sample. A dual-beam charge neutralizer was used to compensate the charge-up effect. The pass energy of the hemispherical analyzer for iron (Fe 2p) spectra was fixed at 23.5 eV and for other elements at 46.95 eV. The calibration energy used was C1s = 284.8 eV of the atmospheric carbon and hydrocarbon adsorbed on the sample surface. The spectrum background subtraction was performed using the Shirley method. Data analysis software from PHI MultiPak was used to calculate elemental compositions from the peak areas.
-
X-ray absorption spectra (XAS) were collected at room temperature using the high-energy resolution fluorescence detection (HERFD) method at ID26 beamline of the European Synchrotron Radiation Facility (Grenoble, France). A Si(311) double-crystal monochromator was employed to select incident photon energy with the resolution of approximately 0.2 eV, while a set of four Ge(440) spherically bent crystal analyzers and avalanche photodiodes was used to detect Fe Kα emission intensity;
-
57Fe Mössbauer spectroscopy in the transmission geometry at room (300 K) and cryogenic (80 K) temperatures. Measurements were performed using a constant acceleration type spectrometer Renon MS-4 with 57Co source in Rh matrix kept at room temperature.
4 Results and Discussion
4.1 Chemical Characterization of the As-prepared Samples
4.2 X-ray Diffraction analysis
Sample | Phase | Lattice Constant Parameter a (nm) | d (nm) XRD | D (nm) TEM |
---|---|---|---|---|
As-prepared nanoparticles | ||||
S1 | Spinel type Zn-ferrite | 0.84824 (9) | 3.15 (2) | 3.2 ± 0.7 |
S2 | 0.84675 (7) | 3.62 (2) | 4.0 ± 0.7 | |
S3 | 0.84291 (5) | 4.57 (4) | 4.9 ± 0.8 | |
S4 | 0.84080 (4) | 6.50 (7) | 6.2 ± 1.3 | |
Solid product after thermal treatment up to 1400 °C | ||||
S1′ | Spinel type Zn- ferrite | 0.84519 (2) | 51.2 (7) | — |
S2′ | 0.84367 (1) | 131 (6) | — | |
S3′ | 0.84263 (1) | 293 (50) | — | |
S4′ | 0.84133 (1) | 44.4 (3) | — |
Samples | Volume Composition (ICP-OES) | Surface Composition (XPS) |
---|---|---|
S1 | ZnFe2O4 | Zn1.3Fe1.70 |
S2 | Zn0.86Fe2.14O4 | Zn1.14Fe1.86 |
S3 | Zn0.53Fe2.47O4 | Zn0.73Fe2.27 |
S4 | Zn0.35Fe2.65O4 | Zn0.35Fe2.65 |
4.3 Morphology and Composition of Zinc Ferrite
4.4 XPS Analysis
Samples | Zn/Fe Based on XPS Atm Pct | Determined Amount of Zinc x | Samples After Heating 1400 °C | Zn/Fe Based on Xps Atm Pct | Determined Amount of Zinc x |
---|---|---|---|---|---|
S1 | 0.76 | 1.30 | S1′ | 0.43 | 0.90 |
S2 | 0.61 | 1.14 | S2′ | 0.18 | 0.46 |
S3 | 0.32 | 0.73 | S3′ | 0.09 | 0.25 |
S4 | 0.13 | 0.35 | S4′ | 0.11 | 0.30 |
Fe Attribution | As-Prepared Samples | Area (Pct) | Samples After Heating 1400 °C | Area (Pct) |
---|---|---|---|---|
Fe2+Oh | 0 | 20 | ||
Fe3+Oh | S1 | 45 | S1′ | 43 |
Fe3+Td | 55 | 37 | ||
Fe2+Oh | 11 | 22 | ||
Fe3+Oh | S2 | 41 | S2′ | 38 |
Fe3+Td | 48 | 40 | ||
Fe2+Oh | 17 | 24 | ||
Fe3+Oh | S3 | 38 | S3′ | 41 |
Fe3+Td | 45 | 35 | ||
Fe2+Oh | 22 | 49 | ||
Fe3+Oh | S4 | 34 | S4′ | 32 |
Fe3+Td | 44 | 19 |
4.5 HERFD-XAS Analysis
4.6 Mössbauer Spectroscopy
Sample | 300 K | 80 K | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Comp. | Ci. pct | IS (mm/s) | 〈IS〉 (mm/s) | σ | Comp. | Ci pct | IS (mm/s) | 〈IS〉 (mm/s) | σ | |
S1 | 1 | 39 | 0.346 | 0.347 | 0.78 | 1 | 34 | 0.452 | 0.453 | 0.68 |
2 | 61 | 0.348 | 2 | 66 | 0.454 | |||||
S2 | 1 | 44 | 0.348 | 0.348 | 0.80 | 1 | 43 | 0.423 | 0.451 | 0.78 |
2 | 56 | 0.348 | 2 | 57 | 0.478 | |||||
S3 | 1 | 50 | 0.349 | 0.349 | 0.77 | 1 | 39 | 0.430 | 0.430 | 0.49 |
2 | 50 | 0.490 | 2 | 61 | 0.430 | |||||
S4 | 1 | 46 | 0.353 | 0.345 | 0.57 | 1 | 41 | 0.453 | 0.454 | 0.44 |
2 | 54 | 0.339 | 2 | 59 | 0.459 |
Sample | 300 K | 80 K | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Comp. | Ci pct | IS (mm/s) | 〈IS〉 (mm/s) | B (kGs) | 〈B〉 (kGs) | Comp. | Contrib. pct | IS (mm/s) | 〈IS〉 (mm/s) | B (kGs) | 〈B〉 (kGs) | |
S1′ | 1 | 100 | 0.369 | 0.369 | — | — | 1 2 | 76.9 23.1 | 0.466 0.657 | 0.510 | — | — |
S2′ | 1 | 31.5 | 0.235 | 385 | 1 | 12.6 | 0.420 | 500 | ||||
2 | 27.0 | 0.436 | 0.410 | 351 | 280 | 2 | 29.8 | 0.500 | 0.534 | 480 | 419 | |
3 | 14.3 | 0.410 | 268 | 3 | 16.2 | 0.435 | 442 | |||||
4 | 27.2 | 0.587 | 96 | 4 | 12.1 | 0.861 | 416 | |||||
5 | 29.3 | 0.538 | 312 | |||||||||
S3′ | 1 | 26.6 | 0.399 | 457 | 1 | 29.1 | 0.418 | 512 | ||||
2 | 12.8 | 0.717 | 0.437 | 421 | 413 | 2 | 37.5 | 0.531 | 0.586 | 494 | 468 | |
3 | 31.5 | 0.439 | 404 | 3 | 20.6 | 0.816 | 443 | |||||
4 | 29.1 | 0.345 | 380 | 4 | 12.9 | 0.755 | 332 | |||||
S4′ | 1 | 28.0 | 0.265 | 476 | 1 | 38.8 | 0.418 | 506 | ||||
2 | 34.5 | 0.591 | 0.479 | 433 | 418 | 2 | 31.89 | 0.556 | 0.573 | 492 | 474 | |
3 | 6.0 | 0.576 | 395 | 3 | 24.6 | 0.866 | 448 | |||||
4 | 31.5 | 0.528 | 352 | 4 | 4.8 | 0.427 | 212 |
Sample | Mole Content of Fe2+ Ions Before Decomposition | Decomposition Ratio | Mole Content of Fe2+ Ions, Formed as a Result of Reduction | Molar Ratio of Fe2+/Fe total (Pct Fe2+ Ions Formed as a Result of Reduction in Solid Products) | Chemical Formula for Zinc Ferrite After Thermal Decomposition |
---|---|---|---|---|---|
S1: ZnFe2O4 | 0 | 10 pct | 0.06 | 0.03 (3.00 pct) | S1′: Zn0.94Fe2.06O4 |
S2: Zn0.86Fe2.14O4 | 0.14 | 20 pct | 0.13 | 0.06 (6.07 pct) | S2′: Zn0.73Fe2.27O4 |
S3: Zn0.53Fe2.47O4 | 0.47 | 21 pct | 0.14 | 0.05 (5.66 pct) | S3′: Zn0.39Fe2.61O4 |
S4: Zn0.35Fe2.65O4 | 0.65 | 24 pct | 0.16 | 0.06 (6.03 pct) | S4′: Zn0.19Fe2.81O4 |
4.7 Magnetic Properties
Sample | Ms (emu/g), 1.5 T, 80 K | Sample | Ms (emu/g), 1.5 T, 300 K | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
As-Prepared | Sample | After Thermal Treatment at 1400 °C | As-Prepared | Sample | After Thermal Treatment at 1400 °C | ||||||
Measured | LAS fit | Measured | LAS Fit | Measured | LAS fit | Measured | LAS Fit | ||||
S1 | 15.0 | 12.0 | S1′ | 40.1 | 34.5 | S1 | 2.0 | 0.2 | S1′ | 7.5 | 3.2 |
S2 | 34.7 | 35.2 | S2′ | 127.8 | 136.2 | S2 | 20.5 | 21.0 | S2′ | 76.6 | 74.3 |
S3 | 59.2 | 59.7 | S3′ | 137.3 | 144.4 | S3 | 30.3 | 31.3 | S3′ | 108.8 | 109.3 |
S4 | 78.4 | 81.8 | S4′ | 142.0 | 145.9 | S4 | 52.8 | 54.85 | S4′ | 116.5 | 118.3 |
-
for the as-prepared (S1–S4) samples:
-
for the solid products after decomposition at 1400 °C (S1–S4′):
5 Conclusion
-
annealing of ZF and NZF NPs leads to re-growing of grains by means of coalescence and sintering (XRD, TEM, Mössbauer spectroscopy);
-
the tested NZF NPs samples (S2–S4) are undergoing thermochemical decomposition in approximately 20 pct under the applied conditions (annealing up to 1400 °C, inert atmosphere), as shown by Mössbauer spectroscopy, XPS, XANES and VSM;
-
for ZF NPs of stoichiometric composition (S1), the decomposition degree under the applied conditions is twice lower than for NZF NPs;
-
Mössbauer spectroscopy proves that after annealing NZF NPs are enriched in Fe2+ ions and depleted of Zn2+ ions (shown by XRD and XPS);
-
zinc ferrite of a different composition than that of the initial sample is a solid solution of “initial zinc ferrite” and magnetite Fe3O4 (cf. Table VI, Mössbauer spectroscopy, XRD, XANES, XPS);
-
XRD investigations indicate that annealing at a temperature up to 1400 °C causes a decrease of the lattice constant of samples;
-
zinc ferrites formed after annealing indicate a significant increase of the magnetization saturation (in relation to their initial values), probably being the effect of reduction and/or relocation of cations in the spinel lattice.