Phase Formation, Microstructure, and Permeability of Fe-Deficient Ni-Cu-Zn Ferrites (II): Effect of Oxygen Partial Pressure
We have investigated the phase formation, microstructure, and permeability of stoichiometric and Fe-deficient Ni-Cu-Zn ferrites of composition Ni<sub>0.30</sub>Cu<sub>0.20</sub>Zn<sub>0.50+z</sub>Fe<sub>2−z</sub>O<sub>4−(z/2)</sub> with 0 ≤...
Saved in:
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-12-01
|
| Series: | Magnetochemistry |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2312-7481/10/12/97 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | We have investigated the phase formation, microstructure, and permeability of stoichiometric and Fe-deficient Ni-Cu-Zn ferrites of composition Ni<sub>0.30</sub>Cu<sub>0.20</sub>Zn<sub>0.50+z</sub>Fe<sub>2−z</sub>O<sub>4−(z/2)</sub> with 0 ≤ z ≤ 0.06 sintered at 1000 °C in various oxygen partial pressures <i>p</i><sub>O2</sub>, which range from 0.21 atm down to 10<sup>−5</sup> atm. The density of the sintered samples is almost independent of the <i>p</i><sub>O2</sub>, whereas the grain size of the Fe-deficient ferrites decreases in more reducing atmospheres. Stoichiometric ferrites show a regular growth of single-phase ferrite grains if sintered in air. Sintering at <i>p</i><sub>O2</sub> ≤ 10<sup>−2</sup> atm leads to the formation of a small amount of Cu<sub>2</sub>O at grain boundaries and triple points. Fe-deficient compositions (z > 0) form Cu-poor stoichiometric ferrites, which coexist with a minority CuO phase homogeneously distributed between the grains after sintering in air. At <i>p</i><sub>O2</sub> ≤ 10<sup>−2</sup> atm, the CuO grain boundary phase starts to transform into Cu<sub>2</sub>O, which concentrates at some triple points at <i>p</i><sub>O2</sub> = 10<sup>−2</sup> atm, and it is more homogeneously distributed between the ferrite grains at the lower <i>p</i><sub>O2</sub>. Formation of the Cu oxide second phases is investigated using XRD, SEM, and EDX. The permeability at 1 MHz of the stoichiometric ferrites (z = 0) is between <i>µ</i>′ = 200 and <i>µ</i>′ = 300 within the studied range of the <i>p</i><sub>O2</sub>. The permeability at 1 MHz of the Fe-deficient samples decreases with the <i>p</i><sub>O2</sub>, e.g., from <i>µ</i>′ = 750 at <i>p</i><sub>O2</sub> = 0.21 atm to <i>µ</i>′ = 320 at <i>p</i><sub>O2</sub> = 10<sup>−5</sup> atm for z = 0.02, respectively. |
|---|---|
| ISSN: | 2312-7481 |