Fundamentals of the Densification Mechanism of NiCuZn-Ferrites

Holz, D.; Pagana, A.E.; Tsakaloudi, V.; Kogias, G.; Zaspalis, V.T.

doi:10.2497/jjspm.61.s75

Cited by 3 publications

(1 citation statement)

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“…Reduction of Cu 2+ to Cu + may proceed through the creation of oxygen vacancies as charge compensating defect according to the following reaction: In ionic solids with closed-packed oxygen structures, such as the spinel structure, the densification rate is determined by the diffusion rate of the large oxygen ions through anion vacancies [24,25]. This is also the reason that almost all commercially available NiZn-ferrite components for power applications are iron deficient [26]. Such a mechanism could explain the densification enhancement already from the initial sintering stage (at ca.…”

Section: Resultsmentioning

confidence: 99%

The Effect of Sintering Temperature on the Densification and Magnetic Performance of NiCuZn-Ferrites (CuO: 0–6 wt.%)

Zaspalis,

Kogias,

Zaspalis

2024

Materials

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This article reported on the effect of Cu-content and sintering temperature on the magnetic permeability and power losses of monolithic iron-deficient NiCuZn-ferrite components with low Cu-contents aimed to be used for power applications at frequencies up to 1 MHz. In particular NiαZnb1−xCuxFe1.9O4 ferrite compositions are investigated with a constant Ni/Zn atomic ratio a/b = 0.9 and 0 < x < 0.017. As found, the addition of Cu enables the achievement of good magnetic performance at lower sintering temperatures and, therefore, lower production cost. At all Cu-contents, the initial permeability as a function of the sintering temperature passes through a maximum above which structural deterioration due to asymmetric grain growth occurs. The temperature at which this maximum permeability occurs depends on the Cu content and coincides with the achievement of the maximum density of 5.1–5.2 g cm−3 (relative density ~97%). At Cu-contents x = 0.006–0.012 and sintering temperatures 1200–1100 °C power losses (tan(δ)/μ at 1 MHz, 25 °C) οf 50 × 10−6 could be achieved and initial permeabilities (10 kHz, 0.1 mT, 25 °C) of around 400 with very good frequency and temperature stability. At CuO content higher than 4 wt.% (i.e., x > 0.012) and sintering temperatures higher than 1150 °C, pronounced microstructural disturbances due to asymmetric grain growth result in low permeabilities and high losses. It is suggested that at low CuO contents and low sintering temperatures, the densification enhancement may not proceed through Cu-rich phase segregation but through the creation of oxygen vacancies.

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Section: Resultsmentioning

confidence: 99%