Ni-Cu-Zn Ferrites for low temperature firing: II. Effects of powder morphology and Bi2O3 addition on microstructure and permeability

Abstract

The morphology of Ni-Cu-Zn ferrite powders obtained by milling of a calcined raw materials mixture strongly effects the densification behavior during sintering at 900 • C. In order to obtain dense samples sub-micron powders with enhanced reactivity are required. The addition of Bi 2 O 3 as sintering additive is beneficial: the density of samples sintered at 900 • C increases with the bismuth oxide concentration up to 0.75 wt.%. The process of liquid phase sintering was studied by dilatometry. The grain size of the sintered samples slightly increases for 0.25 wt.% Bi 2 O 3 compared to bismuth-free samples, whereas for 0.3-0.5 wt.% Bi 2 O 3 additions bimodal grain growth is observed with a significant fraction of very large grains. For >0.5 wt.% Bi 2 O 3 a homogeneous coarse-grained microstructure is obtained. The permeability increases for small bismuth oxide additions, but decreases for a Bioxide content of more than 0.5%. Maximum permeability of μ i = 900 is observed for intermediate Bi 2 O 3 concentrations.

Development of magneto-dielectric materials based on Li-ferrite ceramics

“…The impedance of the sample is very close to that of free space (∼1), while both the magnetic and dielectric tangents are very close to or lower than 10 −2 , over 3-30 MHz (HF band). The real permeability and permittivity (13)(14)(15) of the Li-Co ferrite ceramics obtained in the present study are higher than those of ferrite composites (6-7) [19,20] and Mg-Cu-Co ferrite ceramics (6)(7)(8)(9)(10)(11)(12) [21] that we have achieved previously.…”

“…The authors attributed the decrease in permeability with increasing concentration of Bi 2 O 3 to the possible incorporation of excess nonmagnetic material at grain boundaries. Another example was Ni-Cu-Zn ferrite doped with Bi 2 O 3 of ≤1 wt% [11]. The samples with highest permeability were found to have Bi 2 O 3 between 0.375% and 0.5%.…”

Development of magneto-dielectric materials based on Li-ferrite ceramics

“…In the present study, Bi 2 O 3 was used as sintering aid to improve the sintering property of Li 0.50 Fe 2.50 O 4 ceramics. Bi 2 O 3 has been widely used to improve the densification behavior of various ferrites because it forms a liquid phase during sintering process due to its relatively low melting point (∼820 • C) [15][16][17][18]. Although 1% Bi 2 O 3 is sufficient to attain almost fully dense Li 0.50 Fe 2.50 O 4 ceramics, 3% was found to be necessary to maintain sufficiently low dielectric loss tangent (see Part II) [19].…”

Effect of oxygen partial pressure on co-firing behavior and magnetic properties of LTCC modules with integrated NiCuZn ferrite layers

“…Significant progress in the low-temperature sinterability of NiCuZn ferrites was reported in the last few years and the successful development of such low-fired ferrite materials was demonstrated in various papers [5][6][7][8][9][10]. Alternatively, MnZn ferrites were suggested as lowtemperature co-firable magnetics [11,12].…”