BEHAVIORS OF ADDITIVES IN FERRITES

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BEHAVIORS OF ADDITIVES IN FERRITES

J. Tasaki, T. Izushi

To cite this version:

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JOURNAL DE PHYSIQUE Colloque C1, supplkment au no 4, Tome 38, Avril 1977, page C1-175

BEHAVIORS OF ADDITIVES

IN FERRITES

J. TASAKI and T. IZUSHI

Government Industrial Research Institute, Nagoya, Japon

R h m 6 .

-

On discute I'influence de diffkrents cations allant des mktaux alcalins aux mktaux de transition de la classification pkriodique. Les ferrites utilisks sont le ferrite de Ni, le ferrite de Mg et le ferrite de Zn qui prksentent une distribution diffkrente des cations dans le rtseau spinelle. Les cations ayant un rayon ionique et une valence adkquates sont solubles dans le feirite. Plusieurs additifs prksentent une seconde phase a I'intkrieur de la phase spinelle. On trouve de nombreux additifs qui influent sur les propriktks magnktiques et klectriques des ferrites.

Abstract.

-

The influence of various cations ranging from alkali metals to transition metals according to the periodic table were discussed. The ferrites used were Ni ferrite, Mg ferrite and Zn ferrite having different cation distributions in the spinel lattice. Cations having appropriate ionic radii and valencies are soluble in ferrite. Several additives formed other phase in addition to the spinel phase. There are many additives by which magnetic and electric properties of ferrites are affected.

1 . Introduction. - It is well known that additives play an important role in improving the magnetic characteristics of ferrites. For instance, the role of small amounts of Ca and Si in high permeability of Mn-Zn ferrite [I] and the role of a small amount of Bi in improving the residual magnetization and the coercive force of Ba ferrite [2] were investigated. Moreover magnetic properties of various oxides with spinel structures were investigated [3]. It is possible to expect many effects from various additives in ferrites. However, the behaviors of additives have not been clarified enough. In this report the influence of various cations ranging from alkali metals to transition metals according to the periodic table were studied.

2. Experimental.

-

Three kinds of ferrite having different cation distributions in a spinel lattice were selected. They were Ni ferrite as an inverse spinel, Mg ferrite as an intermediate spinel, and Zn ferrite as a normal spinel. They were synthesized by usual methods. Ni ferrite or Zn ferrite having a stoichiometric composition could be obtained always. Mg ferrite was also stoichiometric a t the initial stage of the experiment, but in subsequent procedure after adding lIIb group metals the composition of the used ferrite deviated slightly to the magnesium excess side. As additives 1-6 at

%

of cations were added to each ferrite respectively, in the form of carbonate in the case of alkali metals and alkaline earth metals except Be and Mg, or in the form of oxide in the case of other metals including Be and Mg. After satisfac- tory mixing, each ferrite powder with additives was pressed into toroids and disks. Firing was carried out at 1 300 OC for 3 hours in air. To identify the

formed phases and to determine the lattice constants of the ferrites after adding additives, X-ray diffraction pattern measurements were made with a diffractometer with manganese filtered iron radiation. The formed phases were identified by the diffraction patterns at 2 8 < 80°, and lattice constants were determined from the (533), (731) and (800) spinel reflections. Curie temperatures were measured with a magnetic balance using small pieces taken from a fixed position of the disk specimens. Magnetic permeabilities at 10 kHz were measured on toroidal specimens with an impedance bridge and electric resistances were measured on disk specimens with a vibrating reed volt ammeter. Observations with an electron micro- scope or analysis with an electron probe micro analyser were carried out when necessary.

3. Result.

-

3.1 ALKALI METALS.

-

The lattice constant, Curie temperature and the electric resistance showed the replacement of divalent cations in each ferrite by Li or Na within a limited amount. Li is not so effective for Ni ferrite as for nickel oxide. The behavior of Li in Mg ferrite is particular. The electric resistance decreased remarkably by adding up to 4 at 0/,, and the magnetic permeability increased correspondingly (Fig. 1). The behavior of Na in Ni ferrite is similar to Li in Mg ferrite (Fig. 2). K has a too large ionic radius to form a solid solution with each ferrite. The possibility of formation of a solid solution was suggested in a slight increase of the lattice constant by adding K to Zn ferrite as shown in figure 3. Rb and Cs formed neither solid solutions nor other phases with any ferrite. However, it is observed that the existence of Rb affects the micro structure of sintered ferrites.

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C1-176 J. TASAKI AND T. IZUSHI

. \ ~ n o t ~ n t

o f

. \ d t l i t i v c s at'A , \ m o u n t

o f

A d d i t i v e s a t " ,

FIG. I . - Magnetic permeabilities of Mg ferrite with several _FIG._3._-_{Lattice constants of Zn ferrite with alkali metals.} additives.

FIG. 2. - Magnetic permeabilities of Ni ferrite with several additives.

3 . 2 ALKALINE EARTH METALS. - Except Ca, alkaline earth metals had little effect on the lattice constant of Ni ferrite or Zn ferrite. The replacement of Ni or Zn by Mg is confirmed from the drop of Curie temperature of Ni ferrite and the slight decrease of the lattice constant of Zn ferrite. In Mg ferrite these cations except Be are effective for the lattice constant (Fig. 4) and Curie temperature. The behavior of Ca in each ferrite is particular. The variation of the lattice constant or Curie temperature is remarkable. The magnetic permeability increases in Ni ferrite

Amount

o f

Additives

a t %

FIG. 4.

-

Lattice constants of Mg ferrite with alkaline earth metals.

(Fig. 2) and especially in Mg ferrite (Fig. 1). As the amount of Ca increased above 4 at

%

another phase Ca2Fe20, was confirmed with Ni ferrite and Zn ferrite by X-ray diffraction. Another phase, SrFe,O,, was also found by adding Sr above 2 at

%

to Zn ferrite.

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BEHAVIORS OF ADDITIVES IN FERRITES C1-177

0 1 2 3 4 5 h

Amonnt

of

; \ d c l i t i v c s

a t %

FIG. 5. - Lattice constants of Ni ferrite with IIIb group metals.

especially In raised the permeabilities of both Ni ferrite and Mg ferrite. In addition, insoluble B was more effective than Ga. B lowered the electric resistance remarkably. It was observed that the intensity of the diffraction pattern obtained from the surface of sintered body decreased extremely when B and A1 were added to Zn ferrite.

3 . 4 IVb GROUP METALS.

-

IVb group metals are little effective for the lattice constant or Curie temperature in Ni ferrite or Zn ferrite. Therefore the solubility is very small if any. Sn is probable among them. As well as in the case of IIlb group the lattice constant and Curie temperature of Mg ferrite were

somewhat complicated because of the deviation of magnesium content of the starting ferrite. The com- sumption of excess magnesium in Mg ferrite by the interaction between additives and ferrite was shown in the rise of Curie temperature by adding Si or in the decrease of the lattice constant by adding Ge. The variation of the lattice constant showed the possibility of a slight solubility of Sn. It is evident that Pb is insoluble in any ferrite. The addition of Pb improves the permeability especially in Ni ferrite (Fig. 2). The electric resistance also dropped sud- denly by adding Pb. These variation caused by pro- motion of sintering as a result of adding Pb.

3.5 Vb GROUP METALS.

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From the lattice constant and Curie temperature, it is confirmed that this group is insoluble except a slight solubility of Sb in Mg ferrite or Zn ferrite. Bi improved the permeabilities of both Ni ferrite (Fig. 2) and Mg ferrite (Fig. 1). This effect is similar to that of Pb.

3 . 6 IJla GROUP TRANSITION METALS. - The lattice constant increased by adding Sc in any ferrite. Except a very slight increase by adding Y in Mg ferrite, Y and La were not effective for the lattice constant. The observation by an electron probe micro analyser also showed that Y and La are insoluble in the spinel lattice. The variation of Curie temperature was also observed in Mg ferrite remarkably. Lowering of Curie temperature by Sc is due to the formation of the solid solution. When Y was added to Mg ferrite, a n anomaly of the temperature dependency of the magnetization was observed near the Curie temperature as shown in figure 7. It is considered that such anomaly is caused by the ununiformity of magne-

700

400 Temperature

O

C

FIG. 7. - Temperature dependency of magnetization of Mg ferrite when 1 at % of Y was added. An anomaly was observed near the Curie temperature. In an ordinary case magnetization

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CI-178 J. TASAKI AND T. IZUSHI sium distribution in the spinel lattice resulted from

addition of Y. A small amount of Y increases the magnetic permeability of Mg ferrite remarkably (Fig. 1).

3 . 7 IVa GROUP TRANSITION METALS. - With

increasing the amount of Ti, another phase TiFeO, appeared with spinel phase. The formation of TiFeO, is most difficult in Mg ferrite in which the lattice constant increases with the amount of Ti. Curie temperature dropped by adding Ti in both Ni ferrite and Mg ferrite. By adding Zr, so far as the amount is small the single phase of the spinel is identified in each ferrite. With increasing the amount of Zr, the phase of ZrO, is identified. The observation with an electron probe micro analyser indicated the fine and uniform dispersion of ZrO,. This means Zr dissolved in ferrite appreciably at high temperature and it precipitated during cooling period. The steep increase of the electric resistance with increase of Zr was resulted from this dispersion of ZrO,. Hf is hardly effective in each ferrite.

3 . 8 V a GROUP TRANS~TION METALS. - Neither the formation of solid solution nor other crystalline phase was observed by adding V to each ferrite. The magnetic permeability of Ni ferrite increased steeply by adding V below 1 at

%,

but it decreased steeply with increasing the amount of V (Fig. 1). The electric resistance dropped and rose corresponding to the variation of the permeability. By adding Nb or Ta, another phase FeNbO, or FeTaO, with Ni ferrite and Mg5Nb40,, or Mg,Ta,O,, with Mg ferrite were identified by X-ray diffraction. The formation of other phase in Mg ferrite caused the rising of Curie temperature by the consumption of excess magnesium. The lattice constant showed the solubility of Nb and Ta in Zn ferrite.

3 . 9 VIa GROUP TRANSITION METALS. - Cr is soluble in any ferrite. A decrease of the lattice constant was found in each ferrite. It was most in Zn ferrite.

In Mg ferrite the effect of dissolution of Cr in the spinel lattice and that of consumption of excess magnesium by added C r appeared in the same time. Mo formed another phase MgMoO, with Mg ferrite and W formed another phase NiWO,, MgWO, and ZnWO, with each ferrite respectively.

4. Summary. - 1) The soluble additives in each ferrite are as follows,

Ni ferrite :

-

Na*, Be*, Mg, Ca, Al, Ga, In, Si*, Sn*, Sc, Cr,

Mg ferrite :

-

Li, Na, Mg, Ca, Sr*, Ba*, Al*, Ga, In, Sb*, Sc, Y*, Ti, Cr,

Zn ferrite :

-

Li, Na, Mg, Ca, Al, Ga, In, Sn, Sc, Nb, Ta, Cr,

* small amount.

2) Several additives form other phases in addition to the spinel phase. They are as follows,

Ni ferrite : - Ca,Fe,O,, TiFeO,, FeNbO,, FeTaO,, NiWO,,

Mg ferrite : - TiFeO,, Mg5Nb4015, Mg,Ta4015, MgMo04, MgWO4,

Zn ferrite : - Ca2Fe,05, SrFe,O,, TiFeO,, ZnWO,.

3) Several additives soluble in the spinel lattice improve the magnetic permeability. They are as follows,

Ni ferrite : - Na, Ca, In, Ga*, Mg ferrite : - Li, Ca, In, Ga*, Y + ,

*

slightly, f by addition of small amount.

4) Several additives insoluble in the spinel lattice improve the magnetic permeability. They are as follows,

Ni ferrite : - B, Pb, Bi, V+, Nb*t, Mo, Wt, Mg ferrite : - B*, Pb*, Bi, Mot, W*+,

*

slightly,

t

by addition of small amount. References

[I] AKASHI, T., Trans. Jupan Inst. Met. 2 (1961) 171 ;

AKASHI, T. and ONODA, Y., J . Appl. Phys. Japan 30 (1961) 597 ;

AKASHI, T., J. Appl. Phys. Japan, 30 (1961) 708.

[2] SUGIMOTO, M. and TAKEI, T., Sci. Papers Inst. Phys. Chem.

Res. 54 (1960) 21 2 ;

KOJIMA, H. and SAKAI, K., J. Japan Inst. Met. 30 (1966) 640

in Japanese.