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ELECTRICAL AND THERMOELECTRIC PROPERTIES OF NANO

SIZED TITANIUM SUBSTITUTED MnZn FERRITE

Anup Kumar V and Vasudevan Nair N

Department. of Physics, M.G.College, Thiruvananthapuram.

Introduction

Soft ferrites have been used widely in many electronic devices, because of their excellent

magnetic, electric and thermoelectric properties. These properties of the magnetic

semiconductor ferrites are very sensitive to the chemical composition, type and amount of

additives, grain size, sintering temperature and time. TiO2 is a well known additive, broadly

used in the manufacture of power MnZn ferrite to vary their electric properties. The purpose

of this study is to investigate the effects of substitution of nanosized titanium in MnZn

ferrites. Here we have studied the electric, thermo electric and magnetic properties of Mn.5Zn.5

Tix Fe2-x O4 with x=0to.2 for different temperatures

Materials and Methods

Titanium substituted MnZn ferrites (Mn.5Zn.5 Tix Fe2-x O4 for x=0to.2) were prepared by solid

state reaction method with A R grade MnO, ZnO, Fe2O3 and TiO2 as starting materials. Here

TiO2 is nanosized (17nm) which was synthesized in our laboratory by tartarate gel method

from TiCl4 provided by KMML, Chavara.[S.R.Dhage,2004]. These constituent chemicals

were mixed in stoichiometric ratio for the corresponding compositions and the mixed powders

were grinded and calcinated at 970K for 10 hours. The samples were again grinded to fine

powder For measurement purpose the fine powder was made in to a paste by adding the

binder (polyvinyl alcohol) and then pressed into pellets and toroids and then sintered at a

temperature of 1370K in air for 18 hours followed by slow cooling to room temperature. The

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phase identification (Fig 1) is carried out by an automated X ray diffractometer. SEM

(JEOLJSM 5600) is employed to record and analyse the surface morphology (Fig 2) of the

samples. Electrical resistivity was measured by a four probe for different temperatures from

10 20 30 40 50 60 70

0

200

400

600

800

1000

Fig 1

Inte

nsity

2 Theta

Fig 2

310K to 440K Thermoelectric power was studied by measuring the seebeck voltage for

different temperatures from 310K to 440K by a two probe apparatus fabricated in our

laboratory. Magnetization studies were carried out by Vibrating Sample Magnetometer for

various temperatures from 80K to 300K. From this we obtained the Curie temperature Tc of

all the samples. Using toroids we measured the permeability μ of all the samples

Results and Conclusion

From resistivity studies it was found that the conductivity increases non linearly with the

temperature showing a hopping type of conduction. It was observed that the graph (Fig 3)

with log σ T against 1/T is a straight line indicates that the conductivity is by small polarons.

(σ is the conductivity, and T the temperature in absolute scale) The graph also shows that

there are two regions with two different slopes corresponding to different activation energies.

From this we found the transition temperature Tt of all the samples are greater than the

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corresponding Curie temperature Tc . The change in slope is due to change in activation

energy caused by the change in hopping of electrons between Fe2+ and Fe3+. The activation

energy of each sample E is calculated by using the equation σ =(A/T)exp(-E/kT) (Mott,1948),

where A is a constant, T the absolute temperature and k the boltzmann constant The decrease

in conductivity σ with the increase in Ti concentration are shown in Table 1.The particle size

D was calculated from the X-ray broadening technique as per the Debye Scherrer equation

D=.9λ / β cos θ (Cullity,1978) where λ is the wavelength of the radiation, β is the full width at

half maximum, and θ is the diffraction angle. It can be seen that the activation energy

increase with the increase in particle size. This is because, the particle with large size have

more well depth. Hence their activation energy is also high.

Table 1

Composition D

(nm)

σat 330 K(Ω-1 m-1)

E (eV)

n at 330 KX 1025

(m-3)

μ Tc

(K)Mn.5Zn.5Ti0Fe2O4 32.18 8.72 x 10-7 .43 5.39 4.207 298Mn.5Zn.5Ti.05Fe1.95O4 25.74 4.53 x 10-7 .33 6.8 3.144 293Mn.5Zn.5Ti.1Fe1.9O4 32.17 1.65x 10-7 .41 7.6 4.176 282Mn.5Zn.5Ti.15Fe1.85O4 32.16 1.62x 10-7 .40 8.6 3.196 270Mn.5Zn.5Ti.2Fe1.8O4 25.72 .1.27 x 10-7 .28 9.64 3.522 259

The thermoelectric power was calculated by using the relation S = ΔE/ ΔT where ΔE is the

thermo emf produced across the sample due to the temperature difference ΔT.As S has

positive sign these nano sized titanium substituted MnZn Ferrites are P type ferrites. The

charge carrier concentration of these ferrites were calculated by using the equation n=N exp

(-Se/k) (Morin, 1955) Where S is the seebeck coefficient, e the charge of an electron, k the

boltzmann constant and N the density of states or concentration of electronic levels involved

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2.2 2.4 2.6 2.8 3.0 3.2 3.4

-10

-9

-8

-7

-6

-5

-4

Fig 3

log(si

gma

T)

1000/T(1/K)300 320 340 360 380 400 420 440 460

0

2

4

6

8

10

Fig 4n x

10 ^2

6 (/m

3)T (K)

in the conduction process. In the case of ferrites N can be taken as 1028 m-3 (Ravinder, 2000)

Increase in n with the Ti concentration is given in Table 1. Variation of n with temperature is

shown in Fig 4. As there is a slope variation in n-T graph, here also the conduction

mechanism is the same as that in electric conduction.

References

Cullity B.D. (1978), Elements of X-ray diffraction, Addison Wesley Publishing Co Inc,Menlo park CA, p102

Dhage S.R et al, (2004), Synthesis of nanocrystalline TiO2 by tartarate gel method, Bull.Mater.Sci, 27, p487-489

Morin F.J., T.H.Geballe, (1955), Phys.Rev, 99 p467

Mott N.F, R.W.Gurney ,(1948), Electronic Processes in Ionic Crystals, Oxford University Press, Oxford

Ravinder D, (2000), Electrical conductivity and thermo electric power studies of aluminium substituted lithium ferrites, Materials Letters, 43, p 122-128

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