Effect of Zn on dielectric properties of Mn-Zn spinel ferrite synthesized by coprecipitation

14958 
A. Yusmar et al./ Materials Today: Proceedings 5 (2018) 14955–14959 
not follow the applied field. As the frequency of the field continues to increase, at some stage, the space charge 
polarization will barely start to move before reversing and making virtually no contribution to the polarization and 
finally dielectric constant saturated. 
Fig. 3. (a) Frequency dependence of real dielectric constant, (b) Frequency dependence of imaginary dielectric constant, with various concentration of Zn. 
The Zn concentration dependence of dielectric constant is shown in Table 1. From Table 1, it is apparent that the 
dielectric constant for zinc rich (x = 0.5 - 0.8) decreases by increasing Zn concentration.
Table 1. Data on dielectric constant (ε
’
), imaginary dielectric constant (ε
”
), dielectric loss tangent (tanδ) and AC conductivity (σ) 
for Mn
1-x
Zn
x
Fe
2
O
4 
spinel ferrite at 25 kHz. 
x 
ε’ 
ε” tanδ 
σAC (10-4 
0.2 51 15 0.3 0.3 
0.3 149 247 1.6 3.4 
0.4 75 36 0.4 0.5 
0.5 147 229 1.5 3.2 
0.6 101 65 0.6 0.9 
0.7 88 52 0.5 0.7 
0.8 51 15 0.3 0.2 
Decreasing dielectric constant with increasing Zn concentration is due to reduction in average particle size. As a 
result, the surface area with high resistivity in grain boundary region increase along with poor contact with the 
neighboring grains [10]. The increase of grain boundary causes accumulation of charge carriers at the interface so 
that the dielectric polarization decreases when AC electric field is applied.
Another reason, the concentration 
dependent dielectric constant can be explained on the basis of the number of available Fe
2+
ions on octahedral sites. 
In x = 0.8, the number of ferrous ions is lower than in the other concentration of Zn at octahedral sites. As a result, 
the minimum polarization is possible. From Table 1, the minimum polarization it is observed for x = 0.8, this result 
in lower dielectric constant owing to the transfer electrons between the Fe
2+
/Fe
3+
ions. 
Table 1 shows the variation of dielectric loss tangent with various concentration of Zn. It can be seen that the 
maximum dielectric loss is observed at x = 0.3 and it decreased by increasing Zn concentration. In spinel ferrite, the 
dielectric and conduction mechanism are strongly related to each other. The dielectric loss tangent in spinel ferrite 
materials is related to the strong dielectric dispersion owing to interfacial polarization. Since the Zn concentration 
increases, the crystal sizes decreases, lowering the carrier mobility which reduces the energy storage mechanism. 
Hence the dielectric loss tangent is low at higher Zn concentration. 
The frequency dependence of AC electrical conductivity can be explained on the basis of Maxwell-Wagner and 
Koop’s model. From Table 1, it is observed that AC conductivity for zinc rich decreases with the increase of Zn 
b 
a 

 
A. Yusmar et al./ Materials Today: Proceedings 5 (2018) 14955–14959 
14959 
concentration. As the concentration of Zn
2+
ion in the synthesized increases some of Zn
2+ 
ions may occupy 
tetrahedral sites, resulting a migration of Fe
3+
ion to octahedral sites. The increases in concentration of Fe
3+
ions at 
octahedral sites increase the hopping rate of electron. Hopping of electrons between Fe
2+
and Fe
3+ 
ions on octahedral 
sites is responsible for conduction in ferrites [11]. Among all the samples, the maximum AC conductivity is reached 
for sample x = 0.3. In contrast, the lower AC conductivity obtained for the sample x =0.8 may due to the unviability 
of ferrous and ferric ions at B-sites. 

tải về 0.64 Mb.

Chia sẻ với bạn bè của bạn: