| Summary: | Metal oxide of manganese (Mn) and vanadium (V) are widely studied due to their
interesting fundamental physical properties. There were several works on Mn-V mixed
oxide done previously, but it still lacks comprehensive electrical studies on Mn-V
oxide system which can gives more information to describe the mixed oxide. In this
project, the investigation toward morphology, electrical conductivity, dielectric
properties and thermal diffusivity of the mixed oxides was carried out. The samples
were prepared by conventional solid state (SS) and mechanical alloying (MA) methods.
The samples were prepared with a ratio of 40 mol% of V2O5 and 60 mol% of 2MnO2
and were sintered at different sintering temperatures from 500 to 800oC and
characterized. In the meantime, samples of pure oxides, Mn and V were also prepared
to compare with the mixed oxides.
X-ray Diffraction confirmed that the samples prepared are multi phases and Rietveld
refinement method was employed to estimate the phase composition in each sample.
MA method successfully reduced the sintering temperature for the reaction to occur at
a much lower temperature compare to SS method. Also, the surfaces of the sample
were visualized using Field emission scanning electron microscopy (FESEM) and the
average grain size was calculated. From FESEM images, MA method produced very
fine particles in nano-scale while SS method in micro-scale.
The DC and AC conductivities of the samples showed the semiconducting behavior
because the electrical conductivity increases when temperature increased. The Mn-V
oxides have lower electrical conductivity as compare to the starting materials. Since the
samples are multi phases, hence the dielectric constant obtained is a contribution from
different phases. The polarization mechanism in this frequency region (40 to 1 MHz)
can be explained by interfacial and dipolar polarization. On the other hand, the spectra
of electric modulus and impedance of the samples successfully revealed the dielectric
relaxation process which cannot be observed directly from dielectric loss spectrum.
Equivalent circuit modeling was adopted to further describe and predict the electrical properties of the material. The samples were successfully fitted to single parallel RC
circuit or two parallel RC circuits connected in series.
The sample sintered at 500oC prepared using MA method gave the best dielectric
properties. This is possibly due to MA method reduces the particle size and increases
the grain boundary volume of the sample. Also, the MA series have better thermal
stability and gave higher thermal diffusivity compare to SS series where the heat from
energy dissipation can be easily transferred for the cooling process.
Lastly, a more comprehensive electrical and thermal study on Mn-V oxide system is
done and it can be a reference for future researchers.
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