Study of the hyperfine structure, thermal stability and electric–dielectric properties of vanadium iron phosphate glasses

In the present study the thermal analysis, hyperfine structure and electric transport properties were investigated for the (60−X) P2O5 (20+X) V2O5 20Fe2O3 [PVF] (X=10, 15, 20, 30 and 40 mol%) glasses. The glassy state of the samples was characterized using DTA and Mössbauer spectroscopy. Two glass transition temperatures Tg1 and Tg2 were detected at the DTA traces of the investigated system. The glassy sample with X=20 mol% (PVF3) is of the highest glass thermal stability where ΔT=177±2 K. Also, it has the highest value of crystallization activation energy for the first and the second crystallization peaks (305 and 316±3 kJ/mol%) among the other samples. The obtained ME spectra showed the presence of Fe3+ alone located in the tetrahedral and octahedral sites. Increasing V2O5 content, the dc conductivity increases while the activation energy decreases. The room temperature dc conductivity is typically 2.9×10−7–2.5×10−5 with an activation energy 0.60–0.37±0.011 eV. The power law exponent s was found to be temperature dependent and exhibited a minimum, for PVF3 and PVF4. The dielectric constant ε1(ω) increases with increasing V2O5 content which was attributed to the increase in the deformation of glass network.