Effect of heat treatment on the hyperfine structure and the dielectric properties of 40P2O5–40V2O5–20Fe2O3 oxide glass

Oxide glass with a starting composition of 40P2O5–40V2O5–20Fe2O3 (mol%) is prepared by the usual melt quenching technique. The prepared sample is heat treated at 500 K for 4, 6 and 8 h. The effect of heat treatment on the hyperfine structure and dielectric properties is studied in more details. The hyperfine structure of these glasses is investigated using Mössbauer spectroscopy. The measured isomer shifts showed that, the ferric ions (Fe3+) are in octahedral and tetrahedral coordinations. The infrared spectra of these glasses is recorded over a continuous spectral range (400–1400 cm−1) as an attempt to study their structure systematically. The structure of these glasses has investigated by means of IR studies which shows the presence of ν(VO3) single chains, VO4 octahedral and VO5 trigonal bipyramids. Unmonotonic variation in the ac conductivity, σac(ω), the dielectric constant, ε1(ω), and the dielectric loss, ε2(ω), is found with increasing the HT time. The room temperature ac conductivities at a fixed frequency (10 kHz) of the as quenched and the heat treated for 4, 6 and 8 h samples are 1.4 × 10−4, 4.1 × 10−4, 1.7 × 10−5 and 4.15 × 10−6 (S cm−1), respectively. The ferroelectric transition temperature is shifted to lower temperature with increasing the HT time.