Study of nanostructural behavior and transport properties of BaTiO3 doped vanadate glasses and glass-ceramics dispersed with ferroelectric nanocrystals

Nanostructural behavior and electrical properties of BaTiO3-(100-x)V2O5 glasses (where x = 35, 40, 45 and 50 mol%) and their corresponding nanocrystalline glass-ceramics were studied. Scanning electron microscopy (SEM) of quenched glasses, confirm the amorphous nature of the glasses present. Also, the overall features of X-ray diffraction (XRD) confirm the amorphous nature of the present glasses. Transmission electron micrograph (TEM) and XRD of the corresponding heat treated sample indicate nanocrystals with a particle size of 20-35 nm. It was found that density (d) increases gradually with the increase of the BaTiO3 content in the nanocrystalline glass-ceramics. It is observed that the conductivity of the nanocrystalline glass-ceramics is higher than that of the corresponding glassy phase. The high conductivity of these narrocrystalline glass-ceramics is considered to be due to the presence of nanocrystals with a particle size of 20-35 nm. This is attributed to the formation of extensive and dense network of electronic conduction paths which are situated between V2O5 nanocrystals and on their surface. The electrical conductivity of this system can be fitted with Mott's model of nearest neighbor hopping at high temperature. From the best fits, reasonable values of various small polaron hopping (SPH) parameters are obtained. From dielectric permittivity of the as-cast glass samples, no ferroelectric behavior can be observed. Also, the dielectric permittivity (epsilon) values of these glasses are found to be very high compared to familiar vanadium containing glasses. By annealing the glass system around 450 degrees C for 1 h in air, nanocrystalline BaTiO3 phase precipitates and the corresponding nanocrystalline glass-ceramics showed average broad peak around 352 K in the dielectric permittivity (epsilon). It is interesting to note that pure nanocrystalline BaTiO3 phase with average particle size less than 100 nm also shows ferroelectric phase transition around this temperature as predicted from the dielectric permittivity measurements. This observation of these glass-ceramics nanocrystals can be utilized to control BaTiO3 particle size and hence transition temperature by proper adjustment of annealing time and BaTiO3 content. Such a feature can be used for industrial applications where the shape of the application article is a necessary requirement. Published by Elsevier B.V.