Abstract
Three glasses of Na2O-TiO2-P2O5 system were prepared by melting the appropriate amounts of Na2CO3, TiO2 and (NH4)2HPO4 in an open crucible. The DTA thermal analysis showed crystallization temperature decreases with increasing sodium content in the sample. The structures of the virgin and annealed glasses (at 900 K for 4 h) were studied using FT-IR, X-ray diffraction (XRD) and scanning electron microscope (SEM). Different crystalline phases depending on the compositions of the glasses were formed after annealing. The framework of the glasses was found to be made of PO4, TiO4 tetrahedral groups as well as TiO6 entities that coexist with sodium modifier ions. TiO2 enters the structure in tetrahedral or octahedral coordination in all samples. The temperature dependence of electrical conductivity, dielectric constant and dielectric loss for the virgin and annealed glasses is studied over a temperature range between 300 and 600 K and at a frequency from dc to 106 Hz. Many breaks, depending on both the composition and heat treatment of the samples, are observed on the plots of ln σ vs. 1/T. The conductivity increased by annealing and the results were explained on the basis of hopping Na+ ions in the glass matrix. The ac-onductivity increased with frequency according to σac(ω)=Aωs, where s has a value in the range 0.4--0.8 depending on the temperature and the composition of the sample. The temperature dependence of the dielectric constant showed that at relatively lower temperatures the electric dipoles formed in the glasses are frozen and starting to rotate at higher temperatures. Each of ε′ and ε′ ′ was found to be dependent on the composition and the crystalline phases formed in the matrix. All the results have been discussed and correlated together.
