Journal of the Physical Society of Japan Vol. 69, No. 5, May, 2000, pp. 1423-1429 Physical Studies On Vitreous Na 2 O-TiO 2 -P 2 O 5 System Mervat G. El-Shaarawy ∗ and Fayza A. Radwan 1 Physics Department, Faculty of Science, Benha University, Benha, Egypt 1 Physics Department, Faculty of Science, Helwan, University, Cairo, Egypt (Received November 12, 1999) Three glasses of Na 2 O-TiO 2 -P 2 O 5 system were prepared by melting the appropriate amounts of Na 2 CO 3 , TiO 2 and (NH 4 ) 2 HPO 4 in an open crucible. The DTA thermal analysis showed crys- tallization 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 ere formed after annealing. The framework of the as found to be made of PO 4 , TiO 4 tetrahedral groups as well as TiO 6 entities that coexist with sodium modifier ions. TiO 2 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 10 6 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 σ ac (ω)= Aω s , where s has a value in the range 0.4–0.8 depending on the temperature and the composition of the sample. The tem- perature 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. KEYWORDS: electrical conductivity, dielectric loss, phosphate glasses, dielectric constant w glasses w glasses §1. Introduction The electrical properties of phosphate glasses have at- tracted much attention because of their scientific inter- est and technological applications. 1, 2) Some phosphorus glasses are suitable for insulating dielectric layers 3) in de- vices such as integrated circuit. In order to understand the nature of the electronic states and charge transport in the phosphate glasses, both structural analyses and experiments concerned with electrical properties have been performed on a variety composition of phosphate glasses. 4-6) The structural information obtained from the tradi- tional techniques of solid state physics 7) have shown that, in phosphate glasses, the phosphorus is attached by cova- lent bonds to four oxygen atoms, which lie at the corners of a tetrahedron. The PO 4 tetrahedral groups are then linked together to form the “network” or “backbone” of the glass structure. When different cations are added to phosphate network, either the phosphorus atoms are replaced by the new cations, or, the cations enter the interstitial positions of the phosphate network. In the first case, the infrared spectra show graduate shifts in the characteristic band group frequencies of phosphate. While in the second case, new spectral bands may ap- pear corresponding to the vibration character of charged structural units formed in the glass matrix. In the phos- phate glasses the metal cations are usually rather weakly ∗ To whom correspondence should be sent. 1423 The corresponding mixtures were taken in the ratio of their molecular weights and heated in a platinum cru- cible first at 500 K for 30 hours and then at 1400 K for one hour. The materials were then quenched to room temperature in air. Half the amounts of the materials ob- tained were annealed at 900 K (above the crystallization temperatures) for 4 hours. All virgin and annealed glass bonded to the non-bridging oxygen of the tetrahedral units. The aim of the present study was to prepare three dif- ferent glassy samples of (Na 2 O) x -(TiO 2 ) y -(P 2 O 5 ) z and to investigate their structures and electrical properties (conductivity σ, dielectric constant ε ′ and dielectric loss ε ′′ ) before and after heat treatment. The effect of the addition of Ti + 4 ion on the structure and the electrical properties of phosphate glasses was one of our target. This study is also essential for obtaining materials with specified electric properties. §2. Experimental Three glasses (G 1 ,G 2 and G 3 ) having molar compo- sitions of (Na 2 O) x -(TiO 2 ) y -(P 2 O 5 ) z : (for G 1 : x = 37.1, y = 35.0, z = 27.9; G 2 : x = 44.5, y = 22.2, z = 33.3 and G 3 : x = 50.0, y =5.0, z = 45.0) were prepared from laboratory reagent grades of analar (NH 4 ) 2 HPO 4 , TiO 2 and Na 2 CO 3 according to the following equation: xNa 2 CO 3 +yTiO 2 +2z(NH 4 ) 2 HPO 4 -→ [xNa 2 O+yTiO 2 +zP 2 O 5 ]+4zNH 3 +3zH 2 O+xCO 2 molten