en Research Paper Research Paper <div style="text-align: justify;">Phosphate glass with different Al₂O₃ and Na₂CO₃ compositions [80NaH₂PO₄-(20-x) Na₂CO₃-xAl₂O₃ with a step from 0 to 4] were prepared through melt quenching technique furnace at 900 &deg;C. In order to determine the structure and microstructure modification of the samples after heat treatment the IR and Raman spectroscopy were performed. The X-ray diffraction (XRD) result shows an amorphous character of the prepared glass. The result obtained by differential scanning calorimetry (DSC) reveals a good thermal stability in the temperature range of 25 to 400 &deg;C. The impedance Nyquist diagrams were investigated and modeled by resistors and constant phase elements (CPE) equivalent circuits. These measurements show a non-Debye type dielectric relaxation. Both AC and DC conductivity, dielectric constant, and loss factors were determined. Thermal activation energies were also calculated. A changes in the electrical conductivity and activation energy depend upon the chemical composition were observed. Also, a transition in the conduction mechanism from ionic to mixed ionic polaronic was noted. In the same line, electrical modulus and dielectric loss parameters are also deduced. Their frequency and temperature dependency exhibited relaxation behavior. Likewise, activation energies value obtained from the analysis of M&rsquo;&rsquo; and those obtained from the conductivity are closes, which proves the optimal character of the preparation conditions.</div> ,Phosphate glasses,Nyquist diagrams,X-ray diffraction,Conductivity,Activation energy,Thermal properties 1 14 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-4018-1&slc_lang=en&sid=1 Nihel Hsouna 1800319475328460015092 1800319475328460015092 No 1Laboratory of Physico-Chemistry of Mineral Materials and their Applications, National Center for Research in Materials Sciences, Borj Cedria Technopark, BP 73, 8027 Soliman, Tunisia Mohsen Mhadhbi mohsen.mhadhbi@inrap.rnrt.tn 1800319475328460015093 1800319475328460015093 Yes Laboratory of Useful Materials, National Institute of Reserach and Physicochemical Analysis Chaker Bouzidi 1800319475328460015094 1800319475328460015094 No Laboratory of Physico-Chemistry of Mineral Materials and their Applications, National Center for Research in Materials Sciences, Borj Cedria Technopark, BP 73, 8027 Soliman, Tunisia