Theoretical and experimental study of Ac electrical conduction mechanisms of KZn sub(1.5)P sub(2)O sub(7) compound

The KZn sub(1.5)P sub(2)O sub(7) compound was obtained by the solid-state reaction. Rietveld refinement of the X-ray powder diffraction pattern suggests the formation of a pure phase which crystallizes in the orthorhombic system. Vibrational study by means of Raman spectroscopy confirms the existence of the P sub(2)O sub(7) functional group. The material is characterized by impedance spectroscopy technique measured in the 209 Hz - 1 MHz frequency and 603 K - 721 K temperature ranges. The analysis of Nyquist plots reveals the presence of tow contributions. The Ac conductivity for grain contribution follows the universal Jonscher's power law. The frequency exponent s increase with increasing temperature, indicating that the non-overlapping small polaron tunneling (NSPT) is the appropriate conduction mechanism. Thermodynamic parameters such as the free energy for dipole relaxation Delta F, the enthalpy Delta H, and the change in entropy Delta S have been calculated.