Molecular and impedance spectroscopy of Na 2 Mo 2 O 7 ceramics

The fine (i.e. 38 nm) powder of polycrystalline Na₂Mo₂O₇ was prepared by the high-temperature solid-state reaction technique. The formation of the compound in orthorhombic system is confirmed by preliminary structural analysis using X-ray diffraction (XRD) data. Spectroscopic studies of the compound have been carried out by vibration spectroscopy (Raman/FTIR) to understand its molecular structure at microscopic level. The complex impedance spectroscopy (CIS) technique has been used to study the electrical properties of the material as a function of frequency (10²–10⁶ Hz) at different temperatures (23–450^°C), and also to investigate the fundamental mechanism involved in the material. Impedance analysis also indicates that below 300^°C, the electrical conduction in the material is due to grain interior only. At and above 325^°C, the contribution of grain boundary is clearly evident. The electrical processes in the material are found to be temperature-dependent and are due to the relaxation phenomena in it. A frequency-dependent maximum of the imaginary electrical impedance is found to obey the Vogel–Fulcher law.