Structural and Electrical Transport Properties of NASICON type Na₃Zr_{2 - x}Ti_xSi₂PO₁₂ (x = 0.1-0.4) Solid Electrolyte...

The structural, resistivity, impedance, and dielectric studies of isovalent substituted Na₃Zr_{2 - x}Ti_xSi₂PO₁₂ (x = 0.1-0.4) NASICON type solid electrolyte materials is reported. The Rietveld refinement of X-ray diffraction patterns shows the monoclinic phase with space group of C 2/c for all the samples. The resistivity analysis shows the Arrhenius-type thermal conduction with an increase in activation energy with doping is explained based on decreased unit cell volume. Maxwell-Wagner-Sillars (MWS) relaxation and space charge or interfacial polarization models are used to explain the frequency and temperature-dependent variations of electric permittivity. The double relaxation peaks in the dielectric loss data show the two types of relaxation mechanisms of different activation energy. The real ( ${\epsilon }^{\text{'}}$ ) and imaginary ( ${\epsilon }^{\text{'}\text{'}}$ ) parts of permittivity are fitted using the modified Cole-Cole equation, including the conductivity term, which show the non-Debye type relaxation over the measured frequency and temperature range. The impedance analysis shows the contributions from grain and grain boundary relaxation. The fitting performed using the impedance and constant-phase element (CPE) confirm the non-Debye type relaxation. Moreover, the electric modulus analysis confirms the ionic nature having thermally activated relaxation and the scaling analysis shows a similar type of relaxation in the measured temperature range. The modified power law is used to understand the frequency dependence of a.c. conductivity data. The temperature dependence of exponent (s) in modified power law suggests the change in the conduction mechanism from near small polaron tunneling (NSPT) to correlated barrier hopping (CBH) above room temperature. The larger values of ϵ_r indicate these materials as a potential candidate for charge-storage devices.