Temperature dependent dielectric relaxation and ac–conductivity of alkali niobate ceramics studied by impedance spectroscopy

Highlights: • The polycrystalline NaNbO₃ ceramics is successfully prepared by conventional solid state reaction method. • Structural analyses reveals the formation of pure NaNbO₃ having clean and regular orthorhombic grains with reasonable density (93 %) and least porosity. • The average grain size and surface coverage of the NaNbO₃ ceramic are 2.5 mm and 97.6 %, respectively. • The activation energy is estimated as 0.58 eV at 10 kHz and the NTCR behaviour is revealed from impedance studies. • The relaxation processes is non-Debye type in nature and the dominant conduction mechanism is the hopping mobility of mobile charge carriers. - Abstract: Sodium niobate (${NaNbO}_3$) ceramics is prepared by conventional solid state reaction method at sintering temperature $1150$ °C for 4 h. The structural information of the material has been investigated by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM). The XRD analysis of ${NaNbO}_3$ ceramics shows an orthorhombic structure. The FE-SEM micrograph of ${NaNbO}_3$ ceramics exhibit grains with grain sizes ranging between 1 µm to 5 µm. The surface coverage and average grain size of ${NaNbO}_3$ ceramics are found to be 97.6 % and 2.5 µm, respectively. Frequency dependent electrical properties of ${NaNbO}_3$ is investigated from room temperature to $500$ °C in wide frequency range (100 Hz–5 MHz). Dielectric constant, ac–conductivity, impedance, modulus and Nyquist analysis are performed. The observed dielectric constant (1 kHz) at transition temperature (400 °C) are 975. From conductivity analysis, the estimated activation energy of ${NaNbO}_3$ ceramics is 0.58 eV at 10 kHz. The result of Nyquist plot shows that the electrical behavior of ${NaNbO}_3$ ceramics is contributed by grain and grain boundary responses. The impedance and modulus spectrum asserts that the negative temperature coefficient of resistance (NTCR) behavior and non-Debye type relaxation in ${NaNbO}_3$.