Structural evolution, dielectric and energy storage properties of Na (Nb1-xTax)O3 ceramics prepared by spark plasma sintering

Phase pure NaNb1-xTaxO3 ceramics have been successfully prepared by spark plasma sintering (SPS) process at 950-1150 degrees C. The structural evolution, dielectric and energy storage properties as a function of Ta-doping level were studied by X-ray diffraction (XRD) Rietveld refinement, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, scan electron microscopy (SEM) and ferroelectric analyzer. It was found that small level of Ta-doping induced the stabilization of ferroelectric phase from antiferroelectric NaNbO3, while high level of doping induced further transition from ferroelectric to paraelectric phase. The doping of Ta led to the decrease in Tc and dielectric loss. The NTN4 and NTN6 composition exhibited enhanced dielectric response due to the coexistence of ferroelectric/antiferroelectric or paraelectric phases. The presence of oxygen vacancies in the sintered body were confirmed, which gave rise to the loss at high temperature. The doping of Ta decreased the concentration of oxygen vacancies. Maximum energy density of -0.9 J/cm(3) could be obtained for x = 0.6 composition with the BDS of -similar to 160 kV/cm and efficiency of similar to 87%.