Structure, ferroelectric, and dielectric properties of (Na1−2xCax)NbO3 ceramics

Abstract

Mimicking the scheme of incorporating La3+ to Pb(Zr1−xTix)O3, Ca2+ is used to substitute Na+ in the lead-free NaNbO3 compound, with A-site vacancy introduced to maintain charge neutrality. The anticipated relaxor behavior is expected to suppress the remanent polarization and improve the energy storage properties of NaNbO3-based ceramics. Specifically, (Na1−2xCax)NbO3 (x = 0.01, 0.02, 0.04, 0.08) ceramics were prepared with the solid-state method, and their structures and electric properties were investigated. X-ray diffraction and transmission electron microscopy reveal the existence of minor amount of CaNb2O6 second phase. Polarization vs. electric field hysteresis loop measurements verify the suppression of remanent polarization in compositions of x ≤ 0.04. The temperature-dependent dielectric tests indicate that both the relaxation and diffuseness parameters monotonically increase with Ca2+ content. The results demonstrate that the introduction of a smaller donor dopant and charge-compensating vacancies on the A-site in NaNbO3 is an effective strategy to disrupt the long-range dipole order.