Significant differences in NaNbO3 ceramics fabricated using Nb2O5 precursors with various crystal structures

NaNbO 3 (NN)-based solid solutions show potential applications in energy storage capacitors, strain actuators, and electrocaloric cooling devices. However, NN ceramics with distinct structures, which are prepared using various Nb 2 O 5 precursors, have not been studied. In this work, two types of Nb 2 O 5 precursors were used, including coexisting orthorhombic and monoclinic phases (denoted as OM), and single orthorhombic phase (denoted as O). Phase structure, grain morphology, sintering characteristics, ferroelectric performance, dielectric properties , and thermal-expansion properties were systematically investigated. Rietveld refinement of XRD data revealed that synthesized and sintered samples showed different phase structures. The content of ferroelectric phase (Q phase, space group P2 1 ma) was 82.7% in synthesized NN-OM, whereas it was only 73.2% in synthesized NN-O; it was 33.8% in sintered NN-OM, while it was 18.6% in sintered NN-O. Raman spectra verified that the Q phase in NN-OM was more than that in NN-O. Curie temperature ( T c ) of NN-OM was 363 °C, whereas T c of NN-O was only 352 °C. Furthermore, compared with NN-O, NN-OM showed an inhomogeneous grain size distribution, lower optimum sintering temperature , higher phase transition temperature, stronger ferroelectric performance, and larger thermal-expansion displacement. Therefore, crystal structure of Nb 2 O 5 has a great influence on the structure and performances of NN ceramics.