1：Experimental Design and Method Selection:

The NBN nano-powders were prepared by a novel sol–gel method, involving the transformation of Nb2O5 into a water-soluble species and the use of ethanolamine to prevent the hydrolysis of Bi3+ ion.

2：Sample Selection and Data Sources:

Raw materials included Nb2O5, KOH, Na2CO3, Bi(NO3)3·5H2O, acetic acid, oxalic acid, citric acid, nitric acid, ammonia, and ethylene glycol.

3：List of Experimental Equipment and Materials:

X-ray diffraction (XRD, Bruker D8 Advance), transmission electron microscope (TEM, FEI Tecnai F20), scanning electron microscopy (SEM, Hitachi S4800), multi-frequency inductance capacitance resistance (LCR) analyzer (Agilent E4980A), ferroelectric tester (Premier II, Radiant Technologies Inc.), piezoelectric d33 metre (ZJ-6A).

4：Experimental Procedures and Operational Workflow:

The sol was heated to prepare dried gels, which were then calcined at various temperatures to obtain NBN nano-powders. These powders were pressed into pellets and sintered to obtain dense ceramics.

5：Data Analysis Methods:

The crystal structures were examined by XRD, morphology by TEM and SEM, dielectric properties by LCR analyzer, ferroelectric properties by ferroelectric tester, and piezoelectric properties by d33 metre.