Coexistence of piezoelectricity and electric conduction in oxygen-deficient NaNbO3−δ sub-micron cubes

We have investigated the effect of oxygen vacancy on the structural and electrical properties of NaNbO3 sub-micron cubes. Through the Rietveld analysis and Raman scattering, we have confirmed that both NaNbO3 and oxygen deficient NaNbO3−δ have Pmc21 symmetry, which has no space-inversion. The oxygen vacancy seems to induce the change from the ferroelectricity of NaNbO3 to the piezoelectricity of NaNbO3−δ and the increase of electric conduction. This work may provide the plausible way to realize sub-micron-size lead-free piezoelectric semiconductors with perovskite structure, which should be quite useful for piezoelectric energy harvesting, switchable diode, and photovoltaic applications.