Improving photostriction of KNN-based ceramics by MnO2 additive and polarization

The effects of sintering additives on photostriction properties have been rarely reported and the polarization effect of KNN-based ceramics on the photostriction characteristics remains uncertain. In the present work, a highly feasible approach has been adopted to obtain improved photostrictive coefficient (α = 2.4 × 10−9 m2/W) for KNN-based ceramics by adding appropriate amount (x = 0.5 wt%) of MnO2 as sintering additives into 0.97(K0.5Na0.5)NbO3-0.03(La0.51Na0.49)(Zr0.54Ni0.46)O3 (97KNN-3LNNZ) ceramics. The appropriate amount of MnO2 (x ≤ 0.5 wt%) in the ceramics does not alter the inherent multi-phase structure and results in uniform grain growth of the ceramics. The ferroelectricity and piezoelectricity can be optimized by the “softening” effect of Mn2+ and Mn3+ in KNN-based ceramics. The addition of MnO2 increases energy band gap and also optimizes the optical absorption properties in the near-infrared band. 97KNN-3LNNZ+0.5 wt% MnO2 ceramics show optimum overall performance. In addition to this, for x = 0.5 wt% sample, the power-dependent Raman spectra of ceramics measured before and after the electrical poling shows that the prior E-field poling can enhance the red shift corresponding to F2g bending vibration mode. Subsequently, there are changes in bond angle of elements induced by light in oxygen octahedron. These phenomena play active roles in getting a deep understanding of the underlying mechanisms of photostriction for ferroelectric ceramics.