Improving photostriction of KNN-based ceramics by MnO 2 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  m 2 /W) for KNN-based ceramics by adding appropriate amount ( x  = 0.5 wt%) of MnO 2 as sintering additives into 0.97(K 0.5 Na 0.5 )NbO 3 -0.03(La 0.51 Na 0.49 )(Zr 0.54 Ni 0.46 )O 3 (97KNN-3LNNZ) ceramics. The appropriate amount of MnO 2 ( 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 Mn 2+ and Mn 3+ in KNN-based ceramics. The addition of MnO 2 increases energy band gap and also optimizes the optical absorption properties in the near-infrared band. 97KNN-3LNNZ+0.5 wt% MnO 2 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 F 2g 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.