Ferroelectricity driven by charge ordering in theA-site ordered perovskite manganiteSmBaMn2O6

Phase transitions in charge and orbital degrees of freedom occur successively in the $A$-site ordered perovskite manganite ${\mathrm{SmBaMn}}_{2}{\mathrm{O}}_{6}$ at ${T}_{\mathrm{CO}1}\ensuremath{\approx}370\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{CO}2}\ensuremath{\approx}190\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. To determine the $3d$ electronic state in each phase, we performed crystal structure analyses on a single-crystal sample at 150, 300, and 400 K using synchrotron x-ray diffraction. The results indicate that the charge and orbital ordering on the distorted and alternately tilted ${\mathrm{MnO}}_{6}$ octahedra should accompany electric polarization in each ${\mathrm{MnO}}_{2}$ layer. The stacking of the polarized ${\mathrm{MnO}}_{2}$ layers along the $c$ axis changes from a staggered configuration to a ferroic configuration at ${T}_{\mathrm{CO}2}$.