Charge Ordered States inLa1−xSrxFeO3

The presence of complex charge ordering (CO) phenomena in ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{FeO}}_3$ $\left(0\le x\le 0.7\right)$ has been revealed by transmission electron microscopy at low temperatures. In ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{FeO}}_3$ $(x=0.3\mathrm{})$ the precursory CO reflections become visible as streaks at $\sim 250\mathrm{K}$ upon cooling. Below 150 K these streaks condense to sharp spots at the systemic $(\frac{1}{2},0,0\mathrm{})$ positions. The real-space images are suggestive of charge segregation occurring at low temperatures. At high doping levels $\left(0.5\le x\le 0.7\right)$, the CO has been observed in the $〈111{〉}_{\mathbf{p}}$ direction below $\sim 200\mathrm{K}$. In particular, the results obtained ${\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7}{\mathrm{FeO}}_3$ $(x=0.7\mathrm{})$ can be well understood in terms of CO in sequence $\dots {\mathrm{Fe}}^{3+}{\mathrm{Fe}}^{3+}{\mathrm{Fe}}^{5+}{\mathrm{Fe}}^{3+}{\mathrm{Fe}}^{3+}{\mathrm{Fe}}^{5+}\dots$, as proposed previously.