The charged domain walls in ferroelectric materials exhibit intriguing physical properties. We examine herein the charged-domain-wall structures in Ca$_{3-x}$Sr$_x$Ti$_2$O$_7$ using transmission electron microscopy. When viewed along the [001] axis, the wavy charged domain walls are observed over a wide range ($>$5 $mu$m). In contrast, short charged-domain-wall fragments (from 10 to 200 nm long) occur because they are intercepted and truncated by the conventional 180$^{deg}$ domain walls. These results reveal the unusual charged domain structures in Ca$_{3-x}$Sr$_x$Ti$_2$O$_7$ and will be useful for understanding their formation process.
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