X-ray structure of Cs-doped polyacetylene

The x-ray powder profile of heavily doped [(CH)${\mathrm{Cs}}_{\mathrm{y}}$ ${]}_{\mathrm{x}}$ is analyzed on the basis of three dimensionally ordered intercalate channels. Fifteen peaks representing 27 unique reflections are well described (positions and intensities) by a tetragonal pseudocell with ā=b¯=9.093 Å, c¯=7.950 Å containing 24 (CH) and 4 Cs units (y=0.167). The Cs and (CH) sublattices are actually incommensurate along c¯, with 6.46 undistorted (CH) units per Cs implying y=0.15. Reflections with nonzero L are significantly less intense than calculated neglecting the Debye-Waller factor, indicating large-amplitude c-axis thermal motion of Cs ions. The fractional linear in-plane dilation upon replacing K with Cs is within 20% of the corresponding value in graphite intercalates.