X-ray structure of Cs-doped polyacetylene
摘要
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 \ifmmode \bar{a}\else \={a}\fi{}=b\ifmmode\bar\else\textasciimacron\fi{}=9.093 A\r{}, c\ifmmode\bar\else\textasciimacron\fi{}=7.950 A\r{} containing 24 (CH) and 4 Cs units (y=0.167). The Cs and (CH) sublattices are actually incommensurate along c\ifmmode\bar\else\textasciimacron\fi{}, 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.