The structure of the incommensurate phase of ${\mathrm{NaNo}}_2$ at 162.5 °C is elucidated using x-ray data collected by Böhm [Z. Kristallogr. 148, 207 (1978)]. The analysis is based on the four-dimensional super-space-group $P_{1¯s1}^{\mathrm{Immm}}$, and shows that the sinusoidal modulation of the dipole moment of ${\mathrm{NO}}_2$ is accompanied by displacive modulation. The displacement wave is a transverse acoustic mode with the wave vector k→∼0.1a${\to }^{\mathrm{*}}$, the amplitude of which is parallel to the b axis. This is in phase with the modulation wave of the dipole moment in accordance with theoretical expectation.

• Received 7 February 1985

DOI:https://doi.org/10.1103/PhysRevB.31.5941