Converse piezoelectric effect in cellulose I revealed by wide-angle X-ray diffraction.

The converse piezoelectric effect in cellulose I was studied by exposing thin pine wood slices to an electric field. Macroscopically, a strong extension of wood was observed in its transverse anatomical direction (grain angle 90°), perpendicular to the direction of the electric field. The same effect, albeit to a lesser extent, was observed for specimens with a 45° grain angle, whereas no measurable dimensional change was observed for specimens with grain oriented parallel to the testing direction (0° grain angle). The measured extension in the transverse direction was proportional to the intensity of the applied electric field and amounted to 0.0278% on average at a field intensity of 1 MV m−1, which results in a piezoelectric charge constant of 278 pm V−1. At the nanoscale, changes in the cellulose crystallites due to the applied electric field were studied by means of wide-angle X-ray diffraction using the same specimens as in macroscopic experiments. Significant radial shifts of the scattering intensi...