The influence of an external electric field on the X-ray scattering of 2-methyl-4-nitroaniline, an organic crystal with nonlinear optical properties

The influence of an electric field on the X-ray scattering of the nonlinear optical organic crystal MNA (2-methyl-4-nitroaniline) has been studied, using a three-step pulsed alternating electric field. The field changes are synchronized with the gating to three different counting chains (the three-step modulation method). A field strength of 39 kV cm-1 induces 0.2% maximum variation in the integrated intensity and a small shift in Bragg angles (an inverse piezoelectric effect). A special electron density refinement method, which uses the differences between the zero- and applied-field intensities as observations, has been developed and applied in the interpretation of the results. (orig.)