Synchrotron-radiation x-ray multiple diffraction applied to the study of electric-field-induced strain in an organic nonlinear optical material

In this work, distortions produced in the unit cell of a MBANP [(-)-2-(a-methylbenzylamino)-5-nitropyridine] nonlinear organic crystal under the influence of an applied electric field, E?, are investigated by using synchrotron-radiation x-ray multiple diffraction (XRMD). The method is based in the inherent sensitivity of this technique to determine small changes in the crystal lattice, which provide peak position changes in the XRMD pattern (Renninger scan). A typical Renninger scan shows numerous secondary peaks, each one carrying information on one particular direction within the crystal. The (hkl) peak position in the pattern, for a fixed wavelength, is basically a function of the unit cell lattice parameters. Thus small changes in any parameter due to a strain produced by E give rise to a corresponding variation in the (hkl) peak position and the observed strain is related to the piezoelectric coefficients. The advantage of this method is the possibility of determining more than one piezoelectric coefficient from a single Renninger scan measurement [L. H. Avanci, L. P. Cardoso, S. E. Girdwood, D. Pugh, J. N. Sherwood, and K. J. Roberts, Phys. Rev. Lett. 81, 5426 (1998)]. The method has been applied to the MBANP (monoclinic, point group 2) crystal and we were able to determine four piezoelectric coefficients: |d₂₁l=0.2(1)×10^-11CN^-1, |d₂₂|=24.8(3)×10^-11CN^-1, |d₂₃| =1.3(1)×10^-11CN^-1, and |d₂₅|=5.9(1)×10^-11CN^-1. The measurements were carried out using the SRS stations 16.3, Daresbury Laboratory, Warrington, UK. ©2000 The American Physical Society.