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-(alph a-methylbenzylamino)-5-nitropyridine] nonlinear organic crystal under the i nfluence of an applied electric field, (E) over bar, are investigated by us ing synchrotron-radiation x-ray multiple diffraction (XRMD). The method is based in the inherent sensitivity of this technique to determine small chan ges in the crystal lattice, which provide peak position changes in the XRMD pattern (Renninger scan). A typical Renninger scan shows numerous secondar y peaks, each one carrying information on one particular direction within t he crystal. The (hkl) peak position in the pattern, for a fixed wavelength, is basically a function of the unit cell lattice parameters. Thus small ch anges in any parameter due to a strain produced by (E) over right arrow giv e rise to a corresponding variation in the (hkl) peak position and the obse rved strain is related to the piezoelectric coefficients. The advantage of this method is the possibility of determining more than one piezoelectric c oefficient from a single Renninger scan measurement [L. H. Avanci, L. P. Ca rdoso, S. E. Girdwood, D. Pugh, J. N. Sherwood, and K. J. Roberts, Phys. Re v. Lett. 81, 5426 (1998)]. The method has been applied to the MBANP (monocl inic, point group 2) crystal and we were able to determine four piezoelectr ic coefficients: \d(21)\ = 0.2(1) X 10(-11) CN-1, \d(22)\ = 24.8(3) X 10(-1 1) CN-1, \d(23)\ = 1.3(1) x 10(-11) CN-1, and \d(25)\ = 5.9(1) X 10(-11) CN -1. The measurements were carried out using the SRS stations 16.3, Daresbur y Laboratory, Warrington, UK.