Is Second Harmonic Generation a reliable tool for studying solid-solid phase transition and structural purity?

Abstract : The second harmonic generation (SHG) is a nonlinear optical effect occurring only in noncentrosymmetric space groups. Two photons (at the fundamental angular frequency ω) can interact in a noncentric crystal structure to give a new photon at twice the fundamental frequency (2ω). In previous studies, we demonstrated that the measurement of the intensity of the signal at 2ω (SHG signal) is a very sensitive probe to detect the noncentrosymmetry of crystal arrangements such as conglomerates [1]. This technique was also used, in rare occasions, to follow centrosymmetric to noncentrosymmetric solid-solid phase transitions [2], [3]. Because of the origin of the SHG signal, only centric to noncentric or noncentric to noncentric phase transitions can be investigated via SHG. However, SHG has proved to be highly sensitive even to a slight deviation from centrosymmetric conditions and could be used to detect noncentric nuclei and as a consequence to follow the nucleation of new phases. This could give great information about the order of the transition (as defined by Ehrenfest classification). Indeed, if the transition is of the first-order kind the signal should be discontinuous at the temperature transition but continuous in the case of a second order transition. In this study, we present the results obtained using a device developed to perform SHG measurements versus temperature for the solid-solid phase transition (from centrosymmetric to noncentrosymmetric structures) of several compounds. The case of 3-Hydroxybenzoic Acid is particularly considered. MHBA is an intermediate in the production of germicides, plasticizer and pharmaceuticals and exhibits two polymorphic forms [4] one of which is noncentrosymmetric. Finally, we evaluate the potential of the SHG signal measurements to follow phase transitions by comparison with other usual techniques such as Differential Scanning Calorimetry (DSC), X-Ray Diffraction or Raman Spectroscopy. REFERENCES [1] A. Galland, V.Dupray, B.Berton, S. Morin-Grognet, M. Sanselme, H. Atmani and G.Coquerel, “Spotting Conglomerates by Second Harmonic Generation,” Crystal Growth & Design, vol. 9, no. 6, pp. 2713–2718, Jun. 2009. [2] J. P. Dougherty and S. K. Kurtz, “A second harmonic analyzer for the detection of non- centrosymmetry,” Journal of Applied Crystallography, vol. 9, no. 2, pp. 145–158, Apr. 1976. [3] L. Smilowitz, B. F. Henson, and J. J. Romero, “Intercomparison of Calorimetry, Raman Spectroscopy, and Second Harmonic Generation Applied to Solid−Solid Phase Transitions,” The Journal of Physical Chemistry A, vol. 113, no. 35, pp. 9650–9657, Sep. 2009. [4] F. L. Nordström and Å. C. Rasmuson, “Polymorphism and thermodynamics of m- hydroxybenzoic acid,” European Journal of Pharmaceutical Sciences, vol. 28, no. 5, pp. 377– 384, Aug. 2006.
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Soumis le : mardi 24 septembre 2019 - 14:49:21
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  • HAL Id : hal-01942447, version 1


S. Clevers, V. Dupray, Florent Simon, G. Coquerel. Is Second Harmonic Generation a reliable tool for studying solid-solid phase transition and structural purity?. XXXVIII èmes JEEP, Mar 2012, Rouen, France. ⟨hal-01942447⟩



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