Ferroelectric domains in nitrobenzene-nitromethane solutions measured by hyper-Rayleigh scattering

Hyper-Rayleigh scattering (HRS) spectra were measured for liquid solutions of C6H5NO2 and CH3NO2 at T=300 K. The depolarized HRS spectra at small frequency shift are dominated by two components due to reorientation of the nitrobenzene molecules. One is a Lorentzian with spectral width nu1=0.16-0.45 cm(-1) and corresponding orientation relaxation time tau=33-12 ps. The second component is a narrow spike with spectral width <2 MHz and corresponding relaxation time tau>80 ns, attributed to HRS from slowly relaxing ferroelectric domains. The dipole order parameter g0=0.053+/-0.005, saturation parameter p=0.9+/-0.1, and volume V=20+/-6 nm3 for these domains in nitromethane were determined from measurements of the nitrobenzene-concentration dependence of the intensity ratio for these two spectral components. Orientation of the 230 nitromethane molecules within each domain is inhomogenous but highly ordered.