Thermodynamic properties of KDP single crystal are discussed in terms of microscopic model which includes a fluctuation concept. In fitting experimental data of spontaneous shear strain in ferroelectric state, the Curie and transition temperatures are used to reduce two free fitting parameters and one additional parameter which characterizes correlation length is used. Including quantitative correlation concept the anomalous behavior of specific heat near transition temperature, the rounding peak of transverse susceptibility near Tc, the expansion along z-axis near Tc, and domain freezing effect near 90K can be explained.
The calculation of longitudinal susceptibility with this model gives very small quantity in ferroelectric state. However in experimental data domain motion gives very large effects. To estimate this contribution an R-C circuit experiment is performed and analyzed in terms of simple damped harmonic oscillator to give susceptibility and dissipation. Comparison of these calculations to direct measurement shows the contribution of domain motion.
A novel deconvolution algorithm is developed, which do not specify the functional forms of output spectrum and instrumental function but use only numerical data as observed. Some merits of the algorithm include: divergence problem is avoided by iterative methods of treating data in the order of magnitudes, background and delta function type elastic components are treated automatically as part of the built-in signal, and very low level signals can also be retrieved from the strong background.
Brillouin scattering experiments are performed about fluids, methanol, tetra chloride and water, with single mode Ar-ion laser and Fabry-Perot interferometer. The data are deconvoluted with the previous algorithm and analyzed in terms of simple Lorentzian shape.
