Diffusion theory of slow responses

When an action is applied to a macroscopic substance, there is a particular sort of slow response besides the well-known fast response. Using diffusion theory, the characteristics of slow response in dielectric, elastic, piezoelectric, and pyroelectric relaxation may be explained. A time domain spectroscopy method suitable for slow and fast responses in linear and nonlinear effects is given. Every relaxation mechanism contributes a peak in differential spectroscopy, and its position, height, and line shape show the dynamical properties of the mechanism. The method of frequency domain spectroscopy is suitable only for linear fast response. Time domain spectroscopy is another nonequivalent powerful method. The theory is confirmed by a lot of experimental data. Project supported by the National Natural Science Foundation of China and the Science Foundation of Zhongshan University.