Spontaneous and field-induced linear birefringence is measured at low temperatures on singledomained single crystals of weakly doped SrTi0,:Ca (x=0.002 and 0.007) in order to investigate polar ordering processes near to T,-4 and 18 K, respectively. In agreement with direct polarization measurements the size of mesoscopic polar nanodomains is determined within the framework of a nonlinear polarization optical response model. Quasi-first-order Raman scattering of soft and hard polar modes, TO,, TO, and TO,, is observed on local precursor nanodomains above T,. Below T, the change of the global symmetry from D,, to C,, is reflected by selection rules imposed on first-order Raman lines in various scattering geometries.
Microscopic calculations of the intrinsic radiative recombination probability B(ω,T) of Si have been performed to obtain the absolute values of the spectral distribution and of its temperature dependence. In these calculations we use the concepts of k⋅p theory, consider excitonic effects, and take into account the electron-phonon interaction. The calculated spectra are compared with measured absolute values of the intrinsic radiative recombination spectra obtained from forward biased Si p-i-n diodes and also with spectra obtained from the detailed balance theory of van Roosbroeck and Shockley [W. van Roosbroeck and W. Shockley, Phys. Rev. 94, 1558 (1954)]. Quantitative agreement is obtained for higher temperatures (about 300 K) and deviations for lower temperatures are critically discussed.
Temporal relaxation of the electric field-induced polarization in single crystalline PbMg,,,Nb,,,O, has been measured at temperatures 180 < T< 230 K and times up to lo4 s via polarization-optically induced linear birefringence, An'''. The data are excellently described within the framework of Chamberlin's dynamically correlated domain theory. Whereas activated Curie-von Schweidler-type cluster-flip behavior prevails in the paraelectric regime, T > 210 K, Kohlrausch-Williams-Watts-type domain wall relaxation characterizes the ferroelectric nanodomain state at low temperatures.
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