Abstract:
The Raman spectra on external vibrations of the crystal lattice in an ammonium chloride crystal in the temperature range close to the temperature of the order-disorder phase transition are measured. The temperature dependence of the parameters of the Raman spectral lines on TO- and LO-phonons is analyzed. It is shown that in the temperature range close to the temperature of the phase transition, the ordered and disordered phases coexist simultaneously. It is proposed that near the temperature of the phase transition, the ordered phase exists in the form of clusters of nanometer size. Using phonon confinement model, an estimate of the cluster size was made. In the region of phase transition temperature, the cluster size is units of nanometers, and the temperature dependence of the cluster size is close to linear. Measuring the degree of polarization Raman scattering of light made it possible to isolate the proportion of radiation of the ordered phase in the total intensity recorded in the experiment and correct the results of calculating the size of clusters.
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