ITC technique as a tool to monitor a new phase nucleation in LiF-Ti single crystals

Thermal treatment of LiF:Ti/sup 3+/ at temperatures close to the melting point in moist atmosphere causes the growth of new phase occlusions. Optical and electron microscopy and X-ray diffraction have shown that they are parallelepipeds and cubes of a FCC phase coherent with the host matrix. ITC spectra (in the range 100 to 380 K) support that the crystal behaves as a heterogeneous dielectric: in fact the occlusion growth is accompanied by the appearance of new ITC bands at the expense of the band due to the reorientation of dipoles built by Ti/sup 3+/ and two cation vacancies. OH ions play a key role in such a process as supported by isotopic substitution experiments with OD and by infrared absorption spectra. The nucleation kinetics have been studied in such a way, and the Maxwell-Wagner-Sillars model has been applied, to interpret the new ITC bands.<
>