Soft mode SrTiO

High-resolution dilatometric measuranaits have revealed the appearance of anisotropy in the cubic-phase thermal strain in the precursive tempo-ature region for the soft-mode martensitic transformations in VsSi/ Ni-Al, In-Tl/ and SrTiOs In the case of Ni-Al and SiTiOs, the onset temperatures for the strain anisotropy are close to those at which the appearance of central peak behaviour occurs. 

Fig.l a Schematic view of the ferroelectric capacitor considered in [87], The epitaxy on SrTiOs is effectively taken into account by choosing the appropriate lattice parameter in the direction parallel to the interfaces, b Evolution of the energy as a function of the soft-mode I for different thickness of the ferroelectric film m. Symbols stand for the first principles results and lines present the results of a simpUfied electrostatic model. Reproduced with permission from [87]... 

Fig. 5.14 Temperature dependence of the soft mode in SrTiOs (Cowley 1977)...

The temperature dependence of the soft mode Eq. (5.76) has been studied in several oxide perovskites (among them in SrTiOs, BaTi03, PbTiOs and KTa03) by the neutron scattering, infrared reflectivity and Raman scattering (Fig. 5.14). 

In ionic lattices these shifted (off-central) impurities are known to be the electric dipoles. The indirect interaction of such dipoles via soft phonon mode of a dielectric host exists in the incipient ferroelectrics like KTaOs, SrTiOs, PbTe. It leads to following fixed sign interaction ... 

It should be noted that in the last years EuTiOs attracts a lot of attention of scientists. For instance, the comparative analysis of EuTiOs and SrTiOs has been performed recently. This analysis is based upon specific heat and soft phonon mode measurements. Refs. [23] and [24, 25] respectively. The obtained results made it possible for authors to ascribe new 282 K instability of EuTiOs to antiferrodistortive phase transition. 

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