Origin of ferroelectricity in cubic phase of Hf substituted BaTiO3

The origin of ferroelectricity in the cubic phase of BaTi1-xHfxO3 has been investigated. The presence of well-defined ferroelectric PE hysteresis loop in the samples with global cubic symmetry suggests the presence of 'local polar regions', induced possibly due to the huge difference in the electronegativity and also difference in the ionic radii of Hf+4 and Ti+4 ions, which may lead to local structural disorder. The presence of polar regions is also supported through the appearance of A1(TO) polar mode in Raman spectra which in principle should be absent in the samples with cubic symmetry. The results are discussed in terms of disorder-induced local dipoles due to the electronegativity difference between Hf and Ti ions.