The recent observation of pyroelectricity in quasiamorphous thin films of BaTiO 3 introduced a previously unreported type of polar ionic solid where the appearance of a macroscopic dipole moment is not accompanied by long-range crystal-like order. This poses a question regarding the mechanism of polarity in noncrystalline ionic systems and the nature of their local dipoles. By combining x-ray diffraction and x-ray-absorption fine-structure spectroscopy techniques we have identified the local dipoles as stable but distorted TiO 6 octahedra. The magnitude of the off-center displacement of the Ti ion and the concomitant dipole moment in both quasiamorphous (polar) and amorphous (nonpolar) BaTiO 3 were found to be nearly twice as large as those in bulk BaTiO 3. We propose that the mechanism of macroscopic polarity in quasiamorphous BaTiO 3 is in a weak orientational ordering of the TiO 6 bonding units. In this view, one may expect that other amorphous ionic oxides containing stable local bonding units, for example NbO 6, TiO 6, or VO 6, may also form noncrystalline polar phases.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Jan 1 2005|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics