Absence of a PbTiO3 phase transition in PbTiO3/BaTiO3 superlattices

We have performed X-ray diffraction and Raman spectroscopy on three PbTiO3/BaTiO3 superlattices (PTO/BTO) from room temperature (RT) to 600 degreesC. The superlattices were 4000 Angstrom thick and the modulation wavelengths Lambda, with equally thick layers of PTO and BTO, were 136, 187 and 357 Angstrom. The samples were laser deposited onto single crystal MgO substrates buffered with 50 Angstrom of SrTiO3 (STO). We observe no X-ray evidence of a phase transition in the PTO layers of these three superlattice samples up to 600 degreesC. This result was reinforced by X-ray modeling of the samples. We also monitored the E(ITO) or "soft" mode by Raman spectroscopy up to 550 degreesC and found only a linear decrease of mode frequency with temperature for all three superlattices: another sign that no phase transition is taking place in this temperature range. (C) 2001 Elsevier Science Ltd.