Crystallographic and microstructural studies of BaTiO3 thin films grown on SrTiO3 by laser molecular beam epitaxy J. Vac. Sci. Technol. A 15, 275 (1997); 10.1116/1.580524 BaTiO3 thin films grown on SrTiO3 substrates by a molecular-beam-epitaxy method using oxygen radicals Epitaxial ultrathin films of BaTiO 3 were prepared using molecular beam epitaxy. For the substrate, ͑001͒-oriented SrTiO 3 single crystals were used. Controlling the growth conditions of these films as well as the semiconductor thin films, led to the successful growth of the BaTiO 3 films as single crystals, characterized by x-ray diffraction even in the ultrathin range. The ultrathin BaTiO 3 films are highly c-axis-oriented tetragonal phaselike bulk BaTiO 3 crystals. The tetragonality of the thin film crystals is much larger than bulk crystal's. We also measured the saturated polarization ( Ps͒ of the BaTiO 3 films at temperatures ranging from room temperature to 600°C. The results confirmed again that the films are ferroelectric tetragonal phase crystals. Moreover, they showed that the transition temperature for the ferroelectric-paraelectric phase transition of the films is higher than bulk crystal's.

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Phase transition temperatures of hydrogen-bonded ferroelectrics DKDP ( KD2PO4) and KDP ( KH2PO4) vanish at pressure p larger than respective critical pressures p(c). The dielectric constants epsilon(c) has been observed to be suppressed with decreasing temperature for p>p(c) and analyzed as the quantum paraelectricity by fitting with the Barrett formula in terms of three parameters. The dependences of the three parameters on p-p(c) are found to be expressed by almost similar lines, and the phase transition mechanism near p(c) is explained from the viewpoint of an anharmonic phonon system in KDP and DKDP.