Single-domain BFO thin films are prepared on a SrRuO3-buffered SrTiO3 (STO) (001) substrate by RF planar magnetron sputtering. A domain structure is controlled by vicinal direction of the STO substrate. The BFO thin films on vicinal STO along <110> show single-domain structure without any domain walls. To confirm the influence of epitaxial strain on lattice distortion and ferroelectricity, single-domain BFO thin films with thicknesses ranging from 10–1000 nm are prepared. Synchrotron X-ray diffraction reveals that lattice relaxation and step bunching occur in the thickness range of 50–200 nm. The BFO films with thicknesses over 300 nm are almost free from the influence of the epitaxial strain induced by (001)-oriented substrates. The remanent polarization P r is almost constant at about 60 µC/cm2. However, P r slightly increases in the BFO films with thicknesses less than 200 nm. Even the 100-nm-thick BFO film show fully saturated D–E hysteresis at RT, and the P r is 65 µC/cm2.

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Titanium aluminide intermetallic compound is studied to find out good welding conditions using CO2 laser irradiation. In the experiment, we used the casting titanium aluminide containing iron, vanadium and boron with a thickness of 2 mm. We carried out bead-on-plate laser welding at various initial temperatures of specimens varied from room temperature to 873 [K] in inert gas environment filled with argon. We measured fused depth, bead width and Vickers hardness. As a result of experiments, welding speeds that allow full bead-on-plate welding to be possible were strongly by dependent on the initial temperature, 3000 [mm/mm], initial temperature 873 [K], 2600 [mm/mm], initial temperature 673 [K], and 2000 [mm/mm] with 300 [K]. Transverse crack-free welding was achieved, when initial temperature was at 873 [K].

We evaluated the thicknesses of domain walls (DWs) in rhombohedral BiFeO 3 thin films epitaxially grown on SrRuO 3 -covered SrTiO 3 (100), (110), and (111) single crystals by scanning nonlinear dielectric microscopy (SNDM). The SNDM phase signal revealed an abrupt change in the sign of polarization components normal to the surface at DWs within one or two unit cells. On the other hand, the SNDM amplitude signals gradually changed across DWs, corresponding to the change in the electrostatic potential. The minimum thicknesses estimated from the SNDM amplitude signals are 4, 1, and 2 nm for 71, 109, and 180°DWs, respectively. The relationship between these DW thicknesses and the nature and situation of DWs is discussed taking account of the polarization configuration in adjacent domains.

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