内田 寛

Abstract Lead-free antiferroelectric (AFE) materials with non-perovskite structures are of increasing interest for environmentally friendly high-power energy storage applications. Titanite CaTiSiO ₅ thin films with different thicknesses were fabricated on (111)Pt/(100)Si substrates by pulsed laser deposition. Post-annealing under oxygen partial pressures of 50 Torr or higher reduced the leakage current density, owing to the suppression of oxygen-vacancy-related defects. XRD analysis confirmed the formation of single-phase monoclinic P 2 ₁ / a titanite films with 011 preferred orientation. The Lotgering factor for the 011 orientation reached approximately 0.8 for films thicker than 280 nm. With increasing thickness, the relative permittivity decreased from approximately 100 to 50, approaching the value reported for bulk titanite. Films thicker than 280 nm exhibited clear double polarization–electric field hysteresis loops, confirming stable antiferroelectric behavior. These results reveal the thickness-dependent evolution of texture growth and electrical properties in titanite CaTiSiO ₅ thin films.

Abstract The compositional dependence of phase-formation behavior in fluorite-type ferroelectric films of the binary HfO ₂ – ZrO ₂ system was systematically evaluated while considering the size effect associated with film thickness. The crystalline phase of the CSD-derived films (1- x ) HfO ₂ - x ZrO ₂ films ( x = 0 - 1.00) generally exhibited a transition from the monoclinic fluorite (m-phase) to orthorhombic and / or tetragonal phases (o-/t-phase) with increasing the ZrO ₂ content. However, the phase boundary between m-phase and o-/t-phases shifted toward the ZrO ₂ -rich region as the film thickness decreased. The composition exhibiting enhanced ferroelectricity also shifted toward the ZrO ₂ -rich side, coincident with the phase boundary: the 40 nm-thick films showed the maximum remnant polarization at x = 0.75, which is noticeably different from the commonly reported optimum composition of x = 0.50 (i.e., Hf0.5Zr0.5O ₂ ) for ultrathin (~9 nm) films.

Abstract This study systematically investigated the role of Ba(OH)₂ concentration on the properties of thin films. Films of (001)-oriented barium titanate (BaTiO₃) were grown on (100) La-doped SrTiO₃ substrates at 200°C by hydrothermal synthesis. X-ray diffraction analysis confirmed the films showed epitaxial and highly (100)-oriented growth with no secondary phases. The as-deposited films exhibited a significant unit cell volume expansion relative to bulk BaTiO₃, which is attributed to the incorporation of hydroxyl (OH^-) groups inherent in the hydrothermal process. Scanning electron microscopy revealed that a high Ba(OH)₂ concentration (2.0 mol dm^⁻3) was essential to achieving a uniform film approximately 150 nm thick, lower concentrations resulted in discontinuous growth. The dense film exhibited a clear ferroelectric domain structure and good dielectric properties. These results demonstrate that precise control over precursor concentration is a key factor in fabricating high-quality epitaxial ferroelectric oxide thin films via low-temperature hydrothermal methods.