内田 寛

(Bi,K)TiO<inf>3</inf>films were grown on (001)<inf>c</inf>SrRuO<inf>3</inf>// (100)SrTiO<inf>3</inf>substrates by pulsed laser deposition (PLD) at various temperatures. The K/Ti and Bi/Ti ratios of the films were almost the same at 350 and 500 °C, but decreased markedly at 650 °C. The ferroelectric property was ascertained for epitaxial tetragonal (Bi,K)TiO<inf>3</inf>films grown at 500 °C from polarization–electric field relationships, and their saturation polarization (P<inf>sat</inf>) and coercive field (E<inf>c</inf>) at a maximum electric field of 800 kV/cm were 18 µC/cm²and 300 kV/cm, respectively. To improve the ferroelectric property, the films were heat-treated at 650 °C while keeping the films in the PLD chamber after film deposition. These films also maintained a (001)-oriented epitaxy and had a tetragonal symmetry. The P<inf>sat</inf>and E<inf>c</inf>obtained at an electric field of 800 kV/cm were changed to 22 µC/cm²and 95 kV/cm, respectively. Moreover, these P<inf>sat</inf>and E<inf>c</inf>values increased to 31 µC/cm²and 165 kV/cm, respectively, at a maximum electric field of 1500 kV/cm. These heat-treated (Bi,K)TiO<inf>3</inf>films showed piezoelectricity with an apparent piezoelectric coefficient (d<inf>33(AFM)</inf>) of 22 pm/V.

Lead- and alkali-metal-free BaTiO<inf>3</inf>–Bi(Mg<inf>0.5</inf>Ti<inf>0.5</inf>)O<inf>3</inf>–BiFeO<inf>3</inf>solid-solution thin films were prepared on (111)<inf>c</inf>SrRuO<inf>3</inf>/(111)Pt/TiO<inf>2</inf>/SiO<inf>2</inf>/(100)Si substrates by chemical solution deposition (CSD) and their crystal structure and dielectric properties were investigated. The lattice spacing as a function of z/(x + z) in xBaTiO<inf>3</inf>–0.1Bi(Mg<inf>0.5</inf>Ti<inf>0.5</inf>)O<inf>3</inf>–zBiFeO<inf>3</inf>indicated the existence of phase boundaries (pseudocubic/rhombohedral) in the range of z/(x + z) = 0.33–0.56, where the relatively high relative dielectric constant, ε<inf>r</inf>, of above 800 was obtained. On the other hand, dielectric loss, tan δ, of below 0.2 was confirmed in the range z/(x + z) = 0–0.87, which rapidly increased toward z/(x + z) = 1.0. The relatively high ε<inf>r</inf>values of these films deposited on Si substrates by a solution-based process suggest that they can be used as alternative to Pb(Zr,Ti)O<inf>3</inf>, KNbO<inf>3</inf>, and (Bi<inf>1/2</inf>Na<inf>1/2</inf>)TiO<inf>3</inf>-based films.

Thin films of the BaTiO<inf>3</inf>–Bi(Mg<inf>1/2</inf>Ti<inf>1/2</inf>)O<inf>3</inf>(BT–BMT) solid-solution system were fabricated with the aim of achieving a stable temperature coefficient of capacitance (TCC) favorable for high-temperature electronics. A single perovskite phase with pseudocubic symmetry was obtained for the films fabricated by chemical solution deposition on (111)Pt/TiO<inf>2</inf>/(100)Si substrates in the composition range of x = 0–0.80 for (1 − x)BT–xBMT. BMT added to the BaTiO<inf>3</inf>-based films enhanced the crystallinity of the perovskite phase and resulted in saturated P–E hysteresis behavior with remanent polarization of up to 13 µC/cm². BMT addition led to gradual dielectric relaxation, which also resulted in stable TCC behavior with a relative dielectric constant of approximately 400 in the temperature range of RT − 400 °C, especially for the BT–BMT films with x = 0.20–0.40.