内田 寛

Mg<inf>2</inf>Si thin films were deposited at 320 °C on (001)Al<inf>2</inf>O<inf>3</inf>and (100)CaF<inf>2</inf>substrates by radio-frequency magnetron sputtering. Both films showed a preferential (111) out-of-plane orientation with an in-plane random orientation irrespective of post-heat treatment. Mg<inf>2</inf>Si films on (001)Al<inf>2</inf>O<inf>3</inf>substrates were under in-plane tensile strain, while those on (100)CaF<inf>2</inf>substrates were under in-plane compressive strain both before and after heat treatment. Heat-treated films showed p-type conduction up to 500 °C. Their electrical conductivity and Seebeck coefficient were almost independent of the kind of substrate within the limit of the present study, from 0.22% compressive strain to 0.34% tensile strain at room temperature.

(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.