Orientation Dependence of Transverse Piezoelectric Properties of Epitaxial BaTiO₃ Films

<jats:p> The orientation dependence of the piezoelectric properties of epitaxial BaTiO<jats:sub>3</jats:sub> (BTO) films was investigated. The (001), (101), and (111)-oriented BTO films of 2–2.5 µm thickness were deposited on SrRuO<jats:sub>3</jats:sub>/Pt/MgO or SrRuO<jats:sub>3</jats:sub>/SrTiO<jats:sub>3</jats:sub> substrates by rf magnetron sputtering. X-ray diffraction measurements showed that (001), (101), and (111)BTO films were epitaxially grown on the substrates. The lattice parameters of each BTO film were different from those of the bulk single crystal, and the unit cell volume of the BTO films was larger than that of bulk BTO. The transverse piezoelectric coefficients <jats:italic>e</jats:italic> <jats:sub>31</jats:sub> <jats:sup>*</jats:sup>=<jats:italic>d</jats:italic> <jats:sub>31</jats:sub>/<jats:italic>s</jats:italic> <jats:sub>11</jats:sub> of (001)BTO films was almost independent of applied electric field, whereas <jats:italic>e</jats:italic> <jats:sub>31</jats:sub> <jats:sup>*</jats:sup> of (111)BTO increased with voltage owing to the domain motion. The piezoelectric properties of (101)BTO films strongly depended on the in-plane alignment of the crystal structure, and a relatively large <jats:italic>e</jats:italic> <jats:sub>31</jats:sub> <jats:sup>*</jats:sup> of -1.3 C/m<jats:sup>2</jats:sup> could be achieved by enhancement of the domain motion. Although the absolute values of <jats:italic>e</jats:italic> <jats:sub>31</jats:sub> <jats:sup>*</jats:sup> are smaller than theoretical calculation values, we could demonstrate that the optimization of crystal orientation is effective for enhancing BTO-based lead-free piezoelectric films. </jats:p>