摘要： Herein, ferroelastic domain switching from the nonpolar b-axis to the polar c-axis oriented domain in ferroelectric ?lms is demonstrated. Scanning 7%-YO1.5-substituted HfO2 (YHO-7) epitaxial transmission electron microscopy (STEM) indicates that the polarization of a pristine ?lm deposited on a Sn-doped In2O3/(001)YSZ substrate by the pulsed laser deposition method tends to be along the in-plane direction to avoid a strong depolarization ?eld with respect to the out-of-plane direction. Applying an electric ?eld aids in ferroelastic domain switching in YHO-7 ?lms. Such ?lms exhibit ferroelectric characteristics with a relatively large saturated polarization around 30 lC/cm2 by polarization reorientation from the in-plane to the out-of-plane directions and an increased dielectric constant. The synchrotron X-ray diffraction measurements with a focused beam for the pristine and poled area indicate ferroelastic 90(cid:2) domain switching as the odd number re?ection disappears, which is only allowed in the nonpolar b-axis orientation. STEM observations also show a signi?cant increase in the c-axis oriented domain. This observation of ferroelastic domain switching strongly supports the conclusion that the ferroelectricity of HfO2 originates from the non-centrosymmetric orthorhombic phase.