Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf0.5Zr0.5O2: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

• Published in: Physica status solidi. PSS-RRL. Rapid research letters 2021-05, Vol.15 (5), p.n/a
• Main Authors: Shimizu, Takao, Tashiro, Yuki, Mimura, Takanori, Kiguchi, Takanori, Shiraishi, Takahisa, Konnno, Toyohiko J., Sakata, Osami, Funakubo, Hiroshi
• Format: Article
• Language: English
• Subjects: ferroelectric thin films; field-induced phase transitions; fluorite oxide materials
• ISSN: 1862-6254; 1862-6270
• DOI: 10.1002/pssr.202000589

The ferroelectric phase transformation from the tetragonal phase to the orthorhombic phase, induced by an electric field, is demonstrated in a 5%YO1.5‐doped Hf0.5Zr0.5O2 epitaxial film which is grown on Sn‐doped In2O3‐covered (111) yttria‐stabilized zirconia by the pulsed laser deposition method at room temperature and subsequent heat treatment. Although X‐ray diffraction shows the film to consist of a paraelectric tetragonal phase after the heat treatment, polarization–electric field (P–E) measurements reveal a hysteresis loop attributed to the ferroelectricity. To clarify the discrepancy between the crystal structure and electric characteristics, the crystal structure after electric field loading is determined by scanning transmission electron microscopy and synchrotron X‐ray diffraction measurements. Both structural characterizations clearly reveal that the application of an electric field promotes the phase transition from the paraelectric tetragonal phase to the ferroelectric orthorhombic phase. This ferroelectric transition is irreversible, as the ferroelectric phase remains after the removal of the electric field. These results facilitate the elucidation of the mechanism by which ferroelectricity is displayed in HfO2‐based fluorite ferroelectric materials and imply unimportance of the orthorhombic phase for as‐prepared films. The phase transition in ferroelectric Y‐doped Hf0.5Zr0.5O2 epitaxial thin film induced by an electric field is demonstrated, which triggers the emergence of ferroelectric characteristics from the nonpolar tetragonal phase to the polar orthorhombic phase. This ferroelectricity induced by the electric‐field‐induced phase transition is quite an important mechanism by which ferroelectricity is exhibited in flurorite‐oxides ferroelectrics.