High temperature phase transitions in NaNbO3 epitaxial films grown under tensile lattice strain

• Published in: Applied physics letters 2022-05, Vol.120 (20)
• Main Authors: Bin Anooz, S., Wang, Y., Petrik, P., de Oliveira Guimaraes, M., Schmidbauer, M., Schwarzkopf, J.
• Format: Article
• Language: English
• Subjects: Applied physics; Electric polarization; Epitaxial growth; Ferroelectric materials; Ferroelectricity; High temperature; Lattice strain; Phase transitions; Refractivity; Room temperature; Sodium compounds; Strain analysis; Substrates; Temperature dependence; Thin films; Vapor phase epitaxy; Vapor phases
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0087959

We have investigated high temperature phase transitions in NaNbO3 thin films epitaxially grown under tensile lattice strain on (110) DyScO3 substrates using metal-organic vapor phase epitaxy. At room temperature, a very regular stripe domain pattern consisting of the monoclinic a1a2 ferroelectric phase was observed. Temperature-dependent studies of the refractive index and the optical bandgap as well as in situ high-resolution x-ray diffraction measurements prove a ferroelectric–ferroelectric phase transition in the range between 250 and 300 °C. The experimental results strongly suggest that the high-temperature phase exhibits a distorted orthorhombic a1/a2 crystal symmetry, with the electric polarization vector lying exclusively in the plane. A second phase transition was observed at about 500 °C, which presumably signifies the transition to the paraelectric phase. Both phase transitions show a pronounced temperature-dependent hysteresis, indicating first-order phase transitions.