Growth of Single Crystals of (K1−xNax)NbO3 by the Self-Flux Method and Characterization of Their Phase Transitions

• Published in: Materials 2024-09, Vol.17 (17), p.4195
• Main Authors: Doan Thanh Trung, Uwiragiye, Eugenie, Tran Thi Lan, Fisher, John G, Jong-Sook, Lee, Mok, Jungwi, Lee, Junseong, Furqan Ul Hassan Naqvi, Jae-Hyeon Ko
• Format: Article
• Language: English
• Subjects: Alumina; Charged particles; Crystal growth; Dielectric properties; Electric fields; Electron probe microanalysis; Ferroelectric materials; Ferroelectricity; Heat; Hysteresis loops; Impedance spectroscopy; Low temperature; Niobates; Permittivity; Perovskite structure; Perovskites; Phase transitions; Radiation; Raman spectra; Room temperature; Single crystals; Spectrum analysis; Symmetry; Temperature; X-ray diffraction
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma17174195

In this study, single crystals of (K1−xNax)NbO3 are grown by the self-flux crystal growth method and their phase transitions are studied using a combination of Raman scattering and impedance spectroscopy. X-ray diffraction shows that single crystals have a perovskite structure with monoclinic symmetry. Single crystal X-ray diffraction shows that single crystals have monoclinic symmetry at room temperature with space group P1211. Electron probe microanalysis shows that single crystals are Na-rich and A-site deficient. Temperature-controlled Raman scattering shows that low temperature monoclinic-monoclinic, monoclinic-tetragonal and tetragonal-cubic phase transitions take place at −20 °C, 220 °C and 440 °C. Dielectric property measurements show that single crystals behave as a normal ferroelectric material. Relative or inverse relative permittivity peaks at ~−10 °C, ~230 °C and ~450 °C with hysteresis correspond to the low temperature monoclinic-monoclinic, monoclinic-tetragonal and tetragonal-cubic phase transitions, respectively, consistent with the Raman scattering results. A conduction mechanism with activation energies of about 0.5–0.7 eV was found in the paraelectric phase. Single crystals show polarization-electric field hysteresis loops of a lossy normal ferroelectric. The combination of Raman scattering and impedance spectroscopy is effective in determining the phase transition temperatures of (K1−xNax)NbO3.