Effects of La Doping on Local Structure of Hafnium Oxide Studied by X-Ray Absorption Spectroscopy

Abstract

HfO₂-based films prepared by the integration of the sol-gel method and spin-coating procedure were used as the study system to investigate the influence of La doping by varying the La contents of 20, 40, 50, and 60 wt%. GIXRD, XANES, and EXAFS measurements were performed to analyze phase formation, crystal structure, and local structure of the films. The XANES data of the Hf L₃-edge show no significant difference with respect to an increase in La content, indicating a considerable stability of the hafnium ion in the +4 oxidation state. Moreover, the EXAFS spectrum shows that the coordination number of Hf⁴⁺ is seven and the Hf–O bond length is ∼2.11 Å, which additionally confirms the formation of monoclinic HfO₂ structure. The contributions of the second coordination shells, which are assigned to the Hf–Hf and Hf–La bonds, become well-structured with increasing La concentration in the HfO₂ structure. However, the study suggests that the La-doped concentration affects the phase transformation from monoclinic to tetragonal and finally orthorhombic phase, leading to the presence of ferroelectric materials.

Keywords:

• La-doped HfO₂
• thin films
• phase transition
• XANES
• EXAFS

Acknowledgments

This work was supported by the Suranaree University of Technology (SUT) by Office of the Higher Education Commission under NRU Project of Thailand and Synchrotron Light Research Institute (Public Organization), SLRI, Thailand at BL 6A for all facilities and financial supports. The authors wish to thank the Synchrotron Light Research Institute for the provision of beamtime for GIXRD and XAS at BL1.1W. Dr. Prae Chirawatkul and Dr. Chatree Saiyasombat of BL1.1W are acknowledged for their fruitful discussion and assistance during the experiment. The figures in this article were created using Adobe Illustrator, SketchUp, BioRender, CaRIne v.3, and Microsoft PowerPoint.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.