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.