Stoichiometric and Nonstoichiometric Surface Structures of Pyrochlore Y2Zr2O7 and Their Relative Stabilities: A First-Principles Investigation

• Published in: Coatings (Basel) Vol. 13; no. 7; p. 1203
• Main Authors: Wu, Huajian, Zhang, Jianning, Wang, Yiren, Shang, Jiacheng, Jiang, Yong
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.07.2023
• Subjects: Approximation; First principles; Free energy; Heat of formation; High temperature; Partial pressure; Phase diagrams; Pyrochlores; Stoichiometry; Structural stability; Symmetry; Zirconium
• ISSN: 2079-6412; 2079-6412
• DOI: 10.3390/coatings13071203

First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y2Zr2O7. The stoichiometric Y2Zr2O7 (110) and (100) surfaces were predicted, with lowest formation energies of 1.20 and 1.47 J/m2, respectively. Based on a thermodynamic defect model, non-stoichiometric Y2Zr2O7 surface energies were further evaluated as a function of environmental oxygen partial pressure (pO2) and temperature (T). With all of the results, we were able to construct the surface phase diagrams for T = 300 and 1400 K. The strong correlation between the structural stabilities and the surface stoichiometry was revealed as varying T and pO2. At a given T, the most stable termination of the (110) surfaces would change from a (Y,Zr)−rich (ns−2Y2Zr6O) to O−rich ones (ns−4O_2 and ns−4O_1) as increasing pO2, while that of the (100) surfaces would change from the stoichiometric (stoi−1Y1Zr_1) to the O−rich one (ns−5O). The critical pO2 value for termination transition moves to its higher end as increasing T.