Issue 4, 2014

Hydrogen defects in tetragonal ZrO2 studied using density functional theory

Abstract

In the energy-structure paradigm, we analyzed the defects that can arise in tetragonal zirconium oxide (T-ZrO2) involving the hydrogen atom or the hydrogen molecule using density functional theory. Our results indicate that the dominant hydrogen defect under reducing conditions is Image ID:c3cp54153c-t1.gif, a complex formed between the hydride ion and a doubly charged oxygen vacancy. This result is consistent with the experimental observation that under reducing conditions, the solubility of hydrogen is proportional to the degree of hypostoichiometry of T-ZrO2. Under oxidizing conditions we found three different hydrogen defects, each predominating in a specific range of the chemical potential of electrons. Starting from the valence band top toward the conduction band bottom, these defects are the interstitial proton, Image ID:c3cp54153c-t2.gif, a complex formed between two hydrogen species and a zirconium vacancy with a net effective charge of (2−), Image ID:c3cp54153c-t3.gif, and finally a complex similar to the latter but with a net effective charge of (4−), Image ID:c3cp54153c-t4.gif. In Image ID:c3cp54153c-t5.gif the two hydrogens exist in the form of hydroxyl groups, while in Image ID:c3cp54153c-t6.gif they exist in the form of a hydrogen molecule. In addition, we found that up to three hydrogen species can favorably accumulate in a zirconium vacancy under oxidizing conditions. The clustering of hydrogen in cation vacancies can be a precursor for the deleterious effects of hydrogen on the mechanical properties and stability of metal oxides, in analogy with hydrogen embrittlement in metals. Finally we observed a red-shift and a blue-shift for the vibrational frequencies of all the hydroxyl groups and all the hydrogen molecules, respectively, in T-ZrO2 when compared to the gas phase frequencies. This is an important characteristic for guiding future experimental efforts to detect and identify hydrogen defects in T-ZrO2. The insights presented in this work advance our predictive understanding of the degradation behavior of T-ZrO2 as a corrosion resistant passive layer, as a gate dielectric and in biomedical applications.

Graphical abstract: Hydrogen defects in tetragonal ZrO2 studied using density functional theory

Supplementary files

Article information

Article type
Paper
Submitted
01 Oct 2013
Accepted
11 Nov 2013
First published
11 Nov 2013

Phys. Chem. Chem. Phys., 2014,16, 1354-1365

Hydrogen defects in tetragonal ZrO2 studied using density functional theory

M. Youssef and B. Yildiz, Phys. Chem. Chem. Phys., 2014, 16, 1354 DOI: 10.1039/C3CP54153C

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements