Remarkably stable amorphous metal oxide grown on Zr-Cu-Be metallic glass.

Ka Ram Lim,Young Su Yun,Chang Eun Kim,Aloysius Soon,Do Hyang Kim,Won Tae Kim

doi:10.1038/srep18196

Ka Ram Lim, Young Su Yun + Show 4 more

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https://doi.org/10.1038/srep18196

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Abstract

In the present study, we investigated the role of an aliovalent dopant upon stabilizing the amorphous oxide film. We added beryllium into the Zr50Cu50 metallic glass system, and found that the amorphous oxide layer of Be-rich phase can be stabilized even at elevated temperature above Tg of the glass matrix. The thermal stability of the amorphous oxide layer is substantially enhanced due to Be addition. As confirmed by high-temperature cross-section HR-TEM, fully disordered Be-added amorphous layer is observed, while the rapid crystallization is observed without Be. To understand the role of Be, we employed ab-initio molecular dynamics to compare the mobility of ions with/without Be dopant, and propose a disordered model where Be dopant occupies Zr vacancy and induces structural disorder to the amorphous phase. We find that the oxygen mobility is slightly suppressed due to Be dopant, and Be mobility is unexpectedly lower than that of oxygen, which we attribute to the aliovalent nature of Be dopant whose diffusion always accompany multiple counter-diffusion of other ions. Here, we explain the origin of superior thermal stability of amorphous oxide film in terms of enhanced structural disorder and suppressed ionic mobility due to the aliovalent dopant.

Highlights

According to the previous report[18,19], the solid solubility in crystalline zirconia is strongly influenced by valences and sizes of the multivalent cations, which means that aliovalent dopants with low solubility in crystalline zirconia can stabilize the amorphous structure by destabilizing the crystalline phases
In the case of Zr–Cu–Be metallic glass, the crystallized substrate did not induce the crystallization of the amorphous oxide film
We investigated the effect of beryllium addition into the Zr50Cu50 metallic glass system on the glass stability of thermally grown amorphous oxide film

Summary

Introduction

According to the previous report[18,19], the solid solubility in crystalline zirconia is strongly influenced by valences and sizes of the multivalent cations, which means that aliovalent dopants with low solubility in crystalline zirconia can stabilize the amorphous structure by destabilizing the crystalline phases. Between Al and Be, Be dopant is considered to play a key role in stabilizing the amorphous structure of the Zr-rich oxide film, since Be (+ 2) has much lower solid solubility in crystalline zirconia than Al (+ 3), considering the number of valence electrons and the ionic sizes. We focus on the role of Be dopant, which has a different oxidation state of Be (2+ ) compared to major glass component Zr (4+ ), and conduct a series of systematic analyses using both of the experimental and theoretical tools. The Be ions used in this study are found to suppress the oxygen mobility of the amorphous layer compared to its crystalline counterparts

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