Tantalum pentoxide (Ta₂O₅) is a semiconducting material which has broad technological applications. For instance, the excellent dielectric properties make Ta₂O₅ a good candidate material to replace SiO₂ as the insulating layer for advanced electronic devices.

Owing to its high refractive index, Ta₂O₅ could also be applied to the coating material of optical devices (e.g., lens of camera) and the instruments for ultraprecise measurement such as the well-known Laser Interferometer Gravitational-wave Observatory (LIGO). In LIGO's two long arms which are vertically arranged to each other, alternating thin layers of SiO₂ and Ta₂O₅ serve as mirror coatings for the test masses of the detectors. Additionally, Ta₂O₅ finds its place in other applications such as corrosion resistant coatings and catalysts like water splitting.

Despite the efforts of more than half a century, the low-temperature crystal structures of Ta₂O₅, namely, L-Ta₂O₅, still remain an issue of debate. Different types of crystals have been reported for L-Ta₂O₅: e.g., LSR, LGMR, βAL, βR, λ, δ, B, Z, etc. Previous studies found that, the B type crystal of Ta₂O₅ is the most stable, and λ is the second.

Then one may ask, is it possible to find new type of crystals of L-Ta₂O₅?

Recently, researchers from the Institute of Solid State Physics (ISSP), Hefei Institutes of Physical Science and Tohoku University examined this topic and made positive reply to this problem.

Using most advanced method of theoretical calculations, they predicted the existence of a new crystal type of L-Ta₂O₅ (named as γ-Ta₂O₅).

It is demonstrated by calculations that the new type of L-Ta₂O₅ crystal is much more stable than any types of Ta2O5 crystals reported previously. If the crystal is compressed, it may change to the known B or λ type crystals of Ta₂O₅.

On the other hand, common features are found not only in the local arrangement of atoms of the new type of crystal and the other types of Ta₂O₅ crystals, but also in their dynamical properties such as the stretching and dangling motions of the atoms .

"We are very happy that we can have our contribution to resolve such a long-standing structural problem of Ta₂O₅ and we are in touch with the some experts in crystal growth from the IOP of CAS, and discuss about future collaborations", said YANG.

"I am happy to know that Ta₂O₅ can have such a new phase. Due to the high melting point of elemental Ta, it is not so easy to get controllable growth of Ta₂O₅  thin films", Prof. MA Xucun from Tsinghua University, a recipient of the National Science Fund for Distinguished Young Scholars, commented.

This work is financially supported by the National Natural Science Foundation of China (Grant No. 11474285).

Link to the paper: Prediction of new ground-state crystal structure of Ta₂O₅

Fig. 1. (a)-(e): Schematics of some typical crystals of Ta₂O₅. (f) The predicted γ-Ta₂O₅. (Image by YANG Yong)

Fig. 2. The total energies of B, λ, and γ-Ta₂O₅ as a function of crystal volume, where the pressure-induced transformation of crystal structure is indicated by dashed lines. (Image by YANG Yong)

Contact:

ZHOU Shu

Hefei Institutes of Physical Science (http://english.hf.cas.cn/)

Email: zhous@hfcas.ac.cn