A thorough investigation of the crystal structure of willemite‐type Zn2GeO4

Joachim Breternitz,Susan Schorr,Daniel Fritsch,Alexandra Franz

doi:10.1002/zaac.202100231

Abstract

AbstractThe thermodynamically stable phase of Zn2GeO4 contains tetrahedrally coordinated cations only and crystallizes isostructurally to Zn2SiO4 (willemite, space group , no. 148). While this material is considered for a plethora of energy‐related applications, such as transparent conducting oxide, battery material and photocatalyst, cation ordering in the crystal structure has not been investigated thoroughly. We have therefore re‐determined the crystal structure of Zn2GeO4 using a combination of X‐ray and neutron powder diffraction. The additional neutron diffraction study helps to distinguish between the isoelectronic Zn2+ and Ge4+ cations and yields valuable information about a partial or complete cation permutation in this material. The experimental study is supported by first‐principles calculations on the structural properties of Zn2GeO4 utilizing a standard generalized gradient approximation, and the more accurate hybrid functional HSE06. In order to better understand cation permutations, additional calculations including defective Zn2GeO4 have been performed based on a supercell approach. Our results show that, with the preparation conditions applied, cation permutation is unlikely to occur in our samples.

Highlights

The structural properties of Zn2GeO4 render it useful for a multitude of potential applications
In order to advance our current knowledge, we applied a combination of X-ray and neutron diffraction techniques in order to re-determine the crystal structure of Zn2GeO4, and supplemented the experimental results with first-principles calculations based on density functional theory (DFT)
Supplementing the neutron diffraction with DFT calculations based on the PBE and the more accurate hybrid functional HSE06, we further confirmed the cation ordering that is not directly accessible through X-ray diffraction

Summary

Introduction

Despite the notable interest in this compound, and in particular in its structural and defect behavior, it is surprising that, to the best of our knowledge, no comprehensive neutron diffraction study has been conducted. Such a study is, very valuable since Zn2+ and Ge4+ are isoelectronic and virtually indistinguishable by X-ray diffraction and a partial or even complete permutation of the cations on the three independent crystallographic sites (Ge1, Zn1, and Zn2) would go unnoticed. In order to advance our current knowledge, we applied a combination of X-ray and neutron diffraction techniques in order to re-determine the crystal structure of Zn2GeO4, and supplemented the experimental results with first-principles calculations based on density functional theory (DFT). The combined efforts brought about a more comprehensive understanding of the structural features present in Zn2GeO4 and provided an insight on the effects behind the observed features of the material

Results and Discussion

Conclusions

Conflict of Interest