From Stable ZnO and GaN Clusters to Novel Double Bubbles and Frameworks

Matthew Farrow,John Buckeridge,Alexey Sokol,Andrew Logsdail,C Catlow,David Scanlon,Scott Woodley

doi:10.3390/inorganics2020248

Matthew Farrow, John Buckeridge + Show 5 more

Open Access

https://doi.org/10.3390/inorganics2020248

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Journal: Inorganics	Publication Date: May 28, 2014
Citations: 42	License type: CC BY 4.0

Affiliation: University College London, Diamond Light Source

Abstract

A bottom up approach is employed in the design of novel materials: first, gas-phase “double bubble” clusters are constructed from high symmetry, Th, 24 and 96 atom, single bubbles of ZnO and GaN. These are used to construct bulk frameworks. Upon geometry optimization—minimisation of energies and forces computed using density functional theory—the symmetry of the double bubble clusters is reduced to either C1 or C2, and the average bond lengths for the outer bubbles are 1.9 Å, whereas the average bonds for the inner bubble are larger for ZnO than for GaN; 2.0 Å and 1.9 Å, respectively. A careful analysis of the bond distributions reveals that the inter-bubble bonds are bi-modal, and that there is a greater distortion for ZnO. Similar bond distributions are found for the corresponding frameworks. The distortion of the ZnO double bubble is found to be related to the increased flexibility of the outer bubble when composed of ZnO rather than GaN, which is reflected in their bulk moduli. The energetics suggest that (ZnO)12@(GaN)48 is more stable both in gas phase and bulk frameworks than (ZnO)12@(ZnO)48 and (GaN)12@(GaN)48. Formation enthalpies are similar to those found for carbon fullerenes.

Highlights

A new class of materials is sought that will support the separation of electrons and holes typically generated during photo-excitation by solar radiation
The average bond lengths of zinc oxide and gallium nitride are similar; the average bond length for zinc oxide inner bubbles are slightly greater than the average bond lengths of gallium nitride inner bubbles
We found that the average bond lengths of both ZnO and GaN are similar, the average bond lengths for ZnO inner bubbles were larger than the GaN inner bubbles of both the double bubble cluster systems and the frameworks

Summary

Introduction

A new class of materials is sought that will support the separation of electrons and holes typically generated during photo-excitation by solar radiation. For binary oxide and semiconductor II-VI and III-V materials with a 1-1 stoichiometry, fullerene type structures have been the focus of materials modelling at the nanoscale in the last decade This interest has partly been spurred by reports of synthesis of (MX)n clusters of these materials, where M denotes metals, or cations, and X represents anions, with the mass spectra of such systems showing unexpected preference for certain sizes n. On further size increase (cluster growth), the appearance of layered structures becomes a possibility, in which a smaller sized cluster unit is contained within a larger bubble structure Such structures have been discovered in molecular dynamical studies of ZnS, where the smallest is found for n = 60: an n = 48 bubble forms a concentric shell around an n = 12 sodalite cage [12]. We investigate the different possible atomic structural relaxations of the double bubble and the effect of mixing components of different compositions, for both the individual clusters and the constructed frameworks

Construction of Double Bubbles

Double Bubble Clusters

Double Bubble Frameworks

Interatomic Potentials Calculations

Density Functional Theory Calculations

Conclusions