The Potential of Overlayers on Tin-based Perovskites for Water Splitting

Ned Taylor, Conor Price, Alex Petkov, Marcus Carr, Jason Hale, and Steve Hepplestone have just published an article. The initial work was performed by Conor Price, Alex Petkov, Marcus Carr and Jason Hale during their Masters Physics course at the University of Exeter, with it then being expanded upon by Conor, Steve and Ned.

In this article, the authors explore the capabilities of tin-based oxide perovskites as photocatalysis. An investigation of their electron properties, as well as the reaction pathways associated with their surfaces, is presented. It is determined that SrSnO3 offers some potential as a photocatalyst.

The addition of an overlayer to the surface of the oxide perovskite SrSnO3 is then considered. It is determined that the inclusion of this thin surface coating leads to a drastic improvement of both the oxygen and the hydrogen evolution reactions. SrSnO3 with a ZrO2 overlayer is found to be capable of sustaining bifunctional water splitting at its surface (simultaneous hydrogen and oxygen gas production from water).

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The Fundamental Mechanism Behind Colossal Permittivity in Oxides

Ned Taylor, Frank Davies, Shane Davies, Conor Price, and Steve Hepplestone have published an article describing the atomic-scale mechanism that gives rise to colossal permittivity within samples of CaCu3Ti4O12 (CCTO). This work was conducted at the University of Exeter during Ned, Frank, Shane and Conor’s PhDs.

For two decades, experimental samples of CCTO have shown extremely high values of relative permittivity (typically on the order of 104). Thus far, it has been shown that such high permittivity values are not present in the bulk material, and that, instead, this phenomenon is caused by the formation of a strongly insulating material at the boundary between CCTO grains (which are characterised as semiconducting) – commonly termed as the internal barrier layer capacitance (IBLC).

In this article, the authors explore the origin of this phenomenon at the atomic scale in order to determine the exact cause of the IBLC. The authors identify the formation of a thin metallic region at the interface between the insulating grain boundaries and the semiconducting grains. This metallic layer could allow for a rapid dielectric response from the large grains, but prevent transport between grains, due to the insulating boundary; this manifests itself as a large dielectric response, or high permittivity, of the sample.

In understanding the mechanism behind this colossal permittivity, the capabilities and limits of this phenomenon can be better understood. This article can aid in the engineering of artificial systems with colossal permittivity.

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First principles electronic and elastic properties of fresnoite Ba2TiSi2O8

Ned Taylor, Frank Davies, and Steve Hepplestone published an article detailing a theoretical study of the electronic and elastic properties of fresnoite, Ba2TiSi2O8. The work was performed during the first six months of Ned and Frank’s PhDs. This material has potential due to its large band gap, strongly anisotropic structure and a second gap directly above the band gap.

Using PBE density functional theory (DFT), the electronic and elastic properties are determined for defect-free fresnoite. To more accurately capture the band structure and band gap, results are also reported using the hybrid functional, HSE06.

Electronic properties such as the Bader charge, band structure, density of states, species- and atom-projected density of states are presented here (obtained and presented using both PBE and HSE06). The electronic contributions to the static and high-frequency permittivities along X and Z are also presented (obtained using PBE). The dielectric properties of fresnoite are of interest as it is known to form between layers of BaTiO3 and Si (or SiO2), a composite structure that is known to exhibit unusually high permittivity values (~104), even for BaTiO3. However, in this study, the authors show that fresnoite exhibits permittivity values only around 12.

Mechanical properties such as the bulk, shear and Young’s moduli are calculated. The elastic tensor values and the Raman-activated phonon frequencies are also presented. All mechanical properties are obtained using PBE.

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