Ned Taylor, Arnaldo Galbiati, Monica Saavedra, and Steve Hepplestone have just published an article exploring the potential of calcium-doped stannous oxide, (Sn:Ca)xO, for its potential as an active layer in a solar device. By identifying a suitable oxide active layer, the authors hope to design an all-oxide solar cell. This work was performed by Ned and Steve at the University of Exeter whilst working with Solaris Photonics.
In this article, the authors explore how doping stannous oxide, SnO, with calcium affects the electronic and optical properties. It is determined that a doping concentration of x=7:1 results in the most favourable properties for photovoltaic applications – a direct band gap of 1.5 eV. The study is expanded upon by exploring potential transport layers for this particular solid solution. CaO and TiO2 are identified as potential candidates for the hole and electron transport layers, respectively.
A potential all-oxide solar cell design is put forward by the authors, CaO/(Sn:Ca)7:1O/TiO2. It is hoped that this study grow new interest in all-oxide solar cells, which have been touted as potential replacements for current silicon solar cells due to their possible improved stability and efficiency, and reduced environmental and economic costs.
Ned Taylor, Frank Davies, Isiah Rudkin, Conor Price, Ed Chan, and Steve Hepplestone have published an article detailing the group’s first large-scale commercial scientific software package, ARTEMIS. This work was led by Ned, Frank and Steve, with help from the entire ARTEMIS research group. Isiah aided in development of crucial modules and subroutines of the program during his Summer project with the group.
In this article, the authors detail the workflow of ARTEMIS, in addition to the methods and capabilities of its major subroutines: Lattice Matching, Surface Terminations, Interface Identification, Interface Shifting, and Intermixing. ARTEMIS can be used to generate a set of potential interfaces between any two given crystals, which are provided by the user. These structures can then be modelled using first principles or empirical modelling tools to identify the most energetically interface.
This software package has great potential to aid scientists in studying interface structures by reducing the time taken to explore then, as well as potentially removing human bias from the study. ARTEMIS identifies lattice matches within user-specified tolerances and shifts the two materials to compensate for missing bonds at the interface. To introduce the concept of diffusion, intermixing can be performed across the interface, which can relieve interface strain.
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).
Our project lead and lead developer have given the clear to to release the ARTEMIS code version 1.0.0 (Download from http://artemis-materials.co.uk/). For ARTEMIS enquires you can contact us at firstname.lastname@example.org. Also we have got our web page and wiki up and running.
Our lead developer, Ned, will be posting more about ARTEMIS soon!
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.
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.