Ab Initio Exploration of Interface Structures and Their Properties

Abstract

In this thesis, material interfaces, structures and properties are studied at the atomic scale, with an emphasis on their use in clean energy applications. Inter- faces can exhibit intriguing and unique physical phenomena not seen in periodic crystals. Oxide interfaces are the main focus due to the wealth of phenomena they can exhibit, in addition to the composite materials’ abundance, stability and relative ease of fabrication. CaCu3Ti4O12 samples have previously been shown to exhibit colossal permittivity, which has been attributed to their grain boundaries. The high permittivity of the samples is attributed to the formation of a thin dilute metal at the interface between the grain and inter-grain materials. This under- standing should allow for one to artificially engineer systems that exhibit colos- sal permittivity, which would have uses in areas such as gas sensing and elec- tric capacitors. The need to properly characterise interfaces is then discussed. The BaTiO3/SiO2 system is used as an example to highlight the need to prop- erly measure and characterise interface regions, as a new material, Ba2TiSi2O8, can form across the junction. The work then shifts to the use of interfaces di- rectly in device designs. All-oxide solar cells have great potential to be cheaper and easier to manufacture than current silicon-based solar cells. A set of ma- terials are explored to identify a potential all-oxide solar cell design. The setup of CaO/(Sn:Ca)7:1O/TiO2 is put forward as a potentially viable design for a p–i–n solar cell device. Next, oxide perovskites are investigated to identify their capa- bilities as photocatalytic materials for the purposes of water-splitting. SrSnO3 is identified as a potential candidate for water-splitting. By introducing a thin ZrO2 overlayer to the surface of SrSnO3, the photocatalytic properties of the slab can be improved. This allows allows for bifunctional water-splitting on the surface of the SrSnO3|ZrO2 overlay system. Finally, ARTEMIS, a tool to aid in interface stud- ies is discussed. This tool is designed to generate potentially viable interfaces, with a rudimentary function for predicting interface separation through bonding analysis. The results presented here should be of great use to anyone exploring energy technologies, as well as those studying the fundamentals of interfaces.