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Title: Energy storage at perovskite interfaces
Author: Davies, Peter
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Thin-film capacitor interfacial effects produce a voltage drop across conductor/dielectric interfaces, equivalent to a small capacitance in series with the larger, bulk, dielectric capacitance. These inhibit maximum charge storage in fixed-voltage devices, such as integrated circuits, and are seen as unhelpful, "dead-layer"' effects. The novel proposal in this research is to deliberately exploit intrinsic interfacial voltage drops to enhance the energy stored in a capacitor. A theory of interfacial energy storage is proposed which identifies maximum dielectric polarisation as a key factor for energy storage. A simple, tight-binding model of dielectric breakdown indicates increased localisation of electronic orbitals at high electric fields. Using a novel algorithm, DFT simulations of slabs were performed using SrRuO₃ as the conductor and SrTiO₃ and PbTiO₃ as dielectrics. These simulated interfacial effects up to an applied external electric field of 24 GV/m, dielectric polarisation of 0.21 C/m², energy storage of 0.06 J/m² per pair of interfaces (equivalent to 3 J/cc), and an interfacial voltage drop of 0.28 V per interface. Research by others suggests a leakage time constant for interfacial storage devices of up to several minutes. On application of a strong external electric field, the slab length changes and the cations and anions in each plane separate, dissociating the position definitions with no electric field from those with a field applied. A novel approach allows definition and calculation of local polarisation changes and voltage drops for half-unit cell regions, using planes with zero net charge on each side. The project also explores ways of optimising interfacial energy storage, and the possibility of using high-polarisation (1.5 C/m²) ferroelectric BiFeO₃ as the dielectric. Follow-on simulations and experimental work are suggested, including methods of constructing real devices.
Supervisor: Foulkes, Matthew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral