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  • 1.
    Kubyshkina, Elena
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Unge, Mikael
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymera material. ABB Corporate Research, Västerås, SE 72178, Sweden.
    Impact of interfacial structure on the charge dynamics in nanocomposite dielectrics2019Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 125, nr 4, artikel-id 045109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate that the chemistry at the interface between nanoparticle and polymer matrix influence charge dynamics in polymer nanocomposite. Applying density functional theory, we investigate the influence of crystal surface termination, silicon treatment, and water and carboxyl defect on the electronic properties of interfaces in MgO-polyethylene nanocomposite. The band offsets between the nanofiller and base matrix materials show a strong dependence on the chemical composition at the interface. Based on the calculated electronic structure, we propose a band alignment model for charge dynamics in nanocomposite dielectrics. The model not only provides a mechanism of reduction of space charge and conductivity but also predicts an increase in thermal stress and susceptibility to the chemical additives. It is suggested that the suppression mechanisms of space charge and conductivity in nanocomposites can be inherently unstable and promote material aging. The results of the study show a need for long-term performance tests of nanocomposite dielectrics.

  • 2.
    Kubyshkina, Elena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Ab initio modelling of interfaces in nanocomposites for high voltage insulation2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Dielectric nanocomposite materials have been experimentally proven to have properties that are beneficial in applications for efficient energy transport. However, today there are still no empirical models or rules that can predict the performance of a certain combination of materials in the nanocomposite, and there are also no definitive explanations of their dielectric behavior. A deeper understanding of the phenomena behind these materials' response to an applied electric field can open new possibilities for improvement of the insulating properties of nanocomposites.

    The goal of this work is to locate the key processes that are responsible for dielectric performance. The methodology of the study is based on ab initio technology, that relies solely on the knowledge of chemical and structural composition of the material. In this work, the charge-related properties of nanocomposite interfaces are studied. The primary material of the study is chosen to be polyethylene-based composite with magnesium oxide nanoparticles.

    The impact of the nanoparticle crystal surface termination and its silane treatment on the electronic structure of the interface between MgO and polyethylene are investigated here. Moreover, the effects of presence of carboxyl defect and water molecule near the interface are considered in this work as well.

    Based on the calculated electronic structure data, a model for charge dynamics is proposed. The model explains mechanisms for conductivity and space charge reduction in nanocomposites, but also predicts an increase in thermal stress and susceptibility for chemical defects. It is suggested here that the suppression mechanisms for space charge and conductivity in nanocomposites are inherently unstable and can also accelerate material aging.

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  • 3.
    Kubyshkina, Elena
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Unge, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Communication: Band bending at the interface in polyethylene-MgO nanocomposite dielectric2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 5, artikel-id 051101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Polymer nanocomposite dielectrics are promising materials for electrical insulation in high voltage applications. However, the physics behind their performance is not yet fully understood. We use density functional theory to investigate the electronic properties of the interfacial area in magnesium oxide-polyethylene nanocomposite. Our results demonstrate polyethylene conduction band matching with conduction bands of different surfaces of magnesium oxide. Such band bending results in long range potential wells of up to 2.6 eV deep. Furthermore, the fundamental influence of silicon treatment on magnesium oxide surface properties is assessed. We report a reduction of the surface-induced states at the silicon-treated interface. The simulations provide information used to propose a new model for charge trapping in nanocomposite dielectrics.

  • 4.
    Kubyshkina, Elena
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. ABB Corporate Research, Sweden.
    Unge, Mikael
    KTH, Skolan för kemivetenskap (CHE).
    ZnO-polyethylene interface: Band alignment2017Ingår i: Proceedings of the International Symposium on Electrical Insulating Materials, Institute of Electrical Engineers of Japan , 2017, Vol. 1, s. 363-365Konferensbidrag (Refereegranskat)
    Abstract [en]

    Zinc oxide-polyethylene nanocomposites have a potential to be used for high voltage insulation. Here, we investigate electronic properties of zinc oxide-polyethylene interface using density functional theory. Interface states up to 1 eV below conduction band edge are found in polyethylene. Our results suggest that the energy bands of ZnO and polyethylene align to comply with vacuum level equality. We use our findings to establish mechanisms of band alignment at the interfaces between polyethylene and crystal materials.

  • 5.
    Kubyshkina, Elena
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Unge, Mikael
    KTH, Skolan för kemivetenskap (CHE).
    Electronic properties of magnesium oxide-polyethylene interface2016Ingår i: Proceedings of the 2016 IEEE International Conference on Dielectrics, ICD 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 788-791Konferensbidrag (Refereegranskat)
    Abstract [en]

    We use density functional theory to calculate band offsets for different configurations of magnesium oxide-polyethylene interface. Our study shows that band bending occurs at the contact between the polymer and the MgO particle. As a result, the surface of the MgO nanoparticle introduces deep traps up to 2 eV in the material. Also, the calculations indicate the possibility of a double layer formation within the nanoparticle.

  • 6.
    Kubyshkina, Elena
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Unge, Mikael
    Ab-initio Modeling of Interfacial Region in Nanocomposite Dielectrics2015Ingår i: 2015 Electrical Insulation Conference (EIC), IEEE , 2015, s. 618-620Konferensbidrag (Refereegranskat)
    Abstract [en]

    The interfacial region between a base matrix and nanoparticles in nanocomposite dielectrics is often referred to as the main cause of good performance of nanocomposites as insulating materials. In the present work we compare electronic structure of the interfacial region in the polyethylene magnesium oxide nanocomposite with the electronic structures of its bulk constituents. The calculations were performed with density functional theory, the LDA and AM05 functionals were used. Hydroxylated, silanol-terminated (-SiOH) MgO surfaces and an interface (a surface with grafted through Si alkane chains) were studied. Investigation has shown the presence of surface states in untreated (hydroxylated) MgO (111) surface, while for both silanized surfaces these states are removed. It results in 1.7 eV higher band gap energy compared to the untreated case. Untreated regions present in treated nanoparticle are proposed to behave as traps for electrons.

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