ETD Collection

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Subject: search.filters.subject.Metal oxide semiconductors

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    Degradation analysis of metal oxide varistors under harmonic distortion conditions
    (2016-10-11) Bokoro, Pitshou Ntambu
    Modern electrical networks provide an opportunity for inevitable interaction between metal oxide arresters and power system harmonics. Therefore, these arrester devices are continuously exposed to the combined e ect of distorted system voltage and envi- ronmental thermal stresses. Recent studies supported by eld experiments have shown signi cant rise in the leakage current through these surge arrester devices when exposed to ac voltage with harmonics. However, the major shortcoming in the current knowledge and applications of varistor arresters resides on the reliability and the electrical stabil- ity of these overvoltage protection units, when subjected to long-term and continuous distorted ac voltage and thermal stresses from the environment. Commercially-sourced ZnO arresters of similar size and electrical properties are tested using standard ac accelerated degradation procedure or electro-thermal ageing test. The times to degradation, the coe cient of non-linearity, the reference voltages, as well as the clamping voltage measured are used to analyse the reliability and the electrical stability of the metal oxide-based arrester samples. The resistive component of the leakage current is extracted from the measured total leakage current. The three-parameter Weibull probability model is invoked in order to analyze the degradation phenomenon.
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    Determination of elastic constants of transition metal oxide based thin films using surface brillouin scattering
    (2016-09-19) Ayele, Fekadu Hailu
    Bismuth ferrite BiFeO3 is a transition metal oxide that exhibits both antiferromagnetic and ferroelectric orderings and is termed a magnetoelectric multiferroic. These functional properties make it crucial for applications in various nanoelectronic devices and sensors. However, the integration of BiFeO3 in devices requires the scaling down of bulk BiFeO3 to nano dimensional length scales in thin lm format. For this purpose, the elements of the elastic constant tensor of BiF eO3 thin lms are requisite, especially in multilayered or single layer-on-substrate device con gurations. It is thus essential that mechanical properties of BiFeO3 thin lms be established due to their size and growth mode dependence. Therefore, the study aims to determine the propagation of the surface acoustic waves and the elastic constants of BiFeO3 BFO thin lms in order to tailor the mechanical properties for device applications. In this approach the e ect of morphology and microstructure on the elastic constants has been investigated.