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Item type:Publication, Access status: with files , Thickness-dependence of the breakdown strength: analysis of the dielectric and mechanical failureThe breakdown strength as well as the mechanical strength of ceramic materials decreases with increasing volume. The volume-effect of the mechanical strength can be explained by the Weibull theory. For the breakdown strength the same explanation has been often assumed. In order to validate this assumption breakdown strength and mechanical strength of alumina samples with defined porosities were compared. Differences in the Weibull moduli of breakdown and mechanical strength distributions indicate that the volume-effect cannot explain the thickness-dependence of the breakdown strength. In particular, the thickness-dependence of the breakdown strength always leads to a Weibull modulus of two which is not in agreement with the measured Weibull moduli for samples with constant thickness. It can be concluded that the thickness-dependence of the breakdown strength cannot be explained by the Weibull concept. A recently developed breakdown model which is based on space charge injection is able to explain the experimental results.Publicationtype: Journal ArticleScopus© Citations 85 645 3576 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Dielectric breakdown of alumina single crystalsThe bulk breakdown behaviour of alumina single crystals with two different crystal orientations, {11-20}-plane (single crystal A) and {0001}-plane (single crystal C), have been studied. Therefor plan-parallel single crystal samples were electrically loaded until dielectric breakdown was achieved. For each crystal orientation, a characteristic breakdown channel direction through the sample could be defined. In C-oriented crystals the breakdown channel originated parallel to the c-axis. For A-oriented crystals however, the breakdown channel crossed the sample in an oblique direction; the angle between crystal surface and breakdown channel was 60°. Here, the breakdown channel crossed the sample along an A-plane. Although the breakdown channel paths of A and C crystals are different, the observed breakdown strength are identical within the scatter range.Publicationtype: Working Paper822 1644 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , What do we know about surface charges on cracks in ferroelectric ceramics?The present work investigates the static and time dependent electric potential distribution around cracks in a poled ferroelectric ceramic by Kelvin Probe Force Microscopy (KFM). In a first step a Vickers indentation crack in poled lead zirconate titanate (PZT) was subjected to static electric fields of up to 500 V/mm in poling direction, and the potential distribution around the crack as measured. In a second step, the polarity of the applied voltage was reversed against the poling direction during the measurement of the potential. Using a simple model, an effective dielectric constant of the crack, as well as the surface charge density on the crack face were calculated as a function of the distance from the crack tip, the applied field and the time. The results are discussed with reference to free charges on the crack surface, electrically induced domain switching at the crack tip and crack bridging.Publicationtype: Conference Paper620 844 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimenteller Aufbau zur Messung der Energiefreisetzungsrate für Risswachstum in PZT unter elektromechanischer LastFour-point-bending V-notched specimens of PZT poled parallel to the long axis are fractured under conditions of controlled crack growth in a custom-made device. In addition to the mechanical loading an electric field is applied parallel or anti parallel to the poling direction. This is a typical loading condition for the application of piezo- and ferroelectric ceramics, respectively. To determine the different contributions to the total energy release rate the mechanical and piezoelectric compliance as well as the electrical capacitance of the sample are acquired continuously with a special technique as a function of the crack length. The derivation of the data with respect to the crack surface allows calculating all parts of the total energy release rate on the basis of a single bending experiment for the first time. The main focus here is the presentation of the experimental method.Publicationtype: Conference Paper812 527