© Max-Planck-Institut für Eisenforschung GmbH

Coupling defects and electrical properties of ceramic materials

This project aims to correlate the localised electrical properties of ceramic materials and the defects present within their microstructure. A systematic approach has been developed to create crack-free deformation in oxides through nanoindentation, while the localised defects are probed in-situ SEM to study the electronic properties. A coupling of dielectric spectroscopy is made with in-situ micro/nano-mechanical testing. The correlation between defects and electrical properties provides information about the local deformation-conductivity phenomena, improving electrical properties of material, and may enable predicting failure of materials.

Despite the brittleness of oxides, we are able to deform the material without crack-formation. This is done through nanoindentation pop-in-stop experiments utilising small indenter tip dimensions [1]. Mechanical behaviour of materials in the plastic regime is studied with electron channelling contract imaging (ECCI) to identify the deformation mechanisms (Fig. 1). The novel approach of this project involves performing low-load mechanical deformation which does not lead to failure of the material (Fig. 2), as well as having the ability to locally approach the plastic zone for electrical characterisation.

Local electrical properties of deformed zones in the oxides are studied through impedance spectroscopy inside SEM. Microcontacts are deposited with GIS-FIB system, while nanometre-sharp needles are driven by the micromanipulator to probe the microcontacts. Such experiments aim to develop a correlation between the changes in the dielectric properties and the plastic deformations inside the ceramic materials. This technique represents a promising non-destructive method to improve reliability of ceramic materials at the micro- and nanoscale as well as to predict their mechanical behaviour, while they are exposed to mechanical load.

Fig. 1: Images taken on indented regions on (001) TiO2 where pop-in stop tests were carried out: (a) ECCI measurement showing no crack induced but features of (partial) dislocations which are not yet developed to twins [1] in the indented region and pileups (white arrows) with R = 1 μm; (b) ECCI measurement showing cracks initiated mainly on (110) planes, together with slip lines (white arrows) on all four  systems with R = 5 μm.

Fig. 2: Representative load-displacement curves for TiO2 with different tip radii, demonstrating the pop-in-stop tests.
 

 

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