Minimising defects to maximise functionality on the nanoscale
Composites are made of two or more individual materials where the interfaces are maintained and they form the basis of innumerable components and devices. With the advent of nanotechnology, such composite structures can now be formed on the nano scale, comparable to the size of individual molecules. Characterisation of the interfacial properties of composites is critical to the development of novel materials’ systems with enhanced functionalities. Scientists initiated the EU-funded project 'Electron paramagnetic resonance as a probe for extended interfaces in nanomaterials' (EPREXINA) to explore the use of spectroscopic analyses. Electron paramagnetic resonance (EPR) spectroscopy is used to investigate paramagnetic systems with unpaired electrons for detecting free radicals, transition metal ions and defects in materials. Researchers chose barium titanate (BaTiO3), the first ferroelectric oxide discovered. It is also the most widely used ferromagnetic material showing up in applications such as computer memories, sensors and infrared detectors. Using EPR, researchers conducted the first detailed analysis of charged defects in BaTiO3-based powders, ceramics, single crystals, composites, thin films and multi-layers. Data compilation enabled conclusions, many of which have already been published, about the nature of the charged defects and their location in the various materials. EPR revealed a high concentration of charged defects at the surface of nanopowders and at interfaces in composites, and demonstrated a direct link with dielectric properties. Scientists were able to significantly enhance dielectric properties and decrease dielectric losses with modifications based on previous results. In the end, scientists produced an optimal material for selected applications, highlighting the effectiveness of EPR in guiding materials design. EPREXINA conducted the first detailed studies of the influence of surface and interface-charged defects on the properties of nanomaterials. This will pave the way for development of novel, tailored materials’ systems having radically improved properties in comparison to conventional counterparts for many applications. The technique is expected to have major impact on future device functionalities.
