As everal atomic layers thick magnesium fluoride (MgF 2 )f ilm is successfully deposited onto each individual grain of an ultrahigh-potential LiMn 1.5 Ni 0.5 O 4 -powder material for Li-ion batteries. The resulting film has am arked protection action, as it does not compromise the cathode performance substantially,w hile it extends the cycle life of the cathodes prepared from the coatedp owder.T he protective effect is pronounceda t4 58Ca nd the catastrophicc apacity fading is halted. The essence of the protecting action is suggestedt ob ei nb lockingt he access of aggressive electrolyte-decompositionb yproducts to the cathode material surface.

We present a method for investigating the spatial changes of elastic moduli in a nm-scale vicinity of interfaces. The method is demonstrated on twin walls in PbTiO(3) single crystals. It is revealed that the region near the twin wall is significantly softer than the two domains surrounding it. A comparison with finite element simulations relates this effect to an anelastic relaxation due to point defect accumulation around the twin wall. Local softening around the twin wall can affect the overall elastic modulus in thin films and nanostructured ferroelectric materials, in which the average distance between twin walls is smaller than the thickness of the softer region.

No abstract

Modulus mapping using nanoDMA (Dynamic Mechanical Analysis) is a recently developed technique based on a nanoindentation instrument equipped with an AFM-like piezoscanner and dynamic force modulation system. The surface properties, storage and loss moduli are quantified based on the Hertz model for the contact mechanics of the sample-tip configuration. In this approach, the applied load, topography features, and their size may have a pronounced effect on the obtained results. In order to demonstrate that, internal interfaces of deep sea sponge (Monorhaphis chuni), which comprises alternating layers of relatively thick (4 μm in average) biosilica and thin (60 nm) organic material, were characterized using the nanoDMA modulus mapping technique. Experimental data were analyzed in tight interrelation with finite element simulations. This combination allowed us to evaluate elastic modulus of a 60 nm wide organic layers in M. chuni.

Nacre, also known as mother-of-pearl, is a hard biological composite found in the inside layer of many shells and composed of ~95% mineral (aragonite) and ~5% protein-rich organic material [1]. Amazingly, although the mineral is a very brittle material, nacre can still sustain significant inelastic deformation and exhibit toughness 2-3 orders of magnitude larger than that of the mineral alone [1,2]. Numerous studies have been conducted with an aim of understanding the origin for the superior properties of the nacre and mimicking them. Recent theoretical and experimental mechanic studies show that the high toughness is a result of a large crack process zone induced by sliding of interfaces [3][4][5].We apply nanoscale modulus mapping method, for visualizing the 2D-distribution of the mechanical characteristics in samples which were cut across two perpendicular directions from Perna canaliculus shells. Measured elastic moduli of the aragonite were in good agreement with bulk properties. Moreover, we found that the aragonite elastic moduli are anisotropic and we explained it by taking x-ray diffraction measurements which indicate on a strong preferred orientation of the aragonite crystalline tablets within the nacre. Further analysis was conducted by comparing the measured results with finite element simulations, which took into account the tip radius of curvature and the physical thickness of the organic layers as measured by means of Electron Back Scattered Diffraction (EBSD). This analysis showed that the Young modulus of the organic material is significantly higher than previous assumptions and is about 40GPa. The measured elastic moduli across mineral/organic interfaces exhibit gradual changes within a thickness at least 3 times larger than that of the EBSD and the simulations.We explain this phenomenon to be a result of organic molecules that penetrate into the mineral material, having relatively high concentration in the vicinity of the organic/mineral interface. Thus, the nacre should be considered as a natural functionally graded material. A behavior of this type is unique to biogenic materials and distinguishes it from synthetic composite materials. Basing on these finding we suggest a mechanism for massive plastic deformation through interface sliding, which may explain their superior fracture toughness.