Nanomaterials: Specificities of Properties and Synthesis

The concept of material concerns matter in solid state that is endowed with usable properties for practical applications. It is indeed in the solid state that matter exhibits the highest mechanical strength and chemical inertness, providing solidity and sustainability because the solid is based on an extended stiff crystalline framework. It is also in the solid state that many properties exist, including optical, electrical, and magnetic properties, providing great technological progress. A typical example is electronics which owes its enormous development to doped silicon. A material may therefore be defined as a useful solid. The properties of a solid depend directly on its chemical composition, crystalline and electronic structures, texture, as well as morphology and casting. This last point, which is often neglected, is illustrated by amorphous silica glass, which is used largely for its properties such as chemical inertness, mechanical strength, optical transparency, and low thermal and electrical conductivities. These various properties are highlighted through the many possibilities of casting and shaping: flat glass (optical transparency for glazing); hollow glass (chemical inertness and mechanical strength for bottling); short fibers (glass wool for heat insulation) and long fibers (optical fibers); massive pieces (insulators for electric power lines); and thin films (insulating layers for miniaturized electronics). Metal oxides exhibit a wide range of exploitable properties useful for innumerable applications. Silica, SiO2, as flat glass, has excellent optical properties, but other oxides such as LiNbO3 and KTiOPO4 exhibit interesting nonlinear optical properties, allowing changes in the wavelength of the transmitted light. Certain oxides are good electrical insulators (SiO2), but others are true elec­tronic conductors (VO2, NaxWO3), ionic conductors (β-alumina NaAl11O17, NaSiCON Na3Zr2PSi2O12, yttria-stabilized cubic zirconia Zr1–xYxO2–x/ 2), and also superconductors (cuprates such as YBa2Cu3O7–x and Bi4Sr3Ca3Cu4O16+x). Compounds such as BaTiO3, PbZr1–xTixO3, and PbMg1/3Nb2/3O3 are ferroelectric solids used largely as miniaturized electronic components, whereas spinel ferrite γ-Fe2O3, barium hexaferrite BaFe12O19, and garnet Y3Fe5O12 are more or less coercive ferrimagnetic solids used in magnetic recording or as permanent magnets.