Synthesis of superhard materials
Résumé
With recent advances in high-pressure techniques, it has become possible to achieve significant compression of densities. Such changes of density will undoubtedly lead to new and unexpected effects. Highly compressed solids reveal a broad variety of unusual phenomena, such as the metal-insulator transition 1-4 , electronic isostructural transitions 5 , unexpected behavior in melting curves 6,7 , pressure-induced amorphization 8-10 , as well as incommensurate and 'host-guest' structures 11,12. The focus on extreme conditions is also fueled by industrial interest in the synthesis of new materials with potentially useful properties such as superhardness or superconductivity. Superhard materials can be defined as having a Vickers hardness H V > 40 GPa. In addition to high hardness-the capability of a material to withstand imprinting or scratching with another material-superhard materials usually possess other unique properties, such as compressional strength, shear resistance, large bulk moduli, high melting temperature, chemical inertness, and high thermal conductivity. This combination of properties makes the materials highly desirable for a number of applications 13. The design of novel materials with a hardness comparable to that of diamond (H V = 115 GPa 14) poses a considerable experimental challenge 15. Recent experimental efforts to synthesize new superhard phases have been based on the assumption that hardness is determined primarily by elastic moduli: bulk modulus 16 (a measure of resistance to volume change created by applied pressure) and shear modulus 17 (a measure of resistance to reversible deformation upon
Domaines
Planète et Univers [physics]
Origine : Fichiers éditeurs autorisés sur une archive ouverte
