Materials potentially harder than diamond : quenchable high-pressure phases of transition metal dioxides

• Published in: Journal of materials science letters Vol. 13; no. 23; pp. 1688 - 1690
• Main Authors: LEGER, J. M, HAINES, J, BLANZAT, B
• Format: Journal Article
• Language: English
• Published: Dordrecht Kluwer Academic Publishers 01.01.1994
• Subjects: Condensed matter: structure, mechanical and thermal properties; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Physics; Solid-solid transitions; Specific phase transitions; Cubic lattices; Pressure volume ratio; Inorganic compounds; Pressure effects; Equations of state; Tetragonal lattices; Phase transformations; Transition element compounds; Ruthenium oxides; Experimental study; Lattice parameters; Knoop hardness
• ISSN: 0261-8028; 1573-4811
• DOI: 10.1007/BF00451741

Findings are presented from pressure-volume relationships obtained by angle-dispersive x-ray powder diffraction on the high-pressure phases of RuO sub 2 and HfO sub 2 . The results indicate that both are significantly stiffer than cubic boron nitride and are as stiff or stiffer than diamond. It is the first time that a high-pressure phase that can be kept in a metastable state under normal pressure is reported to display a higher bulk modulus than diamond. This raises the possibility of finding new stiff materials. From the correlation between bulk modulus and hardness, it is evident that the high-pressure phases of these oxides, and possibly of several other transition metal dioxides, could present a new family of ultra-hard materials. Partial reverse transformation occurred in both compounds, and stabilization of these and other high-pressure oxide phases is discussed.