Seminars Archive

Experimenting at extreme conditions

Abstract
Application of extreme conditions to the matter not only helps to understand intrinsic properties of materials but allows uncovering the potential of the matter in response to high pressures and temperatures. That knowledge is used for an explanation of phenomena occurring at naturally high P and T (e.g. planets interior) as well as for production of novel advanced materials possessing unique and often also tunable properties. Thus, materials with the desirable structural motif and a bond pattern can be designed to show variable electronic and magnetic properties. Examples of high-pressure synthesis of transition metal- and main group elements nitrides will be presented. High pressure is not only an additional parameter for tuning properties in existing materials but also a powerful tool for creating non-existing at ambient conditions compounds. As, no compounds can be formed at ambient pressure between heavy alkali metals and transition elements (except for gold). However, electron band calculations predict a pressure-induced s-to-d electronic transition in alkali metals favouring an alloy formation with transition elements. We report new chemistry for rubidium under high pressure leading to a synthesis of a novel compound with transition metal platinum. Alloying of Rb and Pt became possible upon compression due to the pressure-induced s-to-d electronic transition monitored experimentally by means of XANES at the Rb K-edge at pressures above 9 GPa. Subsequent alloying with Pt in the pressure range 12-20 GPa was revealed both by synchrotron XANES and x-ray diffraction. The new compound was assigned hexagonal unit cell with parameters a=5.054 and c=12.405 Ã… at 20 GPa. Observation of the novel compound in-between Rb and Pt is an important step for understanding the trend within heavy alkali metals-transition metal series. These compounds are of interest since they are expected to exhibit unusual crystal and electronic structures as a result of the transition to directional d electron bonding in the alkali metals under pressure. Possibilities and advantages of the free-electron laser for studies of matter under extreme conditions will be discussed.