Secure the emergence of metallic properties in oxide managed under incredibly high pressure, which almost 2.5 million times greater than atmospheric pressure (240 GPa). Report on the opening published in the journal Physical Review Letters.
Fig. 1. Diamond grip while holding them in the sample (photo Steve Jacobsen / Northwestern University).
The achievement is considered the scientific world as a significant contribution to the science of condensed matter.
Physics of the past have repeatedly predicted for nickel oxide possibility of transition from state prison to the conductor of the metal type, but it is not found practical confirmation. But science itself has considered the importance of this result is about the level of the opening of the metallic conductivity of hydrogen.
Recall that in the case of simple substances and chemical behavior of the electrical conductivity are determined only by the nature of valence electrons. Metals generally have one or three valence electrons while nonmetals blocked at 5-7 on an external electron level (this is of course very primitive description, which is suitable for the elements of the first two periods, all the alkali and alkaline earth metals, and also for halogen and chalcogen, as with the others, one of whom he falls and nickel, are not easy to get). Metals — perfect electric conductors, as their valence electrons are easily parted with the nucleus, forming a so-called free-electron gas.
Nickel oxide — a typical transition metal oxide, which, despite having only partially filled outer electron level, is still an insulator.
The authors have put a very thin crystals (less than a micron in thickness) in a specially designed diamond grip, carrying out a resistance measurement with four ultra-thin pieces of lead foil.
According to the observations, the measured resistance drop was recorded for the first time at a pressure of about 1.3 million atmospheres (130 GPa). However, when the level of 2.4 million there was a jump of conductivity by three orders of magnitude, and announced to the world that the transition from the semiconducting (by that time had semiconducting) to the metallic state.
Moreover, the metal of the material to be only in the region of maximum compression, and not throughout the entire volume.
The results not only prove the efficiency of the theoretical concept, but it will serve to further improve, so that in the future be able to more accurately predict the properties of new materials and offer rational methods for their preparation.