By Gary Thomas
Scientists at the Carnegie Institution for Science have determined the conditions under which the compound nickel oxide can be changed into a metal that is capable of conducting electricity. Nickel oxide has the distinction of being the first compound to be researched for its electronic properties. The compound is an insulator, that is, it does not conduct electricity.
Atmospheric Pressure of 240 Gpa
Physicists have been of the belief that nickel oxide can become a conductor of electricity if it is induced to a metallic state under pressure. However, there has been no confirmation of this belief until the experiment at Carnegie Institute in which enormous pressure 2.4 million times the atmospheric pressure at 240 gigapascals was applied to the compound to change it into a metal with very low electrical resistance.
The electrical and chemical behavior of materials is determined by the electrons present in the outermost shell of atoms known as valence electrons. Non-metals typically possess between five and seven valence electrons while metals possess between one and three valence electrons. The valence electrons in metals are bound loosely as a result of which electrons flow freely. This makes metals good conductors of electricity. Nickel oxide is considered as a transition metal oxide which remains an insulator in spite of its atomic outer shell being only partially filled with electrons.
For their experiment, scientists at Carnegie Institute placed crystal samples of the compound measuring not more than 1 µ in thickness in a specially made diamond anvil enclosure. Measurement of electrical resistance was enabled by means of four thin foil leads. The scientists observed a reduction in electrical resistance at 130 gigapascals and a subsequent 3 order magnitude reduction in resistance on increasing the pressure to 240 gigapascals, indicating the transition into metallic state.