A new kind of metal in the deep Earth

Dec 19, 2011
A new kind of metal in the deep Earth

(PhysOrg.com) -- The crushing pressures and intense temperatures in Earth's deep interior squeeze atoms and electrons so closely together that they interact very differently. With depth materials change. New experiments and supercomputer computations discovered that iron oxide undergoes a new kind of transition under deep Earth conditions. Iron oxide, FeO, is a component of the second most abundant mineral at Earth's lower mantle, ferropericlase.

The finding, published in an upcoming issue of , could alter our understanding of deep Earth dynamics and the behavior of the protective magnetic field, which shields our planet from harmful .

Ferropericlase contains both magnesium and iron oxide. To imitate the in the lab, the team including coauthor Ronald Cohen of Carnegie's Geophysical Laboratory, studied the of iron oxide to pressures and temperatures up to 1.4 million times and 4000°F—on par with conditions at the core-mantle boundary. They also used a new computational method that uses only fundamental physics to model the complex many-body interactions among electrons. The theory and experiments both predict a new kind of metallization in FeO.

Compounds typically undergo structural, chemical, electronic, and other changes under these extremes. Contrary to previous thought, the iron oxide went from an insulating (non-electrical conducting) state to become a highly conducting metal at 690,000 atmospheres and 3000°F, but without a change to its structure. Previous studies had assumed that metallization in FeO was associated with a change in its crystal structure. This result means that iron oxide can be both an insulator and a metal depending on temperature and pressure conditions.

"At high temperatures, the atoms in iron oxide crystals are arranged with the same structure as common table salt, NaCl," explained Cohen. "Just like table salt, FeO at ambient conditions is a good insulator—it does not conduct electricity. Older measurements showed metallization in FeO at high pressures and temperatures, but it was thought that a new crystal structure formed. Our new results show, instead, that FeO metallizes without any change in structure and that combined temperature and pressure are required. Furthermore, our theory shows that the way the electrons behave to make it metallic is different from other materials that become metallic."

"The results imply that is conducting in the whole range of its stability in Earth's lower mantle." Cohen continues, "The metallic phase will enhance the electromagnetic interaction between the liquid core and . This has implications for Earth's magnetic field, which is generated in the outer core. It will change the way the is propagated to Earth's surface, because it provides magnetomechanical coupling between the Earth's mantle and core."

"The fact that one mineral has properties that differ so completely—depending on its composition and where it is within the Earth—is a major discovery," concluded Geophysical Laboratory director Russell Hemley.

Explore further: How do liquid foams block sound?

Provided by Carnegie Institution

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tadchem
not rated yet Dec 19, 2011
Between this report and the recent report that PbO2 in lead-acid batteries becomes a conductor when it loses a small amount of oxygen, the 'conventional wisdom' that metal oxides are insulators is being tossed aside.
SteveL
5 / 5 (5) Dec 19, 2011
Do you think that some metals, or metal oxides melted under extreme pressure and allowed to cool under pressure would maintain their highly conductive attribute after the metal had cooled and crystalized?
Isaacsname
not rated yet Dec 19, 2011
Good question Steve

Slower cooling leads to larger grains and fewer boundaries between colony groups in metals. I don't have anything in my metallurgy books about cooling under pressure though..o,O
SteveL
5 / 5 (1) Dec 19, 2011
Thanks. I've also often wondered about metal cooling while under the influence of magnetic flux. If magnetism could be used to align the grains parallel with the conductor as they crystalize under pressure I would tend to believe that would further improve not only the conductive but also the magnetic properties. This would likely alter the physical attributes also.
Graeme
not rated yet Dec 19, 2011
although ferropericlase has the end member of FeO it does not mean that the mineral with Magnesium in it as well is a conductor. Perhaps it will separate out. It would be interesting the know the density of the material under pressure, and what proportion of the rock would be this material. Somehow I suspect that it would not be enough to make the rock a bulk conductor. But if FeO separated out as a layer at the core mantle boundary then it would be highly significant.
Isaacsname
not rated yet Dec 19, 2011
Thanks. I've also often wondered about metal cooling while under the influence of magnetic flux.


I believe the process is called a " Rapid cooling and magnetic field-induced cooperative effect " , a type of fast quenching.
DougCoulter
5 / 5 (2) Dec 19, 2011
In virtually all high pressure experiments, any reversible change caused by pressure reverts when the pressure is removed. Carbon to diamond - different crystal structure, doesn't revert. But they actually made it pretty clear here that this isn't the case with FeO - no permanent change. So take off the pressure and it reverts.

Yes, you can play with the magnetism by cooling in a field, but not all that much.
Blakut
5 / 5 (1) Dec 20, 2011
Imagine how strong the mag field has to be to counteract the thermal movement of the atoms and molecules in hot or melted metal. Iron loses its ferromagnetic properties at aroung 770C, right?
signoftimes
not rated yet Dec 20, 2011
This is exciting information. I see this as being highly useful to researchers studying the earths magnetic field and the increasing variances that are being observed. Also to the research of ground currents. Bravo to these researchers and this new significant information. This is science done right.
hb_
5 / 5 (4) Dec 20, 2011
Since this is a science page, they should use either Kelvin or Celsius. Fahrenheit is just an outdated archaic unit that's used for cooking in some countries
MarkyMark
2.3 / 5 (3) Dec 20, 2011
Since this is a science page, they should use either Kelvin or Celsius. Fahrenheit is just an outdated archaic unit that's used for cooking in some countries

This site also caters to the layperson who is curiouse about science so using such a term does make some sense.
Ojorf
not rated yet Dec 25, 2011
The Fahrenheit temperature scale was replaced by the Celsius scale in most countries during the mid to late 20th century and it only remains the official scale of the United States, Cayman Islands and Belize. It is also a stupid scale. The metric system RULES!
Shelgeyr
not rated yet Dec 25, 2011
I'm glad they're looking at Iron oxide, FeO, at these pressures and temperatures. Now if they'd just add in some Calcium Carbonate and water to their experiments they'd probably be astonished with (one of) the results (petroleum).
sunapi386
not rated yet Dec 26, 2011
Like that lead acid car battery article - I find it strange that oxides can be highly conductive and very non-conductive even if they have very similar structures.
Callippo
1 / 5 (1) Dec 26, 2011
some metals, or metal oxides melted under extreme pressure and allowed to cool under pressure would maintain their highly conductive attribute
Under special arrangement they can form the islands or stripes of highly compressed phase surrounded with layer of atoms, which keep this phase together. Such question is particularly interesting for construction of superconductors, which I do believe work on the same principle. The repulsive electrons are compressed with lattice into dense islands of superconductive phase.

Some of these materials were studied already and they can serve as an accumulators of chemical energy, which is substantially higher, than the common energy density.

http://www.nature...321.html
http://www.fas.or...n/he.pdf
Callippo
1 / 5 (1) Dec 26, 2011
I find it strange that oxides can be highly conductive and very non-conductive even if they have very similar structures.
It's given with the fact, these materials contain islands of highly movable electrons, which are separated with narrow insulating gaps. Even it the voltage required for their breakthrough is in few microelectronvolts range, due the presence of huge amount gaps inside of atom lattice such a material becomes non conductive in bulk. The extreme case of such behavior are topological insulators, the conductivity of which in bulk phase is much lower, than at their surface, where the energy gaps between conductive islands of electrons are lowered. Only subtle change of temperature would lead into pronounced change of their conductivity. After all, the doped semiconductors are behaving in similar way, because the electrons around impurities are behaving like conductive islands separated with gaps.

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