At standard atmospheric or ambient pressure, the lithium beryllium (LiBe) alloy is unstable. However, at high density and at relatively high pressure, the predicted alloy stabilizes. As the atoms are squeezed in tightly, lithium's ionic cores (the larger of the two) begin to overlap. This creates a sort of "wall" that forces the outer (valence) electrons out of the lithium layer, and over to the beryllium layer. It is there that the electrons form a curious two-dimensional gas. In contrast, electrons in most metals bounce about quite freely in a three-dimensional fashion.

Full story at:
http://nsf.gov/news/news_summ.jsp?cntn_id=111031

Praise:
“Cool graphic, thanks! It explains the concept much better than I could.”

--Lauren Gold
Science Writer
Cornell Chronicle