DETROIT—Most solid materials can be neatly divided into two structure systems - crystal or glass. Crystal structures have atoms that fall in to a well-ordered lattice structure, and glass structures have atoms that fall randomly. A team of researchers have discovered that one particular material, Bi₂Ti₂O_7, exhibits unusual characteristics of both glass and crystal. 

According to the researchers, the positively charged nuclei of the material are ordered in a crystalline structure, while the positions of the negatively charged electrons are random. "This mixture of crystalline and glassy behavior has been observed previously in magnetic systems, but the identification of this behavior in Bi2Ti2O7 could confirm a new type of electronic order," stated Gavin Lawes, Ph.D., assistant professor of physics at Wayne State University and resident of Grosse Pointe Woods, Mich.

Their conclusions, found in the June 2009 issue of Physical Review B by The American Physical Society, are based on evidence that low temperature measurements of the thermodynamic properties of Bi₂Ti₂O₇  is an experimental realization of a "charge ice" system, where the electronic disorder arises because the electrostatic interactions are frustrated by the geometry of the underlying atomic lattice. 

"This result is significant," commented Lawes, "because the properties of the disordered electrons in a crystalline material may be very different than what is observed in conventional crystalline systems." This discovery may ultimately lead to new types of technologically important electronic materials.