DOE logos

CIW-GL logos

Efree

More to store with GST

GST in diamond anvil cellGe2Sb2Te5 (GST), a germanium, antimony, and tellurium alloy, is a material which has been used in rewritable optical media (CD-RW and DVD-RW discs) for about two decades. Recent collaborative research effort involving EFree Center scientists focused on the properties of this compound, subjecting samples to pressure as an alternative to heat. Researchers uncovered electrical resistance characteristics which could lead to higher data density storage systems that both last longer and react quicker than current optical, flash, or magnetic media. The findings suggest that GST can be even more useful in the computer and electronics industries.

GST is known as a phase-change material because, when exposed to heat, GST changes from an amorphous alloy to an ordered crystal and back again. In its amorphous state, GST has high resistance to electric current. In its crystalline state, it has low resistance. The two phases also reflect light differently, which allows the GST-coated surface of a storage media, like a DVD, to store information and be read by tiny lasers. 

Although GST was discovered in the early 1980s and manufactured commercially in the 1990s, the precise mechanics of the state change has remained something of a mystery because it happens so quickly, in nanoseconds, when the material is heated. To solve this mystery, the research team used diamond anvil cell (DAC) high-pressure technique to compress the material. A more gradual phase change is achieved thusly. Researchers employed X-ray diffraction, resistivity measurements, and a computer simulation to document what was happening to the material at the atomic level. They found that they could "tune" the electrical resistivity of the material by four orders of magnitudes between its change from amorphous to crystalline phase.

The research was carried out in collaborations between EFree members Lin Wang and Wenge Yang, and researchers at Johns Hopkins, Oak Ridge National Laboratory, George Mason University, and Beijing University of Technology.

See the details in M. Yu et al., Proc. Nat. Acad. Sci.,109, E1055 (2012).