EXAFS Studies of the Local Bonding Structures of Ge$_{2}$Sb$_{2}$Te$_{4}$, Ge$_{2}$Sb$_{2}$Te$_{5}$, AND Ge$_{2}$Sb$_{2}$Te$_{7}$

Bond constraint theory (BCT) and rigidity theory provide powerful frameworks for understanding the structure and properties of a-materials. Application of these theories to switching in a-chalcogenides holds the promise of finding the ideal a-chalcogenide suited for switching applications. Recently a-chalcogenide switching of Ge$_{2}$Sb$_{2}$Te$_{5 }$(GST) has been applied successfully to programmable memory devices as well as DVD technology - where the quest for the discovery of better-suited materials continues. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is an ideally suited technique to investigate the switching properties of these materials. We analyze films of amorphous Ge$_{2}$Sb$_{2}$Te$_{4}$, Ge$_{2}$Sb$_{2}$Te$_{5}$, and Ge$_{2}$Sb$_{2}$Te$_{7}$ through EXAFS and propose predictions of their aptitude for reversible phase change using bond constraint theory.