7 noboru yamada u201c potential of ge u2014 sb u2014 te phase change optical disks for high data rate recording u201d spie v 3109 pp 28 37 1997 more generally a transition metal such as cr fe ni nb pd pt and mixtures or alloys thereof may be combined with ge sb te to form a phase change alloy that has programmable resistive properties specific examples of memory materials that may be useful are given in ovshinsky 39 112 cols 11 13 which examples are hereby incorporated by reference phase change alloys are capable being switched between a first structural state in which the material is generally amorphous and a second structural state in which the material is generally crystalline in its local order these alloys are at least bistable the term amorphous is used to refer to a relatively less ordered structure more disordered than a single crystal which has the detectable characteristics such as high electrical resistivity the term crystalline is used to refer to a relatively more ordered structure more ordered in an amorphous structure which has detectable characteristics such as lower electrical resistivity than the amorphous state typically phase change materials may be electrically switched between different detectable states of local order across the spectrum between completely amorphous and completely crystalline states other material characteristics affected by the change between amorphous and crystalline phases include atomic order free electron density and activation.