1. An electrically operated, single-cell memory element comprising: a volume of memory material comprising a heterogeneous mixture of a phase-change material and a dielectric material, said phase-change material programmable to a plurality of detectable resistivity values in response to an electrical signal, said dielectric material being between about 60 and 90 percent of said volume of memory material; and means for delivering said electrical signal to at least a portion of said volume of memory material.