Tricesium

From Memory Alpha, the free Star Trek reference

Tricesium is a material that can be converted into an energy source.

One of the ships that attacked the USS Voyager upon its entrance into the Void in 2377 had a warp core casing composed of tricesium. When Voyager later found the ship crippled and its crew killed, they salvaged the casing and found "Fantome" hiding inside. (VOY: "The Void")