The "Null Zone weapon," as Seratrix referred to it, was a Time Lord device from the Omega Arsenal. When the War Doctor detonated a Time Destructor to destroy the Dalek Time Fleet, (AUDIO: The Innocent) several Time Lords, including Seratrix, gave the Daleks the weapon as a sign of good faith to end the Last Great Time War. The Daleks used it to create the Null Zone with a Thousand Worlds (AUDIO: The Thousand Worlds) as a powerbase and claimed they'd be content to live in peace with the Time Lords. (AUDIO: The Heart of the Battle)
Following the end of the war, which saw the conflict itself time locked from reality, the usage of the Null Zone weapon was among the wartime incidents which were recorded in the Dalek pathweb but could not be verified by the New Dalek Paradigm. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)