Chronon Blocker

The Chronon Blocker was a temporal device constructed by the Doctor using a different collection of objects on two known occasions.

History
On Kaalann, the Eleventh Doctor collected a Dalekanium coil and a Kontron crystal, using them to construct a chronon blocker to stabilise Amy Pond, who she had became a temporal paradox and started to fade after the Daleks altered history and exterminated humanity before her birth. The Doctor's TARDIS had the same effect, but that could only last for so long. (VG: City of the Daleks)

When Amy was trapped in a version of the TARDIS 1,000 years into the future. The Doctor scavenged parts from the present TARDIS in order to create a tachyon feedfack loop which would reunite him and Amy. The Doctor managed to scavenge three items; his Fob watch, a Oscillator from the distress beacon he picked up earlier and a Kontron crystal to make a Chronon Blocker; using this, the Doctor was able to successfully make the feedback loop. (VG: TARDIS)