Indentation Recovery in GdPO4 and Observation of Deformation Twinning...

A series of nanoindentation tests on both single and
polycrystalline specimens of a monazite rare-earth orthophosphate, GdPO4,
revealed frequent observation of anomalous unloading behavior with a
large degree of recovery, where previously this behavior had only been
observed in xenotime rare-earth orthophosphates. An indentation site in
the polycrystalline sample was examined using TEM to identify the
deformation mechanism responsible for recovery. The presence of a twin
along the (100) orientation, along with a series of stacking faults
contained within the deformation site, provide evidence that the
mechanism of recovery in GdPO4 is the collapse of deformation twins
during unloading.