Motional characteristics of positively charged muonium defects in In 2 O 3

We report on a study of the motional characteristics of positively charged muonium defect centers in In2O3 powder. Zero field muon spin relaxation (ZF-MuSR) measurements were taken from 2 K to 950 K. Results show the positively charged muonium defects occupying two states (Mu(1) and Mu(2)) at low temperatures while a third state (Mu(3)) is introduced as the temperature is increased. Mu(1) is occupied more heavily than Mu(2) at low temperatures by a ratio of +/- 8: 1. The Mu(1) state changes to the Mu(2) state starting at 300 K with site change energy of 0.46+/-0.11 eV and is essentially not occupied above 500 K. The Mu(2) state becomes diffusively mobile with a barrier of 0.78+/-0.07 eV at 350 K and begins trapping at Mu3 at 400 K with a capture energy of 0.56+/-0.019 eV. A metastable region is observed between 500 K and 650 K in which the ratio between Mu(2) and Mu(3) amplitudes and the hop rate of Mu(2) are both roughly constant, implying a steady state trap and release balance between mobile Mu(2) centers and the Mu3 trap state. Above 650 K, the muonium defects release from the Mu(3) trap to the Mu(2) diffusive state with a dissociation energy of 0.901+/-0.003 eV. The upper limit on the high temperature diffusion barrier is determined, from the Mu(2) hop rate, to be 0.43+/-0.03 eV