Motional characteristics of positively charged muonium defects in $In2O3$

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 (Mu₁ and Mu₂) at low temperatures while a third state (Mu₃) is introduced as the temperature is increased. Mu₁ is occupied more heavily than Mu₂ at low temperatures by a ratio of ∼8:1. The Mu1 state changes to the Mu₂ state starting at 300 K with site change energy of 0.46±0.11 eV and is essentially not occupied above 500 K. The Mu2 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 Mu₂ and Mu₃ amplitudes and the hop rate of Mu₂ are both roughly constant, implying a steady state trap and release balance between mobile Mu₂ centers and the Mu₃ trap state. Above 650 K, the muonium defects release from the Mu₃ trap to the Mu₂ 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 Mu₂ hop rate, to be 0.43±0.03 eV.