Kinetics of Cr3+ to Cr4+ ion valence transformations and intra-lattice cation exchange of Cr4+ in Cr,Ca:YAG ceramics used as laser gain and passive Q-switching media (original) (raw)
2019, The Journal of Chemical Physics
This paper focuses on the kinetics of Cr 4+ formation in Cr,Ca:YAG ceramics prepared by solid-state reaction sintering. The kinetics of Cr 4+ formation was studied by annealing of Cr,Ca:YAG ceramics in ambient air under different temperatures at different times, resulting in the transformation of Cr 3+ to Cr 4+. The activation energy (Ea) of Cr 3+ oxidation determined by the Jander model was 2.7 ± 0.2 eV, which is in good correlation with the activation energy of innergrain oxygen diffusion in the YAG lattice. It is concluded that Cr 3+ to Cr 4+ transformation in YAG ceramics is limited by oxygen diffusion through the grain body. It was established that in Cr,Ca:YAG ceramics, the intralattice cation exchange, in which the Cr 4+ ions exchange positions with the Al 3+ ions, switching from "A" to "D" sites, is faster than Cr 3+ to Cr 4+ oxidation. In the temperature range of 900-1300 ○ C, the reaction enthalpy of Al 3+ /Cr 4+ ion exchange between octahedral "A" and tetrahedral "D" lattice sites is close to zero, and this exchange ratio is thermodynamically driven by entropy.
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