Paramagnetic Intrinsic Point Defects in Alkali Phosphate Glasses: Unraveling the P-3 Center Origin and Local Environment Effects

L Giacomazzi and NS Shcheblanov and L Martin-Samos and ME Povarnitsyn and S Kohara and M Valant and N Richard and N Ollier, JOURNAL OF PHYSICAL CHEMISTRY C, 125, 8741-8751 (2021).

DOI: 10.1021/acs.jpcc.0c11281

In this work, we carry out a first-principles investigation of intrinsic paramagnetic point defects in P2O5 and in Na2O-P2O5 glasses as a representative of alkali phosphate glasses. Glass models are generated by combining classical molecular dynamics and Monte Carlo simulations and validated by comparing their corresponding structure factors with the available X-ray and neutron scattering experiments. We use density functional theory to calculate the electron paramagnetic resonance parameters for a large set of paramagnetic oxygen-vacancy configurations. Our investigation, also by unveiling the effect of the local environment and disorder on the hyperfine tensor, enables us to propose a new model for the much debated P-3 center. In particular, we establish the occurrence of two variants, which we name P-3(a) and P-3(b) centers, that are instrumental to explaining the experimental shifts of the hyperfine splittings observed in alkali phosphate glasses as a function of the alkali content x in the phosphate glass. Our scenario predicts that for low to intermediate alkali contents (0 < x < 50%), a mixture of P-1 and P-3(a) centers should be generated under irradiation. For x > 50%, essentially only P-3(a) and P-3(b) centers would be generated, while P-1 will be absent. Therefore, our findings, by providing an improved mapping of P centers in phosphate glasses, pave the way for fine-controlling/tuning the optical absorption in a wide range of technological applications.

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