The role of doping and microstructure on hydrogen solubility in monoclinic ZrO2: Experimental validations of simulated defect chemistry

The effect of chemical doping and ceramic microstructure on H solubility was measured systematically for the first time in monoclinic ZrO2. Excitingly, the influence of chemical doping by Fe, Cr and Ta cations on bulk H solubility was in qualitative agreement with defect chemistry simulations based on density functional theory and statistical thermodynamics. This is the first experimental validation of the recently-developed modeling framework, which is capable of high-throughput defect chemistry computations of light elements in metal oxides. H solubility was quantified using temperature-programmed desorption and was measured for various microstructures and under varied oxygen partial pressure, enabling us to identify the microstructural origin (i.e. bulk, surfaces and grain boundaries) of sorbed H defects and infer their defect type. Doping the oxide resulted in a significant increase in the H-uptake time, indicating that solute cations slowed H defect diffusion. Ta doping offered the lowest bulk H solubility at all measurement temperatures (410 degrees C-60 degrees C), though Fe doping also lowers bulk solubility at lower temperatures and yielded the most tightly bound H defects of all oxides. This could be significant in applications where one wishes to minimize H permeation via limiting diffusion kinetics. Based on this work we emphasize the role of both doping and microstructure on the overall H uptake and highlight the importance of elucidating the relative nuances of each oxide system; we thus reiterate the value of a high-throughput computational analysis. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.