Endogenous ¹⁷O Dynamic Nuclear Polarization of Gd-Doped CeO<inf>2</inf>from 100 to 370 K

17O NMR is an invaluable tool to study the structure and dynamics of oxide materials, but remains challenging to apply in many systems. Even with isotopic enrichment, studies of samples with low masses and/or concentrations of the active species, such as thin films or interfaces, are limited by low sensitivity. Here we show how endogenous dynamic nuclear polarisation (DNP) can dramatically improve sensitivity in the oxide-ion conductor Gd-doped CeO2, with a 17O enhancement factor of 652 at 100 K. This is the highest enhancement observed so far by endogenous DNP or Gd3+ DNP, which is explained in terms of the electron paramagnetic resonance characteristics. The DNP properties are studied as a function of Gd concentration for both enriched and natural abundance samples and the buildup behaviour shows that spin diffusion in 17O-enriched samples improves sensitivity by relaying hyperpolarisation throughout the sample. Notably, efficient hyperpolarisation could still be achieved at elevated temperatures, with enhancement factors of 320 at room temperature and 150 at 370 K, paving the way for characterisation of materials under operational conditions. Finally, the application of endogenous Gd3+ DNP is illustrated with the study of interfaces in vertically aligned nanocomposite thin films comprised of Gd-CeO2 nanopillars embedded in a SrTiO3 matrix, where DNP affords selective enhancement of the different phases and enables a previously infeasible two-dimensional correlation experiment to be performed showing spin diffusion between Gd-CeO2 and the solid–solid interface.This work was supported by Swiss National Science Foundation Grant No. 200020_178860. J.L.M.-D. acknowledges support from the Royal Academy of Engineering Grant, CIET1819_24. A.L. gratefully acknowledges financial support from the ANR contract 17-CE29-0006-01. M.L. gratefully acknowledges Fondazione CR Firenze. We would like to thank Gabriele Stevanato for useful discussions