A comparison between holographic and near-field ptychographic X-ray tomography for solid oxide cell materials

Holographic and near-field ptychographic X-ray computed tomography techniques have been compared by characterizing a typical solid oxide cell hydrogen electrode using a high-energy X-ray beam. The main advantages and drawbacks of both methods are discussed regarding the possibility to image the Ni-YSZ cermet, a complex porous electrode microstructure composed of X-ray absorbent materials. The same innovative sub-pixel alignment algorithm, based on tomographic consistency, was applied to align the different tomographic projections for each technique. It has been shown that a better signal-to-noise ratio (SNR) is obtained using near-field ptychographic tomography, whereas holographic tomography can be faster with similar spatial resolution. Moreover, quantitative electron density maps have been obtained with the two techniques. The quality of the phase identification has also been assessed and compared in both cases using a classical grey-level class separability criterion. After the segmentation, a set of typical microstructural properties describing the electrode morphology was computed. The comparison of the results allowed validating the complementarity of the two X-ray imaging techniques. Despite the more time-consuming data acquisition and processing than holographic tomography, near-field ptychographic tomography is especially well adapted to image samples without any insight on their composition or when the sample is highly absorbent. Yet, holographic X-ray tomography, using high-energy X-rays to reduce the sample absorption, remains a faster 3D imaging technique with spatial resolution and contrast sensitivity sufficient for the characterization of solid oxide cell materials.