The detection and quantification of hydrogen is becoming increasingly important in research on electronic materials and devices, following the identification of the hydrogen content as a potent control parameter for the electronic properties. However, establishing quantitative correlations between the hydrogen content and the physical properties of solids remains a formidable challenge. Here we report neutron reflectometry experiments on 50 nm thick niobium films during hydrogen loading, and show that the momentum-space position of a prominent waveguide resonance allows tracking of the absolute hydrogen content with an accuracy of about one atomic percent on a timescale of less than a minute. Resonance-enhanced neutron reflectometry thus allows fast, direct, and non-destructive measurements of the hydrogen concentration in thin-film structures, with sensitivity high enough for real-time in-situ studies.

We investigated the reversible ferromagnetic (FM) behavior of pure and Co doped CeO 2 nanopowders. The as-sintered samples displayed an increasing paramagnetic contribution upon Co doping. Room temperature FM is obtained simply by performing thermal treatments in vacuum at temperatures as low as 500ºC and it can be switched off by performing thermal treatments in oxidizing conditions. The FM contribution is enhanced as we increase the time Among the various oxides displaying this particular behavior is CeO 2 , which in bulk is a diamagnetic insulator with proven capability as an oxygen ion conductor when doped with trivalent Sm or Gd ions 5 . CeO 2 -based systems have been thoroughly studied after the discovery of RT-FM on both pure 6,7,8,9,10 and slightly doped 11,12,13,14 samples. A large amount of effort has been devoted to the study of thin films 3,12,13,15,16,17,18,19 (see also references in [1]) while few works have focused on powdered samples 8,9,10,11,14 .The use of powders is advantageous because the typically low magnetic signals of these systems can easily be enhanced just by increasing the quantity of the sample. In addition, the surface to volume ratio of the sample can be adjusted simply by performing adequate thermal treatments and this is particularly convenient as the surface is usually the preferred location of point defects.In several works devoted to RT-FM in CeO 2 , the high mobility of oxygen, and As magnetic signals in DMOs are typically small, extreme care must be taken during the synthesis procedure and handling of the samples to avoid contamination, and it is also important to carry out methodological studies to discard the possible influence of spurious magnetic impurities. In this work we performed a systematic study of the magnetic properties of CeO 2 nanopowders with particular focus on the influence of oxygen vacancies in both pure and doped samples. We show that an annealing process in vacuum can induce RT-FM in doped samples and paramagnetic (PM) behavior in pure samples. In all cases, this magnetic behavior can be erased by re-oxidation, ruling out segregation as responsible for the magnetic signal. The use of nanostructures allows us to enhance the surface to volume ratio, thus increasing the relative concentration of defects compared to bulk samples.Pure and Co-doped CeO 2 powders were synthesized by the Liquid-Mix method using 99.99% Ce(NO 3 ):6H 2 O and Cobalt(II) nitrate hexahydrate as reagents. All samples were calcined in air at 300ºC. Additional thermal treatments were performed at 500ºC, both in air at atmospheric pressure and in vacuum, using a mechanical pump to reach a pressure of around 4.10 -2 mbar, with dwell times between 4 and 30 hs. Samples were labeled with a two-number code denoting the atomic percentage of Co (x), and the dwell time of the vacuum treatment (dwt) in hours, namely x-dwt. Magnetic measurements were performed in a Versalab TM VSM from Quantum Design. X-ray diffraction data was obtained at the ID27 beamline of the European Synchrotron Radiation ...

Ceria (CeO2)-based materials are widely used in applications such as catalysis, fuel cells and oxygen sensors. Its cubic fluorite structure with a cell parameter similar to that of silicon makes it a candidate for implementation in electronic devices. This structure is stable in a wide temperature and pressure range, with a reported structural phase transition to an orthorhombic phase. In this work, we study the structure of CeO2 under hydrostatic pressures up to 110 GPa simultaneously for the nanometer- and micrometer-sized powders as well as for a single crystal, using He as the pressure-transmitting medium. The first-order transition is clearly present for the micrometer-sized and single-crystal samples, while, for the nanometer grain size powder, it is suppressed up to at least 110 GPa. We show that the stacking fault density increases by two orders of magnitude in the studied pressure range and could act as an internal constraint, avoiding the nucleation of the high-pressure phase.