Nitrogen doping of TiO2 photocatalyst forms a second eg state in the Oxygen (1s) NEXAFS pre-edge

Close inspection of the pre-edge in oxygen near-edge x-ray absorption fine structure spectra of single step, gas phase synthesized titanium oxynitride photocatalysts with 20 nm particle size reveals an additional eg resonance in the VB that went unnoticed in previous TiO2 anion doping studies. The relative spectral weight of this Ti(3d)-O(2p) hybridized state with respect to and located between the readily established t2g and eg resonances scales qualitatively with the photocatalytic decomposition power, suggesting that this extra resonance bears co-responsibility for the photocatalytic performance of titanium oxynitrides at visible light wavelengths

Magnetic field frustration of the metal-insulator transition in V2 O3

Despite decades of efforts, the origin of metal-insulator transitions (MITs) in strongly correlated materials remains one of the main long-standing problems in condensed-matter physics. An archetypal example is V2O3, which undergoes simultaneous electronic, structural, and magnetic phase transitions. This remarkable feature highlights the many degrees of freedom at play in this material. In this work, acting solely on the magnetic degree of freedom, we reveal an anomalous feature in the electronic transport of V2O3: On cooling, the magnetoresistance changes from positive to negative values well above the MIT temperature, and shows divergent behavior at the transition. The effects are attributed to the magnetic field quenching antiferromagnetic fluctuations above the Néel temperature TN, and preventing long-range antiferromagnetic ordering below TN. In both cases, suppressing the antiferromagnetic ordering prevents the opening of the incipient electronic gap. This interpretation is supported by Hubbard model calculations which fully reproduce the experimental behavior. Our study sheds light on this classic problem providing a clear and physical interpretation of the nature of the metal-insulator transition.Fil: Trastoy, J.. University of California at San Diego; Estados UnidosFil: Camjayi, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Del Valle, J.. University of California at San Diego; Estados UnidosFil: Kalcheim, Y.. University of California at San Diego; Estados UnidosFil: Crocombette, J. P.. Université Paris-Saclay; FranciaFil: Gilbert, D.A.. University of Tennessee; Estados UnidosFil: Borchers, J.A.. Nist Center For Neutron Research; Estados UnidosFil: Villegas, J.E.. Université Paris-Saclay; FranciaFil: Ravelosona, D.. Center For Nanoscience And Nanotechnology; FranciaFil: Rozenberg, M.J.. Université Paris-Saclay; FranciaFil: Schuller, Ivan K.. University of California at San Diego; Estados Unido

Observation of a nuclear recoil peak at the 100 eV scale induced by neutron capture

Coherent elastic neutrino-nucleus scattering and low-mass Dark Matter detectors rely crucially on the understanding of their response to nuclear recoils. We report the first observation of a nuclear recoil peak at around 112 eV induced by neutron capture. The measurement was performed with a CaWO$_4$ cryogenic detector from the NUCLEUS experiment exposed to a $^{252}$Cf source placed in a compact moderator. The measured spectrum is found in agreement with simulations and the expected peak structure from the single-$\gamma$ de-excitation of $^{183}$W is identified with 3 $\sigma$ significance. This result demonstrates a new method for precise, in-situ, and non-intrusive calibration of low-threshold experiments

On the transfer of cascades from primary damage codes to rate equation cluster dynamics and its relation to experiments

International audienceTransferring displacement cascades from primary damage codes to rate equation cluster dynamics (RECD) is not straightforward, due to the inability of RECD to treat spatial correlations explicitly. A method, called ''sphere homogenization kinetic Monte Carlo" (SHKMC), has been proposed to produce a effective source term from a cascade database. This paper reviews the method and a few applications. SHKMC is based on a modified kinetic Monte Carlo algorithm to keep track of the homogenization process of defects within cascades. The crucial parameter is the homogenization distance, which is not an intrinsic parameter of cascades but which is given by RECD simulations. SHKMC leads to a time-varying source term, even under constant irradiation flux. RECD with such a source term is able to reproduce reference kinetic Monte Carlo calculations of microstructure evolution under cascade conditions. It is also possible to provide a spatially-dependent source term for the simulation of ion irradiations. As an example, irradiation of iron with 10 MeV Fe ions is discussed. Analysis of the source term shows that the fraction of mono-defects is close to the fraction of freely-migrating defects determined experimentally and that it significantly varies with depth

Molecular Dynamics Studies of Radiation Induced Phase Transitions in La2Zr2O7 pyrochlore

International audienceWe present a review of our past works and some new results on the molecular dynamics simulation of La2Zr2O7 pyrochlore phase transitions under irradiation. The transition sequence observed experimentally from ordered pyrochlore to disordered fluorite then to amorphous is reproduced. New results, including simulations of electron diffraction images, are given on the relationship between oxygen and cationic disorder. We find that there is no need to call upon preliminary oxygen disorder to reproduce the experimental diffraction patterns. Thermokinetics of the transitions are simulated by the continuous accumulation of cationic Frenkel pairs. The increase of the amorphization dose with temperature and the existence of a critical temperature are obtained. The leading role of Zr cation disoder is highlighted

Key Role of the Cation Interstitial Structure in the Radiation Resistance of Pyrochlores

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