Nanoscale chemistry and Atom Probe Tomography

Geometry of a subelement of an RRP wire

Atom Probe Tomography (APT) has been used to study the effect of fast neutron irradiation on the local chemistry of Nb3Sn samples.  Two RRP(c) wires doped with 2 at% Ti were analysed by the authors of 'Understanding the nanoscale chemistry of as-received and fast neutron irradiated Nb3Sn RRP(R) wires using atom probe tomography' published in Superconductor Science and Technology.  One of the wires was in the as-received condition and the other irradiated to a neutron fluence (E > 0.1 MeV) of 2.82 x 1022m-2 in the TRIGA-II reactor.

The irradiated sample had a reduced Tc, an increase in p, a shift in the peak of the Fp curve suggesting the introduction of secondary point pinning, and an increase in the estimated scaling field B*.  APT analysis showed that the polycrystalline Nb3Sn had three distinct regions of composition, near stoichiometry Nb3Sn (low Nb), regions with a higher Nb content than expected in equilibrium Nb3Sn (high Nb) and grain boundaries.  The summed composition of these three regions lay within the Nb3Sn  phase for both the as-received and irradiated samples. 

The distinct regions of high Nb Nb3Sn demonstrated incomplete diffusion in the as-received sample, and the reduction in volume of these high Nb regions after irradiation implies significant radiation induced diffusion had occurred.  The presence of other features in the atomic-scale chemistry, such as the extent of Cu segregation at grain boundaries, three types of dislocation array, and unreacted Nb nanoparticles, are compared between samples by the authors.