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ZrNb crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two ZrNb sheets oriented in the (0, 1, 0) direction. Zr is bonded in a 8-coordinate geometry to four equivalent Nb atoms. All Zr–Nb bond lengths are 2.98 Å. Nb is bonded in a 8-coordinate geometry to four equivalent Zr atoms.
ZrNb(RuSi)2 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are three inequivalent Zr2+ sites. In the first Zr2+ site, Zr2+ is bonded to five Si4- atoms to form ZrSi5 square pyramids that share corners with five ZrSi5 square pyramids, corners with five NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are four shorter (2.74 Å) and one longer (2.77 Å) Zr–Si bond lengths. In the second Zr2+ site, Zr2+ is bonded to five Si4- atoms to form ZrSi5 square pyramids that share a cornercorner with one ZrSi5 square pyramid, corners with nine NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are three shorter (2.75 Å) and two longer (2.77 Å) Zr–Si bond lengths. In the third Zr2+ site, Zr2+ is bonded to five Si4- atoms to form ZrSi5 square pyramids that share corners with four equivalent ZrSi5 square pyramids, corners with six NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are a spread of Zr–Si bond distances ranging from 2.74–2.77 Å. There are three inequivalent Nb2+ sites. In the first Nb2+ site, Nb2+ is bonded to five Si4- atoms to form distorted NbSi5 square pyramids that share corners with three equivalent NbSi5 square pyramids, corners with seven ZrSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with three ZrSi5 square pyramids, edges with three NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are a spread of Nb–Si bond distances ranging from 2.68–2.76 Å. In the second Nb2+ site, Nb2+ is bonded to five Si4- atoms to form NbSi5 square pyramids that share corners with two equivalent NbSi5 square pyramids, corners with eight ZrSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with three ZrSi5 square pyramids, edges with three NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are a spread of Nb–Si bond distances ranging from 2.69–2.72 Å. In the third Nb2+ site, Nb2+ is bonded to five Si4- atoms to form NbSi5 square pyramids that share corners with five ZrSi5 square pyramids, corners with five NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are two shorter (2.70 Å) and three longer (2.72 Å) Nb–Si bond lengths. There are six inequivalent Ru2+ sites. In the first Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent NbSi5 square pyramids, corners with four ZrSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.48–2.51 Å. In the second Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent ZrSi5 square pyramids, corners with four NbSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.51–2.54 Å. In the third Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent NbSi5 square pyramids, corners with four ZrSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.46–2.52 Å. In the fourth Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent ZrSi5 square pyramids, corners with four NbSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.48–2.57 Å. In the fifth Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent ZrSi5 square pyramids, corners with four NbSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.44–2.57 Å. In the sixth Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent NbSi5 square pyramids, corners with four ZrSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.45–2.58 Å. There are six inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to two equivalent Zr2+, four Nb2+, and three Ru2+ atoms. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to four Zr2+, two equivalent Nb2+, and three Ru2+ atoms. In the third Si4- site, Si4- is bonded in a 9-coordinate geometry to two equivalent Zr2+, four Nb2+, and three Ru2+ atoms. In the fourth Si4- site, Si4- is bonded in a 9-coordinate geometry to four Zr2+, two equivalent Nb2+, and three Ru2+ atoms. In the fifth Si4- site, Si4- is bonded in a 9-coordinate geometry to one Zr2+, two Nb2+, and six Ru2+ atoms. In the sixth Si4- site, Si4- is bonded in a 9-coordinate geometry to two Zr2+, one Nb2+, and six Ru2+ atoms.
Radiation effects in materials often compound and accelerate other detrimental phenomena such as embrittlement, oxidation and creep. However, irradiation can also decrease the oxidation rate, for instance with ZrNb alloys nuclear fuel cladding. In this study, we rationalize this observation on Zr-0.5Nb alloy by introducing a mechanism based on oxide space charge modification, resulting from irradiation enhanced Nb clustering. Here, this mechanism is investigated using a multiscale approach: from the macroscale, to determine post-irradiation oxidation kinetics, to the atomic scale, using in-situ atom probe tomography sample oxidation, to observe elemental solute redistribution across the oxide/metal interface. The mechanism is further supported by high resolution transmission electron microscopy characterization and density functional theory calculations. A point defect model is proposed to account for oxide space charge effects and their changes under irradiation. This integrated, multiscale experimental and modeling approach challenges the current paradigm on irradiation effects and how they can potentially improve materials performance in extreme environments.
The compositionally complex medium/high-entropy design concept can greatly expand the categories and affect the properties of the materials. With such a designing concept, a medium-entropy Li-garnet electrolyte with appropriate yttrium content (formula Li 6.6 La 3 ZrNb 0.3 Ta 0.3 Hf 0.3 Y 0.1 O 12 ) shows a record-high ionic conductivity of ∼5.7 × 10 –4 S/cm, the highest reported for any single-site substituted high/medium-entropy Li-garnet. The assembled Li metal symmetric cells also show stable long-term cycling (0.1 mA/cm 2 for over 200 h). Neutron powder diffraction and Rietveld refinement results indicate that a competing conduction mechanism between (1) occupancy on high mobility of 96h sites and (2) the associated site vacancies and the bond length requires an appropriate content of Y for enhanced ionic conductivity. Li-ion hopping through the bottleneck can also contribute to the conductivity. Finally, density functional theory and Born–Oppenheimer molecular dynamics simulations also indicate the high mobility and number of hopping transitions of Li ions, contributing to the high ionic conductivity.
As part of the Mechanistic Understanding of ZIrconium Corrosion (MUZIC) program, this team has been instrumental to obtain EPRI and Westinghouse sponsorships to prepare the neutron irradiated ZIRLO® and X2® from Vogtle nuclear power plant and ship them from Studsvik’s (Sweden) hot cells to Idaho National Laboratory (INL) to be part of the NSUF library. The uniqueness of these sets of neutron irradiated alloys is that they are at the same two extremes of the fuel cycles, allowing us to study the microchemistry evolution as a function of irradiation doses, exposure time and solute content. Advanced commercial Zirconium-Niobium (Zr-Nb) alloys, such as ZIRLO® and AXIOM®, have been developed by Westinghouse to enhance the corrosion resistance of fuel cladding material for longer service time. This study specifically aims at investigating the neutron irradiation induced Nb redistribution in AXIOM® X2® to understand the effect of neutron irradiation induced microchemistry changes and the irradiation enhanced corrosion resistance observed in ZrNb alloys. The detailed sample information on chemical composition and irradiation is given in shown in Table 1a and 1b respectively. To study the neutron IIP/nanoclusters and Nb concentration in the solid solution, atom probe tomography (APT) is the primary tool to obtain reliable chemical information. APT specimens were prepared in shielded focused ion beam (FIB) at the Irradiated Materials Characterization Laboratory (IMCL) at INL followed by APT analysis at CAES facility using LEAP 4000XR