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TaNb crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. Ta is bonded in a 8-coordinate geometry to four equivalent Ta and four equivalent Nb atoms. All Ta–Ta bond lengths are 2.88 Å. All Ta–Nb bond lengths are 2.87 Å. Nb is bonded in a 8-coordinate geometry to four equivalent Ta and four equivalent Nb atoms. All Nb–Nb bond lengths are 2.88 Å.
TaNb(AgO3)2 is (Cubic) Perovskite-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent NbO6 octahedra, corners with four equivalent TaO6 octahedra, and faces with eight equivalent AgO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There is two shorter (1.99 Å) and four longer (2.00 Å) Ta–O bond length. Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with two equivalent TaO6 octahedra, corners with four equivalent NbO6 octahedra, and faces with eight equivalent AgO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.00 Å) and two longer (2.02 Å) Nb–O bond lengths. Ag1+ is bonded to twelve O2- atoms to form AgO12 cuboctahedra that share corners with twelve equivalent AgO12 cuboctahedra, faces with six equivalent AgO12 cuboctahedra, faces with four equivalent TaO6 octahedra, and faces with four equivalent NbO6 octahedra. There are four shorter (2.83 Å) and eight longer (2.84 Å) Ag–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to two equivalent Nb5+ and four equivalent Ag1+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ta5+ and four equivalent Ag1+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to one Ta5+, one Nb5+, and four equivalent Ag1+ atoms.
TaNb(Cu3S4)2 is Stannite-like structured and crystallizes in the tetragonal P-4m2 space group. The structure is three-dimensional. Ta5+ is bonded to four equivalent S2- atoms to form TaS4 tetrahedra that share edges with six CuS4 tetrahedra. All Ta–S bond lengths are 2.31 Å. Nb5+ is bonded to four equivalent S2- atoms to form NbS4 tetrahedra that share edges with six CuS4 tetrahedra. All Nb–S bond lengths are 2.32 Å. There are three inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with eight CuS4 tetrahedra, an edgeedge with one TaS4 tetrahedra, and an edgeedge with one NbS4 tetrahedra. All Cu–S bond lengths are 2.37 Å. In the second Cu1+ site, Cu1+ is bonded to four equivalent S2- atoms to form CuS4 tetrahedra that share corners with eight equivalent CuS4 tetrahedra and edges with two equivalent NbS4 tetrahedra. All Cu–S bond lengths are 2.38 Å. In the third Cu1+ site, Cu1+ is bonded to four equivalent S2- atoms to form CuS4 tetrahedra that share corners with eight equivalent CuS4 tetrahedra and edges with two equivalent TaS4 tetrahedra. All Cu–S bond lengths are 2.37 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to one Ta5+ and three Cu1+ atoms to form a mixture of distorted corner and edge-sharing STaCu3 tetrahedra. In the second S2- site, S2- is bonded to one Nb5+ and three Cu1+ atoms to form distorted SNbCu3 tetrahedra that share corners with six STaCu3 tetrahedra and edges with three equivalent SNbCu3 tetrahedra.
TaNb(Cu3Se4)2 is Stannite-like structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ta5+ is bonded to four equivalent Se2- atoms to form TaSe4 tetrahedra that share edges with six equivalent CuSe4 tetrahedra. All Ta–Se bond lengths are 2.47 Å. Nb5+ is bonded to four equivalent Se2- atoms to form NbSe4 tetrahedra that share edges with six equivalent CuSe4 tetrahedra. All Nb–Se bond lengths are 2.47 Å. Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with eight equivalent CuSe4 tetrahedra, an edgeedge with one TaSe4 tetrahedra, and an edgeedge with one NbSe4 tetrahedra. All Cu–Se bond lengths are 2.47 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to one Nb5+ and three equivalent Cu1+ atoms to form distorted SeNbCu3 tetrahedra that share corners with six equivalent SeTaCu3 tetrahedra and edges with three equivalent SeNbCu3 tetrahedra. In the second Se2- site, Se2- is bonded to one Ta5+ and three equivalent Cu1+ atoms to form distorted SeTaCu3 tetrahedra that share corners with six equivalent SeNbCu3 tetrahedra and edges with three equivalent SeTaCu3 tetrahedra.
TaNb(AgO3)2 is Orthorhombic Perovskite-derived structured and crystallizes in the orthorhombic P2_12_12 space group. The structure is three-dimensional. Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share a cornercorner with one TaO6 octahedra and corners with five equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 16–24°. There are a spread of Ta–O bond distances ranging from 1.92–2.12 Å. Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share a cornercorner with one NbO6 octahedra and corners with five equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 16–24°. There are a spread of Nb–O bond distances ranging from 1.94–2.14 Å. There are three inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded in a 3-coordinate geometry to three O2- atoms. There are two shorter (2.45 Å) and one longer (2.50 Å) Ag–O bond lengths. In the second Ag1+ site, Ag1+ is bonded in a 3-coordinate geometry to three O2- atoms. There are two shorter (2.46 Å) and one longer (2.48 Å) Ag–O bond lengths. In the third Ag1+ site, Ag1+ is bonded in a 12-coordinate geometry to eight O2- atoms. There are a spread of Ag–O bond distances ranging from 2.50–2.79 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Ta5+, one Nb5+, and two equivalent Ag1+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Ta5+, one Nb5+, and two equivalent Ag1+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Ta5+, one Nb5+, and two Ag1+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Ta5+, one Nb5+, and two Ag1+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Nb5+ and one Ag1+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ta5+ and one Ag1+ atom. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one Ta5+, one Nb5+, and two equivalent Ag1+ atoms.
Abstract High entropy alloys (HEA) are an unusual class of materials where mixtures of elements are stochastically arrayed on a simple crystalline lattice. These systems exhibit remarkable functionality, often along several distinct axes: e.g., the examples [TaNb] 1-x (TiZrHf) x are high strength and damage resistant refractory metals that also exhibit superconductivity with large upper critical fields. Here we report the discovery of an f -electron containing HEA, [TaNb] 0.31 (TiUHf) 0.69 , which is the first to include an actinide ion. Similar to the Zr-analogue, this material crystallizes in a body-centered cubic lattice with the lattice constant a = 3.41(1) Å and exhibits phonon mediated superconductivity with a transition temperatures T c ≈ 3.2 K and upper critical fields H c2 ≈ 6.4 T. These results expand this class of materials to include actinide elements, shows that superconductivity is robust in this sub-group, and opens the path towards leveraging HEAs as functional waste forms for a variety of radioisotopes.
Solid-state cold spraying (CS) of metals and respective blends is becoming increasingly attractive compared to conventional high temperature processes due to the unique properties such as increased yield strength, low ductility, and differences in tensile and compressive strengths that result from microstructural features due to the CS process. Here we report the results of plate impact experiments applied to CS deposits of tantalum (Ta), niobium (Nb), and a tantalum- niobium blend (TaNb). These methods allowed for definition of the Hugoniot for each material type and allowed for assessment of the Hugoniot Elastic Limit (HEL). Scanning electron microscopy was used on recovered samples to characterize the fracture mechanism during spallation.
Thermal spray processing of metals and respective blends is becoming increasingly attractive due to the unique properties such as increased yield strength, low ductility, and differences in tensile and compressive strengths that result from microstructural features due to the spray process compared to other additive manufacturing methods. Here we report the results of plate impact experiments applied to Controlled Atmosphere Plasma Spray deposits of tantalum (Ta), niobium (Nb), and a tantalum-niobium blend (TaNb). These methods allowed for definition of the Hugoniot for each material type and the assessment of the Hugoniot Elastic Limit (HEL). Spallation experiments were conducted, and soft recovery of each material type allowed for scanning electron microscopy to characterize the fracture mechanism during tensile loading.