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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Is solid copper oxalate a spin chain or a mixture of entangled spin pairs?

Macroscopic assemblies of interacting spins give rise to a broad spectrum of behaviors determined by the spatial arrangement of the magnetic sites and the electronic interactions between them. Compounds of copper (II), in which each copper carries spin 1/2, exhibit a vast variety of physical properties. For antiferromagnetically coupled spin sites, there are two limiting scenarios: spin chains in which the spins can exhibit a long-range order or a mixture of dimers in which the spins within each pair are entangled but do not communicate with the spins from other dimers. In principle, the two types can be distinguished on the basis of experimental observations and modeling using empirically parameterized effective Hamiltonians, but in practice, ambiguity may persist for decades, as is the case for copper oxalate. Here we use high-level ab initio calculations to establish the validity of the nearest-site Heisenberg model and to predict the interaction strength between the magnetic sites. Finally, the computed magnetic susceptibility provides an unambiguous interpretation of magnetic experiments performed throughout half a century, clearly supporting the infinite spin-chain behavior of solid copper oxalate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on CuH11C4(NO5)2 by Materials Project

Cu(C2O4)2CuH4(C2O5)2(NH4)4H2O2 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four ammonium molecules, one copper;oxalic acid molecule, two water molecules, and one CuH4(C2O5)2 cluster. In the CuH4(C2O5)2 cluster, Cu1+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Cu–O bond distances ranging from 1.94–2.42 Å. There are two inequivalent C+3.50+ sites. In the first C+3.50+ site, C+3.50+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.24 Å) and one longer (1.30 Å) C–O bond length. In the second C+3.50+ site, C+3.50+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.25 Å) and one longer (1.29 Å) C–O bond length. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a water-like geometry to one Cu1+ and one C+3.50+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Cu1+ and one C+3.50+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one C+3.50+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one C+3.50+ atom. In the fifth O2- site, O2- is bonded in a water-like geometry to one Cu1+ and two H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuC4(NO5)2 by Materials Project

Cu(C2O4)2CuC4(NO6)2N2 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of two ammonia molecules, one copper;oxalic acid molecule, and one CuC4(NO6)2 cluster. In the CuC4(NO6)2 cluster, Cu2+ is bonded in a distorted octahedral geometry to six O2- atoms. There are a spread of Cu–O bond distances ranging from 1.89–2.63 Å. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.17 Å) and one longer (1.18 Å) C–O bond length. In the second C4+ site, C4+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.17 Å) and one longer (1.18 Å) C–O bond length. N1+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.20 Å) and one longer (1.28 Å) N–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one N1+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one C4+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Cu2+ and one N1+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one Cu2+ and one C4+ atom. In the fifth O2- site, O2- is bonded in a single-bond geometry to one C4+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to one Cu2+ and one C4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dissolution and separation of rare earth metals

A chemical dissolution method is provided for use in recycling rare earth metal-containing material such as permanent magnet material including end-of-life magnet shapes, magnet scrap and Terfenol-D alloy material by mixing the rare earth metal-containing material and an aqueous solution of a copper (II) salt to dissolve the material in the solution. The dissolved rare earth metal is then precipitated from the aqueous solution as a rare earth metal compound, such as a rare earth metal oxalate, sulfate or phosphate from which rare earth metal oxide can be obtained.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Gapless spinons and a field-induced soliton gap in the hyperhoneycomb Cu oxalate framework compound [(C 2 H 5 ) 3 NH] 2 Cu 2 (C 2 O 4 ) 3

Here, we report a detailed study of the specific heat and magnetic susceptibility of single crystals of a spin-liquid candidate: the hyperhoneycomb Cu oxalate framework compound [(C 2 H 5 ) 3 NH] 2 Cu 2 (C 2 O 4 ) 3 . The specific heat shows no anomaly associated with a magnetic transition at low temperatures down to T ~ 180 mK in zero magnetic field. We observe a large linear-in-T contribution to the specific heat γT, γ = 98 (1) mJ / mol K 2 , at low temperatures, indicative of the presence of fermionic excitations despite the Mott insulating state. The low-T specific heat is strongly suppressed by applied magnetic fields H, which induce an energy gap, Δ(H), in the spin-excitation spectrum. We use the four-component relativistic density-functional theory (DFT) to calculate the magnetic interactions, including the Dzyaloshinskii-Moriya antisymmetric exchange, which causes an effective staggered field acting on one copper sublattice. The magnitude and field dependence of the field-induced gap, Δ (H) ∝ H 2/3 , are accurately predicted by the soliton mass calculated from the sine-Gordon model of weakly coupled antiferromagnetic Heisenberg chains with all parameters determined by our DFT calculations. Thus our experiment and calculations are entirely consistent with a model of [(C 2 H 5 ) 3 NH] 2 Cu 2 (C 2 O 4 ) 3 in which anisotropic magnetic exchange interactions due to Jahn-Teller distortion cause one copper sublattice to dimerize, leaving a second sublattice of weakly coupled antiferromagnetic chains. We also show that this model quantitatively accounts for the measured temperature-dependent magnetic susceptibility. Thus [(C 2 H 5 ) 3 NH] 2 Cu 2 (C 2 O 4 ) 3 is a canonical example of a one-dimensional spin-1/2 Heisenberg antiferromagnet and not a resonating-valence-bond quantum spin liquid, as previously proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Inverse ZrO 2 /Cu as a highly efficient methanol synthesis catalyst from CO 2 hydrogenation

Enhancing the intrinsic activity and space time yield of Cu based heterogeneous methanol synthesis catalysts through CO 2 hydrogenation is one of the major topics in CO 2 conversion into value-added liquid fuels and chemicals. Here we report inverse ZrO 2 /Cu catalysts with a tunable Zr/Cu ratio have been prepared via an oxalate co-precipitation method, showing excellent performance for CO 2 hydrogenation to methanol. Under optimal condition, the catalyst composed by 10% of ZrO 2 supported over 90% of Cu exhibits the highest mass-specific methanol formation rate of 524 g MeOH kg cat -1 h -1 at 220°C, 3.3 times higher than the activity of traditional Cu/ZrO 2 catalysts (159 g MeOH kg cat -1 h -1 ). In situ XRD-PDF, XAFS and AP-XPS structural studies reveal that the inverse ZrO 2 /Cu catalysts are composed of islands of partially reduced 1–2 nm amorphous ZrO 2 supported over metallic Cu particles. The ZrO 2 islands are highly active for the CO 2 activation. Meanwhile, an intermediate of formate adsorbed on the Cu at 1350 cm -1 is discovered by the in situ DRIFTS. This formate intermediate exhibits fast hydrogenation conversion to methoxy. The activation of CO 2 and hydrogenation of all the surface oxygenate intermediates are significantly accelerated over the inverse ZrO 2 /Cu configuration, accounting for the excellent methanol formation activity observed.

36 MATERIALS SCIENCE↗