Tern�re Phasen des Lithiums mit Kupfer und Phosphor

Redox Chemistries for Vacancy Modulation in Plasmonic Copper Phosphide Nanocrystals

Copper phosphide (Cu3-xP) nanocrystals are promising materials for nanoplasmonics due to their substoichiometric composition, enabling the generation and stabilization of excess delocalized holes and leading to localized surface plasmon resonance (LSPR) absorption in the near-IR. We present three Cu-coupled redox chemistries that allow postsynthetic modulation of the delocalized hole concentrations and corresponding LSPR absorption in colloidal Cu3-xP nanocrystals. Changes in the structural, optical, and compositional properties are evaluated by powder X-ray diffraction, electronic absorption spectroscopy, 31P magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, and elemental analysis. The redox chemistries presented herein can be used to access nanocrystals with LSPR energies of 660-890 meV, a larger range than has been possible through synthetic tuning alone. In addition to utilizing previously reported redox chemistries used for copper chalcogenide nanocrystals, we show that the largest structural and LSPR modulation is achieved using a divalent metal halide and trioctylphosphine. Specifically, nanocrystals treated with zinc iodide and trioctylphosphine have the smallest unit-cell volume (295.2 Å3) reported for P63cm Cu3-xP, indicating more Cu vacancies than have been previously observed. Overall, these redox chemistries present valuable insight into controlling the optical and structural properties of Cu3-xP.

Is Cu3-x P a Semiconductor, a Metal, or a Semimetal?

Despite the recent surge in interest in Cu_3-x P for catalysis, batteries, and plasmonics, the electronic nature of Cu_3-x P remains unclear. Some studies have shown evidence of semiconducting behavior, whereas others have argued that Cu_3-x P is a metallic compound. Here, we attempt to resolve this dilemma on the basis of combinatorial thin-film experiments, electronic structure calculations, and semiclassical Boltzmann transport theory. We find strong evidence that stoichiometric, defect-free Cu₃P is an intrinsic semimetal, i.e., a material with a small overlap between the valence and the conduction band. On the other hand, experimentally realizable Cu_3-x P films are always p-type semimetals natively doped by copper vacancies regardless of x. It is not implausible that Cu_3-x P samples with very small characteristic sizes (such as small nanoparticles) are semiconductors due to quantum confinement effects that result in the opening of a band gap. We observe high hole mobilities (276 cm²/(V s)) in Cu_3-x P films at low temperatures, pointing to low ionized impurity scattering rates in spite of a high doping density. We report an optical effect equivalent to the Burstein-Moss shift, and we assign an infrared absorption peak to bulk interband transitions rather than to a surface plasmon resonance. From a materials processing perspective, this study demonstrates the suitability of reactive sputter deposition for detailed high-throughput studies of emerging metal phosphides.

Sc5Pd4Si6- crystal structure and 29Si/45Sc solid state MAS NMR spectroscopic investigations

The silicide Sc₅Pd₄Si₆ was synthesized from the elements by arc-melting. Its structure was refined from single crystal X-ray diffractometer data: Immm, Li₅Cu_3.75P₆ type, a = 397.12(6), b = 945.4(1), c = 1314.4(2) pm, wR₂ = 0.0245, 578 F² values and 29 parameters. The palladium atoms have slightly distorted tetrahedral silicon coordination and a condensation of these PdSi₄ tetrahedra leads to a two-dimensional substructure which is condensed via Si₂ pairs (234 pm Si-Si), forming the [Pd₄Si₆]^δ- polyanionic network. The Sc₅Pd₄Si₆ structure contains three crystallographically independent scandium sites with coordinations Sc1@Pd₄Si₈Sc₆, Sc2@Pd₆Si₆Sc₃ and Sc3@Pd₄Si₆Sc₄. Sc₅Pd₄Si₆ is a Pauli paramagnet with a low susceptibility of 2.9(5) × 10^-5 emu mol^-1 at room temperature. The ²⁹Si MAS-NMR spectrum confirms the presence of two crystallographically distinct sites in a 2 : 1 ratio. Likewise, the three crystallographic scandium sites are well-differentiated by three ⁴⁵Sc MAS NMR signals in the expected 2 : 2 : 1 ratio. Unambiguous assignments could be made based on the comparison of the nuclear electric quadrupolar coupling parameters with predicted values from WIEN2k calculations.

Mechanistic exploration of the copper(i) phosphide synthesis in phosphonium-based and phosphorus-free ionic liquids

The mechanism of the synthesis of copper(i) phosphide (Cu_3-xP) in the ionic liquid (IL) trihexyl(tetradecyl)phosphonium chloride ([P₆₆₆₁₄][Cl]) was investigated. The phosphide formation is promoted by a transformation of red phosphorus (P_red) into mobile P₄ molecules and a surface activation of copper caused by the IL including the Brønsted acidic impurity. The surface activation is important to obtain a quantitative product yield. Moreover, we demonstrate that single-phase Cu_3-xP can also be synthesized in the nitrogen-based IL tetrabutylammonium chloride ([N₄₄₄₄][Cl]). Further substitution of the anion of the IL using tetrabutylammonium bromide ([N₄₄₄₄][Br]) or the complete replacement of the IL by a deep eutectic solvent consisting of adipic acid and betaine do not lead to single-phase Cu_3-xP. Therefore, the nature of the anions present in the IL also seems to be relevant for the convenient phosphidization reaction.

Electroless deposition of Ni3P–Ni arrays on 3-D nickel foam as a high performance anode for lithium-ion batteries

The array structure of Ni₃P–Ni can accommodate volume changes during the lithiation/de-lithiation progress and promote high-rate capability because the interspaces in such structure can act as ideal volume expansion buffers.