Weak Interactions under Pressure: hp -CuBi and Its Analogues

Bismuth-rich bimetallic clusters (CuBi8)3+ and [MBi10]4+ (M = Pd, Pt) from ionothermal synthesis

The reaction of Bi, BiBr3, and CuBr in the Lewis-acidic ionic liquid [BMIm]Br·4AlBr3 (BMIm = 1-n-butyl-3-limidazolium) at 180 °C yielded air-sensitive, shiny black crystals of (CuBi8)[AlBr4]2[Al2Br7]. Crystals of [MBi10][AlCl4]4 (M = Pd, Pt) were obtained by reacting Bi, BiCl3, and MCl2 under similar conditions. The structures have been determined by X-ray diffraction on single-crystals and were found to be very similar to that of the known analogues with other halogens, although not isostructural. In crystals of the complex salts, polyhedral bimetallic clusters (CuBi8)3+ or [MBi10]4+ are embedded in matrices of halogenidoaluminate anions. The heteroatomic nido-cluster (CuBi8)3+ consists of a (Bi8)2+ square antiprism η4-coordinating a copper(I) cation. In the cluster cation [MBi10]4+, the metal atoms M center a pentagonal antiprism of bismuth atoms.

Enhanced Néel temperature in EuSnP under pressure

We present the combined results of single crystal X-ray diffraction, physical properties characterization, and theoretical assessment of EuSnP under high pressure. Single crystals of EuSnP prepared using Sn self-flux crystallize in the tetragonal NbCrN-type crystal structure (S.G. P4/nmm) at ambient pressure. Previous studies have shown that for Eu ions, seven unpaired electrons impart a 2+ oxidation state. Assuming the oxidation states of Eu to be +2 and P to be -3, each Sn will donate one electron, with one p valence electron left for forming a weak Sn-Sn bond. According to the high-pressure single crystal X-ray diffraction measurements, no structural phase transition was observed up to ∼6.2 GPa. Temperature-dependent resistivity measurements up to 2.15 GPa on single crystals indicate that the phase-transition temperature occurring at the Néel temperature (TN) is significantly enhanced under high pressure. The robust crystallography and enhanced antiferromagnetic transition temperatures can be rationalized by the electronic structure calculations and chemical bonding analysis. The increasing Eu-P bonding interaction is consistent with the lattice parameter changing and enhanced TN. Moreover, the molecular orbital diagram shows that the weak Sn-Sn bond can be squeezed under pressure, acting as a compression buffer to stabilize the structure.

Evidence of High-Temperature Superconductivity at 18 K in Nanosized Rhombohedral Bi Enhanced by Ni-Doping

Superconductivity in bulk rhombohedral Bi has recently been detected to appear below 0.53 mK and 5.2 μT. Here, we unambiguously demonstrate that superconductivity in rhombohedral Bi can be greatly enhanced by incorporating Ni ions onto the Bi sites and reducing the size to the nanometer scale. The superconducting transition temperature T C of 12 nm rhombohedral Bi nanoparticles (NPs) reaches 4 K at ambient pressure. T C is significantly enhanced to reach 7, 12, and 18 K in 6, 8, and 10% Ni-doped Bi NPs, respectively, where superconductivity is found to coexist with ferromagnetism. Ni-doping causes a significant amount of electronic charges to shift toward the interconnecting regions between neighboring Bi ions. First-principles calculations reveal that the Ni ions serve as charge and spin suppliers for the developments of superconductivity and ferromagnetism.

High-Pressure Synthesis and Chemical Bonding of Barium Trisilicide BaSi₃

BaSi₃ is obtained at pressures between 12(2) and 15(2) GPa and temperatures from 800(80) and 1050(105) K applied for one to five hours before quenching. The new trisilicide crystallizes in the space group I4¯2m (no. 121) and adopts a unique atomic arrangement which is a distorted variant of the CaGe₃ type. At ambient pressure and 570(5) K, the compound decomposes in an exothermal reaction into (hP3)BaSi₂ and two amorphous silicon-rich phases. Chemical bonding analysis reveals covalent bonding in the silicon partial structure and polar multicenter interactions between the silicon layers and the barium atoms. The temperature dependence of electrical resistivity and magnetic susceptibility measurements indicate metallic behavior.

Discovery of Cu3Pb

Materials discovery enables both realization and understanding of new, exotic, physical phenomena. An emerging approach to the discovery of novel phases is high-pressure synthesis within diamond anvil cells, thereby enabling in situ monitoring of phase formation. Now, the discovery via high-pressure synthesis of the first intermetallic compound in the Cu-Pb system, Cu₃Pb is reported. Cu₃Pb is notably the first structurally characterized mid- to late-first-row transition-metal plumbide. The structure of Cu₃Pb can be envisioned as a direct mixture of the two elemental lattices. From this new framework, we gain insight into the structure as a function of pressure and hypothesize that the high-pressure polymorph of lead is a possible prerequisite for the formation of Cu₃Pb. Crucially, electronic structure computations reveal band crossings near the Fermi level, suggesting that chemically doped Cu₃Pb could be a topologically nontrivial material.

Yet again, new compounds found in systems with known binary phase diagrams. Synthesis, crystal and electronic structure of Nd3Bi7 and Sm3Bi7

The binary bismuthides Nd3Bi7 and Sm3Bi7 were synthesized and structurally characterized for the first time. The results from the calorimetric analysis show that both compounds are stable only up to about 500 °C, which may explain why they were overlooked during the original assessment of the corresponding phase diagrams.

High-Pressure Synthesis: A New Frontier in the Search for Next-Generation Intermetallic Compounds

The application of high pressure adds an additional dimension to chemical phase space, opening up an unexplored expanse bearing tremendous potential for discovery. Our continuing mission is to explore this new frontier, to seek out new intermetallic compounds and new solid-state bonding. Simple binary elemental systems, in particular those composed of pairs of elements that do not form compounds under ambient pressures, can yield novel crystalline phases under compression. Thus, high-pressure synthesis can provide access to solid-state compounds that cannot be formed with traditional thermodynamic methods. An emerging approach for the rapid exploration of composition-pressure-temperature phase space is the use of hand-held high-pressure devices known as diamond anvil cells (DACs). These devices were originally developed by geologists as a way to study minerals under conditions relevant to the earth's interior, but they possess a host of capabilities that make them ideal for high-pressure solid-state synthesis. Of particular importance, they offer the capability for in situ spectroscopic and diffraction measurements, thereby enabling continuous reaction monitoring-a powerful capability for solid-state synthesis. In this Account, we provide an overview of this approach in the context of research we have performed in the pursuit of new intermetallic compounds. We start with a discussion of pressure as a fundamental experimental variable that enables the formation of intermetallic compounds that cannot be isolated under ambient conditions. We then introduce the DAC apparatus and explain how it can be repurposed for use as a synthetic vessel with which to explore this phase space, going to extremes of pressure where no chemist has gone before. The remainder of the Account is devoted to discussions of recent experiments we have performed with this approach that have led to the discovery of novel intermetallic compounds in the Fe-Bi, Cu-Bi, and Ni-Bi systems, with a focus on the cutting-edge methods that made these experiments possible. We review the use of in situ laser heating at high pressure, which led to the discovery of FeBi₂, the first binary intermetallic compound in the Fe-Bi system. Our work in the Cu-Bi system is described in the context of in situ experiments carried out in the DAC to map its high-pressure phase space, which revealed two intermetallic phases (Cu₁₁Bi₇ and CuBi). Finally, we review the discovery of β-NiBi, a novel high-pressure phase in the Ni-Bi system. We hope that this Account will inspire the next generation of solid-state chemists to boldly explore high-pressure phase space.

High-pressure discovery of β-NiBi

Herein, we present the discovery of a new high-pressure phase in the Ni-Bi system, β-NiBi, which crystallizes in the TlI structure type. The powerful technique of in situ high-pressure and high-temperature powder X-ray diffraction enabled observation of the formation of β-NiBi and its reversible reconversion to the ambient pressure phase, α-NiBi.