Polymorphism in the Ruddlesden-Popper Nickelate La3Ni2O7: Discovery of a Hidden Phase with Distinctive Layer Stacking.

We report the discovery of a novel form of Ruddlesden-Popper (RP) nickelate that stands as the first example of long-range, coherent polymorphism in this class of inorganic solids. Rather than the well-known, uniform stacking of perovskite blocks ubiquitously found in RP phases, this newly discovered polymorph of the bilayer RP phase La3Ni2O7 adopts a novel stacking sequence in which single-layer and trilayer blocks of NiO6 octahedra alternate in a "1313" sequence. Crystals of this new polymorph are described in space group Cmmm, although we note evidence for a competing Imam variant. Transport measurements at ambient pressure reveal metallic character with evidence of a charge density wave transition with an onset at T ≈ 134 K. The discovery of such polymorphism could reverberate to the expansive range of science and applications that rely on RP materials, particularly the recently reported signatures of superconductivity in bilayer La3Ni2O7 with Tc as high as 80 K above 14 GPa.

Aggressive Acquired Demyelinating Neuropathy Caused by NF-155: Initially Treatment-Resistant.

OBJECTIVES: Anti-neurofascin-155 IgG4 (NF-155) antibody disease has previously been associated with a subset of patients with chronic inflammatory demyelinating polyradiculoneuropathy. We report a case of NF-155 positive polyneuropathy that initially presented as an acute inflammatory demyelinating polyradiculoneuropathy. The patient responded appropriately to treatment but subsequently progressed over a 3-month period, resulting in quadriplegia, areflexia, and oculobulbar paralysis. METHODS: Case report and literature review. RESULTS: A 40-year-old male presented with acute bilateral arm and thigh weakness, areflexia, and distal sensory loss. Treatment with intravenous immunoglobulin (IVIg) for acute acquired demyelinating neuropathy resulted in initial improvement but subsequent decline. Lack of response to additional IVIg and plasmapheresis (PLEX) prompted testing for NF-155. Treatment with rituximab and steroids resulted in virtually complete recovery. CONCLUSIONS: Early testing for nodal and paranodal proteins is indicated in patients who present with acute acquired demyelinating neuropathy but fail to respond to conventional treatments, such as IVIg or PLEX. Identification of nodal and paranodal antibodies should prompt treatment with rituximab and steroids to increase likelihood of recovery.

Twists and Puckers: Tuning Crystal Chemistry in the La(AuxGe1-x)2 Compositional Series.

The physical properties of solid-state materials are closely tied to their crystal structure, yet our understanding of how competing structural arrangements energetically compare is limited. In this work, we explore how small differences in composition affect the structure in the La(AuxGe1-x)2 series of compounds, which comprises four unique structure types between LaGe2 and LaAu2. This family includes the previously unknown AlB2-type compound with stoichiometry La(Au0.375Ge0.625)2 as well as La(Au0.25Ge0.75)2, an intergrowth of the AlB2 and ThSi2 structure types. We then study the chemical forces driving the structure changes and use phonon band structure calculations and DFT-Chemical Pressure to evaluate atomic-size effects. These calculations show that the parent AlB2 structure type is disfavored in Au-rich compounds due to soft atomic motions along the c axis. The instability of AlB2-type LaAuGe is confirmed by the presence of imaginary modes in the phonon band structure that correspond to a "puckering" of the hexagonal AlB2-type lattice, resulting in the experimentally observed LiGaGe structure type. The impact of size effects is less clear for Au-poor compositions; instead, twisting the AlB2 structure type to form the ThSi2 type opens a pseudogap at the Fermi level in the electronic density of states. This investigation demonstrates how crystal structure in solid-state materials can be compositionally tuned based on balancing size and electronics when multiple structure types are in close thermodynamic competition.

From simple to complex crystal chemistry in the RE-Au-Tt systems (RE = La, Ce, Pr, Nd; Tt = Ge, Pb).

Polar intermetallics are an intriguing class of compounds with complex relationships between composition and structure that are not fully understood. This work reports a systematic study of the underexplored ternary composition space RE-Au-Tt (RE = La, Ce, Pr, Nd; Tt = Ge, Pb) to expand our knowledge of the intriguing chemistry and diversity achievable with these metallic constituents. These composition spaces are particularly interesting because of the potential to find Au-bearing, highly polar intermetallic compounds. The elements were first reacted through arc welding under an inert atmosphere, followed by annealing at 850 °C. X-ray diffraction of the products identified seven unreported compounds ranging from the simple NaTl-type compounds La1.5Au2Pb0.5 and Nd2-x Au2Pb x to the more structurally complex La5AuPb3 in the Hf5CuSn3-type structure and Pu3Pd4-type RE3Au3Ge (RE = La, Ce, Pr, Nd). First-principles electronic structure calculations investigate the combination of Fermi surface-Brillouin zone interactions, electrostatic interactions, and delocalized metallic bonding that contributes to the formation of these phases. These calculations show that a mixture of electrostatic and metallic bonding plays a dominant role in these phases. The RE-Au-Tt composition space remains full of potential for discovering materials with relevant magnetic and quantum properties, provided the crystal chemistry can be comprehended.

Mn39Si9Nx: Epitaxial Stabilization as a Pathway to the Formation of Intermetallic Nitrides.

The realization of the full potential of nitrogen-containing solid-state materials is limited by the inert and gaseous nature of N2. In this Communication, we describe the simple synthesis yet complex structure of the new phase Mn39Si9Nx (x = 0.84). The formation of this intermetallic subnitride appears to be facilitated by the high solubility of nitrogen in manganese metal, while its structural features are guided by the complementary internal packing strains of Mn-Si and Mn-N domains, an effect known as epitaxial stabilization. These domains intergrow into a composite structure based on the interpenetration of tetrahedrally close-packed (TCP) and Mackay cluster-like modules. We anticipate that other systems combining nitrogen with the TCP packing of metals will be similarly driven toward intergrowth, opening a path to a broader family of intermetallic nitrides.

Intermetallic Reactivity: Ca3Cu7.8Al26.2 and the Role of Electronegativity in the Stabilization of Modular Structures.

The structural chemistry of intermetallic phases is generally viewed in terms of what crystal structure will be most stable for a given combination of metallic atoms. Yet, individual atoms do not always make the best reference points. As the number of elements involved in compounds increases, their structures can often appear to be assembled from structural motifs derived from simpler compounds nearby in the phase diagram rather than fundamentally new arrangements of atoms. In this Article, we explore the notion that complex multinary phases can be viewed productively in terms of motif-preserving reactions between binary compounds, as opposed to direct reactions of the component elements. We present the targeted synthesis and structure solution of Ca3Cu7.8Al26.2, an intermetallic phase whose placement in the phase diagram is suggestive of a reaction between CaAl4 and CuAl2. Single-crystal X-ray diffraction analysis reveals that this compound crystallizes in the Y3TaNi6+xAl26 (or stuffed BaHg11) structure type and is constructed from three modules: Ca@(Cu/Al)16 polyhedra derived from the BaAl4 type, Cu@Al8 cubes, and Al13 cuboctahedra. To help understand this arrangement, we identify forces driving the reactivity of one of the supposed starting materials, CaAl4, through visualization of its atomic charge distribution and chemical pressure (CP) scheme, which suggest that the Al sites closest to the Ca atoms should show a high affinity for substitution by Cu atoms. Such a process on its own, however, would lead to overly long Ca-Cu distances and electron deficiency. When Cu is made available to CaAl4 in the Ca-Cu-Al ternary system, its incorporation in the Ca coordination environments instead nucleates domains of a fluorite-like CuAl2 phase, which act as nodes in the primitive cubic framework of CaAl4- and fluorite-like units. The cubic holes created by this framework are occupied by Al13 face-centered-cubic fragments that donate electrons while also resolving negative CPs in the Ca environments. This structural chemistry illustrates how new elements added to a binary compound at sites with conflicting electronic and atomic size preferences can serve as anchor points for the growth of domains of different bonding types, a notion that can be applied as a more general design strategy for new intermetallic intergrowth structures.

Prior muscle activation affects the compound muscle action potential.

INTRODUCTION: This study was performed to evaluate the effect of prior voluntary activation of a muscle on the subsequently-recorded compound muscle action potential (CMAP). METHODS: The CMAPs from the hypothenar, thenar, and extensor digitorum brevis muscles were recorded in 6 healthy volunteers at rest and for up to 30 min following 5 separate epochs of up to 20 s of voluntary muscle activation. RESULTS: There was consistent, significant (P < 0.02) enhancement of the negative area, amplitude, and duration of the CMAP after activation. The enhancement was maximal, up to 144% of baseline, within about 1 min post-activation; thereafter, the CMAP gradually returned to baseline over about 15 min. DISCUSSION: Activation of a muscle within several minutes prior to testing enhances the subsequently-recorded CMAP. This observation highlights prior muscle activation as a physiological variable that influences the size of the CMAP during motor nerve conduction studies. Muscle Nerve, 2019.

Inducing Complexity in Intermetallics through Electron-Hole Matching: The Structure of Fe14 Pd17 Al69.

We illustrate how the crystal structure of Fe14 Pd17 Al69 provides an example of an electron-hole matching approach to inducing frustration in intermetallic systems. Its structure contains a framework based on IrAl2.75 , a binary compound that closely adheres to the 18-n rule. Upon substituting the Ir with a mixture of Fe and Pd, a competition arises between maintaining the overall ideal electron concentration and accommodating the different structural preferences of the two elements. A 2×2×2 supercell results, with Pd- and Fe-rich regions emerging. Just as in the original IrAl2.75 phase, the electronic structure of Fe14 Pd17 Al69 exhibits a pseudogap at the Fermi energy arising from an 18-n bonding scheme. The electron-hole matching approach's ability to combine structural complexity with electronic pseudogaps offers an avenue to new phonon glass-electron crystal materials.

Intraoperative seizures during craniotomy under general anesthesia.

PURPOSE: An acute symptomatic seizure is a clinical seizure occurring at the time of or in close temporal association with a brain insult. We report an acute symptomatic seizure occurring during a surgical procedure in a patient who did not have a prior history of epilepsy and who did not have a lesion associated with an increased risk of epilepsy. To characterize the incidence and clinical features of intraoperative seizures during craniotomy under general anesthesia, we reviewed cases where continuous EEG was acquired during craniotomy. METHOD: Records of 400 consecutive cases with propofol as general anesthesia during craniotomy were reviewed. Demographic data, indication for surgery, clinical history, history of prior seizures, duration of surgery and duration of burst suppression were recorded. Cases where seizures were observed were analyzed in detail. RESULTS: Two out of 400 patients experienced intraoperative seizures, including one patient who appeared to have an acute symptomatic seizure related to the surgical procedure itself and a second patient who experienced two seizures likely related to an underlying diagnosis of epilepsy. CONCLUSIONS: This is the first report of an acute symptomatic seizure secondary to a neurosurgical procedure. Overall, 0.5% of patients monitored experienced seizures, indicating that intraoperative seizures are rare, and EEG monitoring during craniotomies is of low yield in detecting seizures.