In the past two decades, various classes of topological materials have been discovered, yet the deliberate control of topology in a single material remains largely unexplored. Here we demonstrate full experimental control over the topological nodal loop in the square-net material LaSbxTe2-x by chemical substitution and electron doping. Using angle-resolved photoemission spectroscopy, we show that changing the antimony concentration x from 0.86 to 1.0 in the bulk opens a gap larger than 400 meV in the nodal loop. Symmetry analysis establishes that this effect originates from the breaking of n glide symmetry in the square-net layer. The same topological phase transition can also be driven reversibly on the surface of LaSbxTe2-x by in situ chemical gating via potassium deposition, enabling on-demand switching of topology. The control parameter for both the bulk and surface transition is the electron concentration, providing a pathway towards applications based on switching topology by electrostatic gating.

We report measurements of magnetization, specific heat, and thermal expansion performed on As-deficient MnAs single crystals (MnAs_0.968). Ferromagnetic order is observed near T_C ≃ 306 K on warming and T_C ≃ 302 K on cooling, which is consistent with previously-reported values for stoichiometric MnAs samples. In contrast, the second-order structural phase transition is observed at T_S ≃ 353 K, which is nearly 50 K lower than in the stoichiometric compound. We observe differences in the thermal expansion of our samples when compared to reports of stoichiometric MnAs including: (1) the ∼1.5 (2) the lattice parameters perpendicular to the basal plane exhibit a discontinuous jump of ∼1.1 T_C, and (3) thermal expansion perpendicular to the basal plane for T_C ≤ T ≤ 315 K is negative rather than positive. We also observe a correlation between the ratio of hexagonal lattice parameters, c/a, and T_S, strongly suggesting that the degree of structural anisotropy in MnAs could play an important role in tuning T_S.

High ionic conductivity solid-state electrolytes are essential for powerful solid-state lithium-ion batteries. With density functional theory andab initiomolecular dynamics simulations, we investigated the crystal structures of Li3YBr6and Li3LaBr6. The lowest energy configurations with uniform distribution of lithium ions were identified. Both materials have wide electrochemical stability windows (ESW): 2.64 V and 2.57 V, respectively. The experimental ESW for Li3YBr6is 2.50 V. Through extrapolating various temperature diffusion results, the conductivity of Li3YBr6was obtained at room temperature, approximately 3.9 mS cm-1, which is comparable to the experimental value 3.3 mS cm-1. Li3LaBr6has a higher conductivity, a 100% increase compared with Li3YBr6. The activation energies of Li3YBr6and Li3LaBr6through the Arrhenius plot are 0.26 eV and 0.24 eV, respectively, which is also close to the experimental value of 0.30 eV for Li3YBr6. This research explored high ionic conductivity halide materials and will contribute to developing solid-state lithium-ion batteries.

Quantum fluctuations inherent in electronic systems positioned close to magnetic instabilities can lead to novel collective phenomena. One such material, β-Ti6Sn5, sits close to ferromagnetic (FM) instability and can be pushed to an itinerant FM-ordered state with only minute magnetic or non-magnetic doping. The binary nature of this compound, however, limits the tuning variables that can be applied to study any emergent physics, which are likely to be sensitive to the introduction of chemical disorder.Accordingly, we grew high-quality single crystals of a new quaternary compound Zr3V3GeSn4 from a Sn-rich self flux, and determined the structure with single-crystal X-ray diffraction. Zr3V3GeSn4 forms in an ordered derivative of the hexagonal β-Ti6Sn5 structure with Zr and V atomic positions that show no indication of site interchange. Ge likewise occupies a single unique atomic position. The V site, which would be the one most likely to give rise to any magnetic character, is located at the center of a distorted octahedron of Sn, with such octahedra arranged in face-sharing chains along the crystallographic c axis, while the chains themselves are organized in a kagome geometry. Zr3V3GeSn4 represents the second known quaternary phase within this system, suggesting that other compounds with this structure type await discovery.

We report a synthetic pathway by which amorphous Al(OH)(3) is converted to.-AlOOH through hydrothermal reaction in the presence of water at temperature T = 473 K. X-ray pair distribution function measurements reveal that the initially amorphous Al(OH)(3) possesses a locally gamma-Al(OH)(3)-like structure, while nanocrystalline gamma-AlOOH precipitates within 1 h of continuous hydrothermal exposure. Solid state nuclear magnetic resonance measurements show that resonant features associated with four- and five-member Al clusters persist through 20 min of hydrothermal treatment, and ultraviolet (UV) spectra mark the onset of UV-induced photoluminescent features characteristic to gamma-AlOOH with 10 min of exposure, indicating a coexistence region of gamma-Al(OH)(3)-like and gamma-AlOOH-like amorphous species. Powder x-ray diffraction measurements of desiccated powders reveal that the conversion process takes place in distinct, power law-defined stages with initial gamma-AlOOH nucleation occurring within the first 20 min, followed by a similar to 1 h period of rapid grain coarsening and the subsequent onset of Lifshitz-Slyozov-Wagner-like coalescence.

B. Xia,1 J. Cheng ,2 M. Arengo,1 N. Rajput,1 Y. Janssen,1 J. R. Neilson,3 K. A. Persson,2,4 and J. W. Simonson1,* 1Department of Physics, Farmingdale State College, Farmingdale, New York 11735, USA 2Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA 4Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA

We report the discovery of a trigonal polymorph of the prospective Li-ion battery material Li2MnO3 and its synthesis in bulk, single-crystal form. Crystal growth of trigonal Li2MnO3 is strongly dependent upon the quality of a polycrystalline LiMnO2 precursor consumed in the synthesis process. The crystal structure of the trigonal phase is composed of ordered honeycomb layers of LiO6 and MnO6 octahedra segregated by layers of LiO6 octahedra and represents an ordered stacking variant of the known monoclinic polymorph. Diffuse reflectance spectroscopy reveals a direct optical gap of 2.47 +/- 0.11 eV and a series of charge excitations that are well explained by the expected Mn4+ 3d(3) valence. Density functional theory calculations are in excellent agreement with the spectroscopic measurements and find a near degeneracy in the formation energies of the two polymorphs. Our results suggest that the trigonal structure resolves the compositional and structural disorder often manifested in the monoclinic phase.

The quasi-one-dimensional structure of ${\mathrm{Li}}_{2}{\mathrm{Mn}}_{2}{({\mathrm{MoO}}_{4})}_{3}$ consists of three mutually distinct chains of ${\mathrm{Li}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}$-centered polyhedra in which Mn ostensibly adopts a $J=5/2\phantom{\rule{4pt}{0ex}}{\mathrm{Mn}}^{2+}$ configuration. In situ x-ray scattering experiments carried out as crystallites emerge from a molten oxide solution facilitate the synthesis of large single crystals. Ex situ x-ray diffraction finds no evidence of long-range Li/Mn occupancy ordering, suggesting that the structure is effectively composed of finite chains of Mn moments of statistically varying lengths. UV/visible diffuse reflectance spectroscopy measurements establish a wide 3.43(12)-eV direct charge gap consistent with the local polyhedral coordination of the nominally ${\mathrm{Mn}}^{2+}$ species. The temperature $T$ dependence of the DC magnetic susceptibility $\ensuremath{\chi}$ reveals a fluctuating moment of only $2.74{\ensuremath{\mu}}_{B}\ifmmode\pm\else\textpm\fi{}0.01{\ensuremath{\mu}}_{B}$/Mn, dramatically reduced from the $5.9{\ensuremath{\mu}}_{B}$/Mn expected for ${\mathrm{Mn}}^{2+}$. Meanwhile, the Weiss temperature ${\mathrm{\ensuremath{\Theta}}}_{W}=\ensuremath{-}89\ifmmode\pm\else\textpm\fi{}1$ K reveals antiferromagnetic fluctuations that are stymied from reaching an ordered state apparently by the chemical disorder intrinsic to the polyhedral chains. Measurements of magnetization vs field $H$ at $T\ensuremath{\le}10$ K are far from saturation even at $H=5$ T and are strongly non-Brillouin-like, instead scaling as $H/{T}^{0.24(3)}$ and suggesting the presence of quantum fluctuations associated with an eventual quasi-one-dimensional, disordered magnetic phase.

As part of an effort to characterize clusters and intermediate phases likely to be encountered along solution reaction pathways that produce iron and aluminum oxide-hydroxides from Fe and Al precursors, the complete structure of Al10O14(OH)2 (akdalaite) was determined from a combination of single-crystal X-ray diffraction (SC-XRD) data collected at 100 K to define the Al and O positions, and solid-state nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) data collected at room temperature (~300 K) to precisely determine the nature of hydrogen in the structure. Two different synthesis routes produced different crystal morphologies. Using an aluminum oxyhydroxide floc made from mixing AlCl3 and 0.48 M NaOH, the product had uniform needle morphology, while using nanocrystalline boehmite (Vista Chemical Company Catapal D alumina) as the starting material produced hexagonal plates. Akdalaite crystallizes in the space group P63mc with lattice parameters of a = 5.6244(3) Å and c = 8.8417(3) Å (SC-XRD) and a = 5.57610(2) Å and c = 8.77247(6) Å (NPD). The crystal structure features Al13O40 Keggin clusters. The structural chemistry of akdalaite is nonideal but broadly conforms to that of ferrihydrite, the nanomineral with which it is isostructural.

The 3d transition metal insulator Bi2CrAl3O9 forms with a quasi-one-dimensional structure characterized by linear chains of edge-sharing, Cr-and Al-centered, distorted octahedra. The UV/Vis spectrum of high-quality single crystals is marked by broad absorption edges corresponding to direct transitions across a 1.36-eV insulating gap. Measurements of dc magnetic susceptibility chi reveal a fluctuating moment of 2.60 +/- 0.01 mu(B)/Cr-reduced from the 3.87 mu(B)/Cr expected for Cr3+, while the Weiss temperature Theta(W) = -21 +/- 1 K implies that the prevailing local moment interactions are weakly antiferromagnetic in nature. Some 10% of the fluctuating moment is quenched, presumably due to the onset of an antiferromagnetic or spin glass phase at temperature T-star = 98 +/- 3 K, while measurements of magnetization versus field H at T <= 10 K scale as H/T-0.68(4), suggesting the presence of quantum fluctuations associated with a disordered phase. Density functional theory calculations carried out within the generalized gradient approximation are in excellent agreement with experimental results, asserting that short-range magnetic interactions remnant above T-star stabilize the insulating state.

We report here a course of basic research into the potential suitability of a pseudo-icosahedral Cr aluminide as a material for high-temperature protective coatings. Cr55Al232-delta [delta = 2.70(6)] exhibits high hardness at room temperature as well as low thermal conductivity and excellent oxidation resistance at 973 K, with an oxidation rate comparable to those of softer, denser benchmark materials. The origin of these promising properties can be traced to competing long-range and short-range symmetries within the pseudo-icosahedral crystal structure, suggesting new criteria for future materials research.

The lack of a mechanistic framework for chemical reactions forming inorganic extended solids presents a challenge to accelerated materials discovery. We demonstrate here a combined computational and experimental methodology to tackle this problem, in which in situ X-ray diffraction measurements monitor solid state reactions and deduce reaction pathways, while theoretical computations rationalize reaction energetics. The method has been applied to the La-Cu-S-O quaternary system, following an earlier prediction that enhanced superconductivity could be found in these of new lanthanum copper(II) oxysulfide compounds. In situ diffraction measurements show that reactants containing Cu(II) and S(2-) ions undergo redox reactions, leaving their ions in oxidation states that are incompatible with forming the desired new compounds. Computations of the reaction energies confirm that the observed synthetic pathways are indeed favored over those that would hypothetically form the suggested compounds. The consistency between computation and experiment in the La-Cu-S-O system suggests a new role for predictive theory: to identify and to explicate new synthetic routes for forming predicted compounds.

Significance Discovery of new materials enabling new technologies, from novel electronics to better magnets, has so far relied on serendipity. Computational advances show promise that new materials can be designed in a computer and not in the lab, a proposal called “Materials by Design.” We present here a detailed comparison between theory and experiment, carrying out the synthesis of a high-temperature superconductor in an X-ray beam to elucidate the sequence of chemical reactions as the compound forms. Parallel computations of the stabilities of possible compounds that could form from the selected elements accurately predict the observed reactions. Paired with our chemical intuition, this methodology provides understanding and potentially control of the essential chemical principles responsible for stabilizing virtually any compound.

We present WinATE, a new computer program to measure the electronic transport properties of materials with energy applications. The C++ program we describe here is designed with a user-friendly graphical interface to automate measurement. WinATE controls laboratory test and measurement equipment through a RS-232 serial interface. It was designed to measure electronic properties of synthesized materials at cryogenic temperatures. The material reaches thermal equilibrium within 0.01 K of the target temperature, and the resulting raw data are recorded and displayed to the user in a real-time plot. WinATE will independently capture electrical resistivity and temperature data, thus eliminating user entry errors. Current and voltage data can also be collected. New semiconductor materials can be characterized with this software by calculating the transport gap from resistivity measurements. The goal of WinATE is to increase the discovery rate of more energy efficient materials through automated data collection.