Emerging Materials Recent Highlights

 

Overview:

This program emphasizes materials synthesis and processing, advanced characterizations and studies of materials properties, all aimed at a fundamental understanding of materials that have potential for applications. Currently the program has two activities sponsored by the DOE-BES Materials Science and Engineering Division:

  • Correlated electron phenomena in complex transition metal oxides
  • Rational searches for novel superconductors

A third project is sponsored by the DOE NA-22 office:

  • Design and growth of next generation g-ray detector crystals

Recent highlights:

Searching for the Kitaev Spin Liquid

Argonne Materials Science Division (MSD) Researchers Sae Hwan Chun, Hong Zheng, Constantinos C. Stoumpos, Christos D. Malliakas and John F. Mitchell and Advanced Photon Source (APS) X-ray Science Division (XSD) researchers Jong-Woo Kim, Jungho Kim, Yongseong Choi and Thomas Gog, have published a letter in Nature Physics providing direct experimental evidence for dominant bond-directional magnetic interactions in Na2IrO3, the key element needed to realize a new type of quantum spin liquid.

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Nature Physics 2015

Cuprates and Iridates More than Skin Deep

We used K atoms to donate electrons in situ to the surface of cleaved single-crystal Sr2IrO4 and then measured the electronic structure using ARPES as a function of K coverage and temperature. Our results indicate that the parallel between Sr2IrO4 and cuprates persists in the metallic phase induced by electron doping, and that the ‘breaking up’ of a Fermi surface into disconnected segments is a general phenomenon of a system containing certain generic characteristics of cuprates.

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Science 345, 187 (2014)

Superconductivity in Narrow Gap Semiconductors

Superconductivity was discovered in the narrow-gap semiconductor (Eg ~ 0.08 eV) CsBi4Te6, known as a good thermoelectric material with a thermoelectric figure of merit of 0.82 at 225 K, which is the end member (n = 0) of a larger homologous series Cs4[Bi2n+4Te3n+6]. A superconducting transition around 4.4 K was observed for p-type doped samples in temperature-dependent resistivity and magnetic susceptibility data.

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J. Amer. Chem. Soc., 2013, 135, 14540−14543
Phys. Rev. B. 2014, 90, 020504

Iridate Excitons Shed Light on Cuprates

We have found a composite particle in the Mott insulator Sr2IrO4—an exciton dressed with magnons—that propagates with the canonical characteristics of a quasiparticle (QP). The dynamics of this charge-neutral bosonic excitation mirrors the fundamental process of the analogous one-hole propagation in the background of ordered spins, for which a well-defined QP has never been observed.

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Nature Communications, 5, 1 (2014)

Shining a Light on Hidden Phases

We investigated a class of reactions called liquid flux reactions in situ at the Advanced Photon Source, monitoring the reaction progress in real time and gained a first glimpse of the transient products that precipitate and dissolve in and out of the liquid. Our method of in situ synthesis allows us to identify and these products and to isolate them quickly.

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Proceedings of the National Academy of Sciences, 111(30), 10922–10927 (2014)

New Semiconductors for γ-ray Detection


Metal chalco-halide materials can have energy gaps between those of the corresponding binary chalcogenides and binary halides.
Nuclear detection for the purposes of non-proliferation for homeland security, biomedical, and dental diagnostics as well as other scientific applications requires high sensitivity in order to allow the detection of distant, shielded, or weak nuclear radiation sources.
We have launched a project to develop simpler, scalable new materials for room temperature operation and high performance γ-ray detection with the goal of replacing the current leading material Cd1-xZnxTe, CZT.

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Science 345, 187 (2014)

Mining New Brownmillerites at High Pressure

We successfully prepared single crystals of Ca2Co2O5 using a high pressure optical-image floating zone technique. We find that as-synthesized Ca2Co2O5 is an ordered oxygen-deficient perovskite of the brownmillerite type, and it undergoes an unprecedented re-entrant structural phase transitions (PcmbP2/c11→ P121/m1→ Pcmb) with decreasing temperature.

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Chemistry of Materials, 26(24), 7172–7182 (2014)

Superconductivity in the intermetallic pnictide compound Ca11Bi10−x

We have discovered superconductivity in the intermetallic pnictide phase Ca11Bi9.88. The structure contains isolated Bi atoms, dumbbells,and four-fold rings. It the first member of the M11X10 family to superconduct.

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Phys. Rev. B. 2014, 89, 054512-1-6

Rational Synthesis of Superconductors

As part of a neutron powder diffraction study on the pnictide superconductor Ba1-xNaxFe2As2, we discovered a phase where the material re-enters a four-fold C4 symmetric state, rather than two-fold C2, close to the onset of super-conductivity. The experimental results provide strong evidence for the validity of an itinerant model of nematic order in the iron-based superconductors.

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Nature Comm., 2014, 5, 3845.

Quantum Spins Mimic Refrigerator Magnets

quantum spins The behavior of magnetic moments in metal oxides such as iridates is dominated by strong spin-orbit coupling effects. In layered compounds such as Sr3Ir2O7, the direction of these moments is controlled at the quantum level by dipolar interactions that are akin to those of classical bar magnets. From a functional standpoint, our findings suggest novel routes toward engineered structures that allow manipulation of moments without magnetic fields, a general strategy for future low-power electronics platforms.

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Phase Diagram of Ba1-xKxFe2As2

pnictide phase diagram

A key goal of this work has been controlling the homogeneity of highly volatile K dopants within strict limits(Δx <0.01) that would allow us to identify structural, magnetic, and superconducting phase boundaries reliably. With highly homogeneous samples in hand, a high-precision phase diagram could be determined by systematically combining neutron and x-ray diffraction with precision magnetic data.  The result is a clearer picture of the competing order parameters in this pnictide superconductor system.

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Molten Structure in Polysulfides, from Batteries to Directed Synthesis

Molten structure of potassium polysulfides

A tandem approch of in situ, high-temperature vibrational spectroscopy and x-ray total scattering provides a view of molten salts that challenges the established wisdom about species present in the melt. The polysulfide chain length is strongly controlled by the sulfur content, which helps explain how ions react in sulfur-based batteries and during flux growth of complex materials.

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Magnetic Modes in Sr2IrO4 Revealed by Resonant Inelastic X-ray Scattering

RIXS

Using resonant inelastic x-ray scattering (RIXS), we reveal the nature of magnetic interactions in a 5d transition-metal oxide, Sr2IrO4, where strong spin-orbit coupling induces a complex spin-orbital wave function labeled by the effective total angular momentum. The results bear compelling similarities to high Tc cuprates.

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Additional highlights can be found here.