Our work seeks connections between the solid-state chemistry of materials and the physics of their functional behavior. Our synthetic capabilities range from traditional oxide synthesis to encapsulated flux growth of inorganic (sulfide, intermetallic, etc.) single crystals. We use a wide array of characterization and modeling tools to understand how our materials were formed, measure their properties, and understand new routes to engineering functionality or new synthetic tricks. Selected examples are listed below:
Tuning materials synthesis in situ
Traditional inorganic materials synthesis is often performed ex situ: the products are only examined after the reaction has completed. We use x-ray and neutron scattering and optical spectroscopy to monitor our materials synthesis reactions in situ. In addition to discovering new semiconductors on the fly, we are keenly interested in the mechanisms of how new materials form and how to control these processes. Since 2015 this work is supported by an Early Career Award from the US Department of Energy.
D. P. Shoemaker, et al. Understanding fluxes as media for directed synthesis: in situ local structure of molten potassium polysulfides. J. Am. Chem. Soc. 134 (22) 9456-9463 (2012)
D. P. Shoemaker, et al. Chemical ordering rather than random alloying in SbAs. Phys. Rev. B 87 094201 (2013)
Genomic approaches to superconductor synthesis
The Materials Genome Initiative seeks to accelerate materials development by leveraging data-rich, high-throughput computation and experiment. We are part of a highly collaborative effort from the Center for Emergent Superconductivity (CES) to develop superconductors using a genomic approach. We synthesize superconducting candidates using rapid methods and gas-flow metathesis. We work with the Wagner group and others in the Center to refine our theoretical predictions and data-mining efforts, and to expand our experimental repertoire. The CES is an Energy Frontier Research Center, supported by the US Department of Energy.
A. Narayan, A. Bhutani, S. Rubeck, J. N. Eckstein, D. P. Shoemaker, L. K. Wagner. Computational and experimental investigation of unreported transition metal selenides and sulphides. arXiv:1512.02214 (submitted)
Disordered electronic materials
Many electronic materials exist in a gray area between perfect crystals and perfect glasses. Disorder can be driven by frustration, entropy, or phase transitions. We probe how the transport behavior of these systems depends on their complex structures. Least-squares fitting and reverse Monte Carlo simulations to pair distribution function data has been immensely helpful. We build large-box models constrained by high-energy scattering data obtained at the Advanced Photon Source or Lujan Neutron Scattering Center. These "atom's-eye" descriptions of materials can interface with atomistic simulations to understand how departures from a perfect crystalline lattice can lead to novel properties.
D. P. Shoemaker, et al. Incoherent Bi off-centering in Bi2Ti2O7 and Bi2Ru2O7: Insulator versus metal. Phys. Rev. B 84 064117 (2011)
S. A. Corr, et al. Real space investigation of structural changes at the metal-insulator transition in VO2. Phys. Rev. Lett. 105 056404 (2010)
Synthetic routes to metastable phases and composites
Many inorganic materials with energy relevance lie just outside thermodynamic equilibrium. The difficulty is to locate promising systems and develop synthetic routes to stabilize them. We use chemical metathesis (chemical conversion while maintaining crystallinity) to explore new compounds and composites. These materials often have complicated structures, so we use high-resolution diffraction experiments to identify competing phases.
D. P. Shoemaker, et al. Phase relations in KxFe2-ySe2 and the structure of superconducting KxFe2Se2 via high-resolution synchrotron diffraction. Phys. Rev. B 86 184511 (2012)
D. P. Shoemaker, et al. Exchange biasing of single-domain Ni nanoparticles spontaneously grown in an antiferromagnetic MnO matrix. J. Phys. Cond. Mat. 20 195219 (2008)