Engineering topics

Chan, Julia

Publications and source records attributed to Chan, Julia.

4 records

DOE OSTI2022

In Situ Probing and Investigation of the Crystal Growth of Highly Correlated Intermetallics

The proposal seeks to investigate the synthetic process of a new class of highly correlated intermetallics Ce n+1 Co n Ge 3n+1 (n = 1 – 6). This family of compounds is attractive as members of the series consist of subunits found in quantum materials. With our efforts to grow single crystals, we will address the fundamental questions of 1) how do crystals that are built from subunits form during crystallization and 2) what determines how these subunits arrange. We hypothesize that the complex intergrowth structures of Ce n+1 Co n Ge 3n+1 form upon cooling by the assembly of subunit-like clusters that exist prior to crystallization in the melt. The second hypothesis is layer-by-layer growth. The third hypothesis is an alternative growth mechanism, such as the conversion of metastable structure into a different structure. By understanding the assembly of subunits, strategies to affect process could emerge, which will ultimately lead to controlled heterostructural stacking of various subunits in the growth of bulk materials.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Basic Research Needs Workshop on Synthesis Science for Energy Relevant Technology

The technology that lies at our fingertips becomes more powerful each day. Smartphones connect us instantly to family, friends, and co-workers around the globe; give us access to a limitless stream of information; control the heating in our homes; and serve as our cameras, calculators, flashlights, music players, boarding passes and, on occasion, our phones. Cars are ever more fuel-efficient, safer, semi-autonomous, and have more computing power than the systems that guided humankind to the moon. LED lighting and solar panels are becoming commonplace, replacing less efficient technologies and expanding the energy options available worldwide. Novel polymers and nanoparticles are playing a crucial role in enhanced oil recovery. None of these advances would have been possible without the discovery and development of, and ability to create, new materials and chemical processes. Now imagine what our world would be like if we could accelerate those discoveries a thousandfold. What if the only limit to synthesizing new forms of matter were the imagination? We could build complex assemblies of atoms and molecules with architectures and capabilities far exceeding those of materials found in nature—for example, develop catalysts that turn garbage into fuels, design solar cells to power our homes directly from sunlight, make batteries with the energy density of gasoline, and create one- and two-dimensional solids that transport charge hundreds of times faster than silicon or allow us to build quantum bits based on the spins of electrons or photons to realize the promise of “beyond Moore’s law” computing. Advances in synthesis science are required to bring about this future—we not only must know how to design new molecules and materials with desired functions and properties through theory and computational techniques; we also must be able to make the materials we envision. New approaches to discovering as yet unimagined matter require a sea change in the way we think about the science of synthesis. Chemical and materials sciences have traditionally focused on understanding structure–function relationships with the goal of predicting where the atoms should be placed to achieve a targeted property or process. Much less effort has been directed toward a predictive science of synthesis—understanding how to get the atoms where they need to go to achieve the desired structure. This report, which is the result of the Basic Energy Sciences Workshop on Basic Research Needs for Synthesis Science for Energy Technologies, lays out the scientific challenges and opportunities in synthesis science. The workshop was attended by more than 100 leading national and international scientific experts. Its five topical and two crosscutting panels identified four priority research directions (PRDs) for realizing the vision of predictive, science-directed synthesis.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2012

Synthesis, Structure, and Physical Properties of Ln(Cu,Al,Ga) 13-x (Ln = La-Pr, and Eu) and Eu(Cu,Al) 13-x

Ln(Cu,Al,Ga) 13–x (Ln = La–Pr, and Eu; x ~ 0.2) were synthesized by a combined Al/Ga flux. Single crystal X-ray and neutron diffraction experiments revealed that these compounds crystallize in the NaZn 13 structure-type (space group Fm3⁻c) with lattice parameters of a ~ 12 Å, V ~ 1600 Å, and Z ~ 8. Our final neutron models led us to conclude that Cu is occupationally disordered on the 8b Wyckoff site while Cu, Al, and Ga are substitutionally disordered on the 96i Wyckoff site of this well-known structure-type. The magnetic susceptibility data show that Ce(Cu,Al,Ga) 13–x and Pr(Cu,Al,Ga) 13–x exhibit paramagnetic behavior down to the lowest temperatures measured while Eu(Cu,Al,Ga) 13–x displays ferromagnetic behavior below 6 K. Eu(Cu,Al) 13–x was prepared via arc-melting and orders ferromagnetically below 8 K. The magnetocaloric properties of Eu(Cu,Al,Ga) 13–x and Eu(Cu,Al) 13–x were measured and compared. Additionally, an enhanced value of the Sommerfeld coefficient (γ = 356 mJ/mol-K 2 ) was determined for Pr(Cu,Al,Ga) 13–x . Herein, we present the synthesis, structural refinement details, and physical properties of Ln(Cu,Al,Ga) 13–x (Ln = La–Pr, and Eu) and Eu(Cu,Al) 13–x .

Phelan, W Adam↗

DOE OSTI2011

Structure-property coupling in Sr3(Ru1 xMnx)2O7

Layered ruthenates are prototype materials for the study of structure-property correlations. We report the structural and physical properties of double-layered perovskite Sr3(Ru1 xMnx )2O7 single crystals with 0 < x < 0.7. Single-crystal x-ray diffraction refinements reveal that Mn doping on the Ru site leads to the shrinkage of unit-cell volume and the disappearance of (Ru/Mn)O6 octahedron rotation when x > 0.16, but the crystal structure remains tetragonal. Upon doping, the electrical resistivity reveals a metallic character (d /dT > 0) at high temperatures but insulating behavior (d /dT < 0) below a characteristic temperature TMIT. Interestingly, TMIT is different from TM, at which magnetic susceptibility reaches maximum. While TMIT increases monotonically with increasing x,TM displays a nonmonotonic dependence with x even though the effective spin increases from S 1 (x = 0) to 3/2 (x = 0.7). The phase diagram consists of three distinct magnetic ground states due to local structure change.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗