Browsing by Author "Haugstad, Greg"

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    Data for Crystal-Chemical Origins of the Ultrahigh Conductivity of Metallic Delafossites
    (2023-11-09) Zhang, Yi; Tutt, Fred; Evans, Guy N; Sharma, Prachi; Haugstad, Greg; Kaiser, Ben; Ramberger, Justin; Bayliff, Samuel; Tao, Yu; Manno, Mike; Garcia-Barriocanal, Javier; Chaturvedi, Vipul; Fernandes, Rafael M; Birol, Turan; Seyfried Jr, William E; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Electronic and Magnetic Materials Lab
    Despite their highly anisotropic complex-oxidic nature, certain delafossite compounds (e.g., PdCoO2, PtCoO2) are the most conductive oxides known, for reasons that remain poorly understood. Their room-temperature conductivity can exceed that of Au, while their low-temperature electronic mean-free-paths reach an astonishing 20 um. It is widely accepted that these materials must be ultrapure to achieve this, although the methods for their growth (which produce only small crystals) are not typically capable of such. Here, we first report a new approach to PdCoO2 crystal growth, using chemical vapor transport methods to achieve order-of-magnitude gains in size, the highest structural qualities yet reported, and record residual resistivity ratios (>440). Nevertheless, the first detailed mass spectrometry measurements on these materials reveal that they are not ultrapure, typically harboring 100s-of-parts-per-million impurity levels. Through quantitative crystal-chemical analyses, we resolve this apparent dichotomy, showing that the vast majority of impurities are forced to reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly pure (~1 ppm impurity concentrations). These purities are shown to be in quantitative agreement with measured residual resistivities. We thus conclude that a previously unconsidered “sublattice purification” mechanism is essential to the ultrahigh low-temperature conductivity and mean-free-path of metallic delafossites. This dataset contains all digital data in the published paper of the same name.
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    Data for Crystallinity-independent toughness in renewable poly(L-lactide) triblock plastics
    (2024-03-18) Krajovic, Daniel M; Haugstad, Greg; Hillmyer, Marc A; hillmyer@umn.edu; Hillmyer, Marc A; Hillmyer Research Group
    Poly(L-lactide) (PLLA)’s broad applicability is hindered by its brittleness and slow crystallization kinetics. Among the strategies for developing tough, thermally resilient PLLA-based materials, the utilization of neat PLLA block polymers has received comparatively little attention despite its attractive technological merits. In this work, we comprehensively describe the microstructural, thermal, and mechanical properties of two compositional libraries of PLLA-rich PLLA-b-poly(γ-methyl-ε-caprolactone) (PγMCL)-b-PLLA (“LML”) triblock copolymers. The rubbery PγMCL domains microphase separate from the matrix in the melt and intercalate between PLLA crystal lamellae on cooling. Despite the mobility constraints associated with mid-block tethering, the PLLA end-blocks crystallize as rapidly as a PLLA homopolymer control of similar molar mass. Independent of their degree of crystallinity, LML triblocks exhibit vastly improved tensile toughnesses (63-113 MJ m-3) over that of PLLA homopolymer (1.3-2 MJ m-3), with crystallinities of up to 55% and heat distortion temperatures (HDTs) as high as 148 °C. We investigated the microstructural origins of this appealing performance using X-ray scattering and microscopy. In the case of a largely amorphous PLLA matrix, the PγMCL domains cavitate to enable concurrent PLLA shear yielding and strain-induced crystallization. In highly crystalline PLLA matrices, PγMCL facilitates a lamellar-to-fibrillar transition during tensile deformation, the first such transition reported for PLLA drawn at room temperature. These results highlight the unique attributes of PLLA block polymers and prompt future architectural and processing optimizations to achieve ultratough, high-HDT PLLA block polymer plastics after a simple thermal history on economical timescales.
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    Data supporting Holey Substrate-Directed Strain Pattering in Bilayer MoS2
    (2021-11-10) Zhang, Yichao; Choi, Moon-Ki; Haugstad, Greg; Tadmor, Ellad B; Flannigan, David J; flan0076@umn.edu; Flannigan, David J
    This data set contains transmission electron microscopy (TEM), atomic force microscopy (AFM), and atomistic simulation data supporting "Holey Substrate-Directed Strain Pattering in Bilayer MoS2" manuscript cited in referenced by.