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Mattei, Gerard S.

Publications and source records attributed to Mattei, Gerard S..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Salt-Mediated Coarsening in Conversion-Reaction-Synthesized Nanoporous Metals and Nanocomposites Resolved through In Situ Synchrotron Diffraction Studies

High-energy synchrotron X-rays were used to probe the structural and microstructural evolution in Fe, Co, and Cu nanoporous metals (NPMs) and metal/salt nanocomposites (NCs) produced by recently developed conversion reaction synthesis (CRS) methods. Microstructure analysis of as-synthesized samples via whole pattern fitting showed that the NPMs exhibit domain sizes that increase as Co < Fe < Cu, with both Fe and Co having crystallite sizes below 3.0 nm. The as-synthesized metal/salt NCs had similar metal sizes, and additionally, the salt in the composite had unusually large lattice microstrain whose origin is attributed to chemical substitution of metal ions into the salt (e.g., Li $1–3x$ Fe $x$ Cl for Fe 3+ ). When thermal annealing is used to modify crystallite size, pore collapse often occurs in NPMs but NCs can be effectively tuned without this problem. While the NC coarsening occurs slowly at low temperatures, it was found that there is a drastic acceleration of the reaction rate at a specific onset temperature that results in the crystallite size increasing by an order of magnitude in about a minute. Curiously, there was no evidence in the diffraction data for salt melting at this onset temperature. However, there was a sharp reduction in the salt chemical lattice strain at the onset temperature, indicating that rapid metal coarsening is facilitated by the salt. Importantly, this behavior indicates an unexpectedly coupled reaction mechanism by which the metal ions needed for grain growth are supplied by the salt in a rate-limiting fashion.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Enumeration as a Tool for Structure Solution: A Materials Genomic Approach to Solving the Cation-Ordered Structure of Na 3 V 2 (PO 4 ) 2 F 3

While powder diffraction methods are routinely utilized to optimize structural models for compounds whose crystal structures are known, the determination of unknown structures is far more challenging. When the unknown structure is large, structure solution can become a virtually intractable problem using standard structure solution methodologies, especially when the space group cannot be unambiguously resolved. One such system is the promising Na-ion battery cathode material Na 3 V 2 (PO 4 ) 2 F 3 whose high temperature and room temperature structures were previously solved, but whose more complex low-temperature structure could not be determined. Here, a novel materials genomic approach is demonstrated for the solution of the unknown 100 K structure of Na 3 V 2 (PO 4 ) 2 F 3 in which enumeration methods are first used to generate a large number (~3,000) of trial structures based on plausible orderings of Na ions and then automated Rietveld refinements are carried out to optimize each of these trial structures. Based on both the analysis of the ensemble of optimized trial structures and the density functional theory energy minimization of selected trial structures, the 100 K structure of Na 3 V 2 (PO 4 ) 2 F 3 is best described as belonging to the space group A2 1 am with unit cell dimensions of a = 9.01928(4), b = 27.1379(1), c = 10.73307(5). The 100 K unit cell has a large volume of 2627.07(2) Å 3 with Z = 12 and 33 independent crystallographic sites (9 Na, 3 V, 3 P, 12 O, and 6 F) that is 3x and 6x larger than the room- and high-temperature polymorphs of this phase, respectively. Finally, the novel methods described here will be generally applicable for the solution of the complex cation-ordered structures that commonly occur for battery materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Salt Effects on Li-Ion Exchange Kinetics of Na 2 Mg 2 P 3 O 9 N: Systematic In Situ Synchrotron Diffraction Studies

The kinetics and thermodynamics of solid-state ion exchange of Li+ into Na2Mg2P3O9N were investigated using in situ synchrotron X-ray diffraction methods for a series of Li-containing salts, allowing systematic trends with general applicability to ion exchange reactions to be elucidated. The collection of data for a wide range of reaction conditions was enabled through the use of a novel multiwell sample environment which leverages the ability of the synchrotron beamline to rapidly (similar to 1 s) collect high-quality data suitable for monitoring reaction progress. From these data, it was possible to resolve the influence of salt choice and salt concentration on the ion exchange reaction kinetics. Furthermore, by carrying out experiments at different temperatures, initial estimates of activation energies were obtained. It was generally found that the ion exchange reaction kinetics strongly depended on the salt chosen as the ion source rather than being primarily determined by the ion mobility of the ceramic.

Cosby, Monty R.↗