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Luo Group's Research

Selected Research Highlights (01/28/2022)

Grain boundaries

Compositionally complex ceramics

Ultrafast sintering and field effects

battery anode

Grain Boundary Complexions (2D Interfacial Phases)

grain boundaies in high-entropy alloys

Perdicting Grain Boundary Properties in 7D

Electrochemically Induced Grain Boundary Transition

Earlier Research Highlights

(2018 or Earlier)

A series of discrete grain boundary (GB) 2-D interfacial phases (also designated as “complexion”) has been identified in doped alumina [Dillon and Harmer, Acta Mater. 2007] and subsequently other materials. They can be utilized to control sintering, microstructures, and materials properties, offering a revolutionary method for achieving predictive fabrication of materials by design. This figure is adapted from a prior report in Science 333: 1730 (2011).

There are more details (e.g., in the bilayers in Ni-Bi)...

Ni Bi

Science 358: 97 (2017) UCSD News Release

Development of Interfacial "Phase" (Complexion) Diagrams

Grain Boundary Diagrams

A Few Examples:

PRL 2018

Physical Review Letters 120, 085702 (2018)

PRL 2018

Physical Review Letters 120: 085702 (2018)

Acta Materialia 130: 329 (2017)

Ni Bi

Scripta Materialia 130: 165 (2017)

In general, we purpose to develop grain boundary "phase" (complexion) diagrams as general materials science tool and (perhaps) a useful component for the "Materials Genome" Initiative. Please find some of our earlier studies below. Please also see a "cover article" in the August 2012 issue of the Journal of the American Ceramic Society [95: 2358 (2012)] that reviews some of our recent studies and a related news article in Ceramic Tech Today written by Eileen De Guire.

(a) A computed GB λ-diagram for Ni-doped Mo has been validated by a systematic comparison with (b) measured GB diffusivities. This figure is adapted from an “Editors’ Suggestion” in Phys. Rev. B [84: 014105 (2011)]. (According to the PRB: “As a service to both our readers and authors, we list a small number of papers published in Physical Review B that the editors and referees find of particular interest, importance, or clarity.”)

A counterintuitive phenomenon of decreasing GB diffusivity with increasing temperature predicted by (a) a computed λ-diagram was (b) corroborated experimentally. This phenomenon stems from the retrograde solidus line of the Mo-Ni system. Specifically, for a single-phase alloy of Mo + 0.5% Ni, increasing the temperature from 1200 °C to 1500 °C results in an increasing distance to the solidus line and a greater free-energy penalty for forming liquid-like GBs; thus, the general GBs become “drier” with decreasing diffusivities. Figure adapted from Phys. Rev. Lett. 105: 236102 (2010)