High-Entropy Alloy: changing faces under high pressure - Dr. Qiaoshi Zeng

JUNE 2, 2017—A new study co-led by a HPSTAR staff scientist, Dr. Qiaoshi “Charles” Zeng revealed irreversible polymorphic phase transitions between the fcc and hcp structures in a prototype high-entropy alloy CoCrFeMnNi using in situ high pressure and high temperature x-xay diffraction techniques. Their discovery was just published in Nature Communications (DOI:10.1038/ncomms15687) on June 1st. These results shed new light on the thermodynamics and kinetics of complex HEA systems and also opens a new avenue towards tuning HEAs’ properties via polymorphic structural transitions for applications. --more

A general structural-property relationship in metallic glass - Charles Zeng

Shanghai February 01, 2016 — Structure-property relationship is a central topic in materials science. In crystalline materials, the well-defined lattice structure or defects enable us to describe their properties quantitatively. The structure of glass is basically featureless, very few rigorous laws are currently known for defining its ‘disordered’ structure. Establishing general and exact rules regarding structure-property relationships in glass remain elusive. A breakthrough has been made by a international team led by Dr. Qiaoshi Zeng, a staff scientist from HPSTAR. This team established a general rule correlating the bulk properties (volume V) with most prominent atomic structure information (principle diffraction peak position q1) for metallic glasses, i.e. V∝(1/q1)2.5. It is shown that the 2.5 power law is strictly followed by any metallic glass with its volume tuned by pressure and/or composition. This general 2.5 power law is attributed to the well constrained structure change/modification inevitably happened during pressure and/or composition tuning of metallic glasses, which brings new insight into the structure of metallic glasses. These results are just published by PNAS. --more

Metallic glass: homogenous in appearance, fractal at heart - Dr. Qiaoshi Zeng & Dr. Wendy Mao

Shanghai September 18th, 2015 — The atomic structure of glasses has been a long-standing unsolved mystery in condensed mater physics and materials science. A breakthrough in understanding the atomic structure of an important new category of glass — metallic glasses was made by a joint research team including staff scientists of HPSTAR, Dr. Qiaoshi Zeng and Dr. Wendy L. Mao. From multiple techniques, the team found that a specific fractal model — the percolation cluster packing could provide a perfect explanation of the 2.5 power law observed in the compression experiments of metallic glasses and a unified description of the atomic structure of metallic glasses from short range to macroscopic length scale for the first time. These results are just published by Science (DOI: 10.1126/science.aab1233). --more

A universal fractional noncubic power law for density in metallic glasses - Dr. Qiaoshi Zeng

Tuning with pressure, a research team led by Dr. Qiaoshi Zeng with collaborators from HPSTAR, Stanford University, SLAC National Accelerator Laboratory, and Geophysical Laboratory at Carnegie Institution of Washington made a surprising discovery that the three-dimensional density of metallic glasses is not simply the cube of their one-dimensional average interatomic spacing, but varies with a universal 5/2 fractional power. The result is published by Phys. Rev. Lett. on May 8, 2014.   --more