High Entropy Design as a Route to Inaccessible Metal Diborides

Author

• Abraham A. Rosenberg, University at Albany, State University of New YorkFollow

ORCID

0009-0007-1573-0339

Date of Award

Fall 2026

Language

English

Embargo Period

4-16-2027

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Chemistry

Program

Chemistry

First Advisor

Michael Yeung

Committee Members

Michael Yeung, Alexander Shekhtman, Alan Chen, Ting Wang

Keywords

High-Entropy, Diborides, Poison-Resistance, Hardness, Platinum, Silicon

Subject Categories

Inorganic Chemistry | Materials Chemistry

Abstract

For nearly a century, alloy design has been governed by the Hume–Rothery rules, which define the thermodynamic and structural constraints for solid-solution formation and have traditionally limited accessible compositional space.  The emergence of high entropy alloys introduced a fundamental shift in this paradigm by demonstrating that configurational entropy can stabilize multicomponent systems that would otherwise be thermodynamically inaccessible.  This concept has since expanded beyond metallic systems into ceramics, including oxides, carbides, nitrides, silicides, and borides, enabling access to unconventional chemistries, bonding environments, and local atomic arrangements.

This dissertation demonstrates that high entropy stabilization provides a general strategy for incorporating chemically inaccessible elements into transition metal diborides, enabling both new coordination environments and emergent functional properties.  Particular attention is given to high entropy diborides, where ordered boron sublattices provide a structural scaffold capable of accommodating elements that would be inaccessible through classical alloying approaches, while preserving phase stability.  The dissertation begins by examining the interplay between classical alloying limitations and entropy driven stabilization, highlighting recent advances in the high entropy alloys and ceramics.

Chapter 2 investigates the synthesis and properties of the high entropy boride Al_0.2Nb_0.2Pt_0.2Ta_0.2Ti_0.2B₂.  In this system, platinum is stabilized in a 12-coordinate environment within a boron-rich layered structure, a coordination motif inaccessible in conventional platinum borides.  Beyond its structural novelty, the boron framework imparts resistance to sulfur poisoning, enabling sustained catalytic hydrogenation of sulfur-containing substrates.  This behavior demonstrates the dual role of high entropy stabilization in enabling both unconventional coordination chemistry and functional catalytic robustness.

Chapter 3 investigates the mechanistic basis of this catalytic activity by comparing flux-growth and arc-melted samples, revealing how crystal morphology influences hydrogen activation and catalytic performance.  Hydrogenation studies using mechanistic probe substrates WO₃ and TEMPO to support a hybrid hydrogen atom transfer and hydrogen spillover mechanism, in which hydrogen dissociates on platinum sites before migrating across the diboride surface as reactive intermediates to react with adsorbed substrates.

In chapter 4, the scope of high entropy diboride chemistry is extended to main-group element incorporation through the synthesis of Cr_0.2Nb_0.2Si_0.2Ta_0.2Ti_0.2B₂.  Despite silicon’s incompatibility with classical alloying rules, it is stabilized within the metal sublattice, forming directional Si–B covalent bonds that link boron layers into a three-dimensional covalent network.  Mechanical characterization reveals modest increases in elastic stiffness and load-dependent hardness, demonstrating how silicon incorporation modifies bonding and mechanical response without destabilizing the parent structure.

Collectively, these studies demonstrate that high entropy design transcends classical alloying limitations to stabilize chemically and structurally unconventional diborides.  By leveraging configurational entropy and robust boron frameworks, this work expands the accessible compositional landscape of transition metal borides and establishes new connections between atomic-scale disorder, local bonding environments, catalytic, and mechanical properties, while expanding the design space for next-generation boride and high entropy materials.

Comments

I have an approved 6-month embargo

License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Recommended Citation

Rosenberg, Abraham A., "High Entropy Design as a Route to Inaccessible Metal Diborides" (2026). Electronic Theses & Dissertations (2024 - present). 549.
https://scholarsarchive.library.albany.edu/etd/549