Engineering topics

Gautam, Bhoj

Publications and source records attributed to Gautam, Bhoj.

3 records

DOE OSTI2026

Confinement of quasi-atomic structures in Ti 2 N and Ti 3 N 2 MXene electrides

Metal carbides, nitrides, or carbonitrides of early transition metals, better known as MXenes, possess notable structural, electrical, and magnetic properties. Analyzing electronic structures by calculating structural stability, band structure, density of states, Bader charge transfer, and work functions utilizing first principle calculations, we revealed that titanium nitride MXenes, namely Ti 2 N and Ti 3 N 2 , have excess anionic electrons in their lattice voids, making them MXene electrides. Bulk Ti 3 N 2 has competing antiferromagnetic (AFM) and ferromagnetic (FM) configurations with slightly more stable AFM configuration, while the Ti 2 N MXene is nonmagnetic. Although Ti 3 N 2 favors AFM configuration with hexagonal crystal systems having 6/ mmm point group symmetry, Ti 3 N 2 does not support altermagnetism. The monolayer of the Ti 3 N 2 MXene is a ferromagnetic electride. These unique properties of having non-nuclear interstitial anionic electrons in the electronic structure of titanium nitride MXene have not yet been reported in the literature. Density functional theory calculations show TiN is neither an electride, MXene, or magnetic.

Anionic electrons↗

DOE OSTI2024

Structural and Morphological Characteristics of Rare Earth Element-based MAX Phase and MXene

There has been a tremendous effort for the synthesis of crystalline MAX phases—a family of transition metal carbides and nitrides with a chemical formula of Mn+1AXn, where M is an early transition metal, A belongs to groups XIII – XVI in the periodic table, X is either C or N, and n can be in between 1 and 3. Furthermore, these materials have shown thermal and electrical conductance and have low density and high stiffness which open broad aspects of practical applications. Recently double transition metal MAX phases (M’ 2/3 M’’ 1/3 ) 2 AX - out-of-plane ordered, labeled as o-MAX and in-plane ordered, labeled as i-MAX, were reported. However, there are few reports on the synthesis and characterization of i-MAX and the corresponding MXenes. In this work, we synthesized Molybdenum-based rare earth containing i-MAX phase using arc melt technique. We then removed “A” element of i-MAX phase by acid treatment and sonication which resulted in two-dimensional (2D) transition metal carbides called MXenes. These MXenes offer high conductivity, hydrophilicity, magnetism, good dispersion ability in solvents, mechanical stability, and structural diversity with at least 100 stoichiometric MXene compositions and are recognized as multifunctional materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Luminescence from Self‐Trapped Excitons and Energy Transfers in Vacancy‐Ordered Hexagonal Halide Perovskite Cs 2 HfF 6 Doped with Rare Earths for Radiation Detection

Abstract Compared to halides Cs 2 HfX 6 (X = Cl, Br, I) with a vacancy‐ordered cubic double perovskite structure, the halide Cs 2 HfF 6 (CHF), with a hexagonal Bravais lattice, possesses a higher mass density and chemical stability for radiation detection. Luminescence properties and energy transfer mechanisms of rare‐earths‐doped CHF materials are studied here. The structure of CHF is identified as a new type of vacancy‐ordered hexagonal perovskite, with the same type of building blocks of the double perovskite but stacked with single layers. Density‐functional theory calculations reveal a large bandgap of CHF. A broad emission is observed from the pristine CHF host, which is suggested to be associated with self‐trapped excitons (STEs). A series of rare‐earths‐doped materials are designed utilizing the STE emissions, and efficient energy transfers from STEs and Tb 3+ to Eu 3+ are achieved for tunable emissions. The codoped material shows stable emission under X‐ray irradiation, with 10.2% reduction from its initial emission intensity, associated with possible structural evolution by radiation‐induced deformation of the soft host. The radiation responses of singly and codoped materials are evaluated, and the codoped material is found to be more sensitive to the radiation energy than the singly doped or pristine CHF for radiation detection.

36 MATERIALS SCIENCE↗