Seminaire LMGP 24.06.2025 Aditya SHARMA

Aditya Sharma ⁽¹⁾

PhD student

⁽¹⁾ Université Grenoble Alpes, CNRS, Grenoble INP, LMGP, 38016 Grenoble Cedex 1, France

Chemical Exfoliation of Single Crystals of Layered Ternary Carbides and Borides

Abstract

Ternary layered carbides and borides, known as MAX and MAB phases, are nano-laminated materials recognized for their unique combination of metallic and ceramic properties, including high thermal stability, electrical conductivity, and machinability. MAX phases, with the general formula M_n+1AX_n, crystallize in a hexagonal structure (P6₃/mmc), where M is an early transition metal, A a group IV element, and X a carbon, nitride, or carbonitride. In contrast, MAB phases typically adopt orthorhombic structures with a general formula (M)_2zA_x(B₂)_y, incorporating late transition metals as M, group 13-14 elements as A, and boron (B). In 2011, the discovery of two-dimensional (2D) MXenes, such as Ti₃C₂T_x, via HF etching of Ti₃AlC₂ MAX phase, opened a way of chemical exfoliation of layered ternary MAX phases and MAB phases, resulting in a new class of materials with tunable surface chemistry, high conductivity, and ion intercalation capability. However, the commonly used HF-based synthesis protocols pose environmental and safety hazards and can degrade structural integrity. Recent advances focus on alternative, eco-friendly synthesis routes like molten-salt etching to address these challenges and enhance the stability and performance of corresponding 2D materials.

The objective of the thesis is to explore the chemical exfoliation of ternary layered MAB and MAX phases, focusing on MoAlB (MAB phase) and V₂AlC (MAX phase). A key innovation of this work is applying a molten salt-assisted exfoliation method to convert single crystals of MoAlB chemically. For the first time, the Mo₂AlB₂ phase has been synthesized in a single crystal form, with a typical size of 0.5-1.5 mm. We comprehensively characterized the single crystals and confirmed the high quality and preferred orientation of the converted Mo₂AlB₂ crystals using X-ray diffraction, Laue pattern, polarized Raman spectroscopy, and transmission electron microscopy. The electron transport measurements of the converted Mo₂AlB₂ crystals show a highly metallic nature and exhibit lower resistivity compared to the MoAlB phase, which is associated with the higher density of states at the Fermi energy of Mo₂AlB₂ as compared to MoAlB. The results of chemical exfoliation of MoAlB, in both crystal and powder phases, provide critical insights into the formation mechanism and the stability of MBenes. A similar molten-salt-assisted approach has been applied to chemically convert V₂AlC in the form of single crystals and powders. Through detailed optimization of synthesis conditions (time, temperature, and ratio of molten salts), the exact parameters of the synthesis of V₂C and VC are determined, supported by thorough structural and morphological characterizations. Later, as-prepared VC phase powder has been tested as a cathode material for aqueous Zn-ion batteries, which demonstrate a high specific capacity of 210 mAh g^-¹ at 5 A g^-¹, with a capacity retention of 55% over 2000 cycles when using zinc trifluoromethanesulfonate (Zn(Otf)₂) as the electrolyte.

Short Bio/CV
Accomplished materials researcher with over five years of laboratory R&D experience in 2D materials and energy storage device development for battery and supercapacitors. Currently pursuing a Ph.D. at LMGP, Grenoble-INP, University of Grenoble Alps, with a research focus on the synthesis of two-dimensional carbides and borides from MAX/MAB phase single crystals. Skilled in electrochemical testing (CV, EIS, GCD), advanced materials characterization techniques, XRD, SEM, and Raman Spectroscopy. Has contributed to multiple peer-reviewed publications and received international recognition through awards such as the IDEX Mobility Program for a research visit to CNR-ISM, Roma, Italy, and Best Poster Presentation at E-MRS 2024. Committed to advancing sustainable and scalable solutions for next-generation electronic and energy storage technologies.