Synthesis, Structure and Transport Properties of New Lanthanum-based Ternary Hydrides

The quest for room-temperature superconductivity has driven intense exploration of hydrogen-rich compounds, identified as prime candidates for achieving high Tc, though their stabilization typically requires extreme pressures above 150–200 GPa. This thesis investigates chemical substitution and ternary hydride design that can stabilize superconducting phases of lanthanum hydrides at reduced pressures while retaining favorable superconducting properties. Four classes of lanthanum-based ternary hydrides were synthesized and characterized under high pressure using diamond anvil cells, synchrotron X-ray diffraction, laser heating, and electrical transport measurements. In La–Y–H systems, partial Y incorporation lowered the formation pressure of LaH10-type clathrates while preserving the hydrogen cage network. Synchrotron X-ray diffraction imaging with multi-channel transport revealed Y-stabilized cubic and hexagonal superhydrides persisting down to 136 GPa, with superconducting transitions linked to distinct structural domains. La–Al–H experiments revealed that Al-doping neither substantially modifies the LaH10 framework nor reduces its formation pressure. The (La,Al)H10 system provided a platform for advancing spectroscopic probes of superconducting hydrides. Most promisingly, La–C–H compounds yielded multiple polymorphs stable between 90–115 GPa, substantially lower than the stability range of pure LaH10 (>150 GPa). It is establishing a framework for carbon incorporation into clathrate hydrides and providing transport evidence of enhanced electronic conduction. Finally, LaH3−x and nitrogen-doped LaH3−xNy were explored near ambient pressure, where vacancy ordering and light-element substitution revealed new pathways toward metallicity and potential superconductivity without megabar compression. Collectively, these results demonstrate that targeted chemical substitution, through rare earth alloying, metal-site doping, and light-element incorporation, systematically tunes the stability and superconducting properties of lanthanum-based hydrides. Although room-temperature superconductivity outside the megabar regime remains elusive, the findings outline a roadmap for future progress through multicomponent substitutions and refined synthesis approaches. This work advances both the fundamental understanding and the experimental toolkit required to move hydride superconductivity from spectacular laboratory discoveries toward practical, reproducible materials.

Author dc:creator

• Abdul Haseeb Manayil Marathamkottil (23291383)

• Chemistry, Physical
• Physics, Condensed Matter

Statement dc:rights

• In Copyright

DOI dc:identifier

https://doi.org/10.25417/uic.31451146.v1

OAI identifier oai:identifier

oai:figshare.com:article/31451146