Chemical tuning strategies for layered quantum materials

Novel quantum materials exhibit unusual electronic properties with potential applications in low-power, high-efficiency devices. Their study, however, begins with synthesis and structural and compositional characterization. Published crystal structures and compositions may appear definitive, but every model carries experimental limitations and uncertainties.
The central idea of this thesis is the composition–structure–properties relationship. Material properties cannot usually be tuned directly: composition and synthetic conditions modify atomic and electronic structure, which in turn determine physical behaviour. Crystal quality—including size, internal stress, mosaicity, defect concentration, and compositional uniformity—is likewise controlled by the growth method. Understanding synthesis is therefore essential for interpreting subsequent measurements.
Reliable crystal structures are also required for electronic-structure calculations. As experimental methods have advanced, standards for structural characterization have risen substantially, making increasingly detailed analysis both possible and necessary.
This thesis applies this framework to several layered quantum materials. For trigonal PtBi₂, synthesis is optimized, its disputed lattice symmetry is resolved, and substitutional series are explored. TaTMTe₄ (TM = Ir, Rh, Ru) single crystals are grown and their structures revisited, revealing non-stoichiometry, disorder, and lattice changes, particularly in the Ru compound. Finally, a new synthetic approach is developed for compositionally tunable KₓRhO₂, with preliminary results showing how synthesis influences its magnetic properties.