Bonding in Transition Metal Dichalcogenides: An Experimental and Computational Investigation into the Electronic and Structural Properties of MTe2 (M=Hf, Ta, W, Re) and Their Solid Solution Systems

Abstract

As 2D layered materials, transition metal dichalcogenides (TMDs) exhibit many exotic physical properties that have promising uses in energy applications. TMDs’ chemical versatility allows for transition metal substitutional doping, which changes their electronic and structural properties. In this thesis, density functional theory (DFT) modeling is used alongside various synthesis protocols to elucidate the effect of transition metal doping by investigating a solid solution series of TMDs MTe2 (M = Hf, Ta, W, Re). DFT modeling gave insights into the electronic localization, conductive nature, and bonding contributions within each system, while information about lattice parameters and doping capabilities were extracted from analysis of experimental synthesis products. In the (Hf1-xTax )Te2 system, poor theoretical bonding for the doped TMD and poor experimental doping were found, but flat bands in the DFT-modeled band structure of Hf0.5Ta0.5Te2 suggest other synthesis pathways should continue to be attempted. In the (Ta1-xWx )Te2 system, Rietveld refinements of W-doping of a TaTe2 phase and Ta-doping of WTe2 phases lead to the theory that W-doping of TaTe2 results in pseudo-M3M chains (M = Ta, W) while Ta-doping of WTe2 results in the breaking of W3W intralayer zigzag chains. Non-bulk superconductivity was detected in the Ta3W3Te system. Though the superconducting phase could not be isolated, it warrants further investigation due to the charge-density-wave phase of TaTe2 . Further investigation is also needed for the endmember TMD ReTe2 in order to understand the bonding in the (W1-xRex )Te2 system, as although Re-doping of WTe2 seemed successful with a Te self-flux method, possible inaccuracies in previously reported ReTe2 structures render the W-doping picture of ReTe2 unclear.