Atomic-scale structure elucidation of refractory metal carbides derived from metallocene-based preceramics

Polymer-derived ceramics (PDCs) are becoming an alluring class of materials that can incorporate the ceramic chemistries found in ultra-high-temperature ceramics, such as Ti, Zr, and Hf carbides. The use of polymeric materials intrinsically enables processing techniques with a higher degree of complexity in a more straightforward fashion, such as three-dimensional printing. In this contribution, a series of click-derived preceramic polymers (PCPs) was synthesized using azide-modified metallocene monomers and an alkynyl-modified aromatic monomer, with Ti, Zr, and/or Hf serving as the metals of interest. PDCs were generated via pyrolysis at 800, 1100, and 1500°C and thoroughly examined using a range of synchrotron-based scattering and spectroscopy techniques to better couple atomic-scale structure back to precursor chemistry and pyrolysis conditions. Reverse Monte Carlo (RMC) simulations were implemented to model synchrotron datasets for the extraction of structural metrics, such as local coordination numbers (CNs) and bond angle distributions. Heterogeneous RMC approaches were also used to better reflect the multi-phase structure found in these materials. In addition to examining single metal PDCs, the click chemistry approach implemented here enables the ready inclusion of different metallocene monomers, wherein TiZrHf PDCs were synthesized and further examined to determine the structural evolution of these materials. Overall, our work showcases a pathway for accessing atomic-scale structure in these emergent materials, providing the ability to assess structure-property relationships for future materials development.