Limits to the Stability of the Amorphous Nature of Polymer-Derived HfSiCNO Compounds


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Substituting silicon by transition metals in polymer-derived ceramics (PDCs) holds the potential for a new class of polymer-derived ceramics for ultrahigh-temperature structural applications. We present experiments that show that the solid solubility of HfO2 extends to Hf/Si ratio of <0.22. The materials are synthesized from (miscible) organic precursors. Similar to silicon-based materials they remain amorphous after pyrolysis at 1000°C. Small-angle X-ray scattering and Raman spectra remain essentially unaltered. It is postulated that Hf, like Si, forms mixed-bond tetrahedra with C, O, and N. The difference in the enthalpy of Hf-based, and Si-centered tetrahedra is calculated using single-bond energies, reinforcing the feasibility of substituting Si with Hf or with Zr atoms. Such polymer-based HfSiCNO compounds made directly from liquid organics, by a simple manufacturing process, may also be relevant to nanoscale dielectrics with low leakage electric charge in microelectronics applications.