First-Principles Calculations on the Mechanical and Thermal Properties of HfSiO4

Hafnium orthosilicate (HfSiO4: hafnon) has been proposed as an environmental barrier coating (EBC) material to protect silicon and silicon-based ceramic materials at high temperatures and as a candidate dielectric material in microelectronic devices. It can naturally form at the interface between silicon dioxide (SiO2) and hafnia (HfO2). When used as an EBC, its coefficient of thermal expansion (CTE) should match that of the protecting layer (e.g. silicon and SiC composites). The EBCs with low thermal conductivity can also be used as thermal barrier coating (TBC). To understand and further improve its applications in EBC or TBC fields, the physical, mechanical, thermodynamic, and thermal transport properties of hafnon have been investigated using density functional theory calculations.

Our first-principle calculations agree with experiments and other reliable simulations. The ambient temperature elastic constants and bulk modulus agree below 5% with nanoindentation techniques measurements. The average linear CTE calculated agree with measurements by X-ray diffraction lattice parameter and dilatometry. The predicted thermal conductivity from Boltzmann transport theory is slightly larger than measured thermal conductivity by hot disk and laser flash measurements due to the absence of residual disorder in the theoretical analysis. This agreement validates our computational approach and enables its future use for the study of the thermomechanical properties of rare-earth or Group-IVB oxides or silicates.