High-Pressure and High-Temperature Synthesis and In Situ High-Pressure Synchrotron X-ray Diffraction Study of HfSi<sub>2</sub>
Weiwei Li, Pei Wang, Chao Xu, Hu Tang, Peng Ren, Zhiqing Xie, Xuefeng Zhou, Jian Chen, Shanmin Wang, Songbai Han, Yusheng Zhao, Liping Wang
Abstract
High-quality hafnium disilicide (HfSi2) has been successfully synthesized using a high-pressure and high-temperature (HPHT) method at 3 GPa and 1573 K in a DS6 × 10 MN cubic press. The modest synthesis temperature is aided by significant decreases in both liquidus and solidus temperatures at high pressure for the Si-rich portion of the Hf–Si binary system. The in situ high-pressure X-ray diffraction study yielded a bulk modulus of B0 = 124.4 ± 0.8 GPa with a fixed B0′ = 4.0 for HfSi2, which exhibits a dramatically anisotropic compressibility, with a and c axes nearly twice as incompressible as the b axis. The bulk HfSi2 as synthesized has a Vickers hardness of 6.9 ± 0.1 GPa and high thermal stability of 1163 K in air, indicating its hard and refractory ceramic properties. The core-level XPS data of Hf 4f and Si 2p have been collected on the bulk samples of HfSi2, HfSi, and Hf, as well as Si powder to examine the Hf–Si bonding in hafnium silicides. The Hf 4f7/2 binding energies are 15.0 and 14.8 eV for bulk HfSi2 and HfSi, respectively.