Solid-State Phase Diagram of the Ho-Zr-Si Ternary System at 973 K (700 °C)

The phase equilibria of the Ho-Zr-Si ternary system were experimentally determined at 973 K (700 °C) in the entire concentration range by using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), and differential scanning calorimetry (DSC). The results show that there are 13 single-phase regions, 23 two-phase regions, and 11 three-phase regions in the investigated isothermal section, and no ternary compound is found. The composition ranges of all phases are extremely small. Among these, there are ten extensions of the binary compounds, i.e., ZrSi₂, α-ZrSi, α-Zr₅Si₄, Zr₃Si₂, Zr₂Si, β-HoSi_2-a, α-HoSi_2-b, HoSi, Ho₅Si₄, and Ho₅Si₃, in the ternary system. They are Zr_1–xHo_xSi₂ (x ≤ 0.084), α-Zr_1–xHo_xSi (x ≤ 0.156), α-Zr_5–xHo_xSi₄ (x ≤ 0.945), Zr_3–xHo_xSi₂ (x ≤ 0.550), Zr_2–xHo_xSi (x ≤ 0.180), β-Ho_1–xZr_xSi_2–a (x ≤ 0.124), α-Ho_1–xZr_xSi_2–b (x ≤ 0.147), Ho_1–xZr_xSi (x ≤ 0.220), Ho_5–xZr_xSi₄ (x ≤ 1.368), and Ho_5–xZr_xSi₃ (x ≤ 0.592), respectively. In the present work, the phase transformation temperatures of β-HoSi_2-b → α-HoSi_2–b and Ho₃Si₄ → β-HoSi_2–b + HoSi are determined to be 979.7 K (706.7 °C) and 1479.3 K (1206.3 °C), respectively, by analyzing the DSC results.