The phase equilibria and crystal structure of the phases in the Hf–Ti–P system

• Isothermal section of Hf–Ti–P system at T = 1070 K was constructed in the region 0–67 at.% of P.
• Three ternary compounds were detected.
• The homogeneity ranges of ternary phases were determined.
• The majority of the binary compounds reveal homogeneity ranges by Ti/Hf and Hf/Ti substitutions.

Phase equilibria in the Hf–Ti–P system were investigated at T = 1070 K in the region 0–67 at.% of P, employing X-ray powder diffraction. The three ternary compounds exist in the Hf–Ti–P system at this temperature. Two of them have homogeneity regions and their compositions can be represented as HfxTi2−xP (0.65 ⩽ x ⩽ 1.30; TiNiSi-type, space group Pnma, a = 6.130(3)–6.673(5), b = 3.508(2)–3.557(2), c = 8.050(5)–8.161(2) Å) and HfxTi2−xP0.68. (0.75 ⩽ x ⩽ 1.00; Zn3Cu-type, space group Р-6, a = 4.758(1)–4.803(1), c = 3.005(1)–3.035(1) Å). The crystal structure of the new phosphide Hf5.35Ti8.65P8.93 was determined by X-ray single crystal diffraction. This compound crystallizes with the Zr14P9-type structure (space group Pnnm, cell parameters a = 15.973(1), b = 26.335(2), c = 3.5281(2) Å, R1 = 0.0670; wR2 = 0.0875). The majority of binary compounds form substitution type solid solutions, in their homogeneity ranges the substitution of Ti by Hf or Hf for Ti takes place.

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