Interaction of tantalum, chromium, and phosphorus at 1070 K: Phase diagram and structural chemistry

Solid-state phase equilibria have been established in the Ta–Cr–P system in the region of 0–67 at% P at 1070 K through powder X-ray diffraction analysis. Mutual substitution of Ta and Cr in binary phosphides gives rise to significant homogeneity ranges in Ta 1.00–0.66 Cr 0–0.34 P (NbAs-type; a =3.332(3)–3.1366(3) A, c =11.386(4)–11.364(2) A), Ta 3.0–2.1 Cr 0–0.9 P (Ti 3 P-type, a =10.156(2)–9.9992(2) A, c =5.015(1)–4.956(2) A), and Cr 3.0–2.4 Ta 0–0.6 P (Ni 3 P-type, a =9.186(5)–9.217(4) A, c =4.557(3)–4.5911(3) A). A limited homogeneity range is found in the ternary phase Ta 1.0–0.8 Cr 1.0–1.2 P (TiNiSi-type, a =6.2344(5)–6.141(2) A, b =3.5034(3)–3.3769(6) A, c =7.3769(6)–7.357(2) A). The OsGe 2 -type structures (space group C 2/ m ) of a new P-rich compound, Ta 0.92(2) Cr 0.08(2) P 2 ( a =8.8586(3) A, b =3.2670(2) A, c =7.4871(2) A, β =119.315(2)°) as well as of the Ti-containing analogue Ta 0.93(3) Ti 0.07(3) P 2 ( a =8.8592(5) A, b =3.2663(3) A, c =7.4870(5) A, β =119.309(2)°) were refined from powder X-ray diffraction data.