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_1.00–0.66Cr_0–0.34P (NbAs-type; a=3.332(3)–3.1366(3) Å, c=11.386(4)–11.364(2) Å), Ta_3.0–2.1Cr_0–0.9P (Ti₃P-type, a=10.156(2)–9.9992(2) Å, c=5.015(1)–4.956(2) Å), and Cr_3.0–2.4Ta_0–0.6P (Ni₃P-type, a=9.186(5)–9.217(4) Å, c=4.557(3)–4.5911(3) Å). A limited homogeneity range is found in the ternary phase Ta_1.0–0.8Cr_1.0–1.2P (TiNiSi-type, a=6.2344(5)–6.141(2) Å, b=3.5034(3)–3.3769(6) Å, c=7.3769(6)–7.357(2) Å). The OsGe₂-type structures (space group C2/m) of a new P-rich compound, Ta_0.92(2)Cr_0.08(2)P₂ (a=8.8586(3) Å, b=3.2670(2) Å, c=7.4871(2) Å, β=119.315(2)°) as well as of the Ti-containing analogue Ta_0.93(3)Ti_0.07(3)P₂ (a=8.8592(5) Å, b=3.2663(3) Å, c=7.4870(5) Å, β=119.309(2)°) were refined from powder X-ray diffraction data. - Graphical abstract: 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_1.00–0.66Cr_0–0.34P, Ta_3.0–2.1Cr_0–0.9P, and Cr_3.0–2.4Ta_0–0.6P. A limited homogeneity range is found in the ternary phase Ta_1.0–0.8Cr_1.0–1.2P. The OsGe₂-type structures of a new P-rich compound, Ta_0.92(2)Cr_0.08(2)P₂ as well as of the Ti-containing analogue Ta_0.93(3)Ti_0.07(3)P₂ were establish from powder X-ray diffraction data. No homogeneity ranges for binary compounds Cr₁₂P₇, Cr₂P, Ta₅P₃ were detected. - Highlights: • The phase diagram of Ta–Cr–P at 1070 K has been constructed. • New ternary compounds Ta_0.92(2)Cr_0.08(2)P₂ and Ta_0.93(3)Ti_0.07(3)P₂ were established. • Ta_1.0−0.8Cr_1.0−1.2P and Ta_0.86+xTi_0.15-xP₂(x= 0−0.07) exhibit homogeneity ranges. • The binary compounds reveal homogeneity ranges by Ta/Cr and Cr/Ta substitutions.