Interaction of components in the system Ta−Fe−P at 1070 K

Abstract

The interaction of the components in the ternary Ta−Fe−P system was investigated by means of X-ray powder diffraction. The isothermal section of the Ta−Fe−P phase diagram was constructed at 1070 К in the region up to 67 at. % of P for the first time. The samples preparation: synthesis in an arc-furnace for samples with P content less than 35 at. %; samples with P content more than 35 at. % were just sintered at 1070 K; annealing at 1070 K during 800 hours. Phase equilibria were investigated employing X-ray powder and diffraction. The substitutions of Ta by Fe were observed for Ta 3 P, TaP phases, and Fe for Ta in the case of Fe 3 P, Fe 2 P binary compounds. The composition of these solid solutions can be described as: ~α-Ta 3.0 −2.6 Fe 0 −0.4 P (Ті 3 Р-type, space group P 4 2 / n, а =10.150(3)−9.854(4), с =5.012(2)−4.948(2) Å), ~ Ta 0 −0.4 Fe 3.0 −2.6 P (Ni 3 P–type, I -4, a =8.958(2)−9.117(4), c=4.382(1)−4.468(3) Å), Fe 2.0-1.7 Ta 0-0.3 P (Fe 2 P-type, space group P -62 m , а =5.851(1)−6.086(3), с =3.383(1)−3.447(1) Å), Ta 1.00 −0.81 Fe 0 −0.19 P (NbAs-type, space group I 4 1 md, а =3.3184(1)−3.3177(2), с =11.363(3)−11.344(1) Å). The existence of earlier known ternary phosphides Ta 4 FeP (Nb 4 CoSi-type, space group P 4/ mcc , a =6.1070(4), c =4.9829(7) Å) and Ta 1.1 −0.8 Fe 0.9 −1.2 P (TiNiSi-type, space group Pnma , a =6,118(3)−6.087(5), b =3,576(3)−3,583(2), c =6,976(3)−6,949(1) Å) was confirmed. The new ternary compounds TaFe 2 P and Ta 0.89(3) Fe 0.11(3) P 2 were found during the investigation of the Ta−Fe−P system. The crystal structure of these compounds were determined by means of X-ray powder method: TaNi 2 P-type, space group Pnma, a =8.3650(7), b =3.5203(3), c =6.7065(6) Å), R I =0.081, R P = 0.245 for TaFe 2 P; OsGe 2 -type, space group C 2/ m , a = 8.8581(4), b =3.2655(2), c =7.4868(4) Å, b = 119.318(2)°, R I =0.072, R P =0.173 for Ta 0.89(3) Fe 0.11(3) P 2 . The common features of investigated Ta−Fe−P and related Ta− M' −P systems are formation of Ta 1− x M' x P 2 with OsGe 2 -type, wich can be interrupted as quasi-binary compound ТаР 2 , the formation of which is stabilized by third component. Keywords: ternary phosphide, crystal structure, phase equilibria, solid state solution, X-ray diffraction.