Phase equilibria in the Er–Zr–Ni system and crystal structure of R1+xZr1-xNi (R=Er, Tm, Lu) compounds

Abstract

The isothermal section of the Er–Zr–Ni phase diagram in the Er–Zr–ErNi region at 870 K has been studied by means of X-ray phase and structural analyzes and energy-dispersive X-ray spectroscopy. The mutual solubility of the components Er, Zr and Ni at 800 ° С was established: Zr dissolves up to 3 at. % Er and practically does not dissolve Ni; Ni practically does not dissolve Er and Zr; Er dissolves up to 12 at. % Zr and practically does not dissolve Ni. The following solid solutions of substitution were detected: Er 3- x Zr x Ni (0≤ x ≤0.24; structure type (ST) Fe 3 C, space group (SG) Pnma, a = 6.804–6.801(1) Ǻ, b = 9.430–9.431(3) Ǻ, c = 6.245–6.241(2) Ǻ); Er 3- x Zr x Ni 2 (0≤ x ≤0.04; ST Er 3 Ni 2 , SG R , a = 8.472–8.451(2) Ǻ, c = 15.680–15.665(4) Ǻ). Two ternary compound with the narrow homogeneity range Er x Zr 1- x Ni 2 (0.12≤ х ≤ 0.24) and Er 1+ x Zr 1− x Ni (0.33 ≤ x ≤ 0.48) occurs in the system. The Er x Zr 1- x Ni 2 (0.12 ≤ х ≤ 0.24) compound crystallizes in the cubic MgCu 2 type of structure, а = 6.959(6)–6.987(5) Å). The crystal structure of Er 1+ x Zr 1− x Ni (0.33≤ x ≤ 0.48) compound was investigated by means of EDX and powder X-ray diffraction. It crystallizes in the TiNiSi ST (SG Pnma , No. 62, oP 12, а = 6.8175(7)–6.8253(8) Å, b = 4.6494(5)–4.6575(6) Å, c = 8.1021(9)–8.113(1) Å). In Er 1+x Zr 1−x Ni, the Er/Zr statistical mixture leading to nonequiatomic compositions occupies the position corresponding to the nickel site of the TiNiSi structure type. The isostructural rare earth compounds R 1+x Zr 1−x Ni (0.33≤ x ≤ 0.48; R=Tm, Lu) have been synthesized and their homogeneity ranges were refined. Keywords: ternary system, phase equilibria, intermetallic compounds, crystal structure.