Phase equilibria and crystal structures in the system Ce–Zn–Si

Abstract

Phase relations in the system Ce–Zn–Si have been determined for the isothermal section at 800 °C using electron microprobe analysis and X-ray powder diffraction. Phase equilibria are characterized by extended solid solutions along the section CeSi2–CeZn2, which form a structurally related sequence of structure types: Ce(ZnxSi1−x)2 (αThSi2-type, 0 ≤ x ≤ 0.32), τ2-Ce(ZnxSi1−x)2 (AlΒ2-type, 0.36 ≤ x ≤ 0.76) and Ce(Zn1−xSix)2 (CeCu2-type, 0 ≤ x ≤ 0.18). Silicon stabilizes the ternary compound τ1-Ce7Zn21(Zn1−xSix)2, (0.28 ≤ x ≤ 0.98) for which the crystal structure was derived from X-ray diffraction data for a single crystal of Ce7Zn21(Zn1−xSix)2 (x = 0.28; unique structure type, Pbam; a = 1.55722(3) nm, b = 1.71942(3) nm, c = 0.44772(1) nm; RF = 0.029). The structure of Ce7Zn21(Zn1−xSix)2 can be considered as an arrangement of slightly distorted building blocks of Cu3Au-type (Zn[Ce4Zn8]) and BaAl4-type (Ce[Ce2Zn10M4] and Ce[Ce2Zn13M2]), arranged in form of a zig-zag string of face-sharing units…Cu3Au–BaAl4–BaAl4–BaAl4–Cu3Au… running parallel to the b-axis. Structural analyses proved isotypism for homologous La7Zn21(Zn1−xSix)2 (x = 0.27), Ce7Zn21(Zn1−xSix)2-type, Pbam; a = 1.56817(2) nm, b = 1.72923(3) nm, 0.450887(7) nm; X-ray single crystal data and La(ZnxSi1−x)2, (x = 0.56, AlΒ2-type, P6/mmm, a = 0.42775(4) nm, c = 0.42832(4) nm; X-ray powder data). The structure types of the ternary compounds τ3-Ce(ZnxSi1−x), 0.17 ≤ x ≤ 0.23, and τ4-Ce40Zn37Si23 (in at.%) are still unknown.