BaAl4 derivative phases in the sections {La,Ce}Ni2Si2–{La,Ce}Zn2Si2: phase relations, crystal structures and physical properties

Abstract

Phase relations and crystal structures have been evaluated within the sections LaNi₂Si₂–LaZn₂Si₂ and CeNi₂Si₂–CeZn₂Si₂ at 800 °C using electron microprobe analysis and X-ray powder and single crystal structure analyses. Although the systems La–Zn–Si and Ce–Zn–Si at 800 °C do not reveal compounds such as “LaZn₂Si₂” or “CeZn₂Si₂”, solid solutions {La,Ce}(Ni_1−xZn_x)₂Si₂ exist with the Ni/Zn substitution starting from {La,Ce}Ni₂Si₂ (ThCr₂Si₂-type; I4/mmm) up to x = 0.18 for Ce(Ni_1−xZn_x)₂Si₂ and x = 0.125 for La(Ni_1−xZn_x)₂Si₂. For higher Zn-contents 0.25 ≤ x ≤ 0.55 the solutions adopt the CaBe₂Ge₂-type (P4/nmm). The investigations are backed by single crystal X-ray diffraction data for Ce(Ni_0.61Zn_0.39)₂Si₂ (P4/nmm; a = 0.41022(1) nm, c = 0.98146(4) nm; R_F = 0.012) and by Rietveld refinement for La(Ni_0.56Zn_0.44)₂Si₂ (P4/nmm; a = 0.41680(6) nm, c = 0.99364(4) nm; R_F = 0.043). Interestingly, the Ce–Zn–Si system contains a ternary phase CeZn₂(Si_1−xZn_x)₂ of the ThCr₂Si₂ structure type (0.25 ≤ x ≤ 0.30 at 600 °C), which forms peritectically at T = 695 °C but does not include the composition “CeZn₂Si₂”. The primitive high temperature tetragonal phase with the CaBe₂Ge₂-type has also been observed for the first time in the Ce–Ni–Si system at CeNi_2+xSi_2−x, x = 0.33 (single crystal data, P4/nmm; a = 0.40150(2) nm, c = 0.95210(2) nm; R_F = 0.0163). Physical properties (from 400 mK to 300 K) including specific heat, electrical resistivity and magnetic susceptibility have been elucidated for Ce(Ni_0.61Zn_0.39)₂Si₂ and La(Ni_0.56Zn_0.44)₂Si₂. Ce(Ni_0.61Zn_0.39)₂Si₂ exhibits a Kondo-type ground state. Low temperature specific heat data of La(Ni_0.56Zn_0.44)₂Si₂ suggest a spin fluctuation scenario with an enhanced value of the Sommerfeld constant.