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}(Ni1-xZnx)2Si2 exist with the Ni/Zn substitution starting from {La,Ce}Ni2Si2 (ThCr2Si2-type; I4/mmm) up to x = 0.18 for Ce(Ni1-xZnx)2Si2 and x = 0.125 for La(Ni1-xZnx)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(Ni0.61Zn0.39)2Si2 (P4/nmm; a = 0.41022(1) nm, c = 0.98146(4) nm; RF = 0.012) and by Rietveld refinement for La(Ni0.56Zn0.44)2Si2 (P4/nmm; a = 0.41680(6) nm, c = 0.99364(4) nm; RF = 0.043). Interestingly, the Ce-Zn-Si system contains a ternary phase CeZn2(Si1-xZnx)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 CeNi2+xSi2-x, x = 0.33 (single crystal data, P4/nmm; a = 0.40150(2) nm, c = 0.95210(2) nm; RF = 0.0163). Physical properties (from 400 mK to 300 K) including specific heat, electrical resistivity and magnetic susceptibility have been elucidated for Ce(Ni0.61Zn0.39)2Si2 and La(Ni0.56Zn0.44)2Si2. Ce(Ni0.61Zn0.39)2Si2 exhibits a Kondo-type ground state. Low temperature specific heat data of La(Ni0.56Zn0.44)2Si2 suggest a spin fluctuation scenario with an enhanced value of the Sommerfeld constant.
Highlights
Since its discovery in 1935 by Andress and Alberti,[1] the BaAl4 structure type and its derivatives have been found in more than 200 intermetallic compounds, the three tetragonal ternary variants: the ThCr2Si2-type by Ban and Sikirica[2], CaBe2Ge2 by Eisenmann et al.[4] and the noncentrosymmetric variant BaNiSn3 by Dörrscheidt and Schäfer.[5]
Paper systems contain a compound {La,Ce}Ni2Si2 which was reported to crystallize in the ThCr2Si2 type[34] with a practically negligible homogeneity range
Whilst the quaternary CaB2Ge2-type phase is stable at 800 °C, a reinvestigation of the Ce–Ni–Si system near the stoichiometric composition 1 : 2 : 2 revealed that the CaB2Ge2-type phase exists only at high temperatures (≥1000 °C) in the Ni-rich side
Summary
CeAl2Ga2-type discovered independently by Zarechnyuk et al.[3] in the same year), CaBe2Ge2 by Eisenmann et al.[4] and the noncentrosymmetric variant BaNiSn3 by Dörrscheidt and Schäfer.[5]. Phase equilibria in the Ce–Ni–Si system were investigated in the 70s by Bodak et al.[7,8] more ternary phases were discovered afterwards: Ce2Ni3Si5 (U2Co3Si5-type, orthorhombic superstructure variant of BaAl4),[9] Ce14Ni6Si11,10 Ce3NiSi3,11 etc. Spin density wave transition was found in BaFe2As2,16 followed by the discovery of superconductivity in K-doped[17] and Co-doped BaFe2As2.18 More recently, BCS-like superconductivity was found in noncentrosymmetric BaPtSi3 (BaNiSn3-type)[19] and isotypes.[20]. The present work intends to provide detailed information on the phase equilibria, crystal structures and physical properties of the novel BaAl4-derivative phases in the systems {La,Ce}–Ni–Si as well as in the isopleths {La,Ce}Ni2Si2– {La,Ce}Zn2Si2
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