Evolution of charge density wave order in continuous solid solutions Lu(Ni₁₋ₓCoₓ)C₂

Abstract

Pseudo-ternary solid solutions, Lu(Ni₁₋ₓCoₓ)C₂ (0 ≤ x ≤ 1), were studied by means of powder X-ray diffraction, differential thermal analysis as well as electrical resistivity and heat capacity measurements. The crystal structure of the Lu(Ni₁₋ₓCoₓ)C₂ series, as investigated by means of X-ray powder diffraction, is of structure type CeNiC₂, space group Amm2, Pearson symbol oS8. The structural analysis reveals a non-monotonous evolution, in particular for the a- and c-lattice parameters, resulting in a non-linear decrease of the unit cell volume, markedly deviating from Vegard's rule, due to non-isoelectronic substitution of Ni by Co. Utilizing differential thermal analysis (DTA) data, a pseudo-binary phase diagram LuNiC₂–LuCoC₂ has been constructed. The evolution of charge density wave order in Lu(Ni₁₋ₓCoₓ)C₂, which reaches an ordering temperature TCDW ≅ 450 K for LuNiC₂, was studied by means of electrical resistivity and heat capacity measurements. For solid solutions prepared via the floating-zone melting technique it became feasible to trace charge density wave (CDW) features of the temperature dependent electrical resistivity, thus, indicating a critical composition for the suppression of CDW order in Lu(Ni₁₋ₓCoₓ)C₂ at around x ≈ 0.15 – 0.17, which matches with a distinct drop of the composition dependent electronic Sommerfeld coefficient of the low temperature heat capacity of Ni-rich solid solutions.