Crystal structure and physical properties of new Ca₂TGe₃ (T = Pd and Pt) germanides

The crystallographic, electronic transport and thermal properties of Ca₂PdGe₃ and Ca₂PtGe₃ are reported. The compounds crystalize in an ordered variant of the AlB₂ crystal structure, in space group P6/mmm, with the lattice parameters a = 8.4876(4) Å/8.4503(5) Å and c = 4.1911(3) Å/4.2302(3) Å for Ca₂PdGe₃ and Ca₂PtGe₃, respectively. The resistivity data exhibit metallic behavior with residual-resistivity-ratios (RRR) of 13 for Ca₂PdGe₃ and 6.5 for Ca₂PtGe₃. No superconducting transition is observed down to 0.4 K. Specific heat studies reveal similar values of the Debye temperatures and Sommerfeld coefficients: Θ_D = 298 K, γ = 4.1 mJ mol⁻¹ K⁻² and Θ_D = 305 K, γ = 3.2 mJ mol⁻¹ K⁻² for Ca₂PdGe₃ and Ca₂PtGe₃, respectively. The low value of γ is in agreement with the electronic structure calculations.