Structure and properties of a novel boride: ThNi12B6

Abstract

Investigation of the system Th–Ni–B prompted a novel ternary compound ThNi₁₂B₆. X-ray structure analysis of single crystals obtained by the mechanical fragmentation of an as-cast sample revealed a fully ordered CeNi₁₂B₆-type structure (space group Cmc2₁, no. 36; a = 0.95638(1) nm, b = 0.73852(1) nm, c = 1.10195(1) nm; R_F2 = 0.0305). Density functional theory (DFT) calculations have been performed comprising heat of formation, electronic band structure and density of states, Fermi surface via Wannier functions, phonon band structure and density of states, phonon and electronic contributions to specific heat and elastic constants C_ij. Comparing the parameters evaluated from DFT with the experimental data, an overall satisfactory agreement has been achieved. Measurements of electrical resistivity, magnetic susceptibility and specific heat manifest a Pauli paramagnetic, metallic behaviour for ThNi₁₂B₆ without any anomalies, in close match with the isotypic homologue LaNi₁₂B₆. Static and dynamic hardness data show rather high values; Young's modulus is in the range of 240 GPa. The Debye temperature, θ_D = 490 K, gained via elastic constants, is slightly higher than the values extracted from specific heat or electrical resistivity data. A rather low coefficient of thermal expansion, α = 5.5 × 10⁻⁶ K⁻¹, was derived from the temperature dependent length change.