What question did this study set out to answer?

The research aims to synthesize and characterize a new carbide hydride phase incorporating europium and lithium.

February 22, 2026Open Access

Eu₂Li (C₃) H: A Carbide Hydride Phase Incorporating Eu^2+

Key Points

The research aims to synthesize and characterize a new carbide hydride phase incorporating europium and lithium.
Reactions between carbon and lithium hydride were performed in a europium/lithium flux.
Single-crystal X-ray diffraction and powder diffraction monitored structural phase transitions.
Infrared spectroscopy and gas chromatography analyzed hydrolysis products.
Magnetic susceptibility and Mössbauer spectroscopy evaluated magnetic properties.
Quantum chemical calculations were performed using DFT + U methods.
A new carbide hydride phase, Eu2Li(C3)H, was successfully synthesized and crystallizes in a tetragonal structure.
A structural phase transition occurs below ∼250 K to an orthorhombic form.
Magnetic measurements indicate a transition to a ferromagnetic ground state below 42 K.
High-pressure experiments showed a bulk modulus of 65 GPa, indicating high stability.
Quantum calculations suggest a Zintl phase with complex bonding characteristics.

Abstract

Reactions between carbon and lithium hydride in a mixed metal europium/lithium flux led to the synthesis of Eu₂Li (C₃) H. At room temperature, the compound crystallizes in the tetragonal space group P4/mbm (no. 127, Z = 2; Ca₂Li (C₃) H type) and undergoes a second-order structural phase transition below ∼250 K to an orthorhombic low-temperature modification (no. 55, Pbam; Z = 4), crystallizing in a new structure type. The phase transition was monitored by using single-crystal X-ray diffraction (SCXRD) and temperature-dependent high-resolution powder diffraction data. Infrared (IR) spectroscopy and gaschromatographic analysis (GC) of the hydrolysis products confirm the existence of a first europium compound with an allylenide anion (C₃^4–). Magnetic susceptibility measurements and ^151Eu Mössbauer spectroscopy reveal the presence of divalent europium, suggesting a charge-balanced carbide hydride (Eu^2+) ₂ (Li^+) (C₃^4–) (H^–). A transition to a (soft) ferromagnetic ground state is observed below 42 K. In situ high-pressure, high-temperature (HPHT) investigations indicate a surprisingly high stability of Eu₂Li (C₃) H and yield a bulk modulus K₀ = 65 GPa. Quantum chemical calculations (DFT + U) reveal a pseudogap at the Fermi level and allow the classification as a rare-earth metal Zintl phase exhibiting both ionic and covalent bonding contributions.

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