The low-temperature crystal structure of the multiferroic melilite Ca2CoSi2O7.

Area of Science:

• Solid-state physics
• Crystallography
• Magnetism

Background:

• Ca2CoSi2O7 exhibits multiferroic properties with strong magnetoelectric coupling below TN ≃ 5.7 K.
• Understanding the crystal structure is crucial for theoretical descriptions of the multiferroic phase.

Purpose of the Study:

• To determine the precise crystal structure of Ca2CoSi2O7 in its antiferromagnetic ground state.
• To provide structural data for symmetry-consistent theoretical models of the multiferroic phase.

Main Methods:

• Single-crystal neutron diffraction was performed on Ca2CoSi2O7.
• Measurements were conducted at temperatures ranging from 10 K to 250 K.

Main Results:

• The low-temperature structure at 10 K was refined in the orthorhombic space group P2(1)2(1)2 with a 3 × 3 × 1 supercell.
• Structural parameters were determined and compared with high-temperature data and literature X-ray diffraction results.
• A phase transition from a high-temperature tetragonal structure (P42(1)m) to a low-temperature orthorhombic structure was observed.

Conclusions:

• The precise crystal structure of Ca2CoSi2O7 in its multiferroic phase has been determined.
• The findings provide essential structural information for understanding the magnetoelectric coupling in this material.