The low-temperature crystal structure of the multiferroic melilite Ca2CoSi2O7

• Published in: Acta crystallographica Section B, Structural science, crystal engineering and materials Structural science, crystal engineering and materials, 2016-02, Vol.72 (1), p.126-132
• Main Authors: Sazonov, Andrew, Hutanu, Vladimir, Meven, Martin, Roth, Georg, Kézsmárki, István, Murakawa, Hiroshi, Tokura, Yoshinori, Náfrádi, Bálint
• Format: Article
• Language: English
• Subjects: magnetoelectric coupling; multiferroic melilite; single-crystal neutron diffraction; twinning
• ISSN: 2052-5206; 2052-5206
• DOI: 10.1107/S2052520615023057

In the antiferromagnetic ground state, below TN ≃ 5.7 K, Ca2CoSi2O7 exhibits strong magnetoelectric coupling. For a symmetry‐consistent theoretical description of this multiferroic phase, precise knowledge of its crystal structure is a prerequisite. Here we report the results of single‐crystal neutron diffraction on Ca2CoSi2O7 at temperatures between 10 and 250 K. The low‐temperature structure at 10 K was refined assuming twinning in the orthorhombic space group P21212 with a 3 × 3 × 1 supercell [a = 23.52 (1), b = 23.52 (1), c = 5.030 (3) Å] compared with the high‐temperature normal state [tetragonal space group , a = b ≃ 7.86, c ≃ 5.03 Å]. The precise structural parameters of Ca2CoSi2O7 at 10 K are presented and compared with the literature X‐ray diffraction results at 130 and 170 K (low‐temperature commensurate phase), as well as at ∼ 500 K (high‐temperature normal phase). The crystal structure of the multiferroic melilite Ca2CoSi2O7 is determined by means of single‐crystal neutron diffraction at 10 K.