Published: June 06, 2011 r2011 American Chemical Society 6392 dx.doi.org/10.1021/ic201006q | Inorg. Chem. 2011, 50, 6392–6398 ARTICLE pubs.acs.org/IC High-Pressure Synthesis and Correlation between Structure, Magnetic, and Dielectric Properties in LiNbO 3 -Type MnMO 3 (M = Ti, Sn) Akihisa Aimi, † Tetsuhiro Katsumata, ‡ Daisuke Mori, † Desheng Fu, § Mitsuru Itoh, || T^ oru Ky^ omen, ^ Ko-ichi Hiraki, # Toshihiro Takahashi, # and Yoshiyuki Inaguma* ,† † Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan ‡ Department of Chemistry, Faculty of Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan § Division of Global Research Leaders, Shizuoka University, Johoku 3-5-1, Naka-ku, Hamamatsu 432-8561, Japan ) Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, Kanagawa 226-8503, Japan ^ Graduate School of Engineering, Department of Chemistry and Chemical Biology, Gunma University, Tenjin-cho 1-5-1, Kiryu 376-8515, Japan # Department of Physics, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan b S Supporting Information ’ INTRODUCTION Multiferroic materials, wherein ferroelectricity and (anti)ferro- magnetism coexist, are expected in applications such as memory storage devices, sensors, actuators, and other multifunctional devices. Owing to their technological and scientific importance, much attention has been focused on multiferroic materials in general, and many investigations have been carried out on perovskite-type oxides or related oxides with 3d transition metal ions, such as BiMO 3 (M = Fe, 1 Mn 2 ), hexagonal manganites RMnO 3 (R = Sc, In, Y, and HoÀLu), 3,4 and Pb(Fe 2/3 W 1/3 )O 3 . 5 Recently, we found that LiNbO 3 -type (hereafter, abbreviated as LN-type) ZnSnO 3 synthesized under high pressure was polar. 6 Following this, a thin film fabricated by pulsed laser deposition was reported to exhibit ferroelectricity. 7 After these findings, we conceived that LN-type compounds with magnetic cations may be candidates of multiferroic materials. Fennie has also argued that LiNbO 3 -type oxides with a magnetic ion such as FeTiO 3 , MnTiO 3 , and NiTiO 3 could be multiferroic candidates. 8 He also predicted that in this type of multiferroic materials, magnetism could be controlled by the electric field. In ABO 3 -type complex oxides, the LN-type structure is similar to corundum- and ilmenite-type structures in that the cations occupy two-thirds of the octahedral sites generated by the hexagonal closed packing of oxygen atoms. These structures are distinguished by the cation arrangement. In a corundum-type structure, cations are completely disordered. In an ilmenite-type structure, the cation arrangement along the c axis is A-B-Vac-B-A- Vac-A-... (Vac = vacancy), and the same type of cations are pre- sent in the plane perpendicular to the c axis. In LN-type structures, the cation arrangement along the c axis is A-B-Vac- A-B-Vac-A-..., and both A and B cations are included in the plane perpendicular to the c axis. A LN-type structure is more similar to a perovskite-type structure than a corundum-type structure in terms of the BO 6 octahedra linking at all of their corners. A LN- type structure, unlike corundum- and ilmenite-type structures, belongs to acentric crystal classes, and materials with this structure are expected to exhibit properties depending on polar structure, such as piezoelectricity, ferroelectricity, pyroelectricity, and nonlinear optical effects. 9 Although LN-type oxides would be good candidates for industrial applications, there have been few investigations into their physical properties, except for LiNbO 3 and LiTaO 3 , because most LN-type oxides such as FeMO 3 (M = Ti, 10 Ge 11 ), MgMO 3 (M = Ti, 12 Ge 13 ), ZnMO 3 (M = Ge, 13 Sn 6 ), Received: May 12, 2011 ABSTRACT: LiNbO 3 -type MnMO 3 (M = Ti, Sn) were synthesized under high pressure and temperature; their structures and magnetic, dielectric, and thermal properties were investigated; and their relationships were discussed. Optical sec- ond harmonic generation and synchrotron powder X-ray diffraction measure- ments revealed that both of the compounds possess a polar LiNbO 3 -type structure at room temperature. Weak ferromagnetism due to canted antiferro- magnetic interaction was observed at 25 and 50 K for MnTiO 3 and MnSnO 3 , respectively. Anomalies in the dielectric permittivity were observed at the weak ferromagnetic transition temperature for both the compounds, indicating the correlation between magnetic and dielectric properties. These results indicate that LiNbO 3 -type compounds with magnetic cations are new candidates for multiferroic materials.