High-Pressure Synthesis, Crystal Structures, and Properties of A-Site Columnar-Ordered Quadruple Perovskites NaRMn2Ti4O12 with R = Sm, Eu, Gd, Dy, Ho, Y

Ran Liu; Rebecca Scatena; Dmitry D Khalyavin; Roger D Johnson; Yoshiyuki Inaguma; Masahiko Tanaka; Yoshitaka Matsushita; Kazunari Yamaura; Alexei A Belik

doi:10.1021/acs.inorgchem.0c00938

High-Pressure Synthesis, Crystal Structures, and Properties of A-Site Columnar-Ordered Quadruple Perovskites NaRMn₂Ti₄O₁₂ with R = Sm, Eu, Gd, Dy, Ho, Y

Inorg Chem. 2020 Jul 6;59(13):9065-9076. doi: 10.1021/acs.inorgchem.0c00938. Epub 2020 Jun 9.

Authors

Ran Liu^{1

2}, Rebecca Scatena³, Dmitry D Khalyavin⁴, Roger D Johnson⁵, Yoshiyuki Inaguma⁶, Masahiko Tanaka⁷, Yoshitaka Matsushita⁸, Kazunari Yamaura^{1

2}, Alexei A Belik¹

Affiliations

¹ International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
² Graduate School of Chemical Sciences and Engineering, Hokkaido University, North 10 West 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan.
³ Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
⁴ ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom.
⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
⁶ Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan.
⁷ Synchrotron X-ray Station at SPring-8, NIMS, Kouto 1-1-1, Sayo-cho, Hyogo 679-5148, Japan.
⁸ National Institute for Materials Science (NIMS), Sengen 1-2-1, Tsukuba, Ibaraki 305-0047, Japan.

PMID: 32515189
DOI: 10.1021/acs.inorgchem.0c00938

Abstract

The formation of NaRMn₂Ti₄O₁₂ compounds (R = rare earth) under high pressure (about 6 GPa) and high temperature (about 1750 K) conditions was studied. Such compounds with R = Sm, Eu, Gd, Dy, Ho, Y adopt an A-site columnar-ordered quadruple-perovskite structure with the generic chemical formula A₂A'A″B₄O₁₂. Their crystal structures were studied by powder synchrotron X-ray and neutron diffraction between 1.5 and 300 K. They maintain a paraelectric structure with centrosymmetric space group P4₂/nmc (No. 137) at all temperatures, in comparison with the related CaMnTi₂O₆ perovskite, in which a ferroelectric transition occurs at 630 K. The centrosymmetric structure was also confirmed by second-harmonic generation. It has a cation distribution of [Na⁺R³⁺]_A[Mn²⁺]_A'[Mn²⁺]_A″[Ti⁴⁺₄]_BO₁₂ (to match with the generic chemical formula) with statistical distributions of Na⁺ and R³⁺ at the large A site and a strongly split position of Mn²⁺ at the square-planar A' site. We found a C-type long-range antiferromagnetic structure of Mn²⁺ ions at the A' and A″ sites below T_N = 12 K for R = Dy and found that the presence of Dy³⁺ disturbs the long-range ordering of Mn²⁺ below a second transition at lower temperatures. The first magnetic transition occurs below 8-13 K in all compounds, but the second magnetic transition occurs only for R = Dy, Sm, Eu. All compounds show large dielectric constants of a possible extrinsic origin similar to that of CaCu₃Ti₄O₁₂. NaRMn₂Ti₄O₁₂ with R = Er-Lu crystallized in the GdFeO₃-type Pnma perovskite structure, and NaRMn₂Ti₄O₁₂ with R = La, Nd contained two perovskite phases: an AA'₃B₄O₁₂-type Im3̅ phase and a GdFeO₃-type Pnma phase.