Magnetic Ordering and Structural Transition in the Ordered Double-Perovskite Pb 2 NiMoO 6

作者：Jianfa Zhao, Xiao Wang, Xi Shen, Christoph J. Sahle, Cheng Dong, Hajime Hojo, Yuki Sakai, Jun Zhang, Wenmin Li, Lei Duan, Ting‐Shan Chan, Chien‐Te Chen, Johannes Falke, Cheng‐En Liu, Chang‐Yang Kuo, Zheng Deng, Xiancheng Wang, Richeng Yu, Richeng Yu, Runze Yu, Runze Yu, Zhiwei Hu, M. Greenblatt, Changqing Jin · 发表于：Chemistry of Materials · 年份：2021 · DOI：10.1021/acs.chemmater.1c02826 · 被引用次数：11 · 研究领域：Magnetic and transport properties of perovskites and related materials、Advanced Condensed Matter Physics、Multiferroics and related materials

The B-site-ordered double-perovskite Pb 2 NiMoO 6 was prepared at high pressure and high temperature. The structural analysis of synchrotron powder X-ray diffraction data shows that Pb 2 NiMoO 6 crystallizes into monoclinic symmetry with the space group Pc (no. 7), where the Ni and Mo ions are ordered in a rock-salt-type manner. The magnetic and specific heat characterizations reveal unusual two-step antiferromagnetic (AFM) transitions at 18 and 26 K for Pb 2 NiMoO 6 . The X-ray absorption spectra at the Ni- L 2,3 edge and the Mo- L 3 edge and the high-resolution partial fluorescence yield at the Pb- L 3 edge indicate Pb 2+ 2 Ni 2+ Mo 6+ O 6 valence states. Although in A 2 NiMoO 6 (A = Sr 2+, Pb 2+, and Ba 2+ ), the size of the A cation increases gradually from Sr 2+ (1.44 Å) to Pb 2+ (1.49 Å) to Ba 2+ (1.61 Å), Pb 2 NiMoO 6 exhibits much lower symmetry structure and AFM transition temperature, T N, compared with Sr 2 NiMoO 6 ( I 4/ m, T N = 81 K) and Ba 2 NiMoO 6 ( Fm 3̅ m, T N = 64 K), which is attributed to the large distortion of NiO 6 and MoO 6 octahedra induced by the lone pair electron effect of Pb 2+ with a 6s 2 electronic configuration. Moreover, symmetry-breaking phase transition from a high-temperature centrosymmetric, cubic Fm 3̅ m phase to a low-temperature non-centrosymmetric, monoclinic Pc phase was observed at 393–413 K in Pb 2 NiMoO 6.