Magnetic Ordering and Structural Transition in the Ordered Double-Perovskite Pb2NiMoO6

• Published in: Chemistry of materials Vol. 34; no. 1; pp. 97 - 106
• Main Authors: Zhao, Jianfa, Wang, Xiao, Shen, Xi, Sahle, Christoph J, Dong, Cheng, Hojo, Hajime, Sakai, Yuki, Zhang, Jun, Li, Wenmin, Duan, Lei, Chan, Ting-Shan, Chen, Chien-Te, Falke, Johannes, Liu, Cheng-En, Kuo, Chang-Yang, Deng, Zheng, Wang, Xiancheng, Yu, Richeng, Yu, Runze, Hu, Zhiwei, Greenblatt, Martha, Jin, Changqing
• Format: Journal Article
• Language: English
• Published: American Chemical Society 11-01-2022
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.1c02826

The B-site-ordered double-perovskite Pb2NiMoO6 was prepared at high pressure and high temperature. The structural analysis of synchrotron powder X-ray diffraction data shows that Pb2NiMoO6 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 Pb2NiMoO6. 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 Pb2+ 2Ni2+Mo6+O6 valence states. Although in A2NiMoO6 (A = Sr2+, Pb2+, and Ba2+), the size of the A cation increases gradually from Sr2+ (1.44 Å) to Pb2+ (1.49 Å) to Ba2+ (1.61 Å), Pb2NiMoO6 exhibits much lower symmetry structure and AFM transition temperature, T N, compared with Sr2NiMoO6 (I4/m, T N = 81 K) and Ba2NiMoO6 (Fm3̅m, T N = 64 K), which is attributed to the large distortion of NiO6 and MoO6 octahedra induced by the lone pair electron effect of Pb2+ with a 6s2 electronic configuration. Moreover, symmetry-breaking phase transition from a high-temperature centrosymmetric, cubic Fm3̅m phase to a low-temperature non-centrosymmetric, monoclinic Pc phase was observed at 393–413 K in Pb2NiMoO6.