High-Pressure Synthesis of the Cobalt Pyrochlore Oxide Pb2Co2O7 with Large Cation Mixed Occupancy

Junye Yang; Jianhong Dai; Zhehong Liu; Runze Yu; Hajime Hojo; Zhiwei Hu; Tunwen Pi; Yunliang Soo; Changqing Jin; Masaki Azuma; Youwen Long

doi:10.1021/acs.inorgchem.7b01646

High-Pressure Synthesis of the Cobalt Pyrochlore Oxide Pb₂Co₂O₇ with Large Cation Mixed Occupancy

Inorg Chem. 2017 Oct 2;56(19):11676-11680. doi: 10.1021/acs.inorgchem.7b01646. Epub 2017 Sep 18.

Authors

Junye Yang^{1

2}, Jianhong Dai^{1

2}, Zhehong Liu^{1

2}, Runze Yu³, Hajime Hojo³, Zhiwei Hu⁴, Tunwen Pi⁵, Yunliang Soo⁶, Changqing Jin^{1

2

7}, Masaki Azuma³, Youwen Long^{1

2

7}

Affiliations

¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, People's Republic of China.
² School of Physics, University of Chinese Academy of Sciences , Beijing 100190, People's Republic of China.
³ Laboratory for Materials and Structures, Tokyo Institute of Technology , 4259 Nagatsuta, Midori, Yokohama, 226-8503, Japan.
⁴ Max-Planck Institute for Chemical Physics of Solids , Nöthnitzer Straße 40, 01187 Dresden, Germany.
⁵ National Synchrotron Radiation Research Center , 101 Hsin-Ann Road, Hsinchu 30077, Taiwan.
⁶ Department of Physics, National Tsing Hua University , 101 Section 2 Kuang-Fu Road, Hsinchu 30013, Taiwan.
⁷ Collaborative Innovation Center of Quantum Matter , Beijing 100190, People's Republic of China.

PMID: 28920686
DOI: 10.1021/acs.inorgchem.7b01646

Abstract

The novel A₂B₂O₇-type compound Pb₂Co₂O₇ was synthesized at 8 GPa and 1673 K. Synchrotron X-ray diffraction shows a cubic pyrochlore structure with space group Fd3̅m. Rietveld structural analysis reveals a large cation mixed occupancy at both A and B sites by about 40%, the greatest value found in the pyrochlore family. In combination with the X-ray absorption spectroscopy results, the specific chemical composition and charge states are determined to be (Co_0.6Pb_0.4)³⁺₂(Pb_0.6Co_0.4)⁴⁺₂O₇, in which both the A-site Co³⁺ and the B-site Co⁴⁺ are low-spin. Due to the tetrahedral geometric frustration effects as well as the random Co⁴⁺ and Pb⁴⁺ distribution at the B site, spin glassy behavior is well observed following the conventional critical slowing down feature in Pb₂Co₂O₇.