Charge Transfer Driven Antiferroelectricity in Pyrochlore Cu₂OCl₂
H. C. Wu1*, J. K. Yuan1, K. D. Chandrasekhar1, C. H. Lee2, W. H. Li2, C. W. Wang3, J. M. Chen3, J. -Y. Lin4, H. Berger5, H. D. Yang1
1Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
2Department of Physics, National Central University, Chung-Li, Taiwan
3National Synchrotron Radiation Research Center, Hsinchu, Taiwan
4Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan
5Institute of Physics of Complex Matter, École Polytechnique Fédéral de Lausanne, Lausanne, Switzerland
* Presenter:H. C. Wu
The DC magnetization, specific heat, and neutron diffraction measurements confirm the antiferromagnetic (AFM) ordering (ΤN) of Cu₂OCl₂ near 70 K. The collinear AFM spin structure in Cu₂OCl₂ was obtained from neutron powder diffraction experiments based on the fitting to the combination of two irreducible representations—Г1⨁Г2. The electrical properties such as dielectric constant, pyroelectric current, and polarization-electric field hysteresis-loop measurements suggest a long-range antiferroelectric (AFE) ordering near ΤE ~75 K. A structural distortion is observed from the plot of lattice constants a, b, c, and volume versus temperature near TE. The difference of electronic charge distributions obtained from X-ray diffraction, which develops upon cooling from 79 K to 64 K, shows the new kind of mechanism of AFE behavior due to the charge transfer from Cl to O along the c-axis. These findings rule out the DM interaction on the observed multiferroic behaviors and provide insight into the various origins of high-Tc multiferroics.

Keywords: Charge transfer, Antiferroelectricity , Pyrochlore, Electronic charge distribution, Neutron