摘要
Oxygen vacancies have a profound effect on the magnetic,electronic,and transport properties of transition metal oxides but little is known about their effect on thermal expansion.Herein we report the effect of oxygen defects on the structure formation and thermal expansion properties of the layered perovskite Ca2RuO4(CRO).It is shown that the CRO containing excess oxygen crystallizes in a metallic L-CRO phase without structure transition from 100 K to 500 K and displays a normal thermal expansion behavior,whereas those with oxygen vacancies adopt at room temperature an insulating S-CRO phase and exhibit an enormous negative thermal expansion(NTE)from 100 K to about 360 K,from where they undergo a structure transition to a high temperature metallic L-CRO phase.Compared to the L-CRO containing excess oxygen,the S-CRO structure has increasingly large orthorhombic strain and distinctive in-plane distortion upon cooling.The in-plane distortion of the RuO6 octahedra reaches a maximum across 260 K and then relaxes monotonically,providing a structure evidence for the appearance of an antiferromagnetic orbital ordering in the paramagnetic phase and the A_g phonon mode suppression and phase flip across the same temperature found recently.Both the L-and S-CRO display an antiferromagnetic ordering at about 150-110 K,with ferromagnetic ordering components at lower temperature.The NTE in S-CRO is a result of a complex interplay among the spin,orbital,and lattice.
作者
Sen Xu
Yangming Hu
Yuan Liang
Chenfei Shi
Yuling Su
Juan Guo
Qilong Gao
Mingju Chao
Erjun Liang
徐森;胡杨明;梁源;史晨飞;苏玉玲;郭娟;高其龙;晁明举;梁二军(Key Laboratory of Materials Physics of Education of China,School of Physics and Microelectronics,Zhengzhou University,Zhengzhou 450001,China;Department of Applied Physics,Donghua University,Shanghai 201620,China;School of Physics and Electronic Engineering,Zhengzhou University of Light Industry,Zhengzhou 450001,China)
基金
the National Natural Science Foundation of China(Grant Nos.11874328 and 11574276)
The SXRD experiments were performed at the BL02B2 and BL04B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute(JASRI
proposal Nos.2019A1167,2019A1095,and 2019A1340)
We also acknowledge the help of Beamline Scientists Dr.Lirong Zheng(BSRF),Dr.Shogo Kawaguchi,and Dr.Koji Ohara(SPring-8).
