1.Tonghua Normal University, Tonghua 134002, China 2.University of Science and Technology of China, Hefei 230026, China 3.Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. WK2310000043) and the Science and Technology Program of the 13rd Five-Year Plan of Education Bureau of Jilin Province, China (Grant No. JJKH 20180860KJ).
Received Date:03 April 2019
Accepted Date:04 July 2019
Available Online:01 September 2019
Published Online:20 September 2019
Abstract:Sr2CuO3+δ is cuprate, a high temperature superconducting (HTS) material that has a single copper oxide layer and a relatively high critical temperature. Its structure is simple and contains fewer atoms, but there are many modulation structures in it. A lot of studies have pointed out that the modulation structure is related to its superconductivity. In order to further study the relationship between modulated structure and superconductivity in Sr2CuO3.4 HTS sample, a new explanation for the formation mechanism of modulation structure is proposed in this paper. The synchrotron radiation resonant X-ray diffraction (RXD) technique is used to detect the variation of modulation structure near the absorption edge of Cu atom. Cu2+, Cu3+ valence order is detected and used to explain the formation mechanism of modulation structure in Sr2CuO3.4 high temperature superconducting sample. The energy values of incident light are selected to be 8.52, 8.95, 8.98, 9.05, 9.5, and 10.0 keV near the edge of Cu K. The energy resolution is about 1.5 eV. The detector used in the experiment is Mar165 CCD surface detector. The distance from the detector to the sample is about 315 mm. The two-dimensional diffraction pattern recorded by the CCD plane detector is processed by Fit2D software to obtain the diffraction integral intensity. In addition, the energy calibration for each of the copper foil samples is carried out prior to the start of the experiment and in the process of varying energy value.The experimental results show that the Bragg diffraction peaks corresponding to Tc = 48 K and the modulation structures of Fmmm and Pmmm are visible and calibrated. The intensity of the corresponding (2/5, 4/5, 0) diffraction peak of Fmmm is energy-dependent near the Cu K edge and first increases and then decreases abruptly near the absorption edge. This indicates that a stable ordered arrangement structure of Cu2+ and Cu3+ is formed at this time. The weak diffraction signal of this ordered arrangement structure confirms the fact that the copper-O bonding is stronger.The experiments indicate that oxygen vacancies occupy both the apical position and the CuO2 plane. The ordering arrangement of oxygen vacancies results in the ordering of copper ions with variable valence. The Cu2+, Cu3+ valence order is related to the superconductivity of Sr2CuO3.4. Keywords:high temperature superconductivity/ modulation structure/ resonance X-ray diffraction/ synchrotron radiation
图 4 入射光子能量为8.95 keV时Sr2CuO3+δ (Tc = 48 K)超导粉末样品的衍射曲线以及衍射峰标定 Figure4. Diffraction curve and calibration of diffraction peak of Sr2CuO3+δ superconducting powder samples with incident photon energy of 8.95 keV.
图 1 Sr2CuO3+δ的晶体结构
图 2 RXD实验测量几何示意图
图 3 Sr2CuO3+δ超导粉末样品(Tc = 48 K)在不同入射光子能量下采集的二维衍射图
图 4 入射光子能量为8.95 keV时Sr2CuO3+δ (Tc = 48 K)超导粉末样品的衍射曲线以及衍射峰标定
图 5 Cu2+和Cu3+的原子散射因子的实部和虚部
图 6 (2/5, 4/5, 0)衍射峰强度的能量依赖性