RE₂CuO₄ (RE = rare earth elements) has been widely studied by its doping effect, which is related to the high-transition temperature superconductivity. Recently, the structural effects on the physical properties attract much interest in this family [1, 2]. And there are three types structure, so called T- (six oxygens coordination), T*-(five coordination, see fig. 1) and T’-(four coordination) phase, identified.

For Pr_2-xSr_xCuO₄ (PSCO), it had been shown a structural evolution T’-, T*- and T-phase, when x equals to 0, 0.4 and 1, respectively [3]. Therefore, PSCO is suitable compound to study the relationship between crystal structure and physical properties. However, these three compounds are neither superconductivity nor metallic conductivity. J. Yang et al reported the F doping effect to change the carrier concentration. And the results illustrated that when x = 1, magnetization measurement showed a superconducting (SC) transition at 15 K in the F-substituted sample. When x = 0 and 0.4, there is no SC transition behavior [4]. Since superconductivity in the T’ and T* phase emerges due to oxygen reduction and oxidation annealing respectively, study of annealing effect on the crystal structure is important. In order to understand the mechanism of superconductivity, we firstly study the structural information, especially the annealing effect on the physical properties in T* phase of PSCO.

In this work, we performed neutron powder diffraction measurement on as-sintered, oxidation annealed and Ar-annealed PSCO (x = 0.4) to determine the detail of the local structure. As shown in Fig. 1, we can find the apical oxygen (O(2)), which only appears in the T*-type cuprates. By analyzing the neutron powder diffraction data, we refined the structure of PSCO and get the oxygen stoichiometry for as-sintered and Ar-AN samples. Furthermore, we found that the increase of oxygen deficiency at O(2) site due to Ar-annealing. Meanwhile, combined with the magnetization measurements, we will show how the annealing effect the physical properties of PSCO.

[1] H. Yamamoto, O. Matsumoto, A. Tsukada, and M. Naito, Physica C 470, 1025 (2010) .
[2] Y. Krockenberger, B. Eleazer, H. Irie, H. Yamamoto, J. Phys. Soc. Jpn. 83, 114602 (2014).
[3] H. Y. Hwang, S. W. Cheong et al., Physica C 192, 362 (1992)
[4] J. Yang, J. Liang et al., J. Phys.:Condens. Matter 9, 1249–1259 (1997)

Keywords: Structual analyse, Neutron powder diffraction measurement , T* type cuprates