The phase stability diagrams for the systems Nd2CuO4-δ and Nd1.85Ce0.15CuO4-δ

Microscopic annealing process and its impact on superconductivity in T′-structure electron-doped copper oxides

“…), electron-doping alone is insufficient, and annealing the as-grown sample in a low oxygen environment to remove a tiny amount of oxygen is necessary to induce superconductivity 2,3 . Previous work [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] suggests that oxygen reduction may influence mobile carrier concentrations 7 , decrease disorder/impurity scattering 8,10,11,23 , or suppress the long-range AF order 16,17,22 . However, the microscopic process of oxygen reduction, its effect on the large electron-hole phase diagram asymmetry and mechanism of superconductivity 2,3 are still unknown.…”

“…5%) entirely suppress AF order and superconductivity appears over a wide range of hole concentrations (from 6% to 30%). In the case of T' structured electron-doped superconductors, doping alone by substituting the trivalent ions R 3+ in R 2 CuO 4 with tetravalent Ce 4+ is insufficient to induce superconductivity and the as-grown materials such as Nd 2-x Ce x CuO 4±δ (NCCO), Pr 2-x Ce x CuO 4±δ (PCCO), and Pr 0.88 LaCe 0.12 CuO 4 (PLCCO) are semiconducting with static long-range AF order [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] .In these materials, superconductivity (maximum T c ~25 K) is achieved only when the samples within a relatively narrow dopant range (0.1≤x≤0.18) are annealed in a reducing atmosphere . The reduction process suppresses the AF order most severely at higher Ce-doping levels above x≥0.1 (ref.…”

Competition between Antiferromagnetism and Superconductivity in the Electron-Doped Cuprates Triggered by Oxygen Reduction

“…Jt, 74.25.Jb, 74.62.Dh, Even though most of the work has been focused on hole-doped cuprates, the understanding of their electrondoped counterparts is essential for obtaining a universal picture of high-Tc superconductivity. To achieve this goal, it is necessary to first solve the main mystery that holds since the discovery of the T'-structure electrondoped cuprates RE 2−x Ce x CuO 4 and RE 1−x LaCe x CuO 4 (RE = Pr, Nd, Sm, Eu): why is superconductivity in these compounds achieved only when a tiny amount of oxygen (∼ 1%) is removed from the as-grown (AG) samples following a post-annealing process (reduction) [1,2,3,4,5]? In fact, the AG samples, even with sufficient electron-doping by adding Ce, are antiferromagnetic (AF) insulators at low temperature.…”

At the interface between electron and hole-doped cuprates

“…It is argued that this is required in order to be able to remove oxygen from the CuO 2 planes. However, as a consequence partial decomposition can occur, which is accompanied by the formation of a Cu poor (RE,Ce) 2 O 3 phase [34,[36][37][38]. Therefore, the optimal reduction is a trade-off between a high T c and partial decomposition.…”

“…This reduction step has proved to be necessary for superconductivity [32,33]. The reduction is performed at temperatures and oxygen partial pressures approaching or even crossing the stability line of the RE 2-x Ce x CuO 4 phase and close to the Cu 2 O/CuO stability line [34,35]. It is argued that this is required in order to be able to remove oxygen from the CuO 2 planes.…”