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We investigated the generic phase diagram of the electron doped superconductor, Nd 2-x Ce x CuO 4 , using films prepared by metal organic decomposition.After careful oxygen reduction treatment to remove interstitial O ap atoms, we found that the T c increases monotonically from 24 K to 29 K with decreasing x from 0.15 to 0.00, demonstrating a quite different phase diagram from the previous bulk one. The implication of our results is discussed on the basis of tremendous influence of O ap "impurities" on superconductivity and also magnetism in T' cuprates. Then we conclude that our result represents the generic phase diagram for oxygen-stoichiometric Nd 2-x Ce x CuO 4 .

In this article, we report the superconductivity in T'-RE 2 CuO 4 (RE = Pr, Nd, Sm, Eu, and Gd), which have been for a long time believed as a Mott insulator. Our discovery was achieved by using metal-organic decomposition (MOD), an inexpensive and easy-to-implement thin-film process. The keys to prepare the superconducting films are firing with low partial-pressure of oxygen and reduction at low temperatures. The highest T c of undoped T'-RE 2 CuO 4 is over 30 K, substantially higher than "electron-doped" analogs.Remarkably, Gd 2 CuO 4 , even the derivatives of which have not shown superconductivity so far, gets superconducting with T c onset as high as 20 K. The implication of our discovery is briefly discussed.

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