Residual resistivity and oxygen stoichiometry in Pr2−xCexCuO4+δ single crystals

Predicted properties ofNd1.5Ce0.5Sr2Blackstead1, Dow2 1998Phys. Rev. B16120View full textAdd to dashboardCite

“…In contrast, Pr21-4 superconducts. 24 The trends in the Meissner fractions for R222M -10, show that these fractions are qualitatively consistent with the large-radius Sr-site trivalent rare-earths participating in pair-breaking. 118,119 The explanation 23 of the failure of Pr123-7 to superconduct 120 ͑until recently [15][16][17][18][19][20][21][22] ͒, now confirmed by several experiments, is that Pr occupies Ba sites in addition to Pr sites in Pr123-7, where it causes suppression of the critical temperature, presumably by breaking Cooper pairs in the adjacent chargereservoir.…”

“…15: Nd 0.925 Ce 0.075 . These materials offer an especially appropriate proving ground for theories which purport to offer explanations of high-temperature superconductivity, because they provide clear chemical trends in their crystal structures, because R222M -10 has been studied sufficiently little that many of its properties are unmeasured ͑providing an opportunity for the theorists to make genuine predictions͒, and because they behave very differently: ͑i͒ R123-7 is a Ϸ90 K superconductor for most rare-earth ions, 14 including RϭPr, [15][16][17][18][19][20][21][22] but with the notable ͑current͒ exceptions RϭCe and Cm being larger-radius magnetic ions that are likely to occupy Ba sites in significant quantities, where they would break Cooper pairs and destroy superconductivity if the primary supercurrent were in the charge-reservoir Cu-O chain layers 23 ; ͑ii͒ in contrast, R122M -8 is an insulator for the rare-earth ions studied to date, 3 ͑iii͒ R222M -10 is a superconductor at Ϸ28 K, for RϭNd, Sm, Eu, and Gd, but not for RϭPr, which is an insulator, 9 and ͑iv͒ R21-4 is typically a T c Ϸ21-24 K superconductor with Ce doping, for RϭPr, Nd, Sm, and Eu, with T c ranging from Ϸ9 K for RϭEu, to 24.3 K for RϭPr ͑carefully prepared͒, 24 to 32 K for RϭNd ͑pressure fabricated͒; 25 but R21-4 does not superconduct for RϭGd and trivalent rare-earth ions smaller than Gd ϩ3 . [25][26][27][28][29][30] There are indications 30 that Y 2Ϫz Ce z CuO 4 , if it could be fabricated, would not superconduct.…”

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

“…Some of the nonsuperconducting AG samples have been annealed in an argon environment at temperatures between 850 and 925 o C for a typical period of 5 days encapsulated in a polycrystalline matrix [14] and are referred in the text as reduced samples. The reduced samples exhibit superconducting transitions around 24 K. Using the floating zone technique, high-quality Pr 0.88 LaCe 0.12 CuO 4 single crystals have also been grown and have been annealed as described in Ref.…”

Current Research Issues for the Electron-Doped Cuprates

“…Obviously, the presence of such interstitial oxygen is likely to distort locally the crystal structure and to disturb profoundly the electronic states in the nearby planes. Several recent papers have been dealing with this problem and suggest that oxygen is acting more as a scattering impurity than as a provider of additional carriers [6,7,55,56]. …”