Structural and magnetic data on getter annealed YBa2(Cu0.95M0.05)3Oy, M=Ni are presented. Similar to unsubstituted materials, but different from M=Fe, getter annealings at intermediary temperatures (753 K) produce an extended orthorhombic superconducting region with abrupt cell volume (V) shrinkage around y∼6.50. This orthorhombicity, denoted O42, corresponds most nearly to conventional phenomenology with long chains on Cu(1) with four-(1)4- and two fold-(1)2- O coordination. 673 K annealings produce a smaller orthorhombic range with considerable reduction in Tc. This region is diagnosed to be based on new structural motifs with larger amounts of orthorhombically arranged three fold O coordination (1)3. A yet stronger trend to orthorhombicity based on (1)3, denoted O3, pertains to high temperature annealings (1023 K) which produce a monotonic structural development in c-axis with no stepwise contraction and absence of Tc to y∼6.8. This is also the behavior obtained on direct quenching from elevated temperatures which can in addition result in anomalous cell volume expansion effects (V+) near y=6.5. These materials are further distinguished in that they do not superconduct when reoxygenated up to y∼6.8. A general distinction in the phenomenology of RBa2Cu3Oy is accordingly made between O filling based on (1)3 e.g. (1)3(1)4 (K phenomenology) and (1)2(1)4 (D, or disproportionation phenomenology). In connection with extrapolations from low temperature Tc annealing effects it is realized that O42 pertains only to a limited low temperature modification with reversible ladder type transitions to O3 at intermediary temperatures for substituted and unsubstituted compounds.

Strong cell volume expansions (V+) are observed near y = 6.5 on reoxidation of reduced YBa2(Cu1−xNix)3Oy, x = 0.05 and y ∼ 6.3. These materials develop bulk superconductivity with Tc ∼ 72 K. This superconductivity disappears upon further reoxidation and reappears in fully reoxygenated materials with Tc = 68 K in conventional volume contracted (V−) p doped materials. Bond valence calculations make plausible that the local configuration (1)3, where (1) denotes the Cu(1) site and 3 the O coordination is involved in V+ which is corroborated by TEM. Accordingly the nominally 2 + Cu at y = 6.5 is reduced and O oxidized. Bond valence calculation and the magnitude of Tc (comparable to the fully oxygenated material) suggest that Cu is in a stoichiometric valence vs = 1.67 + creating one hole on O. This represents a new mechanism of self-doping by rebalancing according to YBa2Cu1+Cu22+O5.52− with charge equilibration implied (written for the idealized formula). V+ effects are also found in related systems and by related preparations and discussed as a generic new feature of reductive Cu chemistry.

We report on getter annealed YBa2(Cu0.95Ni0.05)3Oy which are paramagnetic in a range from y = 6.1 to 6.8 with Curie-Weiss temperatures (Θ) remaining near 0 K. Reoxidation of the most reduced materials produces superconductors with enhanced flux pinning followed in temperature by a paramagnetic range with unusually large negative Θ ≈ − 70 K indicative of Ni nanoclusters.

We report here on the changes in behavior, including transitions from superconducting to semiconducting, as a function of heat treatment of YBa2(Cu1-xNix)3Oy with x=0.05. In particular, conventional materials prepared by slow cooling from ∼ 1200 K (designated OP for oxygenating preparations), show superconducting onset temperatures of Tc∼75 K. This is also the case when materials are quenched from air annealing temperatures TA≥1123 K and subsequently reoxygenated at Ta=673 K. However, when OP are air annealed at TA=1023 K, quenched to liquid N2 (designated K parent or Kp in this state), and subsequently reoxygenated at Ta=673 K (designated as Ko compound), no superconductivity is observed in the resistivities down to 4.2 K. Also, magnetic susceptibilities of Ko compounds show relatively large effective magnetic moments and either no, or only trace amounts of, superconductivity. Both Kp (quenched from TA=1023 K) and Ko were orthorhombic, while the conventional parents (quenched from TA≥1123 K) were tetragonal. Possible origins for this unusual Ko phenomenology are discussed and comparisons are drawn with other cases where thermal treatment results in loss of superconductivity.