We have systematically investigated the influence of the three parameters (temperature of sintering, lead content, and duration of the sintering) on the growth of the (2:2:2:3) phase in ceramics of nominal composition Bi2−xPbxSr2Ca2Cu3O10−x/2, and have determined the compositions and thermal conditions leading to ceramics with Tc≊110 K and containing more than 95% of this phase. We show that this result can be obtained by usual calcination near 880°C in air, without recurring to the introduction of excess in the constituants, providing that intermediate grinding are effected, in order to reactivate the formation of the (2:2:2:3) phase which otherwise saturates for long durations of sintering. The suitable nominal compositions (0.3≤x≤0.4) correspond to those that yield inside the grains a lead content in the vicinity of the limit of solubility for lead. From the results of the preceding investigations and of experiments effected on lead-substituted single crystals of the (2:2:1:2) phase, we have clarified the role played by lead, at the microscopic level, in the enhancement of the formation of the (2:2:2:3) phase. The inferred role is the establishment of strong bonding between the slabs which are the buildings blocks of the structure of the superconducting phases, these slabs being almost independent in the lead-free compounds. The origin of the stronger bonding is discussed.

Choosing an appropriate sexual partner is a critical decision for many animal species. However, many mechanisms involved in mate choice are still poorly understood. Do both males and females choose their sexual partners, do both sexes use the same criteria for choosing, and do their own phenotype influence the choices they make, are questions that need further investigation. Over two successive experiments conducted in captivity with hand-reared blue tits (Cyanistes caeruleus), we manipulated the color of the chest plumage, a secondary sexual trait that reflects an individual’s condition, to create two different color morphs (one pale and one colored). We then tested whether both sexes express a preference, whether they are attracted to the same morphs, and if the subjects’ own chest color influences the preference they show. Our data reveal that both sexes are choosy, with females tending to be slightly choosier than males. We also show that both sexes preferentially select individuals with a pale chest plumage over colorful individuals, and this was again more pronounced in females. Finally, paler individuals tend to be selected by birds that are themselves pale, even if this phenotype matching was not very robust. Such a preference for paler individuals is intriguing because mates are predicted to associate with individuals displaying higher, not lower, value of quality signals. It could result from adaptive mechanisms related to avoidance of aggressiveness in a confined environment, avoidance of conflicting sexual signals within individuals, or from cultural mechanisms leading to a preference for individuals that match its own phenotype.

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