LaCoO3 displays a high Seebeck coefficient that makes it a potential candidate for future thermoelectric applications. In this study we provide data on the improvement of the thermoelectric efficiency of LaCoO3 by double substitution with nickel and iron. The improvement is achieved by balancing the opposite effects of nickel and iron ions. Double-substituted perovskites LaCo1–x (Ni0.5Fe0.5) x O3 with compositions having equal amounts (0 < x ≤ 0.25) of Ni and Fe are examined. The perovskites are obtained from freeze-dried citrate precursors at 900 °C. Structural and morphological characterizations are carried out by powder XRD and SEM analyses. The thermoelectric efficiency of the perovskites is determined by the dimensionless figure of merit (ZT) calculated from the independently measured Seebeck coefficient, electrical resistivity, and thermal conductivity. Compared with LaCoO3, the double-substituted perovskites display a higher electrical conductivity which does not depend on the total Ni+Fe content. This is a consequence of the increase in the carrier density. It is shown that the effect of Ni ions (for partial electron delocalization) is more pronounced in comparison with that of Fe ions (for electron localization). The synergic effect of Ni and Fe is demonstrated by the effective reduction of the thermal conductivity in comparison with the single-substituted perovskites. As a result, the perovskite with a composition LaCo0.8Ni0.1Fe0.1O3 exhibits the best thermoelectric efficiency with ZT = 0.16, which is an order of magnitude higher than that of LaCoO3 at room temperature.

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SummaryWe describe in detail a very large nuptial flight of the ant Leptothorax aeervorum at an open hilltop site in Britain. The mating behaviour of these ants involved not only a large mating swarm but also sexual/calling behaviour by the females. The females left the flight to land on vertical objects, where they took up a characteristic calling posture, in which females of closely related species are known to release pheromones that are sexually attractive to males. That Leptothorax acervorum has a complex mating behaviour involving both large nuptial flights and sexual calling has important consequences for the interpretation of the evolution of polygyny in this species and social parasitism in its close relatives.

The calculation of transport effects requires both the knowledge of some intrinsic material parameters (deformation potentials, effective masses, impurities potential well strength, etc. ) and the values of integrals, which as a rule cannot be represented by elementary functions. When a relaxation time for the carrier scattering r can be introduced, these integrals a r e of the formwhere fo is the Fermi-Dirac distribution function, and E, k(E), and m(E) are the energy, the wave number, and the effective mass of the carriers with a relevant energy dependence determined by the adopted energy dispersion law.When narrow band-gap semiconductors are concerned and Kane-type band is applicable, and on the assumption that the relaxation time depends on energy only through the density of energy states, one readily obtains the so-called generalised Fermi-Dirac integralswhere z = E KT, p= kT/E , and x = E/kT a r e the reduced Fermi energy, the non-parabolicity parameter and the dimensionless energy of the carriers (E is the band gap). These integrals were calculated by Zawadski et al. /2/ and listings for some values of z and B can be found in /3/. When p + O these integrals reduce to the ordinary Fermi-Dirac integrals, corresponding to a parabolic energy dispersion law, according to /4/

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