We report the strongly correlated, electrical transport, magnetic, and thermoelectric properties of a series of Fe, Mn, and Cu doped Ca 3 Co 4 O 9 . The results indicate that Fe/Mn substitutes for Co in CoO 2 layers whereas Cu substitutes for Co in Ca 2 CoO 3 layers. Because of the different doping sites, the electronic correlations increase remarkably in Fe and Mn doped series while remaining unchanged in Cu doped series. Correspondingly, the transport mechanism, magnetic properties, and some characteristic parameters along with transition temperatures all exhibit two distinct evolutions for Fe/Mn doping and Cu doping. The thermoelectric characteristics are improved in each series. Nevertheless, the improvement of thermoelectric performance is most significant in Fe doped samples due to the unexpected changes in thermopower and resistivity. The unusual thermopower behavior can be well described by the variations of electronic correlation. Possible approaches for further improvement of the thermoelectric performance in Ca 3 Co 4 O 9 and other relevant strongly correlated systems are also proposed at the end.

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During spermatogenesis, spermiogenesis that releases sperm into the tubule lumen and restructuring of the blood-testis barrier (BTB) that accommodates the transit of preleptotene spermatocytes take place simultaneously, but at the opposite ends of the seminiferous epithelium. These events are tightly regulated and coordinated; however, neither the underlying mechanism(s) nor the involving molecules are known. Herein, the Scribble/Lgl (Lethal giant larvae)/Dlg (Discs large) polarity complex was shown to regulate spermatid polarity during spermiogenesis and tight junction (TJ)-permeability barrier via changes in protein distribution at the apical ectoplasmic specialization and the BTB during the epithelial cycle, respectively. Scribble, Lgl2, and Dlg1 were found to be expressed by Sertoli and germ cells. Scribble also displayed stage-specific expression at the BTB, being highest at stages VII-VIII, colocalizing with TJ proteins occludin and ZO-1. Unlike components of other polarity complex modules, such as partitioning-defective 6, the knockdown of which by RNA interference was found to impede Sertoli cell TJ barrier, a knockdown of the Scribble complex (i.e. simultaneous knockdown of Scribble, Lgl and Dlg or Lgl alone; but not Scribble or Dlg alone) both in vitro and in vivo promoted the TJ integrity. This was mediated by reorganizing actin filament network at the Sertoli cell-cell interface, which, in turn, affected changes in the localization and/or distribution of occludin and/or β-catenin at the BTB. These knockdowns also perturbed F-actin organization at the Sertoli cell-spermatid interface, thereby modulating spermatid adhesion and polarity at the apical ectoplasmic specialization. In summary, the Scribble/Lgl/Dlg complex participates in the regulation of BTB dynamics and spermatid adhesion/polarity in the testis.

Electron-doped perovskite manganite Ca0.9R0.1MnO3 (R=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) polycrystalline samples were prepared and their transport and thermoelectric properties were studied from room temperature to 1000 K. The transport behavior for all the samples is adiabatic small polaron hopping mechanism below 600 K but changes to metallic conductivity at higher temperature. Above 600 K, more 3d electrons of Mn3+ ions will occupy eg orbitals, resulting in the variation in thermoelectric power values. For all the samples, thermoelectric power is only determined by carrier concentration, but resistivity also rests with effective bandwidth. The size matching between Ca2+ and R3+ ions together with heavier R3+ doping can improve thermoelectric performance evidently. Combining these two factors, Ca0.9Dy0.1MnO3 and Ca0.9Yb0.1MnO3 reach ZT=0.2 at 1000 K, suggesting that they can be efficient high temperature n-type thermoelectric oxide materials.

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We report a systematical investigation on the high temperature thermoelectric response of Ca 1-x R x MnO 3 (R = rare-earth) perovskites in the electron-doped range. The results reveal that electron concentration is the dominant factor for the high temperature electrical transport properties whereas the weight and size of R ions dominate the thermal transport properties. As the doping level varies, the best thermoelectric performance is observed at the relative electron concentration around 0.1. However, in the case of a fixed electron concentration, structural distortions become important since bandwidth has an observable influence on resistivity. By combining the three factors, electron concentration, crystal structure, and the weight/size of R ions, the largest thermoelectric figure of merit ZT for Ca 1-x R x MnO 3 reaches 0.2 at 1000 K. But this ZT value is still too far from the application criterion (ZT > 1). Using the dynamical mean field theory, we demonstrate that a ZT value larger than one in electron-doped CaMnO 3 systems seems rather unlikely. Some strategies for searching new thermoelectric materials with high performance in transition metal oxides are proposed.

A series of Fe, Mn, and Cu doped Ca3Co4O9+δ samples, Ca3(Co,M)4O9+δ (M=Fe, Mn, and Cu), were fabricated by cold high-pressure compacting technique. Their thermoelectric properties were investigated from room temperature up to 1000 K. The cold high-pressure compacting method is advantageous to increasing density and texture, in favor of the improvement of thermoelectric performance. The electrical transport measurements indicate that Fe/Mn substitutes for Co mainly in [CoO2] layers whereas the substitution of Cu for Co takes place in [Ca2CoO3] layers. The thermoelectric properties as well as electronic correlations depend not only on the substitution ion but also the Co site that is replaced. Thermopower can be well calculated by the carrier effective mass according to Boltzmann transport model, indicating that the electronic correlation plays a crucial role in the unusual thermoelectric characteristics of this system. From the changes in thermopower, resistivity, and thermal conductivity, thermoelectric performance of Ca3Co4O9+δ is efficiently improved by these transition metals doping. Fe doped samples possess the highest ZT values. Combining cold high-pressure technique, ZT of Ca3Co3.9Fe0.1O9+δ can reach ∼0.4 at 1000 K, which is quite large among ceramic oxides, suggesting that Fe doped Ca3Co4O9+δ could be a promising candidate for thermoelectric applications at elevated temperatures.

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