Oxynitride perovskite SrTaO2N has been attracting attention as a possible new dielectric material owing to the cis-type anion ordering in its crystal structure. It is currently difficult to obtain it in bulk form because it easily loses a part of its nitrogen to become semiconducting during densification at high temperature. We found that its surface layer recovered its original orange color and dielectric properties after postannealing in ammonia. Piezoresponse force microscopy measurements clearly revealed a ferroelectric behavior on the entire orange surface layer peeled off from the black sintered body inside. The present sample was free-standing at about 8 μm thick and clearly distinct from the compressively strained SrTaO2N thin films for which ferroelectricity was recently reported in small domains (10–102 nm) in the locally assumed trans-type anion ordering. The present results represent the first experimental observation of ferroelectric response in a bulk oxynitride perovskite with cis-type anion ordering.

Strontium tantalum oxynitrides were prepared within the nominal composition range of 1.0 ≤ x ≤ 2.0, where x = Sr/Ta atomic ratio. A gradual structural transition was observed between the perovskite SrTaON and the Ruddlesden-Popper phase SrTaON with increasing SrO content. X-ray diffraction analyses showed that a single-phase perovskite was obtained up to x = 1.1, after which SrTaON gradually appeared at x ≥ 1.25. High-resolution scanning transmission electron microscopy observations identified the gradual intergrowth of a Ruddlesden-Popper SrTaON type planar structure interwoven with the perovskite crystal lattice upon increasing x. The crystal lattice at x = 1.4 was highly defective and consisted primarily of perovskite intergrown with a large amount of the Ruddlesden-Popper phase structure. This Ruddlesden-Popper phase layer intergrowth is a characteristic of an oxynitride perovskite rather than the Ruddlesden-Popper defects previously reported in oxide perovskites. Partial substitution of Ta with Sr was also evident in this perovskite lattice. Just below x = 2, a perovskite-type structure was intergrown as defects in the Ruddlesden-Popper SrTaON. Characterization of SrTaON in ambient air was challenging due to its moisture sensitivity. Thermal analysis demonstrated that this material was relatively stable up to approximately 1400 °C in comparison with SrTaON perovskite, especially under nitrogen. SrTaON could keep its structure in a sealed tube, and some amount of SrCO was observed in XRD after 10 days of exposure to 75% relative humidity under prior ambient conditions. A compact of this material had a relative density of 96% after sintering at 1400 °C under 0.2 MPa of nitrogen, even though a drastic loss of nitrogen was previously reported for a SrTaON perovskite under these same conditions. Postammonolysis of the SrTaON ceramics was not required prior to studying its dielectric behavior. This is in contrast to the SrTaON perovskite, which requires postammonolysis to recover its stoichiometric composition and electrical insulating properties.

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Manganese (Mn)-based strong magnets have long been a challenge because their 3 d half-filled nature, owing to the close proximity of Mn atoms, results in antiferromagnetic ordering. Among various Mn magnetic materials, L1 0 -MnAl (τ-phase) has received much attention since it shows ferromagnetism at a high Curie temperature despite the very short Mn–Mn distance. However, because of the difficult synthesis of the stoichiometric and perfectly ordered τ-phase, its intrinsic magnetic properties and mechanism are unclear. Here, we show the first observation of antiferromagnetism, having sixfold magnetic superstructure along the c-axis, in stoichiometric and chemically ordered τ-phase. Moreover, we found that super-exchange interaction between Mn atoms via p -electrons of Al atoms causes antiferromagnetism in τ-phase. The ferromagnetism in the conventional Mn-rich τ-phase results from the suppression of the super-exchange interaction due to the substitution the excess Mn atoms for the Al atoms. The current study of Mn-based magnetic materials mainly focuses on the lattice constant engineering based on the simple Beth-Slater picture of direct exchange. These findings present effective ways to obtain high magnetization without antiferromagnetic ordering.

The hemolysin produced by group B streptococci (GBH) has an isoelectric point (pI) of 5.8 and it shows a hemolytic activity in the absence of 2-mercaptoethanol (2-ME). The hemolytic activities of GBH were compared to that of streptolysin O (SLO) and streptolysin S (SLS). These hemolysins differed with respect to the binding and release of hemoglobin (Hb). GBH was bound to phospholipids on the membranes of target erythrocytes, followed by the gentle release of K+ and slow Hb release without lag time. Incontrast SLO released Hb as rapidly as K+. GBH induced hemolysis was inhibited by the addition of 30 mM raffinose. These results indicate that the effective diameter of the pores formed by GBH was about 1.1 nm. GBH showed a lower hemolytic efficiency than SLO, reflecting the fact that these hemolysins destroy erythrocytes by a different mechanism. Intracellular K+ and Hb were released at a different rate in GBH treated cells, indicating that a colloid-osmotic process is involved in the lytic mechanism.