No abstract

Core-level electronic structure of La1−xSrxMnO3 has been studied by x-ray photoemission spectroscopy (XPS). We first report, by the conventional XPS, the well-screened shoulder structure in Mn 2p3∕2 peak, which had been observed only by hard x-ray photoemission spectroscopy so far. Multiple-peak analysis revealed that the Mn4+ spectral weight was not proportional to the nominal hole concentration x, indicating that a simple Mn3+/Mn4+ intensity ratio analysis may result in a wrong quantitative elemental analysis. Considerable weight of the shoulder at x = 0.0 and the fact that the shoulder weight was even slightly going down from x = 0.2 to 0.4 were not compatible with the idea that this weight simply represents the metallic behavior. Further analysis found that the whole Mn 2p3∕2 peak can be decomposed into four portions, the Mn4+, the (nominal) Mn3+, the shoulder, and the other spectral weight located almost at the Mn3+ location. We concluded that this weight represents the well-screened final state at Mn4+ sites, whereas the shoulder is known as that of the Mn3+ states. We found that the sum of these two spectral weight has an empirical relationship to the conductivity evolution with x.

By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/corelevel x-ray photoemission spectral weight and electrical conductivity in La 1−x Sr x MnO 3 as a function of x. In the Mn 2p 3/2 HX-PES spectra, we observed the shoulder structure due to the Mn 3+ well-screened state. However, the intensity at x=0.8 was too small to explain its higher electrical conductivity than x=0.0, which confirms our recent analysis on the Mn 2p 3/2 XPS spectra. The near-Fermi level XPS spectral weight was found to be a measure of the variation of electrical conductivity with x in spite of a far lower energy resolution compared with the energy scale of the quasiparticle (coherent) peak because of the concurrent change of the coherent and incoherent spectral weight.

Sr 0.67 La 0.33 MnO 3 demonstrates high conductivity with a small temperature coefficient in the range of 423-1173 K. Its conductivity is unaffected by annealing for up to 500 h at 1273 K in air, which is very surprising for an n-type oxide. These features mean that Sr 0.67 La 0.33 MnO 3 can replace noble metals for high-temperature electrodes.

We developed a (K,Na)NbO3-based lead-free piezoelectric ceramic with a KTiNbO5 system, (K1−xNax)0.86Ca0.04Li0.02Nb0.85O3−δ–K0.85Ti0.85Nb1.15O5–BaZrO3–Fe2O3–MgO (K1−xNxN–NTK–FM). K1−xNxN–NTK–FM ceramic exhibits a very dense microstructure and a coupling coefficient of kp = 0.59, which is almost comparable to that of conventional lead zirconate titanate (PZT). The (K,Na)NbO3-based ceramic has the Γ15 mode for a wide x range. The nanodomains of orthorhombic (K,Na)NbO3 with the M3 mode coexist within the tetragonal Γ15 mode (K,Na)NbO3 matrix. Successive phase transition cannot occur with increasing x. The maximum kp is observed at approximately the minimum x required to generate the M3 mode phase. Unlike the behavior at the morphotropic phase boundary (MPB) in PZT, the characteristics of K1−xNxN–NTK–FM ceramic in this region changed moderately. This gentle phase transition seems to be a relaxor, although the diffuseness degree is not in line with this hypothesis. Furthermore, piezoelectric properties change from “soft” to “hard” upon the M3 mode phase aggregation.