In recent years, lead halide perovskites have emerged as excellent photovoltaic materials for solar power generation. However, because they are toxic and chemically unstable in air, lead-free perovskites are also being investigated. In this study, the perovskite variant (CH3NH3)2SnI6 was studied. Polycrystalline films of (CH3NH3)2SnI6 were prepared using the thermal evaporation method. The films had a direct band gap of 1.81 eV with a strong absorption coefficient of ∼7 × 104 cm–1. In addition, the films were n-type with a carrier concentration of ∼2 × 1015 cm–3 and an electron mobility of ∼3 cm2 V–1 s–1. Moreover, the conductivity was increased by a factor of 4 under simulated solar illumination (100 mW cm–2). These results indicate that (CH3NH3)2SnI6 is a lead-free optical semiconductor suitable for solar cell applications.

The dependence of silicon oxycarbides' chemical composition and molecular structure on their reaction conditions was tested by varying the atmosphere under which pyrolysis was performed. To obtain the silicon oxycarbides, densely cross‐linked silicone resin particles with an averaged diameter of 2 μm were pyrolyzed in various atmospheres of H2, Ar, and CO2, in the temperature range 700°C–1100°C. The residual mass of resin after pyrolysis was almost constant at 700°C, although their apparent colors varied distinctly. The sample obtained from the H2 atmosphere was white, whereas that obtained from the CO2 atmosphere was dark brown. Fourier‐transform infrared (FT‐IR) spectra of the residues suggested that the Si–O–Si network evolution was accelerated in the CO2 atmosphere. Beyond 800°C, the chemical compositions of the compounds obtained from a H2 atmosphere increasingly approached near‐stoichiometric SiO2–xSiC composition with increasing the pyrolysis temperature. Compounds from a CO2 atmosphere approached a composition of SiO2–xC with no free SiC as the pyrolysis temperature increased. In the products from an Ar atmosphere, SiO2–xSiC–yC compositions were typically obtained. The observed effects of the pyrolysis atmosphere on the resulting chemical compositions were analyzed in terms of thermodynamic calculations. Electron spin resonance (ESR) spectra revealed broad and intense signals from products obtained from either Ar or CO2. Estimating from the signal intensity, the residual spin concentrations were in the range 1018–1019 g−1. Meanwhile, the spectra from the samples obtained in H2 showed weak and sharp signals with estimated spin concentrations ranging from 1016–1017 g−1. This signal attenuation may have been due to the hydrogen capping of dangling bond formed during pyrolysis.

Single crystals of Na0.44MnO2 (=Na4Mn9O18) have been synthesized by a flux method at 1173 K for the first time. The crystal structure of Na0.44MnO2 has been refined by single-crystal X-ray diffraction method. The framework structure consists of double and triple rutile-type chains of edge-sharing MnO6 octahedra and a single chain of edge-sharing MnO5. The Mn-O bond distance and bond valence analyses revealed the manganese valence Mn3+/Mn4+ ordering in the Na0.44MnO2 structure.

Impurity doping of crystalline Si is one of the most striking techniques in semiconductor technology. A rigid and perfect crystalline lattice is prerequisite for effective doping. However, it has been reported to date that introducing a small amount of impurities drastically improves also the properties of amorphous materials. This paper reviews three pronounced doping effects on optical and electrical properties of amorphous oxides; i.e., (i) F-doping of silica glass to improve the vacuum-ultraviolet optical transmission and radiation toughness, (ii) codoping effects on solubility enhancement of rare earth ions in silica glass melt, and (iii) electron-carrier generation in transparent amorphous oxide semiconductors. It is emphasized that effectiveness of electron doping is determined by the magnitude of electron affinity and stabilization energy of a dopant. Importance of the local structure formed around a dopant ion and the location of conduction band minimum measured from the vacuum level is addressed to understand the doping effects in amorphous oxides.

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