We have investigated defects in beta-type gallium oxide (β-Ga 2 O 3 ) single crystals by X-ray topography, selective etching, and transmission electron microscopy. Two types of defects, namely, dislocations and nanopipes, were found. Dislocations are screw dislocations with Burgers vector parallel to [010]. The majority of them lie on ð 201Þ and (001). Nanopipes are hollow pipes of 0.1 µm diameter and of at least 15 µm length elongated along [010]. No strain field was found around them. From the observation results, we have discussed the formation mechanisms of these defects. © 2015 The Japan Society of Applied Physics λ θ = ) 2d sin(Fig. 1. Schematic of optical arrangement of reflection X-ray topography.

A hollandite-type K x Ti 8 O 16 polycrystalline sample has been prepared and studied by magnetization, resistivity and x-ray photoelectron spectroscopy ͑XPS͒. Room temperature ferromagnetic behavior is observed in the magnetic hysteresis measurement. The sample shows a semiconductive temperature dependence in the resistivity measurement. Analysis of the Ti 2p 3/2 core-level XPS spectrum indicates that the titanium ions have a mixed valence of Ti 4+ and Ti 3+ . In addition, the valence band spectrum reveals that the 3d electrons tend to localize on Ti 3+ ions in the hollandite-type TiO 2 lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide-gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite-type K x Ti 8 O 16 sample can be classified as a TiO 2 -based wide-gap semiconductor with Curie temperature above room temperature. Room temperature ferromagnetism ͑RTFM͒ decreases in the sample prepared under a strong reducing gas atmosphere, accompanied with the decrease in the resistivity. The results imply that the localized 3d electrons are responsible for the RTFM of the K x Ti 8 O 16 sample.

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Polycrystalline sample of hollandite‐type titanium oxide KxTi8O16 has been prepared and studied by magnetization and X‐ray photoelectron spectroscopy (XPS). Room temperature ferromagnetic behaviour is observed in the magnetic hysteresis measurements. XPS measurements of the Ti 2p3/2 core‐level finds that the titanium ions take a mixed valence of Ti4+ and Ti3+. In addition, the valence band spectrum reveals that the 3d electrons tend to local‐ize on Ti3+ ions in the hollandite‐type TiO2 lattice. Also, analysis of the valence band spectrum shows that the prepared sample is a wide‐gap oxide with a band gap of 3.6 eV. These results indicate that the present hollandite‐type KxTi8O16 sample can be classified as a TiO2‐based wide‐gap semiconductor with Curie temperature above room temperature (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)