The electronic and crystal structures of Cs2[Mo6X14] (X = Cl, Br, I) cluster-based compounds were investigated by density functional theory (DFT) simulations and experimental methods such as powder X-ray diffraction, ultraviolet–visible spectroscopy, and X-ray photoemission spectroscopy (XPS). The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV–vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. The XPS valence spectra were fairly well reproduced by simulations based on the projected electron density of states weighted with cross sections of Al Kα, suggesting that DFT calculations can predict the electronic properties of metal-cluster-based crystals with good accuracy.

The crystallization of a high-purity hexamolybdenum cluster chloride, Cs2[Mo6Cl14], was investigated with the aim of improving its intrinsic properties, including optical properties. In particular, we used the hydrophilicities of alcoholic solvents to purify Cs2[Mo6Cl14] by dehydration. The precursor, trigonal Cs2[Mo6Cl14] with water impurities, or monoclinic Cs2[Mo6Cl14]·H2O, was dispersed in methanol (MeOH), ethanol (EtOH), or 1-propanol (1-PrOH) to induce recrystallization during stirring. As a result, regardless of the precursor, Cs2[Mo6Cl14] crystallized from EtOH and 1-PrOH, while Cs2[Mo6Cl14]·H2O crystallized from MeOH, which indicates that EtOH and 1-PrOH behave as dehydrating agents during recrystallization. Subsequent characterization by X-ray diffraction, thermal desorption, and infrared spectroscopic techniques confirmed that the Cs2[Mo6Cl14] crystallized from EtOH or 1-PrOH, particularly 1-PrOH, is of high purity (fewer inserted water molecules) and high crystallinity. Improved luminescence efficiency following purification was evidenced by time-resolved photoluminescence measurements; the Cs2[Mo6Cl14] purified by dehydration on recrystallization clearly exhibited an increased luminescence lifetime.

A new pulverization process utilizing thermal treatment in controlled atmosphere was developed. The samples, including SrTiO3 single crystals, TiO2 single crystals and BaTiO3 ceramic, were pulverized into nano-sized powder by heating in gas stream containing air and ammonia (NH3) at high temperature. Although the detailed mechanism for this pulverization process is still unclear but it is evident that thermal treatment in NH3 based atmosphere containing small fraction of air (5–10%) causes not sintering but pulverization. Efficient synthesis of an oxynitride compound, LaTiO2N, was demonstrated by using nano-sized La2Ti2O7 precursor prepared by utilizing this new powder preparation process.

The electronic states of zinc magnesium oxide (Zn1−xMgx)O thin films were determined exactly by hard X-ray photoemission spectroscopy (HX-PES) using synchrotron radiation. The Zn 2p core level was shifted to a higher binding energy along with widening of the bandgap by alloying with MgO, whereas the shift of the O 1s peak was less than that of the Zn 2p peak. Density functional theory (DFT) calculations revealed that the electronic state of an O ion bonding with an adjacent Mg ion is remarkably different from that not bonding with a Mg ion. As a result, the energy shift observed in the O 1s peak results from a combination of the expansion of the bandgap energy and the chemical shift due to a change in the ionicity. The Fermi level is always situated just below the conduction band; this suggests that a shallow donor can be added, even in the alloy film with very high MgO fraction, for example, x = 0.47.

Very thick (about 0.5 mm) single crystalline films of (Zn1−xMgx)O solid solution have been grown by a liquid phase epitaxy (LPE) technique. The source materials, ZnO and MgO, were dissolved in a molten PbO-Bi2O3 flux and deposited on ZnO substrates as epitaxial (Zn1−xMgx)O layers. The (Zn1−xMgx)O layers thus obtained showed high crystallinity, similar to that of the ZnO substrate, and exhibited n-type conductivity with relatively high Hall mobilities (>90 cm2 V−1 s−1 for x = 0.1 at room temperature). Moreover, the activation energy of the mobile electrons was about 50 meV, and this value was independent of the MgO fraction. Since LPE is an appropriate technique for growing large area films, we examined the growth of (Zn,Mg)O thick films on 2 in. diameter ZnO substrates. The Mg concentration in the LPE grown layer was quite uniform, and the Li concentration was two or three orders lower than an ordinary ZnO substrate.

Bulk properties of gallium (Ga)- and aluminum (Al)-doped zinc oxide (ZnO) were studied using bulky single-crystalline thick films grown by liquid phase epitaxy (LPE). The highest possible dopant concentration was 1×1019 cm–3 for LPE growth at around 800 °C. The electron concentration was nearly same to the Ga and Al concentrations. The donor binding energy decreased to nearly zero with an increase in dopant concentration, and electron mobility of the sample with relatively high dopant concentration (1×1019 cm–3) was more than 60 cm2 V–1 s–1 at room temperature. The LPE technique is a potential solution for the production of ZnO for optical applications because the well-defined excitonic luminescence could be seen from the LPE-grown-doped single-crystals.

•First success of growth of Y2C, 2D-electride, through floating zone process.•Determination of phase relationship in Y–C system to achieve crystal growth.•Revealing the absence of ferromagnetism in hexagonal Y2C.The floating zone method was used to obtain single crystals several mm in size of the low-temperature rhombohedral form of Y2C rather than its typical rocksalt-type cubic form. This was achieved through optimization of the chemical compositions of the starting materials with the aim of producing a two-dimensional electride material. The crystals obtained exhibited a paramagnetic temperature-dependence at 1.8–300 K, with no trace of any obvious magnetic ordering.