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We developed RIETAN-FP and VESTA, which are, respectively, successors to a multi-purpose pattern-fitting system RIETAN-FP and VICS/VEND for three-dimensional visualization. Further, we build an integrated GUI environment to assist structure analysis using RIETAN-FP, VESTA, a MEM analysis program PRIMA, ALBA for the maximum-entropy Patterson method, and an ab initio structure analysis system EXPO2004, etc.

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Crystal structure, structural disorder and hydration behavior of Ca7ZrAl6O18 were investigated by laboratory X-ray powder diffraction and conduction calorimetry. The initial structural model was determined using direct methods, and it was further modified to a split-atom model, in which the five types of Ca atoms and four types of AlO4 tetrahedra were, respectively, positionally and orientationally disordered. The crystal structure is orthorhombic (space group Pmn21, Z = 2) with lattice dimensions a = 1.08486(1) nm, b = 1.05913(1) nm, c = 0.766945(8) nm and V = 0.88123(1) nm3. The electron density distribution was determined by the maximum-entropy methods-based pattern fitting method.

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Densities of coherent-scattering lengths derived from MEM analysis with neutron powder diffraction data reveal that oxide ions at the 4i site (P4/mmm) migrate to nearest-neighbor 4i sites along the [100] and [010] directions near the (004) planes. A two-dimensional diffusion pathways is obtained, where two-dimensionality is attributable to the layered structure of the perovskite-type La0.64(Ti0.92Nb0.08)O2.99.

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First principles calculations combined with the cluster expansion technique is a powerful tool for the quantitative prediction of complicated crystal structures and their energetics, which are difficult to determine merely by experiments. The method has been applied to a few systems, ZnO-MgO pseudo binary system, spinel oxides and a series of substoichiometric SnO_2-x compounds with a rutile structure, in order to verify the validity of the method.

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In order to shed light on the proton distributions and order/disorder in high-pressure delta-Al(OH)3 and delta-AlOOH and isostructural In(OH)3 and InOOH phases, high-resolution 1H CRAMPS (FSLG)-MAS NMR and Raman spectroscopy have been applied. The 1H CRAMPS-MAS NMR revealed two peaks each for delta-Al(OH)3 and In(OH)3, and one each for delta-AlOOH and InOOH. These results are consistent with crystal structures refined from X-ray and/or neutron diffraction. The Raman spectra are also in general agreement with the NMR results.

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In the present study, the Raman spectra of BaTa2O6 have been successfully obtained at temperatures up to 1573 K for the first time, using a new continuous-wave ultraviolet (UV) Raman spectroscopic system designed to measure the Raman scattering from materials at high temperature. The typical Raman spectra of the orthorhombic phase (Type I) were recorded in the region of room temperature to 1573 K. The present result is described in terms of the parameter related to temperature variation at constant pressure, defined in a similar way to the Gruneisen parameter. Raman bands located above 250 cm-1 and the mode at 169 cm-1 show smaller values of the parameter than lower frequency modes below 250 cm-1 except the mode at 169 cm-1, suggesting that these higher frequency modes and the mode at 169 cm-1 are assigned to TaO6 internal modes.

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Some metal nitride or oxynitride compounds as noted as yellow or red phosphors for white LED illumination, e.g. M2Si5N8:Eu2+, MAlSiN3:Eu2+, MSi2O2N2:Eu2+, are consisting of unique structural frameworks. In this contribution, the material design was made for such metal nitride or oxynitride phosphors with high emission intensity.

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Rod-like rutile nanoparticles were obtained by hydrothermal treatment of titanium-glycolate complex aqueous solution. The aspect ratio of the obtained particles increased with addition of glycolic acid or lactic acid. In the presence of additives, anatase tended to form in the temperature range favorable for single phase rutile formation when no additives are used. Later these anatase particles dissolve and titanium ions are incorporated in the growing rutile species. The carboxylic acids act to retard and promote development of the specific crystal facets and allow to control aspect ratio of the rutile nanoparticles.

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Peroxo-titanium complex was prepared as a precursor of TiO₂ powder for the low-temperature synthesis with aqueous solution process. The effects of reaction conditions, such as solution pH and reaction time, on the deposition of TiO₂ were investigated in detail. The obtained TiO₂ powder samples were characterized by X-ray diffraction, transmission electron microscopy, etc. The peroxo-titanium complex was synthesized from titanium (IV) hydroxide, hydrogen peroxide and ammonia solution. The crystallized TiO₂ with the rutile phase was obtained from the solution less than 100 ºC. In addition, it is noteworthy that the polymorphs of TiO₂ (anatase or rutile) and their composition can be controlled by changing the pH of solution. The specific surface area of the samples was also changed by solution conditions.

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We prepared new water-soluble tantalum compound with lactic acid (NH₄)₄[Ta₂(C₃H₄O₃)₄(O₂)₂O]*3H₂O and determined its crystal structure using single crystal X-ray diffraction. The solid-state ¹³C-NMR data, Raman and IR-spectra were consistent with the established structure. Tight coordination and overall negative charge of the complex ion explain stability of this compound against hydrolysis. Indeed water solution of this tantalum complex was stable for more than six month and its crystalline powder did not show any trace of decomposition within the same time. Presence of ammonium as a counter ion makes this new complex an attractive precursor for synthesis of tantalum containing materials by solution methods. The water solution of the tantalum complex was successfully applied for synthesis of two photocatalytic materials NaTaO₃ and Sr₂Ta₂O₇ by Marcilly method [1].
[1] C. Marcilly et al., J. Am. Ceram. Soc. 53, 56 (1970).

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Wulff's relationship was proposed almost hundred years ago and this relationship is well accepted. This relationship was theoretically established, but no experimental evidence for this theory was demonstrated, because measurement of specific surface free energy of crystal surface was believed to be difficult. We measure the specific surface free energy of chlorapatite single crystal using contact angles of liquids and compared with its morphology. In that system, we could confirm Wulff's relationship experimentally. The contact angles of water and formamide droplets on the single crystals were measured at the room temperature by sessile drop method. Although the contact angles have wide distributions, the average of the contact angles was determined after more than hundred repetition of measurement. The specific surface free energy of each face of the crystal was calculated by Fowkes approximation and Wu's mean equations. Wulff's point was postulated at the center of the crystal and the length of the normal line to each face of the crystal from Wulff's point was geometrically calculated and compared with the specific surface free energy. The ratio of specific surface free energy of the face and the normal length from center to the face of crystal was almost constant, which satisfies Wulff's relationship. We are going to discuss about the physical meaning of Wulff's constant from experimental viewpoint.

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Calcite single crystals were grown in organic acid ammonium salt solutions with a temperature gradient under hydrothermal conditions. Effects of growth conditions on growth rate and those of impurities on perfection of the grown crystals were investigated. Chlorapatite single crystals grown by flux method were converted to hydroxyapatite single crystals under alkaline hydrothermal conditions. Crystals with controlled morphology of zinc and yttrium oxyhydroxides including cations were prepared under hydrothermal conditions at relatively low temperatures. It was found that these crystals were converted to polycrystalline oxide particle with the original morphology.

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We succeeded in development of a new technique to grow high-quality Si multicrystal ingot for solar cells named as "Dendritic casting method", which utilizes the dendrite growth along the bottom of the crucible at the initial stage of directional growth. This method permits to obtain a textured Si multicrystal ingot with large-size grains. Furthermore, its crystal quality was highly maintained from the bottom to top in the ingot, which is a great advantage from a view of a material yield. Solar cells based on this Si multicrystal show high energy conversion efficiencies closing to that of Si single crystal solar cells.

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Undoped and Sn-doped b-Ga₂O₃ single crystals have been grown by optical floating zone method, and its growth conditions were optimized. The electrical, optical and crystalline properties were characterized before and after annealing. It was found that transparent conducting oxide semiconductors with wide band gap energies of 4.8eV can be obtained. Using these unique properties, the application to the substrates for GaN based film growth and UV photodetector were investigated and their results were shown.

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Floating-zone growth and lasing properties of vanadate single crystals are reviewed. Because the floating-zone method needs no crucible, vanadate crystals can be grown under a high oxygen partial pressure and the formation of macroscopic defects such as inclusions is effectively suppressed, as a result. Heavily doped crystals are also grown at a high growth rate of over 10 mm/h because of a steep temperature gradient. Excellent lasing performance, i.e., high slope efficiency and low threshold, has been realized using floating-zone-grown Nd:GdVO4 and Nd:LuVO4 single crystals, indicating these crystals to be of superior quality.

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Scintillators are used for the detection of high energy radiation or particles. Research activity in this field has been increasing within last 10 years due to always growing number of applications and their demands particularly in the field of high energy physics, medical imaging (molecular imaging) and safety regulations (imaging for safety). Especially, due to the international situation, the detection of fears of terrorism becomes one of the highest matters in recent years. The market size became third largest scale in the single crystal field after silicon and quartz. However, there is no perfect scintillator. Therefore, huge efforts are devoted in the world. In this presentation, domestic and international research activity will be introduced together with our results. Especially, the problems of single crystalline scintillator will be listed up and the possibility to solve the problems using ceramics will be discussed.

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