(1) Soft preparation process in aqueous solution route for multinary inorganic solids


Nano-sized crystals of functional ceramic materials prepared in gel-combustion method
Citric acid or glycine was added as a gelling agent to a mixed aqueous solution of metal nitrates. Viscous gel was obtained after its aging at around 150Ž. Combustion reaction occurred to form double oxide fine powder in crystallite size of 20`100nm diameter at furnace temperature of 300Ž. The preparation method is being applied for ZnO-In2O3 transparent conductor, BaM-type magnetic ferrite, BaZ ferrite for electric wave absorber in GHz, phosphor for plasma display and cathode material for lithium ion battery. These materials have been prepared by high temperature firing above 100Ž.


Precipitation behavior of metal salts from mixed aqueous solution frozen under microgravity
Aqueous solution of mixed metal salts was frozen under microgravity conditions generated in dropping facility or in parabolic flight of airplane. Metal salts precipitated in dendritic ice formed under microgravity. They mixed much more homogeneously than those precipitated in 1G condition. Double oxides could be obtained more easily from the precipitate under ƒΚG than that in 1G. Crystallinity was improved in the precipitation under ƒΚG, especially on the salts having liner chain unit such as Al(OH2)6 in AlCl3E6H2O.


Formation control and bio-hybridization of mixed metal hydroxides
Selective adsorption to inorganic solids has been reported on bio-molecules such as DNA, ATP, saccharides, bacteria and virus. It might be applied for selective separation of biological or inorganic materials and also for drug delivery system. Hydrotalcite like layered mixed metal hydroxide, (Mg1-xAlx)(OH)2EA-xEn H2O, can intercalate DNA and ATP in its interlayer region. Crystallinity of the hydroxide was much improved by a control of the precipitating behavior.


Study on conduction mechanism of oxide ion conduction in Nd9.33(SiO4)6O2 single crystal and its thin film formation for fuel cell application
Apatite-type Nd9.33(SiO4)6O22 shows higher oxide ion conduction in two orders in magnitude than that of stabilized zirconia in a temperature range between 300 and 600Ž. Nd9.33(SiO4)6O2 single crystal was grown by floating zone method. Conduction mechanism is under investigation using x-ray single crystal structure analysis and neutron powder diffraction. Its thin film will be formed by sol-gel method to apply for a fuel cell operating in a moderate temperature range.


Gallery modification of layered manganese dioxide by intercalation methods
Lithium ion battery is widely used in small devices such as mobile phone. Lithium intercalation materials such as LiCoO2 have been used as its cathode. Manganese oxide is expected to be used in the rechargeable battery as much cheaper cathode material as well as in dry battery. We are studying a gallery modification of layered NaxMnO2 to find out manganese oxide cathode having both large rechargeable capacity and cycle number. Pentavalent V5+ ion could be intercalated by a reaction of propylammmonium ion intercalated manganese dioxide in VCl3 solution.




(2) Development and hybridization of metal nitrides for high density information recording


Low temperature preparation of Fe16N2 with a giant magnetization
Possibility of giant magnetization has been pointed out for Fe16N2. We succeeded to obtain its bulk preparation without impurity. The preparation had been very difficult because of its thermal instability. We could prepare it by ammonia nitridation at 130Ž for 100hr of the reduced oxide fine powder in 30nm particle size in hydrogen. The saturation magnetization was 225emu/g at room temperature. It was 16% larger than that of ƒΏ-Fe. Three kinds of magnetic hyperfine fields were observed in its Mossbauer spectrum with 19% super paramagnetic component. Thus 280emu/g is expected as a saturation magnetization at room temperature for Fe16N2.
Sputter deposited ƒΏ-Fe thin film was directly nitrided with ammonia without any exposure to air. Fe16N2 has not yet been formed in the nitrided film. Another interesting point was found out. Formation temperature of iron nitrides such as Fe3N and Fe4N was reduced with the film thickness. The reactivity might change with crystallite size, lattice parameter and surface texture of ƒΏ-Fe thin film.


GaN crystal deposition from its decomposition products during induction heating
GaN single crystal is the most promising substrate for a formation of GaN based pn junction with low dislocation density for blue laser. Its crystal growth has been investigated applying either high-pressure technique or Na flux method. Another growth method is required to obtain a large crystal. GaN powder was heated in an induction coil above 850Ž in nitrogen atmosphere. GaN crystals deposited on a substrate in a recombination of Ga metal and active nitrogen generated in the induction heating. We are trying to develop a new growth technique modifying the present result.


Preparation of ferromagnetic (Ga1-xMnx)N and ferroelectric (Ga1-yLiy)N from aqueous solution route
Another GaN subject is to hybridize either ferromagnetic or ferroelectric properties to the superior optical characteristic of GaN. There are possibilities to generate these properties in a small amount doping of either Mn or Li, respectively. The present study is going to apply a preparation method in aqueous solution route. Less than 5% Mn could be doped by nitridation of amorphous oxide precursor prepared from citric acid gel.


Formation and magneto resistance of FeNi/AlN/FeNi spin tunnel junction prepared by rf-sputter deosition
More than 10% magneto resistance effect has been reported on ferromagnetic tunnel junction using an Al2O3 insulating barrier formed by oxidation of Al thin film in ambient air condition. The MR effect is going to be applied to magnetic memory and sensor. The oxide barrier is not suitable in high temperature use because it may react with the ferromagnetic metal. Formation of flat and non-reactive barrier is required substituting the Al2O3 barrier. AlN is one of the candidates because of its thermal stability. There will be no electrical insulators formed even if it will react with the iron based ferromagnetic layer. Another advantage of AlN is a possibility to form a flat surface in its preferred oriented film because of its anisotropic crystal structure. We could prepare the ferromagnetic thin films having different coercivities by rf-sputter deposition of 75FeNi target. Preferred oriented AlN thin film has been obtained in the reactive sputter deposition in nitrogen gas pressure of 0.8Pa. We will fabricate tunnel junctions combing these deposited thin films to investigate a flatness of their interface and their magneto resistance effect.