(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. Combustion reaction occurred to form
double oxide fine powder in crystallite size of 20`100nm diameter at furnace temperature of 300.
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. |
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 ΚG than that in 1G.
Crystallinity was improved in the precipitation under ΚG, especially on the salts having liner
chain unit such as Al(OH2)6 in AlCl3E6H2O. |
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)2EA-xEn 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. 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 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 Ώ-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 Ώ-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 Ώ-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 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. |