Shigekazu Udagawa

Experimental assembling of gas cells using beta/beta″-alumina type NH+4-gallates electrolytes

Abstract Polycrystalline disks of NH + 4 -gallate with a β″-alumina structure (NH + 4 -β″-gallate) containing a small amount of β-phase were prepared from Rb + -β″-gallate disks fabricated by hot pressing. The small difference in the lattice parameter between NH + 4 -β″-gallate and Rb + -β″-gallate was responsible for the non cracking ion exchange of disks in molten ammonium nitrate. Electromotive forces of a hydrogen concentration cell using the NH + 4 -β/β″-gallate electrolyte agreed rather well with a simple thermodynamical potential equation.

Chemical composition and crystal structure of β-alumina type R+-gallate (R+ = K+, NH+4)

Abstract The crystal structures of β-alumina type K + -gallate (K + -β-gallate), Mg 2+ -doped K + -β-gallate, and NH + 4 -β-gallate were refined by the single crystal X-ray diffraction method. The positive charges of excess K + ions in K + -β-gallate were compensated by O 2− ions in the mO site which coordinated with interstitial Ga 3+ ions. The charge compensation mechanism mentioned above was changed by doping with Mg 2+ ions. The excess charges in Mg 2+ -doped K + -β-gallate were compensated by the replacement of Mg 2+ ions for Ga 3+ ions at the middle of spinel block. No defects were found in NH + 4 -β-gallate for the charge compensation, which was completely consistent with the result of thermal analysis that indicated a stoichiometric composition of NH + 4 -β-gallate.

Synthesis of a new perovskite Pb(Li14Nb34)O3

Abstract A high-pressure technique was adopted to obtain perovskite-type Pb(Li 1 4 Nb 3 4 ) O 3 . A new perovskite Pb(Li 1 4 Nb 3 4 ) O 3 was characterized to have a cubic symmetry with a o = 4.069 A ; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.

Electrical conductivity and thermal decomposition of β-alumina type NH+4-gallate

Abstract The electrical conductivity and thermal decomposition process were studied for β-alumina type NH+4-gallate (NH+4-β-gallate). The chemical composition of this gallate was represented by the formula 1.25H2O·(NH4)2O·11Ga2O3. It is noteworthy that NH+4-β-gallate contained an exactly stoichiometric amout of ammonium ion. The thermal decomposition of this gallate proceeded as follows: 1.25H2O·(NH4)2O·11Ga2O3 (NH4)2O·11Ga2O3+1.25H2O H2O·11Ga2O3+2.0NH3 11Ga2O3+1.0H2O. The electrical conductivity of a single crystal of NH+4-β-gallate, measured by a complex impedance method, was 5×10-5 (S cm-1 at 200°C. The temperature dependence of the conductivity was explained satisfactorily on the basis of thermal decomposition of NH+4-β-gallate.