Yusuke Okazaki

Divalent magnesium ion conducting characteristics in phosphate based solid electrolyte composites

The divalent Mg2+ ion conducting solid electrolyte was synthesized with a composite form by intentionally changing the starting material mixing ratio to the nonstoichiometric region. By such a preparation technique, spontaneous and microscopic dispersion of the secondary Zr2O(PO4)2 phase was successfully realized and the Mg2+ ion conductivity was considerably enhanced by dispersing the secondary phase, showing the highest conductivity among the Mg2+ ionic conducting solid electrolytes reported. The Mg2+ migration in the composite solid was clearly demonstrated by dc electrolysis and the Mg2+ ion transference number was precisely determined to be unity by a modified Tubandt method. The development of pure Mg2+ ion conducting phosphate based solid electrolytes with high stability and considerably high ionic conductivity contributes greatly to opening a new door for the application of advanced materials such as rechargeable batteries and other specific sensor elements.

Trivalent rare earth ion conduction in the scandium tungstate type structure

Abstract From the consideration of the mobile trivalent ions and the structure which reduces the electrostatic interaction between the framework and the mobile trivalent ionic species as much as possible, a trivalent-ion conduction in solids was successfully realized with the Sc 2 (WO 4 ) 3 -type structure. Among the molybdates and the tungstates with the Sc 2 (WO 4 ) 3 -type structure, Sc 2 (WO 4 ) 3 and Sc 2 (MoO 4 ) 3 were found to be of the most suitable size for the trivalent-ion conduction in the tungstate and the molybdate series, respectively. By a dc electrolysis, the mobile species was clearly demonstrated to be a trivalent ion in the Sc 2 (WO 4 ) 3 -type structure.

Trivalent Sc3+ ion conduction in the Sc2(WO4)3–Sc2(MoO4)3 solid solution

Abstract The solid solutions of the (1− x )Sc 2 (WO 4 ) 3 − x Sc 2 (MoO 4 ) 3 system were synthesized and their ion conducting characteristics were investigated. The electrical conductivity increased and the activation energy decreased linearly with increasing the Mo content. Sc 2 (MoO 4 ) 3 ( x =1) showed the highest conductivity of 2.6 times as high as that of Sc 2 (WO 4 ) 3 ( x =0). By DC electrolysis, the conducting ion species in this system were identified to be trivalent Sc 3+ ion. The enhancement of the Sc 3+ ion conduction in Sc 2 (MoO 4 ) 3 is due to the reduction of the electrostatic interaction between mobile Sc 3+ and O 2− by introducing a smaller Mo 6+ ion into the tetrahedral unit of (MO 4 ) 2− (M=W, Mo). Sc 2 (MoO 4 ) 3 was found to possess the most suitable lattice size for the Sc 3+ ion migration, exhibiting the highest Sc 3+ ion conductivity among the (1− x )Sc 2 (WO 4 ) 3 − x Sc 2 (MoO 4 ) 3 system.

Trivalent scandium ion conduction in the scandium tungstate-alumina composites

Abstract The Al 2 O 3 mixed with Sc 2 (WO 4 ) 3 composites were synthesized and their ionic conducting characteristics were studied. The maximum electrical conductivity was attained for the composite of 0.9Sc 2 (WO 4 ) 3 –0.1Al 2 O 3 . From the electrical conductivity measurements at various oxygen pressures and polarization phenomena, the mobile species in the composite was identified to be only ionic and also the oxide anion was eliminated from the candidates of conducting ion species in the composite. Among the remainders of the candidate cationic species, the mobile ion was verified to be only Sc 3+ ion and the rest of the cations W 6+ and Al 3+ , were found to function as a lattice-forming ion with oxide anions and the insulating oxide constituent, respectively. Here, one of the suitable techniques to enhance the ionic conducting properties was clearly demonstrated by forming a composite with a trivalent ion conductor and a refractory oxide insulator and the relation between the relative density of the composites and the Sc 3+ ion conductivity was explicitly clarified.

Optimization of divalent magnesium ion conduction in phosphate based polycrystalline solid electrolytes

A highest Mg2+ ion conducting polycrystalline solid electrolyte was successfully realized by improving the characteristics of both grain bulks and grain boundaries simultaneously. The former improvement was achieved by making a solid solution to substitute cation site for higher valent one to create Mg2+ ion vacancies in grain bulks. The latter was realized by obtaining a composite in such a manner to microscopically deposit the insulating secondary phase in grain boundaries. By combining above mentioned two effects, the optimization of Mg2+ ion conductivity at around 800 °C was effectively achieved to reach the total Mg2+ ion conductivity of approximately 10−2 S·cm−1 which is applicable in a practical range.