M. Hiraiwa

Thermal contraction behavior in Al2(WO4)3 single crystal

Abstract The anisotropic thermal expansion behavior of a single crystal of Al 2 (WO 4 ) 3 was obtained for the first time and the anisotropic contraction behavior was identified. The direct clarification of the anisotropic behavior contributes greatly towards designing the thermal expansion characteristics along every axis, realizing unique materials such as a zero expansion material.

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.

Single-crystal growth of aluminum tungstate–lutetium tungstate solid solution

Abstract Aluminum tungstate–lutetium tungstate solid solution was obtained in a single-crystal form by the Czochralski (CZ) method. This is the first report to demonstrate that the solid solution which cannot be obtained by a conventional polycrystalline solid-state reaction method, was successfully grown by applying the CZ method to modify the form from polycrystal to single crystal.

Al3+ ion conducting behavior in single crystal of aluminum tungstate–scandium tungstate solid solution

Single crystal of the aluminum tungstate–scandium tungstate solid solution, which is as large as 1 cm in diameter and 0.6 cm in length, was successfully grown by Czochralski (CZ) method. The crystal is in the Sc2(WO4)3 type structure with an orthorhombic symmetry and the lattice constants of the solid solution increased by the substitution of the larger Sc3+ ion in the Al site of Al2(WO4)3 crystal bulk, showing an isotropic expansion. The Al3+ ion conducting characteristics were characterized and the formation of the Al2(WO4)3–Sc2(WO4)3 solid solution was found to contribute greatly in enhancing the Al3+ ion conducting behaviors, especially along c-axis.

Anisotropic trivalent ion conducting behavior in single crystals of aluminum tungstate-scandium tungstate solid solution

An aluminum tungstate-scandium tungstate solid solution was successfully grown in a single crystal form by modified Czochralski (CZ) method. The crystal grown was transparent and a satisfactory quality was examined by a polarizing microscope measurement. The Al3+ ion conductivity was considerably improved by forming the solid solution and these by expanding the crystal lattice size. The lattice expansion contributes greatly to enhancing the Al3+ ion conducting behavior especially along c-axis among the three axes in the orthorhombic symmetry. By comparing the ion conducting characteristics between each axis of the single crystal and the polycrystal, the enhancement of the Al3+ ion conductivity is ascribed to the cooperative effects of both ion conductivity increase along c-axis and the conductivity enhancement in the grain boundaries.

Single crystal growth of trivalent ion conducting aluminum tungstate–scandium tungstate solid solutions

Abstract A modified Czochralski (CZ) single crystal method was developed for the growth of aluminum tungstate–scandium tungstate solid solutions. The crystals were transparent and a satisfactory quality was ensured by polarizing microscope measurements. Both Al and Sc were identified by electron probe microanalysis (EPMA) measurements and the grown single crystals were identified to be solid solutions. The trivalent Al/Sc ion ratio in the single crystal solid solutions was accurately determined from the lattice parameters calculated from X-ray powder diffraction analysis.