Structure determination of La18W10O57.

Area of Science:

• Solid-state chemistry
• Inorganic materials science
• Crystallography

Background:

• The La(2)O(3)-WO(3) binary system is crucial for understanding lanthanum tungstate compounds.
• Previous studies reported La(14)W(8)O(45) as the compound in the 53.3 WO(3) mol % range.
• Accurate structural characterization is essential for materials development.

Purpose of the Study:

• To report the synthesis and structural determination of a new lanthanum tungstate, La(18)W(10)O(57).
• To analyze the crystal structure and compare it with previously reported compounds in the La(2)O(3)-WO(3) system.
• To investigate related properties such as polytypism, ionic conductivity, and thermal expansion.

Main Methods:

• Synthesis of La(18)W(10)O(57) via solid-state reaction.
• Structure determination using synchrotron and laboratory X-ray, neutron, and electron diffraction.
• Characterization using transmission electron microscopy (TEM), ionic conductivity measurements, and thermal expansion analysis.

Main Results:

• A new compound, La(18)W(10)O(57), with 52.65 WO(3) mol % was synthesized, replacing La(14)W(8)O(45).
• The crystal structure was solved in the hexagonal space group P62c, revealing [WO(6)] octahedra and trigonal prisms.
• The compound exhibits a subcell with c' = c/6 and observed polytypism.

Conclusions:

• La(18)W(10)O(57) represents a significant finding in the La(2)O(3)-WO(3) binary system.
• The detailed structural analysis provides insights into the coordination of tungsten and lanthanum.
• Further investigations into its physical properties like ionic conductivity and thermal expansion are warranted.