High-Temperature Structural Evolution in the Ba₃Mo_{(1- x)}W _xNbO_8.5 System and Correlation with Ionic Transport...

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography

Background:

• The Ba₃Mo₍₁-ₓ₎WₓNbO₈.₅ system exhibits a hybrid structure.
• Understanding structural evolution is key to optimizing material properties.

Purpose of the Study:

• To investigate the structural evolution of the Ba₃Mo₍₁-ₓ₎WₓNbO₈.₅ solid solution across a temperature range.
• To correlate structural changes with ionic conductivity.

Main Methods:

• Synchrotron high-resolution powder diffraction was used to probe the structure.
• The study covered a temperature range of 100–900 K for various compositions (x = 0, 0.25, 0.5, 0.75, 1).

Main Results:

• At low temperatures (100–500 K), a chemical-dependent competition between 9R and palmierite structures was observed, with 9R favored as tungsten content increased.
• Above 500 K, structural parameters converged, and at 900 K, the entire solid solution adopted a palmierite-like structure.
• These crystallographic findings explain the temperature-dependent bulk ionic conductivity, linked to palmierite's tetrahedral units.

Conclusions:

• The Ba₃Mo₍₁-ₓ₎WₓNbO₈.₅ solid solution displays a temperature- and composition-dependent structural transition.
• The palmierite structure, favored at higher temperatures, plays a crucial role in the material's ionic conductivity.