Influence of Temperature-Driven Polymorphism and Disorder on Ionic Conductivity in Li

Area of Science:

• Solid-state chemistry
• Materials science
• Crystallography

Background:

• Ionic conductivity is vital for solid-state electrolytes.
• Understanding the relationship between crystal structure, defects, and conductivity is key for designing new materials.
• Lithium-ion conduction is a critical area of research for energy storage applications.

Purpose of the Study:

• To investigate the structural transitions and ionic conductivity of Li6Zn(P2O7)2.
• To elucidate the role of structural disorder and cation mixing in enhancing ionic conductivity.
• To explore the potential of Li6Zn(P2O7)2 as a solid-state electrolyte.

Main Methods:

• Crystallographic analysis of different polymorphs (α and ζ) of Li6Zn(P2O7)2.
• Temperature-dependent conductivity measurements.
• Bond valence energy landscape calculations to analyze ion diffusion pathways.

Main Results:

• Li6Zn(P2O7)2 exhibits multiple structural transitions with temperature, leading to orders-of-magnitude increases in ionic conductivity.
• The high-temperature ζ-polymorph shows significant Li/Zn cation disorder, unlike the ordered α-polymorph.
• Bond valence energy landscape calculations reveal a transition from 2D to 3D Li+ conduction pathways due to cation mixing.

Conclusions:

• Temperature-induced structural disorder, specifically Li/Zn cation mixing, is the primary driver for enhanced ionic conductivity in Li6Zn(P2O7)2.
• The 3D ion diffusion pathways in the ζ-polymorph make it a promising candidate for solid-state electrolyte applications.
• This study highlights the importance of controlling cation disorder in pyrophosphate materials for optimizing ionic conductivity.