Pressure-dependent diffusion coefficients and haven ratios in cation-conducting glasses

Area of Science:

• Materials Science
• Solid State Physics
• Chemical Physics

Background:

• Hydrostatic pressure influences ion transport in glasses, offering insights into atomistic mechanisms.
• Understanding ionic motion is crucial for developing advanced glass materials.

Purpose of the Study:

• To investigate the influence of hydrostatic pressure on tracer diffusion and ionic conduction in sodium and rubidium borate glasses.
• To elucidate the atomistic mechanisms governing ionic motion under pressure.

Main Methods:

• Studied tracer diffusion of 22Na and 86Rb in borate glasses under varying hydrostatic pressures.
• Analyzed pressure dependence of ionic conductivity.
• Applied linear response theory to model transport phenomena.

Main Results:

• Activation volumes for tracer diffusion (DeltaVD) are significantly larger than for charge diffusion (DeltaVsigma) for both Na and Rb.
• Haven ratios decrease with increasing pressure, particularly in rubidium borate glass.
• Experimental findings are consistent with a model of collective ion movement.

Conclusions:

• The difference in activation volumes implies collective ion motion, described as chain- or caterpillar-like.
• Vacant sites are proposed as charge carriers, while ions are matter carriers.
• Pressure-induced changes in conduction pathway topology explain the decreasing Haven ratio.