Anomalous Conductivity in the Rutile Structure Driven by Local Disorder

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• Rutile-type materials often exhibit shear softness under pressure, linked to Raman-active librational motion.
• Understanding pressure-induced electronic property changes in these materials is crucial for novel applications.

Purpose of the Study:

• To investigate the correlation between oxygen sublattice disorder and electrical resistance in tin dioxide (SnO2) under pressure.
• To elucidate the atomistic mechanism behind the observed anomalous decrease in electrical resistance.

Main Methods:

• Direct studies of anion positions in SnO2 using extended X-ray absorption fine structure (EXAFS) spectroscopy.
• Measurements of electronic properties under varying pressure conditions (5-10 GPa).
• Ab initio calculations to evaluate hypotheses regarding the underlying physical mechanism.

Main Results:

• A direct correlation was found between oxygen sublattice disorder and a significant decrease (up to 4 orders of magnitude) in electrical resistance in SnO2 between 5 and 10 GPa.
• The most probable mechanism identified is the displacement of single anions, driven by pressure-induced softening of the librational mode.

Conclusions:

• The study proposes that pressure-induced anion displacement and associated conductivity changes are likely prevalent in materials undergoing a rutile to CaCl2 phase transition.
• It suggests that enhancing specific defects in rutile-type materials could facilitate conductivity at ambient pressure.