EXAFS study of phase transitions in KIO3.

Area of Science:

• Solid State Chemistry
• Materials Science
• Condensed Matter Physics

Background:

• Potassium iodate (KIO3) exhibits successive phase transitions, necessitating detailed structural analysis.
• Understanding local atomic environments is crucial for elucidating phase transition mechanisms in crystalline solids.

Purpose of the Study:

• To investigate local structural changes in KIO3 during successive phase transitions.
• To clarify the nature of bonding between iodine and oxygen atoms.
• To identify the origin of anomalous behavior observed around 50 K.

Main Methods:

• Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy at the iodine K-edge.
• Analysis of pair-distribution functions and Debye-Waller factors.
• Temperature-dependent measurements to probe structural evolution.

Main Results:

• Distinguished two types of oxygen atoms within the IO3- octahedron based on their pair-distribution functions.
• Observed temperature-independent behavior for three oxygen atoms (covalent-like bonding) and temperature-dependent behavior for the other three (ionic-like bonding).
• Identified anomalous behavior in the Debye-Waller factor around 50 K, linked to the orientational glass transition.

Conclusions:

• The results confirm the existence of IO3- molecular units within a pseudo-perovskite-type structure in KIO3.
• The temperature-dependent behavior of oxygen atoms suggests a mixed covalent-ionic character in the local structure.
• The observed anomaly at 50 K is strongly associated with an orientational glass transition phenomenon.