Tuning optical absorption in perovskite (K,Na)NbO₃ ferroelectrics

Area of Science:

• Materials Science
• Solid State Physics
• Ferroelectricity

Background:

• Tailoring electronic band structure and optical absorption in perovskite oxides is crucial for electronic and optoelectronic applications.
• Cationic substitution offers a pathway to modify material properties.

Purpose of the Study:

• To investigate the effect of weak (Ba,Ni)-doping on optical bandgaps in (K,Na)NbO3 ferroelectric films and ceramics.
• To explore the origins of sub-gap optical absorption in these materials.

Main Methods:

• Optical absorption measurements across a broad spectral range (0.7-8.8 eV).
• Analysis of polycrystalline and epitaxial films, as well as ceramics, with varying doping levels and oxygen deficiencies.
• Comparison of optical properties across different material forms and conditions.

Main Results:

• 1-2 at% cationic substitutions or up to 10 at% oxygen vacancies did not significantly affect the direct (~4.5 eV) and indirect (~3.9 eV) bandgaps.
• Substantial sub-gap optical absorption was observed in doped epitaxial films and ceramics.
• This sub-gap absorption was attributed to structural band tailing and lattice strain inhomogeneities.

Conclusions:

• Weak (Ba,Ni)-doping does not effectively reduce the bandgap of (K,Na)NbO3.
• Structurally induced sub-gap optical absorption, influenced by lattice strain, is a significant phenomenon in perovskite ferroelectrics.
• This finding has implications for understanding and utilizing optical properties in related ferroelectric ceramics and thin films.