Establishing the Domain Structure of (K0.5Na0.5)NbO3 (KNN) Single Crystals by Piezoforce-Response Microscopy

Abstract

Piezoforce response microscopy was used for the first time to characterize the domain structure of < 001 >-oriented potassium sodium niobate (KNN) single crystals revealing a long range ordered domain pattern of parallel 180 degrees domains with zig-zag 90 degrees domains. The grown KNN crystals have a high dielectric permittivity (29,100) at the tetragonal-to-cubic phase transition temperature, remnant polarization (19.4 mu C/cm(2)), and piezoelectric coefficient (160 pC/N) when compared with standard KNN ceramics. It is argued that the absence of a long range order with this specific domain pattern in standard KNN ceramics, is a fingerprint for the domain structure of KNN single crystals, and accounts for the improved properties of the single crystals. These results have broad implications for the expanded use of KNN materials, by demonstrating the relation between the domain patterns and dielectric and ferroelectric response of single crystals and ceramics and by indicating ways of achieving maximised properties in KNN materials.