Effects of High-Energy Ball Milling and Sintering Time on the Electric-Field-Induced Strain Properties of Lead-Free BNT-Based Ceramic Composites

Abstract

This study investigated crystal structures, microstructures, and electric-field-induced strain (EFIS) properties of Bibased lead-free ferroelectric/relaxor composites. Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) as a ferroelectric material and 0.78Bi1/2(Na0.78K0.22)1/2TiO3-0.02LaFeO3 (BNKT2LF) as a relaxor material were synthesized using a conventional solid-state reaction method, and the resulting BNKT2LF powders were subjected to high-energy ball milling (HEBM) after calcination. As a result, HEBM proved a larger average grain size of sintered samples compared to conventional ball milling (CBM). In addition, the increased sintering time led to grain growth. Furthermore, HEBM treatment and sintering time demonstrated a significant effect on EFIS of BNKT/BNKT2LF composites. At 6 kV/mm, 0.35% of the maximum strain (Smax) was observed in the HEBM sample sintered for 12 h. The unipolar strain curves of CBM samples were almost linear, indicating almost no phase transitions, while HEBM samples displayed phase transitions at 5~6 kV/mm for all sintering time levels, showing the highest Smax/Emax value of 700 pm/V. These results indicated that HEBM treatment with a long sintering time might significantly enhance the electromechanical strain properties of BNT-based ceramics.