Properties and crystal orientation behavior under high-magnetic-field of Eu-substituted Sr₂NaNb₅O₁₅ lead-free piezoelectric ceramics

The properties of Eu-substituted Sr₂NaNb₅O₁₅ ceramics were investigated in detail, along with the crystal orientation behavior and characteristics of ceramics fabricated under a high magnetic field. Eu was substituted at Sr, Na sites from 0 to 0.06 mol, introducing vacancies, promoting grain growth, and enhancing relaxor behavior. The Curie temperature decreased, and relaxor features appeared at Eu = 0.06. P-E loops showed reduced remanent polarization, which led to decreased piezoelectric properties. These degradations are attributed to reduced ferroelectricity and structural disorder caused by Eu substitution. Crystal orientation changed from the a, b-axis to the c-axis with increasing Eu content, with c-axis orientation factors of 0.7 (Eu = 0.04) and 0.92 (Eu = 0.06). At Eu = 0.06, the relaxor behavior disappeared, likely due to the suppression of disorder. The piezoelectric constant increased by factors of 2.9 and 3.4 at Eu = 0.04 and 0.06, respectively, compared with randomly oriented disks.