Effect of Dopant on Piezoelectric Properties of Lead-Free BiFeO₃–BaTiO₃Film

Abstract

To realize high-performance lead-free piezoelectric materials, we have selected BiFeO 3 as the rhomboheral phase material and BaTiO 3 as the tetragonal phase material, following the MPB mechanism of PZT. To further improve the piezoelectric properties of BiFeO 3 –BaTiO 3 (BFBT) thin films, we investigated the effect of dopant on the piezoelectric properties of BFBT. Considering both Shanon effective ionic radii and valence number, we have selected Sr 2+ (BFBT–SrTiO 3 , abbreviated as BFBT-ST) and Nb 5+ (abbreviated as BFBT-Nb) substitutions. BFBT-ST and BFBT-Nb films were epitaxially grown by pulsed laser deposition on an epitaxial SrRuO 3 /MgO/Si(100) substrate. The piezoelectric constant d 33AFM is estimated from the slope of the maximum displacement and the maximum voltage strength by atomic force microscopy. Compared with 0.8BF0.2BT films with d 33AFM = 65 pm/V, the 0.8BF0.2BT–Nb2.5% films achieved d 33AFM = 78 pm/V. The displacement curve of 0.8BF0.2BT–Nb2.5% became soft with the occurrence of a hysteresis shape, compared with that of 0.8BF0.2BT. Moreover, the d 33AFM of 0.77BF0.13BT–0.1ST (BF/BT ratio= 0.85/0.15) was 83 pm/V, compared with the d 33AFM (58 pm/V) of 0.85BF0.15BT. According to these results, we confirmed that the Sr 2+ and Nb 5+ substitutions improve the piezoelectric properties of BFBT.