Effect of Dopant on Piezoelectric Properties of Lead-Free BiFeO3-BaTiO3 Film

To realize high-performance lead-free piezoelectric materials, we have selected BiFeO3 as the rhomboheral phase material and BaTiO3 as the tetragonal phase material, following the MPB mechanism of PZT. To further improve the piezoelectric properties of BiFeO3-BaTiO3 (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 Sr2+ (BFBT-SrTiO3, abbreviated as BFBT-ST) and Nb5+ (abbreviated as BFBT-Nb) substitutions. BFBT-ST and BFBT-Nb films were epitaxially grown by pulsed laser deposition on an epitaxial SrRuO3/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 Sr2+ and Nb5+ substitutions improve the piezoelectric properties of BFBT. (C) 2011 The Japan Society of Applied Physics