The influence of superstoichiometric additives (1-2 wt.% of MnO2 and Li2CO3) on the properties of 0.7BiFeO3–0.3BaTiO3 (BFBT) ceramics is studied. It is shown that both additives cause a rhombohedral-to-pseudocubic structural phase transition; the stabilization is achieved at 2% MnO2 and already at 1% Li2CO3. The Mn-containing samples demonstrate smaller grain sizes (down to ~3 µm) and higher densities, whereas Li-doped samples exhibit larger grain sizes (up to 7-9 µm) and the presence of liquid-phase layers. All the modified materials exhibit a relaxor-type phase transition. The maximum diffuseness parameter (γ = 1.97) is demonstrated by the sample containing 2% MnO2. The piezoelectric modulus increases up to d33 ≈ 130 pC/N and decreases down to 20-40 pC/N upon MnO2 and Li2CO3 doping, respectively. The most promising material is the BFBT + 2% MnO2 composition characterized by a stable pseudocubic structure, low conductivity, and high piezoresponse.
Zabolotnyi et al. (Sun,) studied this question.