Bismuth Aluminate BiAlO3: A New Lead-free High-TC Piezo-/ferroelectric

Ferroelectric materials have applications in non-volatile random access memory devices and micro electromechanical systems. For such applications, the materials must remain ferroelectric up to high temperatures. The best materials that currently exist for these applications are lead-containing compounds like Pb(Zr_1-xTi_x)O₃. Owing to the toxicity of lead, there is a demand for lead-free high-temperature ferroelectrics. Bismuth aluminate has been predicted to be one such material [1]. In this work, BiA1O₃ is synthesized using a high-pressure high-temperature technique at 6 GPa and 1000degC. The diffraction experiments show that BiAlO₃ crystallizes in a rhombohedral unit cell that is elongated along the c-axis (R3c; Z = 6; a = 5.37546(5) A and c = 13.3933(1) A). The characterization of the dielectric, ferroelectric, and piezoelectric properties of the ceramic BiAlO₃ demonstrate that it is indeed a lead-free ferroelectric with a Curie temperature Tc > 520degC, a piezoelectric coefficient d33 = 28 pC/N and a room-temperature remnant polarization P_r = 9.5 muC/cm². P_r increases with temperature, reaching 26.7 muC/cm² at 225degC. The dielectric, ferroelectric and piezoelectric properties of BiAlO₃ are comparable to those of BiFeO₃ (BFO) and SrBi₂Ta₂O₉ (SBT), making it a promising new high-Tc lead-free piezo-and ferroelectric for memory and transducer applications.