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-x
Ti
_x
)O
₃
. 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, BiA1O
₃
is synthesized using a high-pressure high-temperature technique at 6 GPa and 1000degC. The diffraction experiments show that BiAlO
₃
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 BiAlO
₃
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/cm
²
. P
_r
increases with temperature, reaching 26.7 muC/cm
²
at 225degC. The dielectric, ferroelectric and piezoelectric properties of BiAlO
₃
are comparable to those of BiFeO
₃
(BFO) and SrBi
₂
Ta
₂
O
₉
(SBT), making it a promising new high-Tc lead-free piezo-and ferroelectric for memory and transducer applications.