Large Piezoelectric Response in Hybrid Rare-Earth Double Perovskite Relaxor Ferroelectrics

Piezoelectric
materials are technologically important, and the
most used are perovskite ferroelectrics. In recent years, more and
more emerging areas have put forward new requirements for piezoelectric
materials, such as light weight, low acoustic impedance, good flexibility,
and biocompatibility. In this context, hybrid organic–inorganic
perovskite ferroelectrics have emerged as promising supplements, because
they combine attractive features of inorganic and organic materials.
Among them, hybrid double-metal perovskites have recently been found
to exhibit excellent ferroelectricity. However, their potential as
piezoelectric materials has not been exploited. Here, we describe
large piezoelectric response in hybrid rare-earth double perovskite
relaxor ferroelectrics (RM3HQ)2­RbLa­(NO3)6 and (RM3HQ)2­NH4La­(NO3)6 (RM3HQ = R-N-methyl-3-hydroxyl­quinuclidinium). They are simultaneously
ferroelectric and ferroelastic crystals, with the R3 ferroelectric phase and P213 paraelectric
phase. We found that ferroelectric polar microdomains and paraelectric
nonpolar regions coexist in a wide temperature range through variable-temperature
piezoresponse force microscopy images. The two-phase coexistence reveals
low energy barriers of transitions between the two phases and between
the polar microdomains with different polarization directions. These
lead to the easy polarization rotation of the polar microdomains upon
applying a stress and, accordingly, the large piezoelectric response
up to 106 pC N–1 for (RM3HQ)2­RbLa­(NO3)6. This finding represents a significant step
toward novel applications of piezoelectric materials based on lead-free
hybrid perovskites.