Relaxor-PT single crystals: observations and developments

Relaxor-PT based ferroelectric single crystals Pb(Zn
_1/3
Nb
_2/3
)O
₃
-PbTiO
₃
(PZNT) and Pb(Mg
_1/3
Nb
_2/3
)O
₃
-PbTiO
₃
(PMNT) offer high performance with ultra-high electromechanical coupling factors k33s > 0.9 and piezoelectric coefficients d
₃₃
s > 1500 pC/N. However, the usage temperature range of these perovskite single crystals is limited by TRT-the rhombohedral to tetragonal phase transition temperature, which occurs at significantly lower temperatures than the Curie temperature T
_C
, a consequence of curved morphotropic phase boundaries (MPBs). Furthermore, these 〈001〉-oriented crystals exhibit low mechanical quality Q and coercive fields, restricting their usage in high-power applications. In this survey, recent developments on binary and ternary perovskite relaxor-PT crystal systems are reviewed with respect to their temperature usage range. General trends of dielectric and piezoelectric properties of relaxor-PT crystal systems are discussed in relation to their respective T
_C
/T
_RT
. In addition, two approaches have been implemented to improve mechanical Q, including acceptor dopants, analogous to hard polycrystalline ceramics, and anisotropic domain engineering, enabling lowloss crystals with high coupling for high-power applications.