The Growth and Properties of Relaxor‐Based Ferroelectric Single Crystals

Abstract

Much attention is drawn to the fundamental research and the applications of the relaxor‐based ferroelectrics for the next generation of piezoelectric devices. Mass production of Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMNT) and ternary xPb(In1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)O3–zPbTiO3 (PIMNT) single crystals with a Bridgman method was reported. The piezoelectric, pyroelectric, and electric–optical performances of PMNT single crystals are much more excellent than traditional ceramics with the composition near morphotropic phase boundaries. Compared with PMNT crystal, PIMNT crystals can be used in a more broad range of device applications due to their high Curie temperature Tc and large coercive fields Ec. A relaxor‐based Na0.5Bi0.5TiO3–xBaTiO3 (NBBT) crystal grown by the top seeded solution growth method was also investigated to find a lead‐free material with better piezoelectric performance. The properties of these relaxor‐based single crystals were summarized. The mechanism of the enhanced piezoelectric response is discussed, based on the phase transitions induced by the variations of the temperature, pressure, composition, and electric field.

Mechanical Confinement: An Effective Way of Tuning Properties of Piezoelectric Crystals

“…[1][2][3][4][5][6][7][8][9][10] Due to their ultrahigh piezoelectric properties, these single crystals are of great interest for many different electromechanical device applications. [3,10] The piezoelectric properties of these crystals vary markedly with the chemical composition in the vicinity of the morphotropic phase boundary (MPB), which separates a rhombohedral perovskite structure at low PT-content from a tetragonal perovskite at high PT-content.…”

“…[3,10] The piezoelectric properties of these crystals vary markedly with the chemical composition in the vicinity of the morphotropic phase boundary (MPB), which separates a rhombohedral perovskite structure at low PT-content from a tetragonal perovskite at high PT-content. [7][8][9] Detailed structural analysis on the PMN-PT system reveals that the MPB spans from 30 to 38 mol.% of PT within which a monoclinic (MC) phase coexists with the rhombohedral (30~32 mol.%) or the tetragonal (32~38 mol.%) phase. [9,11] The most remarkable properties are observed when the electric field is applied in the <001>-direction of a rhombohedral crystal.…”

“…[2] This has been attributed to the rotation of the polarization vector from the pseudocubic <111>-direction to the <001>-direction, corresponding to an electric field-induced phase transition from the rhombohedral to the tetragonal via the intermediate monoclinic phase. [2,[7][8][9] Despite the excellent piezoelectric properties of these relaxor-based ferroelectric crystals, their widespread integration into engineering devices has been limited by their low Curie temperatures (Tc) and low coercive fields (Ec). [2,3,9] Typical values of Ec for PMN-PT and PZN-PT single crystals with MPB compositions are 0.2~0.3 kV/mm, [9] making them unsuitable for high-field applications.…”

Промежуточные фазы в [111]- и [001]-ориентированных монокристаллах PbMg-=SUB=-1/3-=/SUB=-Nb-=SUB=-2/3-=/SUB=-O-=SUB=-3-=/SUB=--29PbTiO-=SUB=-3-=/SUB=-

“…В этих монокри-сталлических твердых растворах с составами вблизи морфотропной фазовой границы (МФГ) наблюдаются ультравысокие значения пьезоэлектрических коэффици-ентов (1500−2500 pC/N) и коэффициентов электромеха-нической связи (> 0.9) [4][5][6]. МФГ в системе PMN−xPT (27 < x < 35%) разделяет две сегнетоэлектрические фазы: ромбоэдрическую (R), в которой спонтанная поля-ризация ориентирована вдоль направления [111], и тет-рагональную (T ) с направлением спонтанной поляриза-ции вдоль [001].…”

Achieving single domain relaxor-PT crystals by high temperature poling

“…[1][2][3][4][5][6] Over the last decade, extensive studies have been focused on the piezoelectric response of domain engineered crystals, especially for [001] poled rhombohedral relaxor-PT crystals, with longitudinal piezoelectric coefficient d 33 and electromechanical coupling factor k 33 being on the order of >1500 pC N −1 and >0.9, respectively. Ferroelectric phase instability is thought to be responsible for the high piezoelectric activity in relaxor-PT crystals, 7,8 which can be induced by the phase transition points (for example, morphotropic phase boundary and polymorphic phase transition) and relaxor component.…”