Field-induced polarization rotation in (001)-cutPb(Mg1/3Nb2/3

Abstract

Polarization rotation of field-induced phase transformations was observed by means of a polarizing microscope on a ͑001͒-cut single crystal Pb(Mg 1/3 Nb 2/3 ) 0.76 Ti 0.24 O 3 ͑PMNT24%͒ at room temperature with an electric field applied along the ͓001͔ direction. A hysteresis loop was also measured for comparison. As the electric field increases, polarizations of rhombohedral R domains rotate toward the ͓001͔ tetragonal T 001 phase through M A -type monoclinic distortions, i.e., R→M A →T 001 . The crystal cannot entirely reach the T 001 phase as the field approaches 44 kV/cm. In addition, spotlike domains that perhaps correspond to M B -type monoclinic or triclinic phases were also observed. This field-induced phase transformation is strongly irreversible.A morphotropic phase boundary ͑MPB͒ between rhombohedral (R) and tetragonal (T) phases originally was proposed in relaxor-based ferroelectric ͑FE͒ crystals Pb(Mg 1/3 Nb 2/3 ) 1Ϫx Ti x O 3 (PMNTx) and Pb(Zn 1/3 Nb 2/3 ) 1Ϫx Ti x O 3 (PZNTx) for 0.28рxр0.36 and x Ͻ0.15, respectively. 1,2 However, monoclinic (M ) and orthorhombic (O) phases have been reported in both PMNT and PZNT systems, which depend strongly on Ti concentration, temperature range, strength of the external electric (E) field, and crystallographic orientation. 3-13 Compositional heterogeneities ͑or spatial phase segregation͒ are also commonly observed in these materials, especially for compounds near the MPB.An almost certainly monoclinic phase was induced by the E field applied along ͗001͘ in a PZNT8% single crystal, as observed with in situ x-ray diffraction. 4 A metastable orthorhombic FE phase ͑between R and T phases͒ was proposed in PZNT8% crystals oriented along ͗001͘, ͗110͘, and ͗111͘ from E-field-dependent polarization results. 5 By synchrotron x-ray diffraction with the E field applied along the ͓001͔ direction, various polarization rotation paths of R-M A -M C -T and R-M A -T were proposed in PZNT8% and PZNT4.5% crystals, respectively. 6 An O phase was observed in PZNTx for xϭ8%, xϭ9%, and 10% after a prior E-field application along ͓001͔. 7 With a prior E field poling along a ͑011͒-cut PMNT33% crystal, an extra O phase between R and T phases was claimed from the dielectric result. 8 From polarization results, an E-field-induced transformation from ͗111͘ R to ͗110͘ O phase through M B -type M distortion, i.e., R-M B -O, was proposed on a ͑110͒-cut PMNT30% crystal. 9 Based on synchrotron results, an M A -type M phase was observed in a ͑001͒-cut PMNT35% single crystal previously poled under an E field of 43 kV/cm. 10 However, unpoled and weakly poled PMNT35% samples exhibit an average R symmetry. 10 Irreversible field-induced phase transformations through M A -type monoclinic distortions, i.e., R→M A →T→M A →R 111 were observed in a ͑111͒-cut PMNT33% single crystal. 11 An M C -type M phase has so far been reported in PMNT only for powder and ceramic samples. [12][13][14] It is important to note that the effect of M A -type polarization rotation will be largely cancelled in randomly oriente...

Picturing the elephant: Giant piezoelectric activity and the monoclinic phases of relaxor-ferroelectric single crystals

“…Since 1997, much work has also gone into investigating the various electricfield induced phase transitions that occur from the unpoled or pre-poled state when electric fields are applied to crystals of PMN-xPT or PZN-xPT along a non-polar [001] C , [101] C or [111] C type direction. As a result, various phase transitions and "polarization rotation paths" have been evidenced by bulk strain-field measurements [151][152][153][154], and in situ diffraction [112,[130][131][132] and optical microscopy [110,111,151,[155][156][157]. Moreover, they all share certain characteristics.…”

“…In terms of a "polarization rotation path," the abrupt change in strain corresponds to a "jump" of the polar vector either within or between monoclinic planes [154]. Physically, it corresponds to the nucleation and growth of the new phase within the matrix of the old [151,155], as might be expected of a firstorder phase transition [154]. Furthermore, the induced phase can generally be predicted by simple thermodynamic arguments [154].…”

Hysteretic phase transition sequence in0.67Pb(Mg1/3Nb2/3

“…Interestingly, two different types of M phases have been reported in polycrystalline ceramics and single crystal PMN-PT, i.e., M A with the space group of Cm and M C with the space group of Pm [6,12,15]. Some researchers even reported the coexistence of R, T and M phases in the MPB composition, which makes the domain structure more complicated, but some interesting properties may be produced doe to such phase coexistence [11].…”

Characteristics of electric-field-induced polarization rotation in 〈001〉-poled Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals close to the morphotropic phase boundary

“…With reasonably low PbTiO 3 content, away from the MPB region (approximately x 26% for PMN-xPT), polarization of the rhombohedral R phase seems to rotate through the M A monoclinic phase to the tetragonal T phase with the application of a high enough h001i-directed electric field. 10,20 In a narrow composition range, close to the rhombohedral side of the morphotropic phase boundary region, two different monoclinic phases of M A and M C type have been observed along the rotation pathway. 10,11,17,21 With an even higher PT concentration closer to the tetragonal side of the MPB region, only a monoclinic M C phase is found to be present in the rotation path.…”

“…5,6 Previous structural analysis shows that an electric field applied in the h001i direction transforms a PMN-PT crystal from the rhombohedral phase to the tetragonal phase via different monoclinic M A and/or M C bridging phases, depending on the composition and temperature, quite similarly to other high-performance PZN-PT piezoelectric crystals. [10][11][12]17,[20][21][22] To date, three distinct composition regions with different electric-field-induced phase transition behavior have been distinguished in the MPB region of PMN-xPT and PZN-xPT. With reasonably low PbTiO 3 content, away from the MPB region (approximately x 26% for PMN-xPT), polarization of the rhombohedral R phase seems to rotate through the M A monoclinic phase to the tetragonal T phase with the application of a high enough h001i-directed electric field.…”