Abstract
Fe-substituted PMN-32PT relaxor ferroelectric crystals were grown by a high-temperature flux method. The effects of charged defects on the dielectric relaxor and conductivity mechanism were discussed in detail. The Fe-substituted PMN-32PT crystal showed a high coercive field (Ec = 765 V/mm), due to domain wall-pinning, induced by charged defect dipoles. Three dielectric anomaly peaks were observed, and the two dielectric relaxation peaks at low temperature were associated with the diffusion phase transition, while the high temperature one resulted from the short-range hopping of oxygen vacancies. At temperature T ≤ 150 °C, the dominating conduction carriers were electrons coming from the first ionization of oxygen vacancies. For the temperature range from 200 to 500 °C, the conductivity was composed of the bulk and interface between sample and electrode, and the oxygen vacancies were suggested to be the conduction mechanism. Above 550 °C, the trapped electrons from the Ti3+ center were excited and played a major role in electrical conduction. Our results are helpful for better understanding the relationship between dielectric relaxation and the conduction mechanism.
Highlights
Relaxor-PbTiO3 ferroelectric single crystals with morphotropic phase boundary (MPB), such as (1−x)Pb(Mg1/3 Nb2/3 )O3 -xPbTiO3 (PMN-xPT) and (1−x)Pb(Zn1/3 Nb2/3 )O3 -xPbTiO3 (PZN-xPT), have attracted much attention due to their superior electric properties [1,2,3]
1.7 mol% Fe-substituted PMN-32PT ferroelectric single crystals were grown by the flux method
It can be seen that the relaxation activation energy Erelax is 1.2 eV, indicating that the high-temperature dielectric relaxation peak III is related to the short-range hopping of oxygen vacancies
Summary
Relaxor-PbTiO3 ferroelectric single crystals with morphotropic phase boundary (MPB), such as (1−x)Pb(Mg1/3 Nb2/3 )O3 -xPbTiO3 (PMN-xPT) and (1−x)Pb(Zn1/3 Nb2/3 )O3 -xPbTiO3 (PZN-xPT), have attracted much attention due to their superior electric properties (piezoelectric coefficient d33 ≈ 2500 pC/N, permittivity ε ≈ 5000–7000, and strain S ≈ 1.7%) [1,2,3]. Li et al [5] found the contribution of polar nanoregions to the room-temperature dielectric and piezoelectric properties was up to 80% in relaxor-PT crystals. By introducing the rare-earth element, samarium, to change the local structure, the piezoelectric coefficient d33 of PMN-29PT ceramics was significantly increased from 300 to 1500 pC/N [7]. This discovery provided a new insight into improving material properties. Compared with the ferroelectric ceramics, the effects of charged defects on the dielectric relaxation of PMN-xPT ferroelectric single crystals, especially in the conductivity mechanism, are seldom reported [19,20,21]. Our research will be helpful for better understanding the relationship between charged defects and electrical properties in PMN-32PT ferroelectric single crystals
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