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Xiang Ming Chen - One of the best experts on this subject based on the ideXlab platform.
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Ferroelectric Transition and Low‐Temperature Dielectric Relaxations in Filled Tungsten Bronzes
Journal of the American Ceramic Society, 2014Co-Authors: Xiao Li Zhu, Xiang Ming ChenAbstract:A comprehensive review on the latest development of the Ferroelectric Transition and low-temperature dielectric relaxations of filled tungsten bronze ceramics are presented together with some new issues. In the filled tungsten bronze ceramics M6−pRpTi2+pNb8−pO30 (p = 1, 2; M = Ba or Sr; R = rare earth or Bi), a Ferroelectric Transition is generally indicated together with up to three low-temperature dielectric relaxations. The Ferroelectric Transition is determined as 4/mmm → 4 mm, and the low-temperature dielectric relaxations are deeply concerned with the structure modulations due to the order/disorder of ions in A1 and A2 sites, their random cross occupancy, and the order/disorder of B-site ions. Both the Ferroelectric Transition and low-temperature dielectric relaxations are dominated by the composition and radius difference between A1- and A2-site ions, ∆r. The normal Ferroelectric Transition might be expected if the ratio of the biggest ion and second big ion is 2:1, otherwise the diffuse or relaxor Ferroelectric is expected. Meanwhile, the larger ∆r generally results in the normal Ferroelectric, and the smaller ∆r will lead to the diffuse or relaxor Ferroelectric. Moreover, the effects of A sites order/disorder and the random cross occupancy of A-site ions are primary, and the effects of B-site ordering/disordering are secondary. The right ratio of 2:1 for A2- and A1-site ions and the large ∆r should be the guidelines for designing the possible multiferroic tungsten bronzes.
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Ferroelectric Transition and Curie–Weiss Behavior in Some Filled Tungsten Bronze Ceramics
Chinese Physics Letters, 2014Co-Authors: Xiao Li Zhu, Xiang Ming ChenAbstract:Ferroelectric Transitions in filled tungsten bronze ceramics Sr4R2Ti4Nb6O30, Sr5RTi3Nb7O30 (R=La, Nb, Sm & Eu) and Ba4Nd2Ti4Nb6O30 are investigated with differential scanning calorimetry (DSC) and the Curie—Weiss law fitting to the dielectric constant. The magnitude of the Curie-Weiss constant C ~ 105 suggests displacement-type Ferroelectric Transition in the present compounds. The large ΔT difference between dielectric maximum temperature Tm and Curie—Weiss temperature T0) values indicate the difficult formation of Ferroelectric domains or polar nanoregions in the present compounds and also the characteristics of the first order Ferroelectric Transition. Three categories are suggested for the Ferroelectric Transition in the above tungsten bronzes. The Ferroelectric Transition exhibits large thermal hysteresis. According to the DSC results, gradual recovery of the endothermic peak occurs after aging at temperature below the Curie point, indicating the gradual stability of the Ferroelectric phase after cooling from the high-temperature para-electric phase. The relationship between the Curie—Weiss law fitting parameters and the nature of the Ferroelectric Transition is modified for the filled tungsten bronzes.
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Ferroelectric Transition and low-temperature dielectric relaxations in filled tungsten bronzes
Journal of the American Ceramic Society, 2014Co-Authors: Xiao Li Zhu, Kun Li, Xiang Ming ChenAbstract:A comprehensive review on the latest development of the ferro- electric Transition and low-temperature dielectric relaxations of filled tungsten bronze ceramics are presented together with some new issues. In the filled tungsten bronze ceramics M 6 – p R p Ti 2+p Nb 8 – p O 30 (p = 1, 2; M = Ba or Sr; R = rare earth or Bi), a Ferroelectric Transition is generally indicated together with up to three low-temperature dielectric relaxations. The Ferroelectric Transition is determined as 4/ mmm ? 4 mm, and the low-temperature dielectric relaxations are deeply concerned with the structure modulations due to the order/disorder of ions in A1 and A2 sites, their random cross occupancy, and the order/disorder of B-site ions. Both the fer- roelectric Transition and low-temperature dielectric relaxations are dominated by the composition and radius difference between A1- and A2-site ions, ∆ r . The normal Ferroelectric Transition might be expected if the ratio of the biggest ion and second big ion is 2:1, otherwise the diffuse or relaxor ferroelec- tric is expected. Meanwhile, the larger ∆r generally results in the normal Ferroelectric, and the smaller ∆r will lead to the dif- fuse or relaxor Ferroelectric. Moreover, the effects of A sites order/disorder and the random cross occupancy of A-site ions are primary, and the effects of B-site ordering/disordering are secondary. The right ratio of 2:1 for A2- and A1-site ions and the large ∆r should be the guidelines for designing the possible multiferroic tungsten bronzes
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Ferroelectric Transition of Sr5SmTi3Nb7O30 Tungsten Bronze Ceramics Investigated Using Differential Scanning Calorimetry and Raman Scattering
Journal of the American Ceramic Society, 2012Co-Authors: Xiao Li Zhu, Xiang Ming ChenAbstract:Ferroelectric Transition of Sr5SmTi3Nb7O30 tetragonal tungsten bronze ceramics was investigated using dielectric characterization, differential scanning calorimetry (DSC), and the in situ Raman scattering. The first-order Ferroelectric Transition was indicated around 200°C by the dielectric peak and the endothermic DSC peak on heating. The Ferroelectric Transition exhibited large thermal hysteresis and severe depression of the Curie–Weiss temperature (T0), where the Transition peak did not show up on cooling in both the permittivity and DSC curves. The thermal hysteresis was attributed to the complex nature of the tungsten bronze structure. According to the DSC results, gradual recovery of the endothermic peak occurred after aging at 20°C, indicating the gradual stability of the Ferroelectric phase after cooling from the high temperature paraelectric phase. Meanwhile, anomalies in the Raman spectra were also observed around 200°C, corresponding to the Ferroelectric Transition. Mechanism of the Ferroelectric Transition in Sr5SmTi3Nb7O30 ceramics was discussed according to the variation of the external and internal Raman modes with increasing temperature.
Xiao Li Zhu - One of the best experts on this subject based on the ideXlab platform.
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Ferroelectric Transition and Low‐Temperature Dielectric Relaxations in Filled Tungsten Bronzes
Journal of the American Ceramic Society, 2014Co-Authors: Xiao Li Zhu, Xiang Ming ChenAbstract:A comprehensive review on the latest development of the Ferroelectric Transition and low-temperature dielectric relaxations of filled tungsten bronze ceramics are presented together with some new issues. In the filled tungsten bronze ceramics M6−pRpTi2+pNb8−pO30 (p = 1, 2; M = Ba or Sr; R = rare earth or Bi), a Ferroelectric Transition is generally indicated together with up to three low-temperature dielectric relaxations. The Ferroelectric Transition is determined as 4/mmm → 4 mm, and the low-temperature dielectric relaxations are deeply concerned with the structure modulations due to the order/disorder of ions in A1 and A2 sites, their random cross occupancy, and the order/disorder of B-site ions. Both the Ferroelectric Transition and low-temperature dielectric relaxations are dominated by the composition and radius difference between A1- and A2-site ions, ∆r. The normal Ferroelectric Transition might be expected if the ratio of the biggest ion and second big ion is 2:1, otherwise the diffuse or relaxor Ferroelectric is expected. Meanwhile, the larger ∆r generally results in the normal Ferroelectric, and the smaller ∆r will lead to the diffuse or relaxor Ferroelectric. Moreover, the effects of A sites order/disorder and the random cross occupancy of A-site ions are primary, and the effects of B-site ordering/disordering are secondary. The right ratio of 2:1 for A2- and A1-site ions and the large ∆r should be the guidelines for designing the possible multiferroic tungsten bronzes.
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Ferroelectric Transition and Curie–Weiss Behavior in Some Filled Tungsten Bronze Ceramics
Chinese Physics Letters, 2014Co-Authors: Xiao Li Zhu, Xiang Ming ChenAbstract:Ferroelectric Transitions in filled tungsten bronze ceramics Sr4R2Ti4Nb6O30, Sr5RTi3Nb7O30 (R=La, Nb, Sm & Eu) and Ba4Nd2Ti4Nb6O30 are investigated with differential scanning calorimetry (DSC) and the Curie—Weiss law fitting to the dielectric constant. The magnitude of the Curie-Weiss constant C ~ 105 suggests displacement-type Ferroelectric Transition in the present compounds. The large ΔT difference between dielectric maximum temperature Tm and Curie—Weiss temperature T0) values indicate the difficult formation of Ferroelectric domains or polar nanoregions in the present compounds and also the characteristics of the first order Ferroelectric Transition. Three categories are suggested for the Ferroelectric Transition in the above tungsten bronzes. The Ferroelectric Transition exhibits large thermal hysteresis. According to the DSC results, gradual recovery of the endothermic peak occurs after aging at temperature below the Curie point, indicating the gradual stability of the Ferroelectric phase after cooling from the high-temperature para-electric phase. The relationship between the Curie—Weiss law fitting parameters and the nature of the Ferroelectric Transition is modified for the filled tungsten bronzes.
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Ferroelectric Transition and low-temperature dielectric relaxations in filled tungsten bronzes
Journal of the American Ceramic Society, 2014Co-Authors: Xiao Li Zhu, Kun Li, Xiang Ming ChenAbstract:A comprehensive review on the latest development of the ferro- electric Transition and low-temperature dielectric relaxations of filled tungsten bronze ceramics are presented together with some new issues. In the filled tungsten bronze ceramics M 6 – p R p Ti 2+p Nb 8 – p O 30 (p = 1, 2; M = Ba or Sr; R = rare earth or Bi), a Ferroelectric Transition is generally indicated together with up to three low-temperature dielectric relaxations. The Ferroelectric Transition is determined as 4/ mmm ? 4 mm, and the low-temperature dielectric relaxations are deeply concerned with the structure modulations due to the order/disorder of ions in A1 and A2 sites, their random cross occupancy, and the order/disorder of B-site ions. Both the fer- roelectric Transition and low-temperature dielectric relaxations are dominated by the composition and radius difference between A1- and A2-site ions, ∆ r . The normal Ferroelectric Transition might be expected if the ratio of the biggest ion and second big ion is 2:1, otherwise the diffuse or relaxor ferroelec- tric is expected. Meanwhile, the larger ∆r generally results in the normal Ferroelectric, and the smaller ∆r will lead to the dif- fuse or relaxor Ferroelectric. Moreover, the effects of A sites order/disorder and the random cross occupancy of A-site ions are primary, and the effects of B-site ordering/disordering are secondary. The right ratio of 2:1 for A2- and A1-site ions and the large ∆r should be the guidelines for designing the possible multiferroic tungsten bronzes
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Ferroelectric Transition of Sr5SmTi3Nb7O30 Tungsten Bronze Ceramics Investigated Using Differential Scanning Calorimetry and Raman Scattering
Journal of the American Ceramic Society, 2012Co-Authors: Xiao Li Zhu, Xiang Ming ChenAbstract:Ferroelectric Transition of Sr5SmTi3Nb7O30 tetragonal tungsten bronze ceramics was investigated using dielectric characterization, differential scanning calorimetry (DSC), and the in situ Raman scattering. The first-order Ferroelectric Transition was indicated around 200°C by the dielectric peak and the endothermic DSC peak on heating. The Ferroelectric Transition exhibited large thermal hysteresis and severe depression of the Curie–Weiss temperature (T0), where the Transition peak did not show up on cooling in both the permittivity and DSC curves. The thermal hysteresis was attributed to the complex nature of the tungsten bronze structure. According to the DSC results, gradual recovery of the endothermic peak occurred after aging at 20°C, indicating the gradual stability of the Ferroelectric phase after cooling from the high temperature paraelectric phase. Meanwhile, anomalies in the Raman spectra were also observed around 200°C, corresponding to the Ferroelectric Transition. Mechanism of the Ferroelectric Transition in Sr5SmTi3Nb7O30 ceramics was discussed according to the variation of the external and internal Raman modes with increasing temperature.
X. M. Chen - One of the best experts on this subject based on the ideXlab platform.
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Thermal hysteresis of Ferroelectric Transition in Sr4R2Ti4Nb6O30 (R=Sm and Eu) tetragonal tungsten bronzes
Applied Physics Letters, 2010Co-Authors: X. L. Zhu, X. M. ChenAbstract:Sr4R2Ti4Nb6O30 (R=Sm and Eu) tungsten bronze ceramics were prepared, and the dielectric properties and Ferroelectric Transition were investigated together with the crystal structure. A Ferroelectric Transition peak and a low temperature dielectric relaxation were observed from the curve of permittivity versus temperature during heating process for both ceramics. The Ferroelectric Transition indicated large thermal hysteresis during the heating and cooling cycles for both ceramics, where the Ferroelectric Transition peak disappeared during the cooling process, and the low temperature dielectric relaxation was obviously enhanced. Moreover, extremely large depression of the Curie–Weiss temperature (T0) was observed in the present ceramics. These abnormal features were associated with the complex tetragonal tungsten bronze structure with two Ferroelectrically active cations over two sets of sites and weak superstructure change from incommensurate to commensurate on cooling. The low temperature dielectric rela...
B. Meurer - One of the best experts on this subject based on the ideXlab platform.
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Ferroelectric Transition under hydrostatic pressure in poly(vinylidene fluoride-trifluoroethylene) copolymers
Polymer, 1994Co-Authors: E. Bellet-amalric, J.f. Legrand, M. Stock-schweyer, B. MeurerAbstract:A clear Ferroelectric Transition of first-order type is observed in poly(vinylidene fluoride-trifluoroethylene) (P(VDFTrFE)) random copolymers with TrFE contents higher than 20% and lower than 40%. This structural phase Transition which takes place in the crystalline regions of the polymeric material has been analysed using neutron diffraction under hydrostatic pressure for three copolymer compositions: 8020, 7030 and 6040. The P-T phase diagrams have been determined in the ranges 0.1–300 MPa, 300–500 K both upon heating and upon cooling, and several thermodynamic parameters have been evaluated for the different crystalline phases: compressibility and thermal expansion coefficients, enthalpies of Transition, etc. For the middle composition (7030) the Ferroelectric Transition temperature TC is well separated from the melting temperature Tm of the paraelectric phase and both Transition temperatures increase with increasing pressure: dTCdP = 0.38 K MPa−1 and dTmdP = 0.25 K MPa−1. For the 8020 composition the Curie temperature TC is closer to the melting temperature Tm, and under increasing pressure the two Transition lines are expected to merge at a triple point (P∗ ≈ 500 MPa, T∗ ≈ 560 K), above which a single line corresponds to the melting of the Ferroelectric phase. For the 6040 composition a new ‘low temperature disordered’ phase appears and coexists with the Ferroelectric phase but with a volume fraction which depends on temperature and thermal history.
Alexander K. Tagantsev - One of the best experts on this subject based on the ideXlab platform.
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The Spontaneous Relaxor-Ferroelectric Transition of Pb(Sc0.5ta0.5)O3
Journal of Applied Physics, 1993Co-Authors: F. Chu, N. Setter, Alexander K. TagantsevAbstract:A zero-field spontaneous relaxor-Ferroelectric Transition is reported in Pb(Sc0.5Ta0.5)O3 (PST). This behavior is different from that of other relaxors, where such Transitions occur only under the field. A highly disordered PST that has the wide relaxation spectrum typical of relaxors is shown to transform spontaneously into a macroscopic Ferroelectric state. Introduction of defects (lead vacancies) into the material impedes the Transition resulting in the usual relaxor behavior. Dielectric properties of PST, with and without defects, are analyzed. For the interpretation of the observed properties, a model invoking an additional nonpolar phase is proposed. This model does not imply a freezing in the system. At the low-frequency limit, it is possible to account for the Vogel-Fulcher (VF) law for the temperature of the maximum of the dielectric constant, using only the commonly accepted assumption of an exponentially wide relaxation time spectrum that shrinks on heating. The presented approach interprets the observed proximity between the Ferroelectric phase Transition temperature and that of the freezing temperature obtained from the VF relation.