A double-well potential model is established to explain the dielectric anomaly of ferroelectrics. The dielectric constant consists of two parts. One part is independent of the long-range correlation, following 1/T law...A double-well potential model is established to explain the dielectric anomaly of ferroelectrics. The dielectric constant consists of two parts. One part is independent of the long-range correlation, following 1/T law. The other part originates from the long-range correlation, and can be described by the correlation length well. The deviation from Curie-Weiss law in a small size sample originates from the decrease of the long-range correlation.展开更多
Sr4Ca RTi3Nb7O30（R = Ce, Eu） tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4 Ca RTi3Nb7O30（R ...Sr4Ca RTi3Nb7O30（R = Ce, Eu） tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4 Ca RTi3Nb7O30（R = Ce, Eu） tetragonal tungsten bronzes are investigated. The Sr4 Ca Ce Ti3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr4 Ca Eu Ti3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca^2＋ and Eu^3＋ could lead to the uneven distribution of Ca^2＋ and Eu^3＋ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization–electric field（P–E） curves are evaluated at room temperature and both of them show hysteresis loops. Sr4 Ca Ce Ti3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density–electric field（J–E） curves are measured at room temperature with a largest leakage current density of ～ 10^-6A/cm^2, indicating that their leakage currents are rather low.展开更多
A novel inorganic-organic hybrid supramolecular compound,[（3-nitroanilinium^＋）（18-crown-6）][IO4]（CH3OH）（1）,was discovered as phase-transition materials displaying dielectric anomalous behaviors.The yellow blo...A novel inorganic-organic hybrid supramolecular compound,[（3-nitroanilinium^＋）（18-crown-6）][IO4]（CH3OH）（1）,was discovered as phase-transition materials displaying dielectric anomalous behaviors.The yellow block crystal formed by N-H…O hydrogen bonding that made contact through the cavity of 18-crown-6 was characterized by single-crystal X-ray diffraction,elemental analysis,infrared analysis,thermogravimetric analysis,differential scanning calorimetry,and potential-energy calculations.Differential scanning calorimetry measurements indicate that the compound experiences a reversible phase transition at around 220 K.Temperature-dependent dielectric measurements further confirm the phase transitions.Potential-energy calculations demonstrate that the phase transition occurs due to the molecular order-disorder rotation of CH3OH,whereas the space grouping of the crystal remains unchanged.展开更多
基金Project supported by the Climbing Program of Foundamental Research of China
文摘A double-well potential model is established to explain the dielectric anomaly of ferroelectrics. The dielectric constant consists of two parts. One part is independent of the long-range correlation, following 1/T law. The other part originates from the long-range correlation, and can be described by the correlation length well. The deviation from Curie-Weiss law in a small size sample originates from the decrease of the long-range correlation.
基金Project supported by the National Natural Science Foundation of China(Grant No.11174092)the Key Project of Henan Provincial Educational Committee,China(Grant No.14A140019)
文摘Sr4Ca RTi3Nb7O30（R = Ce, Eu） tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4 Ca RTi3Nb7O30（R = Ce, Eu） tetragonal tungsten bronzes are investigated. The Sr4 Ca Ce Ti3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr4 Ca Eu Ti3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca^2＋ and Eu^3＋ could lead to the uneven distribution of Ca^2＋ and Eu^3＋ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization–electric field（P–E） curves are evaluated at room temperature and both of them show hysteresis loops. Sr4 Ca Ce Ti3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density–electric field（J–E） curves are measured at room temperature with a largest leakage current density of ～ 10^-6A/cm^2, indicating that their leakage currents are rather low.
基金supported by National Natural Science Foundation of China (No. 21561030)Prophase-sustentation Fund of Xinjiang Agricultural University (Nos. XJAU201410 and XJAU201511)
文摘A novel inorganic-organic hybrid supramolecular compound,[（3-nitroanilinium^＋）（18-crown-6）][IO4]（CH3OH）（1）,was discovered as phase-transition materials displaying dielectric anomalous behaviors.The yellow block crystal formed by N-H…O hydrogen bonding that made contact through the cavity of 18-crown-6 was characterized by single-crystal X-ray diffraction,elemental analysis,infrared analysis,thermogravimetric analysis,differential scanning calorimetry,and potential-energy calculations.Differential scanning calorimetry measurements indicate that the compound experiences a reversible phase transition at around 220 K.Temperature-dependent dielectric measurements further confirm the phase transitions.Potential-energy calculations demonstrate that the phase transition occurs due to the molecular order-disorder rotation of CH3OH,whereas the space grouping of the crystal remains unchanged.
