The structure evolution and origin of ultrahigh dielectric properties have been investigated in the low temperature range from 300 K to 5 K for [001]-oriented 0.68 Pb(Mg_(1/3)Nb_(2/3))O_3–0.33PbTiO_3(PMN–33 PT) crys...The structure evolution and origin of ultrahigh dielectric properties have been investigated in the low temperature range from 300 K to 5 K for [001]-oriented 0.68 Pb(Mg_(1/3)Nb_(2/3))O_3–0.33PbTiO_3(PMN–33 PT) crystal. The experimental results reveal that a short-range ordered monoclinic MAis the dominant phase at ambient temperature. As the temperature drops below 270 K, the MAtransforms into monoclinic MC, and the MCremains stable until 5 K. Although no phase transition occurs from 5 K to 245 K, polar nanoregions(PNRs) display visible changes. The instability of PNRs is suggested as responsible for the low temperature relaxation. The ultrahigh dielectric constant at room temperature is associated with the instability of local structure and phase transition. Our research provides an insight into the design of high-performance ferroelectric materials.展开更多
A new phase transition compound,2-methoxyanilinium perchlorate-18-crown-6（1） {（oCH3OC6H4NH3）＋（18-crown-6） ClO4 },has been synthesized and separated as crystals.Differential scanning calorimetry（DSC） measureme...A new phase transition compound,2-methoxyanilinium perchlorate-18-crown-6（1） {（oCH3OC6H4NH3）＋（18-crown-6） ClO4 },has been synthesized and separated as crystals.Differential scanning calorimetry（DSC） measurements show a pair of sharp peaks at 225 K（heating） and 210 K（cooling）,indicating the phase transition is first-order.Dielectric anomalies observed at 225 K（heating）and 210 K（cooling） further confirm the phase transition.The crystal structures determined at 298 K and123 K are both triclinic in P 1.The most distinct difference between room-temperature and lowtemperature structures is the order–disorder transition of the host 18-crown-6 molecule,which is the driving force of the phase transition.展开更多
In the realm of molecular phase transition research,particularly for applications in sensors,data storage and switching technologies,the role of organic-inorganic hybrid perovskite materials has been increasingly reco...In the realm of molecular phase transition research,particularly for applications in sensors,data storage and switching technologies,the role of organic-inorganic hybrid perovskite materials has been increasingly recognized for their significant potential.Nevertheless,hybrid post-perovskites,as a critical subclass of perovskites,have not been thoroughly studied and mainly limit in the instances based on polyatomic bridging agents like dicyanamide(dca^(-))and non-cyclic organic cations.Herein,a polar cyclic quaternary ammonium cation,N,N-dimethylpyrrolidinium(DMP^(+)),was used to assemble a new hybrid post-perovskite,(DMP)[Mn(dca)_(3)](1),which undergoes a phase transition from orthorhombic Bmmb to monoclinic P2_(1)/n space group at 249 K.By employing multiple techniques such as differential scanning calorimetry,variable-temperature single-crystal X-ray analysis,dielectric measurements,and Hirshfeld surface analysis,we disclosed the role of polar cyclic quaternary ammonium DMP^(+)in elevating the phase-transition temperature by 48 K,generating significant dielectric switching effect and facilitating interlayer sliding of inorganic framework.展开更多
Solid-state phase transitions of 4-methylanilinium perchlorate （4-CH3C6H4NH3.C104, 1） and tetrafluoroborate （4-CH3C6H4- NH3-BF4, 2） were investigated with variable-temperature X-ray single-crystal structure analys...Solid-state phase transitions of 4-methylanilinium perchlorate （4-CH3C6H4NH3.C104, 1） and tetrafluoroborate （4-CH3C6H4- NH3-BF4, 2） were investigated with variable-temperature X-ray single-crystal structure analysis and thermal studies. Both 1 and 2 undergo first-order phase transitions and exhibit distinct dielectric anomalies at 385 and 247 K, respectively.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
The pyndazine hexafluorophosphate[C4H5N2]~＋[PF6]^-（1） undergoes a reversible phase transition around140 K,which was confirmed by the DSC measurement.Variable-temperature crystal structures determined at 293 K and 9...The pyndazine hexafluorophosphate[C4H5N2]~＋[PF6]^-（1） undergoes a reversible phase transition around140 K,which was confirmed by the DSC measurement.Variable-temperature crystal structures determined at 293 K and 93 K show that the compound crystallizes in the same space group P21/c,indicating that 1 undergoes an iso-structural phase transition.As the temperature decreases,dielectric measurement of the title compound shows no significant change around the phase transition temperature.Classic hydrogen bonds are found between molecules at 293 K and 93 l〈 with similar packing arrangement.The most distinct difference between the low temperature and room temperature structures is the order-disorder transition of the hexafluorophosphate anion,which is probably the driving force of the phase transition.展开更多
Solid-state structure of the crystalline 1：1 complex [C3H10N（18-crown-6）]＋[I3] （1） between 18-crown-6 and n-propylammonium triiodide has been determined at 293 and 93 K, respectively, showing a change from monoc...Solid-state structure of the crystalline 1：1 complex [C3H10N（18-crown-6）]＋[I3] （1） between 18-crown-6 and n-propylammonium triiodide has been determined at 293 and 93 K, respectively, showing a change from monoclinic P21/m to monoclinic P21/a. Crystal structural analysis shows that in addition to van der Waals＇ forces, conventional N-H..-O hydrogen bonds are the key interactions. Measurements of unit cell parameters versus temperature show that the values of one of the three axes and the crystal volume change abruptly and remarkably at 220 K, indicating a first-order phase transition. The lack of the mirror plane in the low temperature structure is the most important differences between the two structural forms. Dif- ferential scanning calorimetry （DSC） measurement confirms that I undergoes a reversible phase transition at about 220 K with a thermal hysteresis of 3.5 K. The relatively large latent heat makes 1 a good candidate for phase change materials. The phase transition is accompanied by an anomaly of dielectric constant during heating and cooling process near the phase transition temperature.展开更多
Lead-based organic-inorganic hybrids occupy a niche in the field of optoelectronics due to exceptional semiconducting properties and potential ferroelasticity.Nevertheless,the possible toxicity of lead restricts their...Lead-based organic-inorganic hybrids occupy a niche in the field of optoelectronics due to exceptional semiconducting properties and potential ferroelasticity.Nevertheless,the possible toxicity of lead restricts their widespread application to a certain extent.Herein,two new lead-free ferroelastic semiconductors are reported:[DMMClEA]_(3)Bi_(2)Br_(9)(compound 1)and[DMMClEA]_(3)Sb_(2)Br_(9)(compound 2)(DMMClEA=N-(chloromethyl)-N,N-dimethylethylammonium),in which the inorganic framework neatly arranges with[Bi_(2)Br_(9)]^(3−)/[Sb_(2)Br_(9)]^(3−)polyhedrons shared by face,forming an A_(3)B_(2)X_(9)-type structure.Both compounds 1 and 2 possess two-step phase transitions,including a3mF2/m-type ferroelastic phase transition,based on the Aizu rule.In addition,dual dielectric switches endow the application toward sensor devices.This finding enriches A_(3)B_(2)X_(9)-type zero-dimensional hybrid ferroelastics and provides an approach to designing high-performance,lead-free perovskite semiconductors with dielectric functionality.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51602242 and 51472197)the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2018JM5097)
文摘The structure evolution and origin of ultrahigh dielectric properties have been investigated in the low temperature range from 300 K to 5 K for [001]-oriented 0.68 Pb(Mg_(1/3)Nb_(2/3))O_3–0.33PbTiO_3(PMN–33 PT) crystal. The experimental results reveal that a short-range ordered monoclinic MAis the dominant phase at ambient temperature. As the temperature drops below 270 K, the MAtransforms into monoclinic MC, and the MCremains stable until 5 K. Although no phase transition occurs from 5 K to 245 K, polar nanoregions(PNRs) display visible changes. The instability of PNRs is suggested as responsible for the low temperature relaxation. The ultrahigh dielectric constant at room temperature is associated with the instability of local structure and phase transition. Our research provides an insight into the design of high-performance ferroelectric materials.
基金supported by the National Natural Science Foundation of China (No. 21101025)
文摘A new phase transition compound,2-methoxyanilinium perchlorate-18-crown-6（1） {（oCH3OC6H4NH3）＋（18-crown-6） ClO4 },has been synthesized and separated as crystals.Differential scanning calorimetry（DSC） measurements show a pair of sharp peaks at 225 K（heating） and 210 K（cooling）,indicating the phase transition is first-order.Dielectric anomalies observed at 225 K（heating）and 210 K（cooling） further confirm the phase transition.The crystal structures determined at 298 K and123 K are both triclinic in P 1.The most distinct difference between room-temperature and lowtemperature structures is the order–disorder transition of the host 18-crown-6 molecule,which is the driving force of the phase transition.
基金supported by the National Natural Science Foundation of China(22071273 and 21821003)Fundamental Research Funds for the Central Universities,Sun Yat Sen University(23lgzy001).
文摘In the realm of molecular phase transition research,particularly for applications in sensors,data storage and switching technologies,the role of organic-inorganic hybrid perovskite materials has been increasingly recognized for their significant potential.Nevertheless,hybrid post-perovskites,as a critical subclass of perovskites,have not been thoroughly studied and mainly limit in the instances based on polyatomic bridging agents like dicyanamide(dca^(-))and non-cyclic organic cations.Herein,a polar cyclic quaternary ammonium cation,N,N-dimethylpyrrolidinium(DMP^(+)),was used to assemble a new hybrid post-perovskite,(DMP)[Mn(dca)_(3)](1),which undergoes a phase transition from orthorhombic Bmmb to monoclinic P2_(1)/n space group at 249 K.By employing multiple techniques such as differential scanning calorimetry,variable-temperature single-crystal X-ray analysis,dielectric measurements,and Hirshfeld surface analysis,we disclosed the role of polar cyclic quaternary ammonium DMP^(+)in elevating the phase-transition temperature by 48 K,generating significant dielectric switching effect and facilitating interlayer sliding of inorganic framework.
基金supported by the National Natural Science Foundation of China (21071030)Natural Science Foundation of Jiangsu Province(BK2010425)
文摘Solid-state phase transitions of 4-methylanilinium perchlorate （4-CH3C6H4NH3.C104, 1） and tetrafluoroborate （4-CH3C6H4- NH3-BF4, 2） were investigated with variable-temperature X-ray single-crystal structure analysis and thermal studies. Both 1 and 2 undergo first-order phase transitions and exhibit distinct dielectric anomalies at 385 and 247 K, respectively.
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.
基金financially supported by the National Natural Science Foundation of China(No.91222101)
文摘The pyndazine hexafluorophosphate[C4H5N2]~＋[PF6]^-（1） undergoes a reversible phase transition around140 K,which was confirmed by the DSC measurement.Variable-temperature crystal structures determined at 293 K and 93 K show that the compound crystallizes in the same space group P21/c,indicating that 1 undergoes an iso-structural phase transition.As the temperature decreases,dielectric measurement of the title compound shows no significant change around the phase transition temperature.Classic hydrogen bonds are found between molecules at 293 K and 93 l〈 with similar packing arrangement.The most distinct difference between the low temperature and room temperature structures is the order-disorder transition of the hexafluorophosphate anion,which is probably the driving force of the phase transition.
基金supported by the National Natural Science Foundation of China (20701007 & 90922005)Natural Science Foundation of Jiangsu Province (BK2008286 & BK2008029)
文摘Solid-state structure of the crystalline 1：1 complex [C3H10N（18-crown-6）]＋[I3] （1） between 18-crown-6 and n-propylammonium triiodide has been determined at 293 and 93 K, respectively, showing a change from monoclinic P21/m to monoclinic P21/a. Crystal structural analysis shows that in addition to van der Waals＇ forces, conventional N-H..-O hydrogen bonds are the key interactions. Measurements of unit cell parameters versus temperature show that the values of one of the three axes and the crystal volume change abruptly and remarkably at 220 K, indicating a first-order phase transition. The lack of the mirror plane in the low temperature structure is the most important differences between the two structural forms. Dif- ferential scanning calorimetry （DSC） measurement confirms that I undergoes a reversible phase transition at about 220 K with a thermal hysteresis of 3.5 K. The relatively large latent heat makes 1 a good candidate for phase change materials. The phase transition is accompanied by an anomaly of dielectric constant during heating and cooling process near the phase transition temperature.
基金financially supported by the National Natural Science Foundation of China(grant no.21991141).
文摘Lead-based organic-inorganic hybrids occupy a niche in the field of optoelectronics due to exceptional semiconducting properties and potential ferroelasticity.Nevertheless,the possible toxicity of lead restricts their widespread application to a certain extent.Herein,two new lead-free ferroelastic semiconductors are reported:[DMMClEA]_(3)Bi_(2)Br_(9)(compound 1)and[DMMClEA]_(3)Sb_(2)Br_(9)(compound 2)(DMMClEA=N-(chloromethyl)-N,N-dimethylethylammonium),in which the inorganic framework neatly arranges with[Bi_(2)Br_(9)]^(3−)/[Sb_(2)Br_(9)]^(3−)polyhedrons shared by face,forming an A_(3)B_(2)X_(9)-type structure.Both compounds 1 and 2 possess two-step phase transitions,including a3mF2/m-type ferroelastic phase transition,based on the Aizu rule.In addition,dual dielectric switches endow the application toward sensor devices.This finding enriches A_(3)B_(2)X_(9)-type zero-dimensional hybrid ferroelastics and provides an approach to designing high-performance,lead-free perovskite semiconductors with dielectric functionality.
