Pressure applications can enable the tuning of atomic/defect ordering and provide access to new functional materials.Here,we report that pressure-induced structural transformation featuring disorder-order transition o...Pressure applications can enable the tuning of atomic/defect ordering and provide access to new functional materials.Here,we report that pressure-induced structural transformation featuring disorder-order transition of both cations and vacancies in the 8-layer deficient hexagonal perovskite tantalate dielectrics Ba_(8)ZnTa_(6)O_(24),which transformed the structure from twin to shift and remarkably lowered the temperature coefficient of resonant frequencyτ_fdown to near zero(~0.56 ppm/℃)from 38 ppm/℃for the twinned precursor.The atomic scale STEM-HAADF and EDS results confirm the ordering of Zn in the Ta host at the nanometer scale in the shifted material featuring well-ordered Ba_(8)ZnTa_(6)O_(24)slabs intergrown with Ba_(3)ZnTa_(2)O_(9)and Ba_(5)Ta_(4)O_(15)monolayers and anti-phase grain boundaries as planar defects.The pressure-induced twin-shift structural transformation of Ba_(8)ZnTa_(6)O_(24)features the rare constant concentration of the hexagonal stacked layers,which is allowed by the vacancy ordering at the central layers of face-shared octahedral(FSO)trimers avoiding the FSO B-B repulsion,and remarkably the faster cationic ordering kinetics compared with the 2:1 ordered complex perovskites.Although the inclusion of numerous planar defects and the oxidizable atomic defects led to significant p-type conduction and inhomogeneous electrical microstructures,resulting in an extraordinarily high extrinsic dielectric loss for the high-pressure shifted Ba_(8)ZnTa_(6)O_(24)pellet,the intrinsically near-zeroτ_fcould make the shifted Ba_(8)ZnTa_(6)O_(24)perovskite an ideal microwave dielectric resonator candidate if the defects could be eliminated.展开更多
Super-fine L1_(0)-Fe Pt nanoparticles(NPs)with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field(HMF)assis...Super-fine L1_(0)-Fe Pt nanoparticles(NPs)with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field(HMF)assisted post-sintering processes.The particle size of the L1_(0)-FePt NPs was obviously refined by lowering the sintering temperature.By applying the HMF during the post-sintering process,the fine size characteristics of L1_(0)-Fe Pt NPs were retained,and the ordering degree was significantly improved.The L1_(0)-Fe Pt NPs with sizes of about 4.5 nm,ordering degree of 0.940,and coercivity of 22.01 k Oe were obtained by this two-step sintering under a magnetic field of 12 T.The mechanism investigation of HMF enhancing the ordering degree indicates that the HMF enhances lattice distortion and magnetization energy(Zeeman energy).The enhanced lattice distortions cause high stress existing in the lattice,which can effectively promote the disordered-order transition.When the magnetic field reaches to 3 T,the Zeeman energy of the NPs is higher than the thermal disturbing energy of the NPs,and the magnetization effect is stronger.Therefore,the HMF(higher than 3 T)can obviously improve the disorder-order transition by lowering the energy barrier and accelerating the orderly diffusions of atoms.The HMF is a promising assistant to synthesize the L1_(0)-phase NPs with both of high ordering degree and super-fine size.展开更多
For poly(9,9-dioctylfluorene)(PFO),β phase (coplanar conformation with the intra-chain torsion angle of 165°) has a greater conjugation length and higher degree of order compared to those of α phase, which favo...For poly(9,9-dioctylfluorene)(PFO),β phase (coplanar conformation with the intra-chain torsion angle of 165°) has a greater conjugation length and higher degree of order compared to those of α phase, which favors charge carrier transport. However, the highest content of β phase obtained so far is 45%. We propose to increase the content of β phase by promoting the solution aggregation of PFO molecules and extending film-forming time. For this purpose, 1,8-diiodooctane (DIO) is added to PFO o-xylene solution, which enhances the interaction of PFO chains and improves the planarity of PFO backbone, resulting in the formation of ordered aggregation. The aggregates act as nucleation centers to promote the formation of β phase. The content of β phase increases with increasing DIO concentration and reaches a platform of 39% as DIO is more than 4 vol%. Furthermore, the film is kept in a sealed environment with oxylene atmosphere for 3 h, thus the PFO molecules have enough time to diffuse to the crystallization front and achieve disorder-order transition. As a result, the crystallinity of PFO is improved significantly and the content of β phase increases to 52%, reaching the highest value reported so far.展开更多
TEM study was made to explore the mechanism of the strain-age hardening of initially-dis- ordered (Co_(78)Fe_(22))_3V,which was found to be attributed to the formation of a special disloca- tion-stacking fault configu...TEM study was made to explore the mechanism of the strain-age hardening of initially-dis- ordered (Co_(78)Fe_(22))_3V,which was found to be attributed to the formation of a special disloca- tion-stacking fault configuration in company with disorder-order transformation-disloca- tions extended to stacking faults on{111}planes and got connected with each other through partial dislocation reaction at intersections of{111}planes,leading to dense networks with cells bounded by stacking fault tetrahedrons.The results also indicated that ordered (Co_(78)Fe_(22))_3V has very low stacking fault energy on{111}planes and relative high and isotropie antiphase boundary energy,which implies that it is most likely to be Lomer-Cottrell locks,not Kear-Wilsdof locks,that are responsible for the high strength at high temperatures of this alloy.展开更多
基金supported by the Guangxi Natural Science Foundation(AC23026004)the National Natural Science Foundation of China(22161014,22090043)。
文摘Pressure applications can enable the tuning of atomic/defect ordering and provide access to new functional materials.Here,we report that pressure-induced structural transformation featuring disorder-order transition of both cations and vacancies in the 8-layer deficient hexagonal perovskite tantalate dielectrics Ba_(8)ZnTa_(6)O_(24),which transformed the structure from twin to shift and remarkably lowered the temperature coefficient of resonant frequencyτ_fdown to near zero(~0.56 ppm/℃)from 38 ppm/℃for the twinned precursor.The atomic scale STEM-HAADF and EDS results confirm the ordering of Zn in the Ta host at the nanometer scale in the shifted material featuring well-ordered Ba_(8)ZnTa_(6)O_(24)slabs intergrown with Ba_(3)ZnTa_(2)O_(9)and Ba_(5)Ta_(4)O_(15)monolayers and anti-phase grain boundaries as planar defects.The pressure-induced twin-shift structural transformation of Ba_(8)ZnTa_(6)O_(24)features the rare constant concentration of the hexagonal stacked layers,which is allowed by the vacancy ordering at the central layers of face-shared octahedral(FSO)trimers avoiding the FSO B-B repulsion,and remarkably the faster cationic ordering kinetics compared with the 2:1 ordered complex perovskites.Although the inclusion of numerous planar defects and the oxidizable atomic defects led to significant p-type conduction and inhomogeneous electrical microstructures,resulting in an extraordinarily high extrinsic dielectric loss for the high-pressure shifted Ba_(8)ZnTa_(6)O_(24)pellet,the intrinsically near-zeroτ_fcould make the shifted Ba_(8)ZnTa_(6)O_(24)perovskite an ideal microwave dielectric resonator candidate if the defects could be eliminated.
基金financially supported by the National Natural Science Foundation of China(Grant nos.51871045,52071070,and 51690161)the Fundamental Research Funds for the Central Universities(Grant no.N2017003)the Doctoral Start-up Foundation of Liaoning Province(Grant no.2019-BS-116)。
文摘Super-fine L1_(0)-Fe Pt nanoparticles(NPs)with high ordering degree were successfully prepared by a modified two-step sintering method,which includes low-temperature pre-sintering,and the high magnetic field(HMF)assisted post-sintering processes.The particle size of the L1_(0)-FePt NPs was obviously refined by lowering the sintering temperature.By applying the HMF during the post-sintering process,the fine size characteristics of L1_(0)-Fe Pt NPs were retained,and the ordering degree was significantly improved.The L1_(0)-Fe Pt NPs with sizes of about 4.5 nm,ordering degree of 0.940,and coercivity of 22.01 k Oe were obtained by this two-step sintering under a magnetic field of 12 T.The mechanism investigation of HMF enhancing the ordering degree indicates that the HMF enhances lattice distortion and magnetization energy(Zeeman energy).The enhanced lattice distortions cause high stress existing in the lattice,which can effectively promote the disordered-order transition.When the magnetic field reaches to 3 T,the Zeeman energy of the NPs is higher than the thermal disturbing energy of the NPs,and the magnetization effect is stronger.Therefore,the HMF(higher than 3 T)can obviously improve the disorder-order transition by lowering the energy barrier and accelerating the orderly diffusions of atoms.The HMF is a promising assistant to synthesize the L1_(0)-phase NPs with both of high ordering degree and super-fine size.
基金financially supported by the National Natural Science Foundation of China (Nos. 51890871, 91833306, and 51573185)the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB12020300)
文摘For poly(9,9-dioctylfluorene)(PFO),β phase (coplanar conformation with the intra-chain torsion angle of 165°) has a greater conjugation length and higher degree of order compared to those of α phase, which favors charge carrier transport. However, the highest content of β phase obtained so far is 45%. We propose to increase the content of β phase by promoting the solution aggregation of PFO molecules and extending film-forming time. For this purpose, 1,8-diiodooctane (DIO) is added to PFO o-xylene solution, which enhances the interaction of PFO chains and improves the planarity of PFO backbone, resulting in the formation of ordered aggregation. The aggregates act as nucleation centers to promote the formation of β phase. The content of β phase increases with increasing DIO concentration and reaches a platform of 39% as DIO is more than 4 vol%. Furthermore, the film is kept in a sealed environment with oxylene atmosphere for 3 h, thus the PFO molecules have enough time to diffuse to the crystallization front and achieve disorder-order transition. As a result, the crystallinity of PFO is improved significantly and the content of β phase increases to 52%, reaching the highest value reported so far.
文摘TEM study was made to explore the mechanism of the strain-age hardening of initially-dis- ordered (Co_(78)Fe_(22))_3V,which was found to be attributed to the formation of a special disloca- tion-stacking fault configuration in company with disorder-order transformation-disloca- tions extended to stacking faults on{111}planes and got connected with each other through partial dislocation reaction at intersections of{111}planes,leading to dense networks with cells bounded by stacking fault tetrahedrons.The results also indicated that ordered (Co_(78)Fe_(22))_3V has very low stacking fault energy on{111}planes and relative high and isotropie antiphase boundary energy,which implies that it is most likely to be Lomer-Cottrell locks,not Kear-Wilsdof locks,that are responsible for the high strength at high temperatures of this alloy.
