The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray d...The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that （La,Sb）-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3＋ ions and Sb3＋ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of （La,Sb）-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of （La,Sb）-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3＋ ions.展开更多
The phase transition, elastic and electronic properties of three phases（phase Ⅰ,Ⅱ, and Ⅲ） of Sb_2Te_3 are investigated by using the generalized gradient approximation（GGA） with the PBESOL exchange–correlation ...The phase transition, elastic and electronic properties of three phases（phase Ⅰ,Ⅱ, and Ⅲ） of Sb_2Te_3 are investigated by using the generalized gradient approximation（GGA） with the PBESOL exchange–correlation functional in the framework of density-functional theory. Some basic physical parameters, such as lattice constants, bulk modulus, shear modulus,Young＇s modulus, Poisson＇s ratio, acoustic velocity, and Debye temperature Θ are calculated. The obtained lattice parameters under various pressures are consistent with experimental data. Phase transition pressures are 9.4 GPa（Ⅰ→Ⅱ） and 14.1 GPa（Ⅱ→Ⅲ）, which are in agreement with the experimental results. According to calculated elastic constants, we also discuss the ductile or brittle characters and elastic anisotropies of three phases. Phases Ⅰ and Ⅲ are brittle, while phaseⅡ is ductile. Of the three phases, phaseⅡ has the most serious degree of elastic anisotropy and phase Ⅲ has the slightest one.Finally, we investigate the partial densities of states（PDOSs） of three phases and find that the three phases possess some covalent features.展开更多
The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbit...The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbite to rutile structure are investigated by ab initio plane-wave pseudopotential density functional theory method （DFT）, together with quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from anatase to columbite and from rutile to columbite are 4.55 GPa and 19.92 GPa, respectively. The zero-pressure transition temperatures from anatase to rutile and from columbite to rutile are 950 K and 1500 K, respectively. Our results are consistent with the available experimental data and other theoretical results. Moreover, the dependence of the normalized primitive cell volume V/Vo on pressure and the dependences of thermal expansion coefficient α on temperature and pressure are also obtained successfully.展开更多
Neuromorphic computing is known for its efficient computational speed,low latency,and reduced power consumption,which is considered a pivotal technology to overcome the von Neumann bottleneck.Artificial synapses are a...Neuromorphic computing is known for its efficient computational speed,low latency,and reduced power consumption,which is considered a pivotal technology to overcome the von Neumann bottleneck.Artificial synapses are an indispensable component of neuromorphic computational artificial neural networks.To guarantee effective and precise processing of optical signals,it must have a high responsivity,detectivity,and the ability to adapt to various environments.Here,a synaptic transistor based on the HfS_(2)/VO_(2) heterojunction with a responsivity of8.6×10^(3) A·W^(-1)and a detectivity of 1.26×10^(14)Jones at405 nm laser was reported.Meanwhile,the typical synaptic behavior was successfully simulated,including postsynaptic currents(PSCs),the transition from shortterm plasticity(STP)to long-term plasticity(LTP).When VO_(2) converts from the semiconductor state to the metal state,the HfS_(2)/VO_(2) heterojunction transforms into a Schottky heterojunction from a TypeⅡheterojunction with temperature.What's important,the heterojunction still exhibits excellent responsivity and detectivity,as well as stability of synaptic properties.In addition,the classical Pavlovian conditioning experiment is simulated under different laser intensity to study the brain's associative learning behavior.The results demonstrate that the HfS_(2)/VO_(2) heterojunction synapse exhibits significant responsivity and detectivity and is adaptable to high-temperature environments,showing great potential for neuromorphic computational applic ations.展开更多
基金Project (11KJB430007) supported by the University Natural Science Research Program of Jiangsu Province, ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions, China
文摘The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that （La,Sb）-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3＋ ions and Sb3＋ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of （La,Sb）-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of （La,Sb）-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3＋ ions.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11204192 and 11174214)Jointly supported by the National Natural Science Foundation of Chinathe China Academy of Engineering Physics(NSAF)(Grant No.U1430117)
文摘The phase transition, elastic and electronic properties of three phases（phase Ⅰ,Ⅱ, and Ⅲ） of Sb_2Te_3 are investigated by using the generalized gradient approximation（GGA） with the PBESOL exchange–correlation functional in the framework of density-functional theory. Some basic physical parameters, such as lattice constants, bulk modulus, shear modulus,Young＇s modulus, Poisson＇s ratio, acoustic velocity, and Debye temperature Θ are calculated. The obtained lattice parameters under various pressures are consistent with experimental data. Phase transition pressures are 9.4 GPa（Ⅰ→Ⅱ） and 14.1 GPa（Ⅱ→Ⅲ）, which are in agreement with the experimental results. According to calculated elastic constants, we also discuss the ductile or brittle characters and elastic anisotropies of three phases. Phases Ⅰ and Ⅲ are brittle, while phaseⅡ is ductile. Of the three phases, phaseⅡ has the most serious degree of elastic anisotropy and phase Ⅲ has the slightest one.Finally, we investigate the partial densities of states（PDOSs） of three phases and find that the three phases possess some covalent features.
基金Project supported by the National Natural Science Foundation of China (Grant No 10776022)
文摘The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbite to rutile structure are investigated by ab initio plane-wave pseudopotential density functional theory method （DFT）, together with quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from anatase to columbite and from rutile to columbite are 4.55 GPa and 19.92 GPa, respectively. The zero-pressure transition temperatures from anatase to rutile and from columbite to rutile are 950 K and 1500 K, respectively. Our results are consistent with the available experimental data and other theoretical results. Moreover, the dependence of the normalized primitive cell volume V/Vo on pressure and the dependences of thermal expansion coefficient α on temperature and pressure are also obtained successfully.
基金financially supported by the National Key Research and Development Program of China(No.2019YFB2203403)the National Natural Science Foundation of China(Nos.61974043,62074058 and 12104156)+3 种基金the Projects of Science and Technology Commission of Shanghai Municipality(No.21JC1402100)the Natural Science Foundation of ChongqingChina(No.CSTB2022NSCQ-MSX1367)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning。
文摘Neuromorphic computing is known for its efficient computational speed,low latency,and reduced power consumption,which is considered a pivotal technology to overcome the von Neumann bottleneck.Artificial synapses are an indispensable component of neuromorphic computational artificial neural networks.To guarantee effective and precise processing of optical signals,it must have a high responsivity,detectivity,and the ability to adapt to various environments.Here,a synaptic transistor based on the HfS_(2)/VO_(2) heterojunction with a responsivity of8.6×10^(3) A·W^(-1)and a detectivity of 1.26×10^(14)Jones at405 nm laser was reported.Meanwhile,the typical synaptic behavior was successfully simulated,including postsynaptic currents(PSCs),the transition from shortterm plasticity(STP)to long-term plasticity(LTP).When VO_(2) converts from the semiconductor state to the metal state,the HfS_(2)/VO_(2) heterojunction transforms into a Schottky heterojunction from a TypeⅡheterojunction with temperature.What's important,the heterojunction still exhibits excellent responsivity and detectivity,as well as stability of synaptic properties.In addition,the classical Pavlovian conditioning experiment is simulated under different laser intensity to study the brain's associative learning behavior.The results demonstrate that the HfS_(2)/VO_(2) heterojunction synapse exhibits significant responsivity and detectivity and is adaptable to high-temperature environments,showing great potential for neuromorphic computational applic ations.
