Optical switching of ferroelectric polarization is of interest for wireless and energy-efficient control of logic states.So far,this phenomenon has been widely demonstrated only in ferroelectric perovskites,while stud...Optical switching of ferroelectric polarization is of interest for wireless and energy-efficient control of logic states.So far,this phenomenon has been widely demonstrated only in ferroelectric perovskites,while studies on other emerging ferroelectrics remain limited.In this regard,the paradigmatic example of a technologically relevant ferroelectric material is HfO2.However,HfO2has a very wide bandgap,limiting light absorption.So far,the proposed strategies to enhance light absorption in HfO2-based systems are detrimental to ferroelectric properties,i.e.,bandgap lowering or on-purpose defect introduction,which reduce switchable polarization and increase the presence of leakage currents.Here,we show that good ferroelectric properties,i.e.,sizeable polarization(up to 15μC cm-2),low leakage current(under 10-6A cm-2),high endurance(up to 108 cycles)and fast switching(<50 ns),can be achieved in epitaxial Hf0.5Zr0.5O2films through an alternative strategy,BaTiO3capping.While ferroelectric properties are remarkable,we demonstrate that the presence of BaTiO3allows light absorption and the concomitant electric field generation,as supported by density functional theory calculations,which enables optical switching of polarization in Hf0.5Zr0.5O2under 405 nm illumination.It is observed that optical switching is more efficient in films with thicker BaTiO3capping layer.The high polarizability of BaTiO3contributes to minimizing degradation in the ferroelectric response of the system.The results presented here indicate that appropriate designs can be followed to obtain optical switching of polarization in ferroelectric HfO2while preserving main functional properties.展开更多
This study clarifies the influence of single-layer(TiN,HfN,W)and bi-layer(HfN/TiN,W/TiN)bottom electrodes(BEs)on the ferroelectric performance and reliability of the 10-nm-thick Hf0.5Zr0.5O2(HZO)thin films.A ...This study clarifies the influence of single-layer(TiN,HfN,W)and bi-layer(HfN/TiN,W/TiN)bottom electrodes(BEs)on the ferroelectric performance and reliability of the 10-nm-thick Hf0.5Zr0.5O2(HZO)thin films.A smaller thermal expansion coefficient in HfN or W imposes higher in-plane tensile stress on the HZO thin films,facilitating the polar orthorhombic(o-)phase fraction and enhancing remanent polarization(Pr).However,thicker interfacial layers formed when HfN or W single-layer BE and HZO contacted directly,leading to excessive leakage current and degraded ferroelectric performance.These excessive interfacial layers were effectively suppressed by inserting a thin(5 nm-20 nm)TiN layer on the HfN or W BEs.As a result,the HZO thin films on the HfN/TiN and W/TiN bi-layer BEs decrease the HZO grain size,facilitating the o-phase formation(increasing Pr)and lowering the film's coercive field.However,the higher surface roughness of the W/TiN bi-layer BEs induced excessive leakage current and reliability degradation.In contrast,the HfN BEs with a 10-or 20-nm-thick upper TiN layer lower the surface roughness of the BEs,thereby eliminating the adverse effects.As a result,the HfN 40 nm/TiN 10 nm/HZO/TiN stack exhibited enhanced ferroelectric performance up to 109switching cycles with a lower cycling field of 2.7 MV/cm than the TiN 50 nm/HZO/TiN stack with a cycling field of 3.7 MV/cm.展开更多
Zr0.5Ti0.5O2(ZT) and Zr0.25Ti0.25Al0.5O2(ZTA) mixed oxides were prepared by co-precipitation method and characterized by low temperature adsorption-desorption,XRD and NH3-TPD. The activity of Pt/Zr0.5Ti0.5O2 and Pt/ Z...Zr0.5Ti0.5O2(ZT) and Zr0.25Ti0.25Al0.5O2(ZTA) mixed oxides were prepared by co-precipitation method and characterized by low temperature adsorption-desorption,XRD and NH3-TPD. The activity of Pt/Zr0.5Ti0.5O2 and Pt/ Zr0.5Ti0.5Al0.5O2 catalysts was evaluated using the simulated gases. The results show that ZTA samples exhibit higher specific surface area,larger pore volume and proper surface acidic amount and acidity in comparison with ZT. The results of the catalytic test indicate that Pt/ZT and Pt/ZTA catalysts exhibit excellent low-temperature catalytic activity and lower light-off temperatures of hydrocarbon,carbon monoxide and nitrogen oxides,especially better conversion for nitrogen oxides (NOx). The addition of Al2O3 into ZT enhanced the anti-aging property of Pt/ ZTA catalysts due to the excellent textural,structural,surface acidity and thermal stability.展开更多
A series of Ceo.sFeo.30Zr0.20O2 catalysts were prepared by different methods (co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrotherrnal method) and character...A series of Ceo.sFeo.30Zr0.20O2 catalysts were prepared by different methods (co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrotherrnal method) and characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) and H2-TPR measurements. Potential of the catalysts in the soot oxidation was evaluated in a temperature-programmed oxidation (TPO) apparatus. The results showed that all the Fe3+ and Zr4+ were incor- porated into ceria lattice to form a pure Ce-Fe-Zr-O solid solution for the co-precipitation sample, but two kinds of Fe phases ex- isted in the Ce-Fe-Zr-O catalysts prepared by other methods: Fe3+ incorporated into CeO2 lattice and dispersed Fe2O3 clusters. The free Fe2O3 clusters could improve the activity of catalysts for soot oxidation comparing with the pure Ce-Fe-Zr-O solid solution owing to the synergetic effect between free Fe2O3 and surface oxygen vacancies. In addition, the activity of catalysts strongly relied on the surface reducibility of free Fe2O3 particles. Holding both abundant free Fe2O3 particles and high oxygen vacancy concentration, the hydrothermal Ce0.5Fe0.3Zr0.202 catalyst presented the lowest Ti (251℃, ignition temperature of soot oxidation) and Tm (310 ℃, maximum oxidation rate temperature) for soot combustion (with tight-contact between soot and catalysts) among the five samples. Even after aging at 800 ℃ for 10 h, the Ti and Tm were still relatively low, at 273 and 361 ℃, respectively, indicating high catalytic stability.展开更多
Mesoporous Ce0.5Zr0.5O2 mixed oxide with high specific surface area was synthesized under basic condition in the presence of non-ionic surfactant PEG-4000. The effect of synthesis conditions, such as synthesis tempera...Mesoporous Ce0.5Zr0.5O2 mixed oxide with high specific surface area was synthesized under basic condition in the presence of non-ionic surfactant PEG-4000. The effect of synthesis conditions, such as synthesis temperature and the molar ratio of PEG-4000/([ Ce] + [ Zr] ), on specific surface area were investigated. The products were characterized by transmission electron microscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements, respectively. The results showed that synthesis temperature and the molar ratio of PEG-4000/([ Ce] + [ Zr] ) had great influence on specific surface area. Under the optimum synthesis conditions, the prepared Ce0.5Zr0.5O2 mixed oxide presented cubic fluorite-type structure and possessed high surface area of 148.6 m2·g^-1 with wormlike pores.展开更多
Ce Zr O solid solution was prepared by four different methods, i.e., decomposition of nitrate, coprecipiation, hydroxysuainic acid sol gel as well as citrate sol gel, and characterized by using X ray powder diffractio...Ce Zr O solid solution was prepared by four different methods, i.e., decomposition of nitrate, coprecipiation, hydroxysuainic acid sol gel as well as citrate sol gel, and characterized by using X ray powder diffraction, Raman and temperature programmed reduction. The phase composition and the reduction properties of Ce Zr O depend on the preparation method. A cubic Ce 0.5 Zr 0.5 O 2 solid solution can be obtained by using the sol gel method. The Ce Zr O solid solution prepared by using decomposition or coprecipiation was composed of cubic Ce 0.8 Zr 0.2 O 2 and tetragonal Ce 0.2 Zr 0.8 O 2 solid solution. The Ce Zr O solid solution prepared with different methods shows the different reduction properties owing to different phase composition. Results of differential thermal analysis and XRD show that Ce 0.5 Zr 0.5 O 2 solid solution is formed during the decomposition or combustion of the gel.展开更多
One-dimensional and quasi-one-dimensional nanostructure materials are promising building blocks for electromagnetic devices and nanosystems.In this work,the composite Ni0.5Zn0.5Fe2O4(NZFO)/Pb(Zr0.52Ti0.48)O3(PZT)nanof...One-dimensional and quasi-one-dimensional nanostructure materials are promising building blocks for electromagnetic devices and nanosystems.In this work,the composite Ni0.5Zn0.5Fe2O4(NZFO)/Pb(Zr0.52Ti0.48)O3(PZT)nanofibers with average diameters about 65 nm are prepared by electrospinning from poly(vinyl pyrrolidone)(PVP)and metal salts.The precursor composite NZFO/PZT/PVP nanofibers and the subsequent calcined NZFO/PZT nanofibers are investigated by Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),scanning electron microscopy(SEM).The magnetic properties for nanofibers are measured by vibrating sample magnetometer(VSM).The NZFO/PZT nanofibers obtained at calcination temperature of 900°C for 2 h consist of the ferromagnetic spinel NZFO and ferroelectric perovskite PZT phases,which are constructed from about 37 nm NZFO and 17 nm PZT grains.The saturation magnetization of these NZFO/PZT nanofibers increases with increasing calcination temperature and contents of NZFO in the composite.展开更多
Using TiO2 and Ti0.5Zr0.5O2 as carriers, the CuO/TiO2 and CuO/Ti0.5Zr0.5O2 catalystswere prepared by the impregnation method with Cu(NO3)2 as active component. The catalyticactivities in NO+CO reaction were investigat...Using TiO2 and Ti0.5Zr0.5O2 as carriers, the CuO/TiO2 and CuO/Ti0.5Zr0.5O2 catalystswere prepared by the impregnation method with Cu(NO3)2 as active component. The catalyticactivities in NO+CO reaction were investigated using a microreactor-GC system, and structure andreducibility of catalysts were characterized by means of physical adsorption, TPR, XRD, NO-TPDtechnologies. It was found that the activity of CuO/Ti0.5Zr0.5O2 catalyst was higher than that ofCuO/TiO2, probably due to the large specific surface area of Ti0.5Zr0.5O2 that played an importantrole in NO+CO reaction.展开更多
基金Financial support from the Spanish Ministry of Science,Innovation and Universities(MCIN/AEI/http://gffzzd3cc09b8251d45dfsxxpxwfuvfuuo6bux.ffgz.tsg.suse.edu.cn/10.13039/501100011033),through the Severo Ochoa MATRANS42(CEX2023-001263-S)and CEX2023001286-S,PDC2023-145874-I00,PID2023-147211OB-C21,PID2023-147211OB-C22 and TED2021-130453B-C21 projectsGeneralitat de Catalunya(2021 SGR 00804)+1 种基金Gobierno de Aragon project E13_23Rfinancially supported by China Scholarship Council(CSC)with No.202208310089
摘要Optical switching of ferroelectric polarization is of interest for wireless and energy-efficient control of logic states.So far,this phenomenon has been widely demonstrated only in ferroelectric perovskites,while studies on other emerging ferroelectrics remain limited.In this regard,the paradigmatic example of a technologically relevant ferroelectric material is HfO2.However,HfO2has a very wide bandgap,limiting light absorption.So far,the proposed strategies to enhance light absorption in HfO2-based systems are detrimental to ferroelectric properties,i.e.,bandgap lowering or on-purpose defect introduction,which reduce switchable polarization and increase the presence of leakage currents.Here,we show that good ferroelectric properties,i.e.,sizeable polarization(up to 15μC cm-2),low leakage current(under 10-6A cm-2),high endurance(up to 108 cycles)and fast switching(<50 ns),can be achieved in epitaxial Hf0.5Zr0.5O2films through an alternative strategy,BaTiO3capping.While ferroelectric properties are remarkable,we demonstrate that the presence of BaTiO3allows light absorption and the concomitant electric field generation,as supported by density functional theory calculations,which enables optical switching of polarization in Hf0.5Zr0.5O2under 405 nm illumination.It is observed that optical switching is more efficient in films with thicker BaTiO3capping layer.The high polarizability of BaTiO3contributes to minimizing degradation in the ferroelectric response of the system.The results presented here indicate that appropriate designs can be followed to obtain optical switching of polarization in ferroelectric HfO2while preserving main functional properties.
基金supported by the National Research Foundation of Korea(Grant No.2020R1A3B2079882).
摘要This study clarifies the influence of single-layer(TiN,HfN,W)and bi-layer(HfN/TiN,W/TiN)bottom electrodes(BEs)on the ferroelectric performance and reliability of the 10-nm-thick Hf0.5Zr0.5O2(HZO)thin films.A smaller thermal expansion coefficient in HfN or W imposes higher in-plane tensile stress on the HZO thin films,facilitating the polar orthorhombic(o-)phase fraction and enhancing remanent polarization(Pr).However,thicker interfacial layers formed when HfN or W single-layer BE and HZO contacted directly,leading to excessive leakage current and degraded ferroelectric performance.These excessive interfacial layers were effectively suppressed by inserting a thin(5 nm-20 nm)TiN layer on the HfN or W BEs.As a result,the HZO thin films on the HfN/TiN and W/TiN bi-layer BEs decrease the HZO grain size,facilitating the o-phase formation(increasing Pr)and lowering the film's coercive field.However,the higher surface roughness of the W/TiN bi-layer BEs induced excessive leakage current and reliability degradation.In contrast,the HfN BEs with a 10-or 20-nm-thick upper TiN layer lower the surface roughness of the BEs,thereby eliminating the adverse effects.As a result,the HfN 40 nm/TiN 10 nm/HZO/TiN stack exhibited enhanced ferroelectric performance up to 109switching cycles with a lower cycling field of 2.7 MV/cm than the TiN 50 nm/HZO/TiN stack with a cycling field of 3.7 MV/cm.
摘要Zr0.5Ti0.5O2(ZT) and Zr0.25Ti0.25Al0.5O2(ZTA) mixed oxides were prepared by co-precipitation method and characterized by low temperature adsorption-desorption,XRD and NH3-TPD. The activity of Pt/Zr0.5Ti0.5O2 and Pt/ Zr0.5Ti0.5Al0.5O2 catalysts was evaluated using the simulated gases. The results show that ZTA samples exhibit higher specific surface area,larger pore volume and proper surface acidic amount and acidity in comparison with ZT. The results of the catalytic test indicate that Pt/ZT and Pt/ZTA catalysts exhibit excellent low-temperature catalytic activity and lower light-off temperatures of hydrocarbon,carbon monoxide and nitrogen oxides,especially better conversion for nitrogen oxides (NOx). The addition of Al2O3 into ZT enhanced the anti-aging property of Pt/ ZTA catalysts due to the excellent textural,structural,surface acidity and thermal stability.
基金Project supported by National Natural Science Foundation of China(51374004,51204083,51174105,51104074)Natural Science Foundation of Yunnan Province(2010ZC018)
摘要A series of Ceo.sFeo.30Zr0.20O2 catalysts were prepared by different methods (co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrotherrnal method) and characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) and H2-TPR measurements. Potential of the catalysts in the soot oxidation was evaluated in a temperature-programmed oxidation (TPO) apparatus. The results showed that all the Fe3+ and Zr4+ were incor- porated into ceria lattice to form a pure Ce-Fe-Zr-O solid solution for the co-precipitation sample, but two kinds of Fe phases ex- isted in the Ce-Fe-Zr-O catalysts prepared by other methods: Fe3+ incorporated into CeO2 lattice and dispersed Fe2O3 clusters. The free Fe2O3 clusters could improve the activity of catalysts for soot oxidation comparing with the pure Ce-Fe-Zr-O solid solution owing to the synergetic effect between free Fe2O3 and surface oxygen vacancies. In addition, the activity of catalysts strongly relied on the surface reducibility of free Fe2O3 particles. Holding both abundant free Fe2O3 particles and high oxygen vacancy concentration, the hydrothermal Ce0.5Fe0.3Zr0.202 catalyst presented the lowest Ti (251℃, ignition temperature of soot oxidation) and Tm (310 ℃, maximum oxidation rate temperature) for soot combustion (with tight-contact between soot and catalysts) among the five samples. Even after aging at 800 ℃ for 10 h, the Ti and Tm were still relatively low, at 273 and 361 ℃, respectively, indicating high catalytic stability.
基金Project Supported by Open Fund of Key Laboratory of Catalysis Materials and Science of Hubei Province (CHCL0501)
摘要Mesoporous Ce0.5Zr0.5O2 mixed oxide with high specific surface area was synthesized under basic condition in the presence of non-ionic surfactant PEG-4000. The effect of synthesis conditions, such as synthesis temperature and the molar ratio of PEG-4000/([ Ce] + [ Zr] ), on specific surface area were investigated. The products were characterized by transmission electron microscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements, respectively. The results showed that synthesis temperature and the molar ratio of PEG-4000/([ Ce] + [ Zr] ) had great influence on specific surface area. Under the optimum synthesis conditions, the prepared Ce0.5Zr0.5O2 mixed oxide presented cubic fluorite-type structure and possessed high surface area of 148.6 m2·g^-1 with wormlike pores.
摘要Ce Zr O solid solution was prepared by four different methods, i.e., decomposition of nitrate, coprecipiation, hydroxysuainic acid sol gel as well as citrate sol gel, and characterized by using X ray powder diffraction, Raman and temperature programmed reduction. The phase composition and the reduction properties of Ce Zr O depend on the preparation method. A cubic Ce 0.5 Zr 0.5 O 2 solid solution can be obtained by using the sol gel method. The Ce Zr O solid solution prepared by using decomposition or coprecipiation was composed of cubic Ce 0.8 Zr 0.2 O 2 and tetragonal Ce 0.2 Zr 0.8 O 2 solid solution. The Ce Zr O solid solution prepared with different methods shows the different reduction properties owing to different phase composition. Results of differential thermal analysis and XRD show that Ce 0.5 Zr 0.5 O 2 solid solution is formed during the decomposition or combustion of the gel.
基金Funded by the National Natural Science Foundation of China(No.50674048)Research Fund for the Doctoral Program of Higher Education of China(No.20103227110006)
摘要One-dimensional and quasi-one-dimensional nanostructure materials are promising building blocks for electromagnetic devices and nanosystems.In this work,the composite Ni0.5Zn0.5Fe2O4(NZFO)/Pb(Zr0.52Ti0.48)O3(PZT)nanofibers with average diameters about 65 nm are prepared by electrospinning from poly(vinyl pyrrolidone)(PVP)and metal salts.The precursor composite NZFO/PZT/PVP nanofibers and the subsequent calcined NZFO/PZT nanofibers are investigated by Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),scanning electron microscopy(SEM).The magnetic properties for nanofibers are measured by vibrating sample magnetometer(VSM).The NZFO/PZT nanofibers obtained at calcination temperature of 900°C for 2 h consist of the ferromagnetic spinel NZFO and ferroelectric perovskite PZT phases,which are constructed from about 37 nm NZFO and 17 nm PZT grains.The saturation magnetization of these NZFO/PZT nanofibers increases with increasing calcination temperature and contents of NZFO in the composite.
摘要Using TiO2 and Ti0.5Zr0.5O2 as carriers, the CuO/TiO2 and CuO/Ti0.5Zr0.5O2 catalystswere prepared by the impregnation method with Cu(NO3)2 as active component. The catalyticactivities in NO+CO reaction were investigated using a microreactor-GC system, and structure andreducibility of catalysts were characterized by means of physical adsorption, TPR, XRD, NO-TPDtechnologies. It was found that the activity of CuO/Ti0.5Zr0.5O2 catalyst was higher than that ofCuO/TiO2, probably due to the large specific surface area of Ti0.5Zr0.5O2 that played an importantrole in NO+CO reaction.