Dielectric relaxation method was employed to study the properties of oxygen ion diffusion and phase transition in the oxide-ion conductors （Lal-xLnx）2Mo209 （Ln=Nd, Gd, x=0.05-0.25）. Two dielectric loss peaks were ...Dielectric relaxation method was employed to study the properties of oxygen ion diffusion and phase transition in the oxide-ion conductors （Lal-xLnx）2Mo209 （Ln=Nd, Gd, x=0.05-0.25）. Two dielectric loss peaks were observed： peak Pd at about 600 K and peak P5 around 720 K. Peak Pd is a relaxational peak and associated with the short-range diffusion of oxygen ions, while peak P5 hardly changes its position and dramatically decreases in height with increasing frequency, exhibiting non-relaxational nature. With increasing Ln^3＋ concentration, the heights of peak Ph and Pd increase at first and then decrease after passing a maximum at 15% doping. It is suggested that peak P5 is related to the phase transition of a static disordered state to a dynamic disordered state in oxygen ions/vacancies distribution. It is found that the 15%Gd or 15%Nd doped La2Mo209 samples exhibit the highest conductivity in accordance with the highest height of peak Pd at this doping content.展开更多
Kinetics of phase transformation from pseudocubic to tetragonal phase in Bi3NbO7 solid solution is studied by using the ac impedance method under isothermal conditions. Conductivity of the investigated compound is use...Kinetics of phase transformation from pseudocubic to tetragonal phase in Bi3NbO7 solid solution is studied by using the ac impedance method under isothermal conditions. Conductivity of the investigated compound is used to characterize the kinetic process of the transition. The Avrami exponent and the activation energy of phase transition are around 1.5 and 3.5eV, respectively. These kinetic parameters reveal that the pseudocubic-tetragonal transition in Bi3NbO7 .belongs to a three-dimensional diffusion-controlled growth with zero nucleation rate.展开更多
Solid solutions of Na_(0.5) Bi_(0.5) TiO_(3)(NBT)and BiNi_(0.5) Ti_(0.5) O_(3)(BNiT)were prepared by a solid-state reaction route,and their electrical properties investigated by a combination of impedance spectroscopy...Solid solutions of Na_(0.5) Bi_(0.5) TiO_(3)(NBT)and BiNi_(0.5) Ti_(0.5) O_(3)(BNiT)were prepared by a solid-state reaction route,and their electrical properties investigated by a combination of impedance spectroscopy and electromotive force measurements to explore the possibility of developing mixed ionic-electronic conductors based on NBT.Phase analysis showed that BNiT has a large solid solution limit in NBT(60 mol%based on X-ray diffraction),and the room temperature crystal structure changes from rhombohedral to pseudo-cubic with increasing BNiT content.Neutron diffraction revealed the coexistence of rhombohedral and tetragonal phases when the BNiT content≥40 mol%.Electrically,incorporation of BNiT induces p-type electronic conduction into NBT by hopping of holes between Ni^(2+)(Ni_(Ni)^(x))and Ni^(3+)(Ni·Ni),and therefore changes the electrical conduction mechanism systematically from predominant oxide-ion conduction to mixed ionic-electronic conduction and then to predominant p-type electronic conduction.The total conductivity of the solid solutions showed a“V-shape”variation with increasing BNiT content.Possible mechanisms for the phase evolution and the conductivity-composition relationships are discussed.Achieving high levels of ionic and electronic conductivity simultaneously in NBT by introducing elements with variable oxidation states remains challenging due to the competition between an enhanced electronic component and a suppressed ionic component.Low levels of BNiT incorporation are,however,beneficial to reducing the dielectric loss of NBT for dielectric applications.展开更多
Oxide-ion conductors have been widely used as catalytic,conductive,detecting and other materials under oxidizing,reducing,inert,mixed environments and the like.However,so far the evaluation of their oxygen-ion transpo...Oxide-ion conductors have been widely used as catalytic,conductive,detecting and other materials under oxidizing,reducing,inert,mixed environments and the like.However,so far the evaluation of their oxygen-ion transport(such as oxide-ion conductivity and oxygen permeability)either is extrinsic or is limited only in oxidizing or inert environment.Herein,the evaluation of intrinsic oxygen-ion transport for oxide-ion conductors in all environments seems especially important.In this work,a new test system was designed to enable the oxide-ion conductors placing in single oxidizing,reducing,inert or mixed environment separately,which also realized all the oxygen-vacancy concentrations of oxide-ion conductors are in equilibrium in all environments.The intrinsic oxide-ion conductivity and oxygen permeability were evaluated in all environments,and the influencing factors regulated by environments also were analyzed to correlate the variation of oxygen-ion transport.展开更多
基金This work was supported by the Ningbo Civic Natural Science Foundation （No.2006A610057）, the Ningbo Civic Project of International Cooperation （No.2006B100080）, Zhejiang Provincial Project of International Cooperation （No.2007C24022）, and the National Natural Science Foundation of China （No.50672100 and No.50702061）.
文摘Dielectric relaxation method was employed to study the properties of oxygen ion diffusion and phase transition in the oxide-ion conductors （Lal-xLnx）2Mo209 （Ln=Nd, Gd, x=0.05-0.25）. Two dielectric loss peaks were observed： peak Pd at about 600 K and peak P5 around 720 K. Peak Pd is a relaxational peak and associated with the short-range diffusion of oxygen ions, while peak P5 hardly changes its position and dramatically decreases in height with increasing frequency, exhibiting non-relaxational nature. With increasing Ln^3＋ concentration, the heights of peak Ph and Pd increase at first and then decrease after passing a maximum at 15% doping. It is suggested that peak P5 is related to the phase transition of a static disordered state to a dynamic disordered state in oxygen ions/vacancies distribution. It is found that the 15%Gd or 15%Nd doped La2Mo209 samples exhibit the highest conductivity in accordance with the highest height of peak Pd at this doping content.
文摘Kinetics of phase transformation from pseudocubic to tetragonal phase in Bi3NbO7 solid solution is studied by using the ac impedance method under isothermal conditions. Conductivity of the investigated compound is used to characterize the kinetic process of the transition. The Avrami exponent and the activation energy of phase transition are around 1.5 and 3.5eV, respectively. These kinetic parameters reveal that the pseudocubic-tetragonal transition in Bi3NbO7 .belongs to a three-dimensional diffusion-controlled growth with zero nucleation rate.
基金sponsored by the National Natural Science Founda-tion of China(Nos.52072239 and 52234010)the Natural Science Foundation of Chongqing,China(No.cstc2021jcyj-msxmX0720)the EPSRC(No.EP/L027348/1).
文摘Solid solutions of Na_(0.5) Bi_(0.5) TiO_(3)(NBT)and BiNi_(0.5) Ti_(0.5) O_(3)(BNiT)were prepared by a solid-state reaction route,and their electrical properties investigated by a combination of impedance spectroscopy and electromotive force measurements to explore the possibility of developing mixed ionic-electronic conductors based on NBT.Phase analysis showed that BNiT has a large solid solution limit in NBT(60 mol%based on X-ray diffraction),and the room temperature crystal structure changes from rhombohedral to pseudo-cubic with increasing BNiT content.Neutron diffraction revealed the coexistence of rhombohedral and tetragonal phases when the BNiT content≥40 mol%.Electrically,incorporation of BNiT induces p-type electronic conduction into NBT by hopping of holes between Ni^(2+)(Ni_(Ni)^(x))and Ni^(3+)(Ni·Ni),and therefore changes the electrical conduction mechanism systematically from predominant oxide-ion conduction to mixed ionic-electronic conduction and then to predominant p-type electronic conduction.The total conductivity of the solid solutions showed a“V-shape”variation with increasing BNiT content.Possible mechanisms for the phase evolution and the conductivity-composition relationships are discussed.Achieving high levels of ionic and electronic conductivity simultaneously in NBT by introducing elements with variable oxidation states remains challenging due to the competition between an enhanced electronic component and a suppressed ionic component.Low levels of BNiT incorporation are,however,beneficial to reducing the dielectric loss of NBT for dielectric applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.51972146,52072150)and Shandong Province Key Fundamental Research Program(Grant No.ZR2022ZD39).
文摘Oxide-ion conductors have been widely used as catalytic,conductive,detecting and other materials under oxidizing,reducing,inert,mixed environments and the like.However,so far the evaluation of their oxygen-ion transport(such as oxide-ion conductivity and oxygen permeability)either is extrinsic or is limited only in oxidizing or inert environment.Herein,the evaluation of intrinsic oxygen-ion transport for oxide-ion conductors in all environments seems especially important.In this work,a new test system was designed to enable the oxide-ion conductors placing in single oxidizing,reducing,inert or mixed environment separately,which also realized all the oxygen-vacancy concentrations of oxide-ion conductors are in equilibrium in all environments.The intrinsic oxide-ion conductivity and oxygen permeability were evaluated in all environments,and the influencing factors regulated by environments also were analyzed to correlate the variation of oxygen-ion transport.
