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1.
NMR and impedance spectroscopies have been used to study the Li+ ion mobility in the TeO2---LiO0.5---LiX (X = F, Cl) glasses. Activation energies determined from the temperature dependence of dc conductivity data decrease as the lithium or halogen content increases. Activation energies deduced from the analysis of the ac conductivity data in the complex modulus formalism and corresponding to the true one-particle energy barrier of ionic motion according to the coupling model, have been compared to those deduced from NMR data (T1−1 relaxation time): a good agreement is obtained. Finally, the influence of the glass composition and ion distribution on Li+ ion mobility has been discussed.  相似文献   

2.
嘉明珍  王红艳  陈元正  马存良 《物理学报》2016,65(5):57101-057101
在锂二次电池中, 硅酸锰锂作为正极材料得到广泛研究, 但其固有的电子和离子电导率较低, 直接影响着电池的功率密度和充放电速率. 本文建立了不同浓度的Na+离子替位掺杂Li+离子形成的Li1-xNaxMnSiO4(x=0, 0.125, 0.25, 0.5)结构, 采用第一性原理的方法, 研究了掺杂前后硅酸锰锂的电子结构以及Li+离子的跃迁势垒. 发现在Li+位替代掺杂Na+, 导带底的能级向低能方向发生移动, 降低了Li2MnSiO4 材料的禁带宽度, 有利于提升材料的电子导电性能. 随着掺杂浓度的升高, 禁带宽度逐渐变窄. CI-NEB结果表明, 在Li2MnSiO4体系中具有两条有效的Li+离子迁移通道, 掺杂Na+以后扩大了Li+ 离子在[100]晶向上的迁移通道, Li+离子的跃迁势垒由0.64 eV降低为0.48, 0.52和0.55 eV. 掺杂浓度为 x=0.125时, 离子迁移效果最佳. 研究表明Na+掺杂有利于提高Li2MnSiO4材料的离子和电子电导率.  相似文献   

3.
Ag+/Na+ ion-exchanged aluminosilicate glasses with uniform concentration profiles were prepared, and their electrical conductivities were investigated as functions of the ion-exchange ratio and the initial glass compositions. In the case of the ion-exchanged glasses of x20Ag2O–(1−x)20Na2O–10Al2O3–70SiO2 in mol%, the conductivity, σ, and its activation energy, Eσ, showed a minimum and a maximum at the same ion-exchange ratio x=0.3, respectively, and the mixed mobile ion effect (MMIE) was observed. The fully ion-exchanged sample attained σ=3.5×10−5 S/cm at 200 °C, which was 1.5 orders of magnitude larger than that of initial glass. In the case of x25Ag2O–(1−x)25Na2O–25Al2O3–50SiO2, the mixed mobile ion effect was also observed at x=0.5. The maximum conductivity of 2×10−4 S/cm at 200 °C was obtained in the fully ion-exchanged glass sample.

The electric relaxation analysis was also conducted on both systems, and Kohlrausch–Williams–Watts (KWW) fractional exponent β was obtained as a function of x. The decrease of β was observed near x≈0.3 in the former system, while that of the later system was independent of the ion-exchange ratio. Based on the structural analysis results, the observed behaviors were investigated from the point of view of the occupation of Ag+ ions on the non-bridging oxygen-site (NBO-site) and the charge compensation-site (CC-site) of AlO4 tetrahedral unit.  相似文献   


4.
The lithium intercalation into the layered dichalcogenide 3R-WS2 has been investigated by electrochemical reduction and by chemical reaction in n-butyl lithium solution. Essential results are (a) a charge transfer of nearly 0.6e/W in LixWS2, (b) a small increase of the c-axis parameter of about 0.6%, and (c) a high mobility of the Li+-ions. The chemical diffusion coefficient of Li+-ions is estimated to be 8 × 10−9 cm2 s−1 in the composition range 0 ≤ x ≤ 0.25. The appearance of a structural transformation from 3R-WS2 to 2H-LixWS2 is interpreted on grounds of instabilities in the interlayer structure.  相似文献   

5.
KCdF3晶体中Cr3+-Li+中心局域结构研究   总被引:2,自引:0,他引:2  
利用零场分裂参量与晶体结构之间的定量关系,研究了双掺杂晶体KCdF3:Cr3+,Li+的局域结构。指出,对于KCdF3:Cr3+,Li+晶体,四角晶场的形成包含两个方面:(1)由于电荷补偿而产生的等效电荷形成的四角对称晶场;(2)Cr3+的局域结构发生晶格畸变而产生的四角对称晶场。事实上,当Cr3+和Li+掺入KCdF3晶体时,Cr3+代替了Cd2+离子;由于Cr3+离子与Cd2+离子的半径不同、电荷不同、质量不同,导致Cr3+的局域结构发生晶格畸变,由此而产生四角对称晶场;由于电荷补偿,Li+离子取代了[001]方向与Cr3+离子邻近的Cd2+离子,由此产生的等效电荷而形成的四角晶场。这样,Cr3+的局域结构由Oh对称变为C4v点对称。文中建立了ZFS参量和晶体结构之间的定量关系。在考虑晶格畸变和等效电荷的基础上,研究了KCdF3:Cr3+,Li+晶体的ZFS参量,理论结果和实验符合很好。得到了F-离子向中心离子分别移动为ΔR1=0.00268nm,ΔR2=0.001nm,ΔR3=0.00165nm。  相似文献   

6.
Electrochemical lithium insertion into (PO2)4(WO3)2m, where m=9 and 10, has allowed the determination of several phases Lix(PO2)4(WO3)2m between 3.4 and 0.01 V vs Li+/Li0. After the first cycle the electrochemical system was unable to maintain the high specific capacity of the cells (540 Ah/kg) due to irreversible processes. Nevertheless at high voltage values, above 1.4 V vs Li+/Li0, the lithium insertion proceeded through a reversible mechanism. By means of X-ray diffraction experiments we have detected the nature of different phases Lix(PO2)4(WO3)2m formed and we have established a correlation with the reversible/irreversible processes detected during the electrochemical insertion.  相似文献   

7.
Samples of general formula CsAg2−xMxI3, x=0–0.4 and M=Cu and Tl, have been prepared and studied by powder X-ray diffraction, DSC and electrical conductivity measurements. X-ray diffractograms and DSC curves showed the possibility of stabilizing the high-temperature -phase at lower temperatures in Tl-substituted samples, while such results were not obtained in Cu-substituted samples. Ionic conductivity measurements showed two regions corresponding to the low- and high-temperature phases. The transition temperature between the two phases was found to remain unchanged with the addition of Cu+ and decreased gradually with increasing Tl+. The ionic conductivity decreased in Cu-substituted samples and enhanced with the incorporation of Tl+ ion in the lattice of CsAg2I3. Dielectric constant was found to show behaviour similar to that of the ionic conductivity, and this is an evidence of the predominant effect of ion hopping on this property.  相似文献   

8.
M. Sural  A. Ghosh   《Solid State Ionics》2000,130(3-4):259-266
The electric conductivity of ZnF2–AlF3–PbF2–LiF glasses has been studied in the frequency range 10 Hz–2 MHz and in the temperature range from 300 K to just below the glass transition temperature. The conductivity decreases with the increase in the LiF content in the composition, which results from the trapping of F ions by Li+ ions. Small values of the stretching exponent β are observed for the present glasses. The value of the decoupling index decreases with an increase in LiF content, consistent with the composition dependence of the conductivity.  相似文献   

9.
The thermal conductivity and thermopower are reported for a hole doped Eu1.5Ce0.5RuSr2Cu2O10+δ sample that has been annealed at 1100 K under an oxygen pressure of 54 atm. At Tc=45 K superconductivity and weak ferromagnetism coexist (Tm=180 K). Weak features in the thermopower, S(T), and thermal conductivity, κ(T), are observed both at Tm and at T*=140 K. The thermopower begins to decrease sharply toward zero at Tc, and there is an extremely sharp increase of about 30% in the thermal conductivity at Tc. This “first order” transition may be related to the sudden appearance of a spontaneous vortex phase at Tc. A small shoulder is observed in κ(T) in the temperature range T=5–13 K.  相似文献   

10.
In PbWO4(PWO) crystals grown by Czochralski method the influence of atmosphere of the growth (O2, air) and doping with the rare-earth ions of different types (A3+=Lu3+, Gd3+,Tb3+,Eu3+ as well as doubly doped A3+–Li+) on light yield and luminescence decay were analyzed. PWO scintillator with the ultra-fast (τ=0.5 ns) main component of luminescence decay (87% of total light yield) was obtained using the O2-growth atmosphere and doping by Eu2O3 at a concentration of 5000 ppm. It is concluded that the decrease of decay constant of the main scintillation component is the result of the resonant energy transfer between the centers of “blue” PWO luminescence (λmax=420 nm) and the 4f–4f-transitions of Eu3+ ions in this spectral region.  相似文献   

11.
Layer-type oxide NaxMx/2IITi1−x/2IVO2 (M=Co, Ni; 0.60≤x≤1.0) has been prepared by solid state reactions. In both series, two structural variants of type -NaFeO2 (O3) and β-RbScO2 (P2) have been obtained consecutively as x decreases with a borderline composition around xc0.7. With the decrease of x, the ionic conductivity has been found to increase up to 8.4×10−2 S cm−1 at 770 K (Na0.67Co0.33Ti0.67O2). Compositions of P2 have been found to exhibit the conductivity values two to five times greater than those of O3, primarily due to the larger rectangular threshold available for the diffusion of Na+ ions. Such a structural effect has also been considered to depend on the polarizability of alkali ion. HT-XRD and 23Na-NMR data of Na0.67Co0.33Ti0.67O2 strongly suggest that the diffusion of Na+ ion is deeply related with the local distortion of trigonal prismatic sites, leading to the change of activation energy around 430 K.  相似文献   

12.
The effect of Bi2O3 on the glass transition temperature, electrical conductivity and structure of LiBO2 glass has been investigated. Tg vs. composition curve shows three different linear regions, while there is an overall decrease in Tg with the increase in Bi2O3 content. The slope of these three straight lines is in a decreasing order. These results are interpreted in terms of the increase in the number of non-bridging oxygen atoms, substitution of Bi-O bond in place of B-O bond and change in Li+ ion concentration. The conductivity vs. composition curve exhibits two maxima which are interpreted in terms of the structural modification effect of Bi2O3 on LiBO2 network and mixed-former effect, respectively. Results obtained from the XPS studies of the samples of composition x 0.005, have shown that the number of non-bridging oxygen atoms from B-O bond increases with the increase in Bi2O3 content. It has a maximum value at x = 0.003 where the conductivity has also exhibited a maximum value. Further increase of Bi2O3 content causes decrease in it. For higher Bi2O3 content (x * > 0.005), O 1s spectra of Bi2O3 has been separated out from that of Bi2O3. Bismuth ions have been substituted for boron ions as network former ions.  相似文献   

13.
A new lithium ionic conductor of the thio-LISICON (LIthium SuperIonic CONductor) family was found in the binary Li2S–P2S5 system; the new solid solution with the composition range 0.0≤x≤0.27 in Li3+5xP1−xS4 was synthesized at 700 °C and characterized by X-ray diffraction measurements. Its electrical and electrochemical properties were studied by ac impedance and cyclic voltammetry measurements, respectively. The solid solution member at x=0.065 in Li3+5xP1−xS4 showed the highest conductivity value of 1.5×10−4 S cm−1 at 27 °C with negligible electronic conductivity and the activation energy of 22 kJ mol−1 which is characteristic of high ionic conduction state. The extra lithium ions in Li3PS4 created by partial substitution of P5+ for Li+ led to the large increase in ionic conductivity. In the solid solution range examined, the minimum conductivity was obtained for the compositions, Li3PS4 (x=0.0 in Li3+5xP1−xS4) and Li4P0.8S4 (x=0.2 in Li3+5xP1−xS4); this conductivity behavior is similar to other thio-LISICON family with the general formula, LixM1−yMy′S4 (M=Si, Ge, and M′=P, Al, Zn, Ga, Sb). Conduction mechanism and the material design concepts are discussed based on the conduction behavior and the structure considerations.  相似文献   

14.
Initial axial kinetic energy (Ez) distributions of Li+ and F secondary ions desorbed from LiF surfaces, bombarded by low current (500 particles/s) N3+ beams in the 0.075–7.5 MeV primary ion energy (EPI) range, were measured by using the time-of-flight technique. In this energy range, the electronic energy loss, Se, increases from 25 to 160 eV/Å, while the nuclear stopping power, Sn, decreases from 8.0 to 0.25 eV/Å. The observed F initial axial kinetic energy distribution can be described by the linear collision cascade theory and no other contribution was found. The F total yield decreases proportionally to Sn. The Li+ distribution presents a remarkable deviation from the cascade prediction, indicating the existence of additional mechanisms related to the electronic energy-loss process. For the range of EPI studied, these mechanisms produce a Li+ energy distribution with a Maxwell-Boltzman-like shape, which vanishes above Ez 10 eV and presents a maximum at Ez 1.2 eV. The Li+ yield is nonlinear with the electronic energy loss, Se. A simple desorption model, based on the spatial distribution of the energy deposited by the projectile and on the effective energy-loss concept, is presented. This spatial distribution of the deposited energy is due to secondary electron cascades and is connected with a ESD-like mechanism on the surface.  相似文献   

15.
The phase transition of LiNiO2 has been studied by using impedance spectroscopy, DTA, and X-ray diffraction methods. At 720°C the hexagonal phase changes in air to the cubic phase. The phase transition process is rather slow and partially reversible. A peculiar conductivity behavior was observed. From 324°C the conductivity deviates from Arrhenius behavior and is temperature-invariant until 613°C. Subsequently, it decreases rapidly with increase of the temperature. This phenomenon is related to the occupation of Ni2+ in Li+ positions. The optimal sintering temperature for LiNiO2 is suggested to be 700°C.  相似文献   

16.
A series of substituted lead iron niobate compounds with the general formula Pb2+(1−x)AZx(Fe{(1−(2−Z)x)/2}Nb{(1+(2−Z)x)/2})O3 (0<x<0.6 and A=La3+, K+ or Sr2+) were prepared by a modified solid-state synthesis. The relative concentrations of Fe3+ and Nb5+ were adjusted to compensate the charge imbalance due to the aliovalent substitution. The dielectric constant and magnetic susceptibilities were studied as a function of temperature. The temperature of the dielectric maximum, TM, of the substituted compounds decreased linearly with increasing concentration of the substituent ions. The magnetic measurements showed an antiferromagnetic transition at temperatures TN1 due to the superexchange interactions mediated by Fe–O–Fe and an additional antiferromagnetic-type transition at TN2. TN1 linearly increased with the increasing concentration of Fe3+ ion at the B-site of ABO3-type substituted compounds. TM is shown to be directly dependent on the concentration of the ferroactive Nb5+ ions at the B-site and Pb2+ ions at the A-site.  相似文献   

17.
A series of apatite-type La–Ge–O ceramics were prepared and their cation-defect at the 4f+6h sites and oxide ion-defect at 2a site were investigated. In LaxGe6O12+1.5x ceramics of x=6–12, the higher conductivities were obtained in the region of apatite composition, Lax(GeO4)6O1.5x−12 (x=8–9.33), and the highest conductivity was achieved for La9(GeO4)6O1.5 (x=9), where the number of cation (La3+) occupying the 4f+6h sites is 9 and the number of oxide ion occupying the 2a site is 1.5. The ceramics with cation- and oxide ion-defects were La9−0.66xSrx(GeO4)6O1.5 (x=0–1), La9−1.33xZrx(GeO4)6O1.5 (x=0–1), La9−xSrx(GeO4)6O1.5−0.5x (x=0–3), La9−xZrx(GeO4)6O1.5+0.5x (x=0–1), Lax(GeO4)3x−21(AsO4)27−3xO1.5 (x=0–3), Lax(GeO4)33−3x(AlO4)3x−27O1.5 (x=0–3), La9(GeO4)6−x (AlO4)xO1.5−0.5x (x=0–3), La9(GeO4)6−x(AsO4)xO1.5+0.5x (x=0–1), La9.33−xSrx(GeO4)6O2−0.5x (x=0–1.2) and Lax(GeO4)4.5(AlO4)1.5O1.5x−12.75 (x=8.8–9.83), which were prepared by the partial substitution of La3+and GeO44−of the basic apatite La9(GeO4)6O1.5 with Sr2+ or Zr4+ and AlO45− or AsO43−. Such substitutions lowered the conductivity of La9(GeO4)6O1.5. These results were discussed by the electrostatic interaction between Sr2+, Zr4+, AlO45− or AsO43− and oxide ion as a conductive species.  相似文献   

18.
赵佰强  张耘  邱晓燕  王学维 《物理学报》2016,65(1):14212-014212
利用基于密度泛函理论的第一性原理对Cu,Fe单掺及共掺LiNbO_3晶体的电子结构和光学性质进行了计算.结果显示:Cu,Fe单掺杂LiNbO_3晶体禁带内均产生了杂质能级,主要由Cu3d,Fe3d轨道及O 2p轨道贡献;共掺LiNbO_3晶体禁带内出现了双能级结构,深能级由Cu3d和O2p轨道贡献,浅能级由Fe3d和O2p轨道贡献.Cu,Fe单掺和共掺LiNbO_3晶体带隙依次缩小,在可见光区的光吸收明显增强.共掺LiNbO_3在445和630nm左右分别表现出一个宽吸收峰,比单掺LiNbO_3晶体表现出更好的光吸收性质.研究表明,Fe占Nb位比Fe占Li位的双掺样品在双光存储应用中更有优势;同时,浓度比[Fe2+]/[Fe3+]值的适当降低有助于这种优势的形成.  相似文献   

19.
金海杰  田莲花 《发光学报》2011,32(5):451-455
采用高温固相法制备了荧光粉Y2-x(W,Mo)O6:Eu3+,xLi+,利用X射线衍射仪和电子扫描显微镜对样品的结构和形貌进行了表征,并利用荧光光谱法分析了样品的光谱特性.首先在Y2WO6中掺入少量的Mo6+离子,掺入Mo6+后增加了原Y2WO6:Eu3+的激发光谱在近紫外光区的吸收,扩展了激发光谱的谱宽,但却使Y2W...  相似文献   

20.
采用燃烧法制备了Gd2O3:Sm3+和Li+离子掺杂的Gd2O3:Sm3+纳米晶,根据X射线衍射图谱确定所得纳米样品为纯立方相。在室温下,用275 nm和980 nm激发光激发各样品时,可分别观测到Sm3+离子的强荧光发射和上转换特征发射,其主发射峰分别位于560,602,650 nm处,分别对应着Sm3+离子的4G5/26H5/2,4G5/26H7/24G5/26H9/2的电子跃迁,其中以4G5/26H7/2跃迁的光谱强度最大。实验表明Li+离子的掺入使得Sm3+离子的荧光发射强度显著增加。通过对样品的XRD、TEM和激发光谱、发射光谱的研究,分析了引起样品荧光强度变化的原因。  相似文献   

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