Entropy and enthalpy of formation and migration of lattice defects in Na(I)

The self-diffusion coefficients of Na⁺ and I^?, as well as the ionic conductivity, are measured in Na(I) single crystals, pure and doped with Ca²⁺ ions. The computer analysis of the whole set of data shows that the atom transport in Na(I) is ensured essentially by the free vacancies with a very small contribution (～4%) of the vacancy pairs. The thermodynamic parameters of vacancy formation and migration are derived by taking the long range interactions into account (activity coefficients on the concentrations and relaxation factors on the mobilities). The respective entropies of Schottky defect formation, cation migration and anion migration are equal to 7.64, 3.23 and 2.91 k while the corresponding enthalpies are equal to 2.00, 0.58 and 0.77 eV.     

Experimental and theoretical investigation of oxygen diffusion in stabilised zirconia

Oxygen diffusion in stabilised zirconias is investigated by the simultaneous application of computer modelling and experimental techniques to yttria-stabilised zirconia. Using the Mott-Littleton method, migration pathways for oxygen ions have been calculated in perfect cubic zirconia. The oxygen migration occurs through a straight pathway, but not starting from the ideal lattice positions. The calculated activation energy of migration is about 0.2 v eV. Oxygen transport is investigated experimentally in YSZ containing 8-24 v mol% Y 2 O 3 as a function of stabiliser content by combining the stable isotope ( 18 O 2 ) method with ionic conductivity measurements. It was found that for a given temperature, diffusion and conductivity are highest for YSZ containing 8-10 v mol% yttria, but with differing activation energies which can be compared to the calculated values.     

Anion diffusion mechanism in strontium chloride single crystals

Simultaneous measurements of the anion self-diffusion coefficient and of the ionic conductivity have been carried out in the intrinsic range (440–630°C) of pure Sr Cl₂ single crystals. The microtome sectioning method using the radiotracer ³⁶Cl has been successfully applied to this difficult matrial. Accurate values of the correlation factor have thus been derived by applying the Nerst-Einstein relation. Results suggest that the Frenkel defects are predominant in the anion sub-lattice with the enthalpy and entropy of formation of 2.98 eV and 22 K, respectively. The chloride anions diffuse via the vacancy mechanism to which is added to a lesser extent an exchange mechanism where the ions successively occupy lattice and interstitial sites.     

The contribution of anion disorder to ionic conductivity on single crystals of β-PbF2

The effect of the different cooling processes on the disorder of flourine ions and ionic conductivity in β-PbF₂ has been studied by X-ray method and ionic conductivity measurements on single crystals below the transition temperature T_c. The spike-like diffuse scattering was observed along the <111>¹ directions around the Bragg reflections. The activation energies for the conduction process are 0.40 eV for the sample quenched from 970 K and 0.54 eV for the one from 720 K. The higher the quenching temperature is, the higher the conductivity and the lower the activation energy become. The dependence of conductivity on the different cooling processes is more evident in single crystals than in polycrystalline samples. The contribution of the different cooling processes to ionic conductivity can be quantitatively explained by the extent of ordering of mobile fluorine ions. Time dependence of ionic conductivity has not been observed.     

The generation of cationic vacancies in the electrolysis of doped alkali halide crystals

The introduction of metallic cadmium impurity into the melt reduces the electrical conductivity of KCl and KBr in the structure-sensitive range by 2–3 orders of magnitude. The electrolytic introduction of gold and nickel ions restores the impurity conductivity as a result of interaction of gold and nickel ions with the cadmium. The migration energies of cationic vacancies in KCl and KBr were found to be 0.67 eV and 0.62 eV, respectively.     

Na+替位掺杂对Li2MnSiO4的电子结构以及Li+迁移过程的影响

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Li_1-xNa_xMnSiO₄(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.     

Impedance spectroscopy and dielectric analysis in KH2PO4 single crystal

Optical observation, differential scanning calorimetry, thermogravimetric analysis, and differential thermogravimetric measurements have been carried out on KH₂PO₄ single crystals. As compared with the optical observation of crystal under polarizing microscope, the dehydration process occurred gradually over the crystal surface at temperatures above 195 °C and then the interior of the sample. The ac impedance measurements were performed as a function of both frequency and temperature. The electrical conduction and dielectric relaxation have been studied. The activation energy of migration is 1.02 eV in the temperature range between 150 and 179 °C. The conduction mechanism in this temperature range is attributed to the hopping of proton among hydrogen vacancies. At temperatures above 186 °C, a higher conductivity activation energy with 2.94 eV is obtained. In addition to the proton conduction, the migration of the heavier ions (such as potassium ion) is also suggested.     

Characterization of porous structure through the dynamical properties of ions confined in sulfonated polyimide ionomers films

The structure of sulfonated PolyImide (sPI) ionomer membrane has been investigated via the transport properties of ions confined inside. Transport coefficients of N(CH(3))(4)(+) and Na(+) ions have been determined by several techniques in order to get a range of time/space scale as wide as possible: a method using radiotracers, conductivity, pulsed field gradient NMR and NMR quadrupolar relaxation rates determination. For N(CH(3))(4)(+), the self-diffusion has been measured in the direction of membrane plan (parallel) and in the perpendicular direction (transverse), whereas for Na(+) only transverse self-diffusion has been measured. The conductivity of both ions has been measured in the transverse direction. The results show a anisotropic and multiscale structure with a separation phase between hydrophilic and hydrophobic domains that is not well-defined.     

Ionic conductivity and dielectric measurements in single crystal βAgI

Ionic conductivity measurements have been made on pure, copper-doped and cadmium-doped single crystals. Dielectric measurements in the frequency range 30Hz–100Hz showed that there was no anomalously to be (0.64 ± 0.02) eV and migration energies for silver ion intersitials and vacancies in the c direction to be (0.41 ± 0.02) eV and (0.50 ± 0.02) eV respectively. ESR measurements have shown that copper exists as Cu⁺ in these crystals. Dielectric measurements in the frequency range (OHz–100KHz showed that there was no anomalously high value for ? as reported earlier.     

Kinetics of cation site exchange in mixed garnets

The redistribution rate of cations between the a- and d -sites in quasibinary mixed yttrium—iron gallium and—iron aluminum garnet single crystals has been investigated for temperatures between 773 and 1523 K. The frozen-in cation distributions of quenched and of slow cooled samples were derived from magnetization measurements and are described by a phenomenological kinetic equation. The activation energies derived for the thermally activated process range from 1.3 to 4eV and are related to the anion vacancy concentration of the crystals. The zero defect intrinsic a-dbarrier height is 4.5 eV as inferred from the observed linear relation between the frequency factor and the activation energy of the Arrhenius equation. This empirical relation, known as the compensation law, has been further applied to interpret reported intra-sublattice site exchange effects of cations on the c-sites and cation self-diffusion data of YIG. The inferred c-c barrier height of 5.5 eV agrees within the error limits of ± 0.1eV with the enthalpy of formation, 5.4 eV, and the enthalpy of solution, 5.3 eV, derived with equilibrium models based on the ionic fluid (Temkin) model and using experimental results of the kinetics, the cation distribution and the solubility of garnets. Apparently the c-c bonds form the strongest binding scaffold of the garnet structure, which is manifested by a relation to the melting point. While premelting around the anion vacancies assisted by their thermal fluctuations reduces the effective barrier height for cation migration, the apparently uneffected melting point of the compound itself is reflected by the compensation law.     

Electrical conductivity and NMR studies in paraelastic phase of Tl2SeO4

We have carried out the electrical conductivity and NMR measurements and investigated the characteristic features of the electrical conductivity in a paraelastic phase of Tl₂SeO₄. It was found from electrical conductivity measurement that the activation energy in the paraelastic phase (above T_c(= 661 K)) is 0.98 eV. We also found that ²⁰⁵Tl-NMR line width drastically decreases above T_c and becomes approximately 0.5 Gauss. This result indicates that in the paraelastic phase the mobile Tl ions exist. Moreover this result is consistent with the existence of the anomalously large hopping motion of Tl ions observed in X-ray diffraction measurement. Furthermore the activation energy estimated from the motional narrowing of ²⁰⁵Tl-NMR absorption line is 0.92 eV and is in agreement with that obtained from the conductivity measurement. From these results, it is deduced that the mobile Tl ions play an important role in the appearance of electrical conductivity in the paraelastic phase.     

Sodium diffusion in cryolite at elevated temperatures studied by quasielastic neutron scattering

Quasielastic neutron scattering (QENS) has been applied to study the sodium mobility on nanosecond time scales in the perovskite fluoride cryolite, Na₃AlF₆, at high temperatures. Up to T = 1153 K the diffusion of Na ions is well described by a diffusion process of jumps between six and eight-fold coordinated sites. Above this temperature, where a step-like increase in the electrical conductivity occurs, the jump length increases, which indicates additional jumps over larger distances. The electrical conductivity derived from the self-diffusion coefficient via the Nernst–Einstein relation and the corresponding activation energy are in excellent agreement with the previous conductivity measurements. We conclude that the jump diffusion of sodium ions is the dominant mechanism for the electrical conductivity in cryolite at high temperatures up to T = 1153 K.     

ac conductivity of Na-Ag β” -alumina polycrystalline samples

The results of ac conductivity measurements carried out on ceramic samples of Li₂O and NiO-Li₂O-doped β7rdquo;-alumina with Na⁺, Ag⁺ and Na⁺ -Ag⁺ mobile ions are presented. The modifications of doping only slightly influenced either bulk or grain boundary conductivity in Na β” -alumina. The activation energies of conduction in Na β”-alumina equal to 0.28 eV at low temperatures decreased to 0.14–0.15 eV at temperatures above 200°C. The Arrhenius plots for Ag β” -alumina were found to be linear in whole 20–450°C temperature range with the activation energies of 0.19 eV (Li₂O) and 0.24 eV (NiO-Li₂O). The conductivity measurements done on partially exchanged samples revealed the presence of the mixed alkali effect.     

Phase relations, ionic transport and diffusion in the alloys of Cu2S-Ag2S mixed conductors

Results are reported of the phase relations in the (Ag_x-δ/2Cu_1-x)₂ system, ionic conductivity, self-diffusion and chemical diffusion coefficients for the solid solutions as a function of the composition x, degree of non-stoichiometry δ, and temperature in the range 473 – 673 K. The extensions of the homogeneity regions for single-phases are determined. Total and partial ionic conductivity values are given for copper and silver ions for the solid solutions. Measurements of the self-diffusion coefficient and the correlation factors are reported. It is shown that for solid solutions that the chemical diffusion is well described in terms of the phenomenological theory of ionic transport in mixed ionic electronic conductors.     

Radiation enhanced silicon self-diffusion and the silicon vacancy at high temperatures

We report proton radiation enhanced self-diffusion (RESD) studies on Si-isotope heterostructures. Self-diffusion experiments under irradiation were performed at temperatures between 780 degrees C and 872 degrees C for various times and proton fluxes. Detailed modeling of RESD provides direct evidence that vacancies at high temperatures diffuse with a migration enthalpy of H(m)(V)=(1.8+/-0.5) eV significantly more slowly than expected from their diffusion at low temperatures, which is described by H(m)(V)<0.5 eV. We conclude that this diffusion behavior is a consequence of the microscopic configuration of the vacancy whose entropy and enthalpy of migration increase with increasing temperature.     

Quasielastic and inelastic scattering of cold neutrons from silver iodide

New information about the movement of the ions in AgI has been obtained from cold-neutron time-of-flight measurements performed at the Institut Laue-Langevin at Grenoble. Whereas the ordered β-phase shows very pronounced low energy lattice excitations, no well-defined phonon groups are observed in the structurally disordered α-phase. Instead we find enhanced very low energy transfer scattering due to the self-diffusion of the silver ions.     

Mobility of ions in fluid Kr at various densities

We report measurements of mobility of positive and negative ions in fluid Kr at various densities. The experimental results are discussed with the Langevin theory. Comparison between self-diffusion of ions is made.     

Ni2+掺杂和卤素空位填充协同抑制CsPbBr3纳米晶体中的离子迁移

卤化铅钙钛矿(LHPs)由于具有优异的光电性能和制备成本低等优点,已成为新一代光电器件的有力候选材料。然而,缺陷造成的离子迁移会导致LHPs纳米晶的晶体结构解离分解。因此,稳定性成为LHPs实际应用中亟待解决的问题。本文旨在研究镍离子替位掺杂及卤素空位填补对CsPbBr3纳米晶中的离子迁移抑制作用。通过离子迁移活化能的测定和高分辨透射电镜的原位观察,分析了前驱体掺杂剂对加强LHPs稳定性的作用原理。首先,选用乙酰丙酮镍和溴化镍作为掺杂剂,合成了掺杂LHPs纳米晶。其次,通过吸收-荧光光谱,X射线衍射,X射线光电子衍射,透射电子显微镜等测试手段对掺杂样品的光学及化学组成进行分析。最后,通过纳米晶薄膜电导率的温度依赖关系计算出其离子迁移活化能,并结合高分辨电镜原位观察纳米晶在高能电子束辐照下的形貌演变过程,揭示了不同掺杂剂对合成掺杂LHPs稳定性的影响。实验结果表明:Ni²⁺掺杂CsPbBr3样品的离子迁移活化能相较本征CsPbBr3样品(0.07 eV)有显著提升,其中乙酰丙酮镍掺杂样品的离子迁移活化能为0.238 eV,溴化镍掺杂样品的离子迁移活化能为0.487 eV。另外,电子束辐照测试表明溴化镍掺杂钙钛矿晶体表现出更高的结构稳定性,这主要归因于掺杂的Ni²⁺对卤素的强结合和卤素填补空位缺陷的协同钝化作用。Ni²⁺掺杂和卤素空位填充协同可以有效抑制卤化物钙钛矿纳米晶体中的离子迁移。     

具有本征低晶格热导率的硫化银快离子导体的热电性能

硫化银(Ag_2S)是一种典型的快离子导体材料,前期关于Ag_2S的研究主要集中在光电和生物等领域.最近的研究表明, a-Ag_2S具有和金属一样的良好延展性和变形能力.但是, Ag_2S的热电性能尚无公开报道.本工作合成了单相Ag_2S化合物,系统研究了其在300—600 K范围的物相变化、离子迁移特性和电热输运性质.研究发现, Ag_2S在300—600 K温度区间表现出半导体的电输运性质.由于单斜-体心立方相晶体结构转变, Ag_2S的离子电导率、载流子浓度、迁移率、电导率、泽贝克系数等性质在455 K前后出现急剧变化.在550 K, Ag_2S的功率因子最高可达5μW·cm~(–1)·K~(–2). Ag_2S在300—600 K温度区间均表现出本征的低晶格热导率(低于0.6 W·m~(–1)·K~(–1)). S亚晶格中随机分布的类液态Ag离子是导致b-Ag_2S体心立方相具有低晶格热导率的主要原因.在573 K, Ag_2S的热电优值可达0.55,与Ag_2Se, Ag_2Te, CuAgSe等已报道的Ag基快离子导体热电材料的性能相当.     

Ionic conductivity of pure and doped Li3N

The ionic conductivity of Li₃N crystals doped with various metal ions (magnesium, copper and aluminum) or hydrogen has been investigated. The metal ions have a negative effect on the conductivity whereas hydrogen increases it. The intrinsic Li⁺ ionic conductivity of pure Li₃N is (2·-4)×10^-4Ω^-1cm^-1 at room temperature with an activation energy of 0.26?0.27 eV. Doping with hydrogen to a maximum level of 0.5?1.0 atom% results in a conductivity of 6×10^-3Ω^-1cm^-1 and an activation energy which has been lowered to 0.20 eV. A model is proposed for the action of hydrogen whereby the Li-N bonds next to an NH^2- group are weakened thereby facilatating the creation of Li⁺ Frenkel defects and the vacancy migration. Hydrogen-doped Li₃N is termed an enhanced intrinsic conductor.