Yanhao Dong, I-Wei Chen, Ju Li
Oxygen ion migration in Li2MnO3 was systematically studied by first-principles calculations. Hole polaron is found effective to lower the migration barrier of oxygen ion.
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Some possible connection between spin and charge degrees of freedom in magneto-resistive manganites is investigated through a thorough experimental study of the magnetic (AC susceptibility and DC magnetization) and transport (resistivity and thermal conductivity) properties. Measurements are reported in the case of well characterized polycrystalline La_{0.8}Sr_{0.2}MnO_3 samples. The experimental results suggest rather strong field-induced polarization effects in our material, clearly indicating the presence of ordered FM regions inside the semiconducting phase. Using an analytical expression …
Polaron and Strain Effects on Ion Migration in WO$_3$
本研究基于密度泛函理论探讨单斜WO$_3$中H$^+$、Li$^+$、Mg$^{2+}$的迁移机制，揭示极化子通过缔合效应和晶格变形增加能垒、晶格应变对不同离子迁移能垒影响各异的规律，为优化WO$_3$器件性能提供关键见解。
Measurements of the low-frequency (f<= 100 kHz) permittivity at T<= 160 K and dc resistivity (T<= 430 K) are reported for La(1-x)Ca(x)MnO(3) (0<= x<= 0.15). Static dielectric constants are determined from the low-T limiting behavior of the permittivity. The estimated polarizability for bound holes ~ 10^{-22} cm^{-3} implies a radius comparable to the interatomic spacing, consistent with the small polaron picture established from prior transport studies near room temperature and above on nearby compositions. Relaxation peaks in the dielectric loss associated with charge-carrier hopping yield ac…
By combining first principles calculations and experimental XPS measurements, we investigate the electronic structure of potential Li-ion battery cathode materials LiMPO4 (M=Mn,Fe,Co,Ni) to uncover the underlying mechanisms that determine small hole polaron formation and migration. We show that small hole polaron formation depends on features in the electronic structure near the valence-band maximum and that, calculationally, these features depend on the methodology chosen for dealing with the correlated nature of the transition-metal d-derived states in these systems. Comparison with experime…
A theoretical study of the influence of pressure on the dielectric relaxation related with polaron tunneling and phonon assisted hopping in disordered solids is developed. The sign and absolute value of the migration volume, which is obtained by employing the present formulation, evidence about the nature of the relaxation. As a paradigm, positive and negative values of migration volume are evaluated by analyzing recently published dielectric loss measurements under pressure in semiconducting polypyrrole. A straightforward relation between the value of the migration volume and the nature of sh…
The understanding of the Physics underlying the performances of organic spin-valve devices is still incomplete. According to some recent models, spin transport takes place in an impurity band inside the fundamental gap of organic semiconductors. This seems to be confirmed by recent experiments performed with La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The reported results suggest a possible correlation between the magnetoresistance and the variable oxygen doping in the Alq$_3$ spacer. In this paper we investigate by means of first-principles calculations the electronic and magnetic…
Grotthuss-type oxygen hole polaron transport in desodiated Na$_{2}$Mn$_3$O$_7$
本研究在脱钠Na₂Mn₃O₇中发现罕见分裂氧空穴极化子，通过DFT揭示其沿b轴的类Grotthuss分步迁移机制，计算了迁移率等参数，为奇异极化子输运及功能材料研发提供新理论见解。
Nearly half a century ago, I joined an ambitious research project aimed at establishing the mechanism of photodecomposition of ionic salts. We measured the mobilities and lifetimes of photoelectrons and photoholes in silver bromide in order to get an early-stage knowledge of the process. The last pairs of quantities to study were the diffusion coefficients for which we got results, highly controversial at that time. Now we show that the diffusion data suggest the formation of itinerant Jahn Teller small polarons as the next-stage photo-carriers in silver halides.
First-principles study on Small Polaron and Li diffusion in layered LiCoO2
本文通过第一性原理研究层状LiCoO2中极化子对锂扩散的影响，发现磁有序下Co4+极化子虽提高扩散势垒但使迁移更稳定，从而提出空穴极化子迁移机制。
Polaron Conductivity in $α$-Fe2O3 Quenched by Adsorbed NO2
研究通过DFT+U和 nudged elastic band计算，揭示了α-Fe₂O₃表面极化子形成与淬灭机制，发现NO₂吸附导致电子转移，抑制极化子导电性，为铁氧化物气体传感器设计提供新原理。
Acceptor-doped perovskite oxides like BaZrO$_3$ are showing great potential as materials for renewable energy technologies where hydrogen acts an energy carrier, such as solid oxide fuel cells and hydrogen separation membranes. While ionic transport in these materials has been investigated intensively, the electronic counterpart has received much less attention and further exploration in this field is required. Here, we use density functional theory (DFT) to study hole polarons and their impact on hole conductivity in Y-doped BaZrO$_3$. Three different approaches have been used to remedy the s…
Revealing Short- and Long-range Li-ion diffusion in Li$_2$MnO$_3$ from finite-temperature dynamical mean field theory
结合DFT+$U$、有限温度DFT+DMFT和NEB方法，研究顺磁Li$_2$MnO$_3$中单个锂空位存在下的Li$^{+}$迁移，发现动力学关联显著重整最低势垒过程，短程跳跃活化能0.18 eV与μ$^{+}$SR一致，长程输运活化能0.50 eV与交流阻抗测量吻合，无需引入团簇空位或强无序即可统一解释局域和宏观探针。
Uncovering coupled ionic-polaronic dynamics and interfacial enhancement in Li$_x$FePO$_4$
本研究开发微调机器学习力场，揭示LiFePO4中极化子翻转远快于锂迁移，并在相界增强，为多价电池正极耦合输运提供新见解。
Presently, cerium-doped LaMnO$_3$ is vividly discussed as an electron-doped counterpart prototype to the well-established hole-doped mixed-valence manganites. Here, La$_{0.7}$Ce$_{0.3}$MnO$_3$ thin films of different thicknesses, degrees of CeO$_2$ phase segregation, and oxygen deficiency, grown on SrTiO$_3$ single crystal substrates, are compared with respect to their resistance-vs.-temperature (R vs. T) behavior from 300~K down to 90~K. While the variation of the film thickness (and thus the degree of epitaxial strain) in the range between 10~nm and 100~nm has only a weak impact on the elect…
First-principles investigation of small polarons in rhombohedral NaNbO$_{3}$
本研究通过从头原理计算探讨了 rhombohedral NaNbO$_{3}$ 中小空穴和电子极子的稳定性，发现氧是 NaNbO$_{3}$ 内在的空穴陷阱，并强调了在 NaNbO$_{3}$ 基电陶瓷的缺陷模型中包括空穴极子的重要性。
We report on high-dimensional quantum dynamical simulations of torsion-induced exciton migration in a single-chain oligothiophene segment comprising twenty repeat units, using a first-principles parametrized Frenkel J-aggregate Hamiltonian. Starting from an initial inter-ring torsional defect, these simulations provide evidence of an ultrafast two-time scale process at low temperatures, involving exciton-polaron formation within tens of femtoseconds, followed by torsional relaxation on a ~300 femtosecond time scale. The second step is the driving force for exciton migration, as initial conjuga…
Multivalent batteries are an energy storage technology with the potential to surpass lithium-ion batteries, however their performance has been limited by the low voltages and poor solid-state ionic mobility of available cathodes. A computational screening approach to identify high-performance multivalent intercalation cathodes among materials that do not contain the working ion of interest has been developed which greatly expands the search space that can be considered for materials discovery. This approach has been applied to magnesium cathodes as a proof of concept and four resulting candida…
We present and discuss the results of ab initio DFT plane-wave supercell calculations of the atomic and molecular oxygen adsorption and diffusion on the LaMnO3 (001) surface which serves as a model material for a cathode of solid oxide fuel cells. The dissociative adsorption of O2 molecules from the gas phase is energetically favorable on surface Mn ions even on a defect-free surface. The surface migration energy for adsorbed O ions is found to be quite high, 1.6 eV. We predict that the adsorbed O atoms could penetrate into electrode first plane when much more mobile surface oxygen vacancies (…
As a prototypical Mott insulator with ferromagnetic ordering, YTiO3 (YTO) is of great interest in the study of strong electron correlation effects and orbital ordering. Here we report the first molecular beam epitaxy (MBE) growth of YTO films, combined with theoretical and experimental characterization of the electronic structure and charge transport properties. The obstacles of YTO MBE growth are discussed and potential routes to overcome them are proposed. DC transport and Seebeck measurements on thin films and bulk single crystals identify p-type Arrhenius transport behavior, with an activa…
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