Pristine Compound Research Articles

Role of trivalent bismuth ion substitution at Dy site on the physical properties of DyMnO3

Polycrystalline compounds of Dy1−xBixMnO3 (x = 0 & 0.1) synthesized by ceramic method were characterized by X-ray diffraction technique and their vibrational, transport and magnetic properties studied. Refinement of powder X-ray diffraction data showed that both materials exhibit orthorhombic structure with Pnma space group. Although Bismuth substitution retains the crystal structure, bond angles and bond lengths within MnO6 octahedra are altered as compared to the pristine compound, DyMnO3. While bond angle between manganese ions along the b-axis reduces slightly (1°), axial bond angle increased by ∼3° in the substituted compound. Raman bands arising from the atomic vibrations of rare earth dysprosium and oxygen ions have been identified from room temperature Raman spectra. For 10 at.% substitution of Bi3+, these modes are hardened. Transport measurement studies indicated that the materials are semiconducting in nature with small polaron hopping type of conduction. Hopping energy is decreased to 98.52 meV for Bi3+ substituted DyMnO3 (Dy0.9Bi0.1MnO3) from 103.85 meV for DyMnO3. Temperature dependence of dc magnetization studies revealed anomalies around 39 K, 12 K and 3.62 K corresponding to antiferromagnetic ordering involving Mn3+ and Dy3+ ions respectively. Temperature and frequency variation of ac susceptibility data corroborated the dc magnetization results. In both compounds, magnetization versus applied magnetic field curves measured at several temperatures from room temperature down to 10 K showed linear behavior revealing paramagnetic nature. This behavior indicates the absence of magnetic correlations which is in accordance with MT data. On the other hand, hysteresis loops were observed in M-H data registered ∼2 K with coercive fields of 1520 Oe and 1365 Oe for DMO and DBMO respectively. However, magnetization does not saturate even at 7 × 104 Oe field. The origin for the ferromagnetic coupling could be ascribed to the correlations between Dy3+ and Mn3+ ions through apical oxygen ions in the unit cell favoring superexchange interactions.

Theory-Guided Synthesis of an Eco-Friendly and Low-Cost Copper Based Sulfide Thermoelectric Material

Cu3SbS4 is a copper-based sulfide composed of earth-abundant elements. We present a combined theoretical and experimental study of the thermoelectric properties of Ge-doped Cu3SbS4. On the basis of density functional theory, we found that the pristine compound is a semiconductor with a large density-of-state effective mass of ∼2.2 me for holes. Ge was predicted to be an effective p-type dopant that only slightly shifts the band structure of Cu3SbS4. The power factor was predicted to reach a maximum value with 10–15 mol % Ge-doping on the Sb site (n = (6–9) × 1020 cm–3) at high temperature (up to 700 K). Theory was used to guide the synthesis of optimally doped Cu3SbS4 bulk samples. Experimentally, Cu3SbS4 bulk samples were prepared by mechanical alloying and spark plasma sintering. The samples had very fine microstructures, with a grain size of ∼100–300 nm, which contributed to a much lower lattice thermal conductivity than reported in the literature. A maximum power factor of ∼1.08 mW K–2 m–1 was achieve...

Role of O and Se defects in the thermoelectric properties of bismuth oxide selenide

Bismuth oxygen selenide, Bi2O2Se, is a promising thermoelectric material because of its reduced thermal conductivity. In this study, we perform the first-principles calculation and utilize the solution of Boltzmann transport equation in a constant relaxation-time approximation to compute the electronic and thermoelectric properties of Bi2O2Se with O and Se defects. Oxygen vacancies trap bands located inside the band gap of Bi2O2Se, and the compound becomes a conductor. These bands lead to drastic reduction in the Seebeck coefficient. When vacancies are filled by selenide atoms (selenide point defect), the materials return to be a semiconductor and the Seebeck coefficient increases. The increase of S is also found in the system with defects formed by the substitution of oxygen atoms into selenide sites (oxygen point defect) in the pristine compound. The power factor significantly increases during p-type doping compared with that during n-type doping for the selenide point defect. However, differences in the two doping cases are less distinguished for the oxygen point defect. Hence, the selenide point defect, Bi2O2−δSe1+δ with p-type doping, is an effective way to increase the power factor and eventually the thermoelectric efficiency of Bi2O2Se.

Operando Mössbauer Spectroscopy Investigation of the Electrochemical Reaction with Lithium in Bronze-Type FeF3·0.33H2O

The electrochemical reaction of bronze-type FeF3·0.33H2O, synthesized via a simple room-temperature solution route, with lithium was investigated by operando Mossbauer spectroscopy and X-ray diffraction. The two techniques revealed a complex electrochemical mechanism where the pristine crystalline compound is gradually transformed into an amorphous material containing nanodomains of a FeF2-like rutile structure mixed to iron nanoparticles. Upon charge, two steps are dominating the electrochemical behavior: partial reformation of the initial bronze structure and oxidation to Fe(III). This reaction mechanism, however, is not constant, and noticeable variation can be observed during galvanostatic cycling (up to 55 cycles) until eventually an amorphous material containing rutile nanodomains composes the final active electrode. The material performance, under the form of a fluoride/graphene oxide composite, is also assessed with respect to the long-term effect of the depth of first discharge.

Angle-resolved photoemission study of the Kitaev candidateα−RuCl3

$\alpha$-RuCl$_3$ has been hinted as a spin-orbital-assisted Mott insulator in proximity to a Kitaev spin liquid state. Here we present ARPES measurements on single crystal $\alpha$-RuCl$_3$ in both the pristine and electron-doped states, and combine them with LDA+SOC+U calculations performed for the several low-energy competing magnetically ordered states as well as the paramagnetic state. A large Mott gap is found in the measured band structure of the pristine compound that persists to more than 20 times beyond the magnetic ordering temperature, though the paramagnetic calculation shows almost no gap. Upon electron doping, spectral weight is transferred into the gap but the new states still maintain a sizable gap from the Fermi edge. These findings are most consistent with a Mott insulator with a somewhat exotic evolution out of the Mott state with both temperature and doping, likely related to unusually strong spin fluctuations.

Evaluation of hydrotalcite-like compounds with distinct interlaminar anions as catalyst precursors in methylene blue photodegradation

In this work, two hydrotalcite like-compounds with nitrate and acetate as interlaminar anions (uncalcined and calcined) were evaluated as catalysts in the photodegradation of methylene blue (MB) under visible light irradiation. Materials were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis, Scanning Electron Microscopy and Diffuse Reflectance Spectroscopy. The XRD analysis of the pristine compounds demonstrated that they exhibited the characteristic reflections of hydrotalcite-like compounds as the main crystalline phase. The analysis of the (003) reflection confirmed nitrate or acetate presence in the interlaminar region. However, after annealing spinel and MgO obtaining at 350°C was evidenced in both materials. Major absorbance intensity in the visible region was observed in the acetate-containing samples and the highest MB decomposition was achieved with the acetate precursor sample calcined at 450°C. The photocatalytic activity was attributed to a synergy between the crystalline phases, specific surface area and the band gap energy.

Mulliken Occupation as the Indicator of Transition to Superconducting State in SrFe2As2and BaFe2As2

Basing on the ab initio calculations performed within full potential local orbital minimum basis method, the Mulliken occupation of the Sr 5s (n5s) and Ba 6p (n6p) states can serve as an indicator of transition to the superconducting state in doped SrFe2As2 and BaFe2As2 compounds where the iron was substituted with cobalt or in the pristine compounds under pressure. The estimated pressure, at which both compounds exhibit superconductivity based on Sr 5s and Ba 6p occupation is in good agreement with the recently published experimental data.

Phase Separation and d Electronic Orbitals on Cyclic Degradation in Li-Mn-O Compounds: First-Principles Multiscale Modeling and Experimental Observations.

A combined study involving experiments and multiscale computational approaches is conducted to propose a theoretical solution for the suppression of the Jahn-Teller distortion which causes severe cyclic degradation. As-synthesized pristine and Al-doped Mn spinel compounds are the focus to understand the mechanism of the cyclic degradation in terms of the Jahn-Teller distortion, and the electrochemical performance of the Al-doped sample shows enhanced cyclic performance compared with that of the pristine one. Considering the electronic structures of the two systems using first-principles calculations, the pristine spinel suffers entirely from the Jahn-Teller distortion by Mn(3+), indicating an anisotropic electronic structure, but the Al-doped spinel exhibits an isotropic electronic structure, which means the suppressed Jahn-Teller distortion. A multiscale phase field model in nanodomain shows that the phase separation of the pristine spinel occurs to inactive Li0Mn2O4 (i.e., fully delithiated) gradually during cycles. In contrast, the Al-doped spinel does not show phase separation to an inactive phase. This explains why the Al-doped spinel maintains the capacity of the first charge during the subsequent cycles. On the basis of the mechanistic understanding of the origins and mechanism of the suppression of the Jahn-Teller distortion, fundamental insight for making tremendous cuts in the cyclic degradation could be provided for the Li-Mn-O compounds of Li-ion batteries.

Extremely large anisotropic transport caused by electronic phase separation in Ti-doped Ca3Ru2O7

In this paper, we reported an extremely large out-of-plane/in-plane anisotropic transport ( ~ 109) in double layer ruthenates. The mechanism that may be responsible for this phenomenon is also explored here. Distinct from previously well studied layered materials which show large out-of-plane/in-plane electronic anisotropy (103–106), the Ti-doped Ca3Ru2O7 single crystals not only form quasi-2D layered structure, but also show phase separation within the layers. We found that Ti doping in Ca3Ru2O7 induced electronic phase separation between the insulating phase and weak localized phase. The ratio of these two phases is very sensitive to the Ti concentration. At typical concentration, the weak localized phase may form a channel on the background of the insulating phase within the ab plane. However, the small volume of weak localized phase makes it less likely to overlap in different layers. This results in a much larger electronic anisotropy ratio than pristine compound Ca3Ru2O7. This new mechanism provides a route for further increase electronic anisotropy, which will remarkably reduce current leak and power consumption in electronic devices.

Study on the action mechanism of doping transitional elements in spinel LiNi0.5Mn1.5O4

Spinel LiNi0.5Mn1.5O4 is a very important and promising cathode material for lithium ion batteries. The strategy of doping elements is a common used way to improve its electrochemical properties. The action mechanism of doping elements in LiNi0.5Mn1.5O4 is complex. In this study, we synthesized the Cr, Fe-doped compounds LiNi0.45M0.1Mn1.45O4 (M=Cr, Fe) and pristine compound LiNi0.5Mn1.5O4 at the same annealing conditions. The as prepared samples display different morphological features. The thermogravimetric analysis shows different situation for these samples. Oxygen dissipation in the Cr-doped compound at high temperature is less than the other two samples. The XPS spectra display that the doping elements have influences on the chemical valence of Ni, and result in more Ni(III) amount in the Cr, Fe-doped products. The doped compounds exhibit excellent rate capability. At 10C-charge/10C-discharge rate, their capacities are 85mAhg−1, 74mAhg−1 and 50mAhg−1 for LiNi0.45Fe0.1Mn1.45O4, LiNi0.45Cr0.1Mn1.45O4 and LiNi0.5Mn1.5O4, respectively.

Structure, Stoichiometry, and Charge Transfer in Cocrystals of Perylene with TCNQ-Fx

Semiconductor charge transfer (CT) cocrystals are an emerging class of molecular materials which combines the characteristics of the constituent molecules in order to tune physical properties. Cocrystals can exhibit polymorphism, but different stoichiometries of the donor–acceptor (DA) pair can also give different structures. In addition, the structures of the donor and acceptor as pristine compounds can influence the resulting cocrystal forms. We report a structural study on several CT cocrystals obtained by combining the polyaromatic hydrocarbon perylene with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its fluorinated derivatives having increasing electronegativity. This is achieved by varying the amount of fluorine substitution on the aromatic ring, with TCNQ-F2 and TCNQ-F4. We find structures with different stoichiometries. Namely, the system perylene:TCNQ-F0 is found with ratios 1:1 and 3:1, while the systems perylene:TCNQ-Fx (x = 2, 4) are found with ratios 1:1 and 3:2. We discuss the structures on ...

High pressure Raman study of layered Mo0.5W0.5S2 ternary compound

Ternary two-dimensional (2D) transition metal dichalcogenide compounds exhibit a tunable electronic structure allowing for control of the interlayer and the intralayer atomic displacement to efficiently tune their physical and electronic properties. Using a diamond anvil cell, hydrostatic pressure was applied to Mo0.5W0.5S2 up to 40 GPa in order to study the optical phonon vibrational modes. Analysis of the high-pressure Raman spectra shows that the two in-plane E2g modes resembling that of pristine MoS2 and WS2, as well as disorder-activated longitudinal acoustic phonon mode, are hardened and suppressed as pressure increases. The two A1g modes of the ternary compound that resemble the A1g modes of pristine MoS2 and WS2, displayed similar Raman shifts to the pristine compounds as pressure increases. A Raman peak at 470 cm−1 that is close to A1g peaks emerges at ∼8 GPa, which represents a disorder-activated pressure-induced out-of-plane Raman mode observed only in the ternary compound under high pressure. At pressures above ∼30 GPa, a Raman peak at approximately 340 cm−1 is observed, signifying additional disorder-activated vibration mode. Our results reveal the enhanced interactions in the structural and vibrational behavior of the MoS2 and WS2 domains in the Mo0.5W0.5S2 compound under hydrostatic pressure. These results could have implications in understanding the electronic, optical, and structural properties of the new 2D ternary compound materials under extreme mechanical conditions.

Iron phthalocyanine on Cu(111): Coverage-dependent assembly and symmetry breaking, temperature-induced homocoupling, and modification of the adsorbate-surface interaction by annealing.

We have examined the geometric and electronic structures of iron phthalocyanine assemblies on a Cu(111) surface at different sub- to mono-layer coverages and the changes induced by thermal annealing at temperatures between 250 and 320 °C by scanning tunneling microscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. The symmetry breaking observed in scanning tunneling microscopy images is found to be coverage dependent and to persist upon annealing. Further, we find that annealing to temperatures between 300 and 320 °C leads to both desorption of iron phthalocyanine molecules from the surface and their agglomeration. We see clear evidence of temperature-induced homocoupling reactions of the iron phthalocyanine molecules following dehydrogenation of their isoindole rings, similar to what has been observed for related tetrapyrroles on transition metal surfaces. Finally, spectroscopy indicates a modified substrate-adsorbate interaction upon annealing with a shortened bond distance. This finding could potentially explain a changed reactivity of Cu-supported iron phthalocyanine in comparison to that of the pristine compound.

Confined ZrO2 encapsulation over high capacity integrated 0.5Li[Ni0.5Mn1.5]O4·0.5[Li2MnO3·Li(Mn0.5Ni0.5)O2] cathode with enhanced electrochemical performance

Confined ZrO2 encapsulation over high capacity spinel-layer-layer structured 0.5Li[Ni0.5Mn1.5]O4·0.5 [Li2MnO3·Li(Mn0.5Ni0.5)O2] with various concentration by sol-gel process is reported. Presence of homogeneous ZrO2 layer is evident from the TEM studies. Various electrochemical studies such as optimization of ZrO2 concentration followed by rate performance, elevated temperature studies, and potential windows are also performed. Among the studies, 1wt.% ZrO2 modification is found superior in 2 − 4.9V vs. Li region compared to rest of the coating concentration and pristine compound. Cyclic voltammetry and impedance studies are also performed to understand the reaction mechanism and other electrochemical aspects.

Investigation of near room temperature magnetocaloric, magnetoresistance and bolometric properties of Nd0.5La0.2Sr0.3MnO3: Ag2O manganites

In the present research, we have studied the manganites for their promising applications in magnetoresistive, bolometric (infrared detectors) and magnetic refrigeration based devices. In order to explore the manganite for different applications near the room temperature, we have investigated Nd0.5La0.2Sr0.3MnO3: xAg2O (x = 0–30 wt%) polycrystalline composites synthesized by solid state reaction route. These composites have been found to be crystallized in orthorhombic structure with Pnma space group. The lattice constants and volume of the unit cells have not been substantially changed, but the transport properties have been greatly influenced with addition of silver oxide. A significant improvement in magnetoresistance (MR%) has been observed from 22 % (for x = 0.0) to 47 % (for x = 0.3) in an applied magnetic field of 1 T. The temperature coefficient of resistance (TCR %) has been found to be increased from 2.9 % (for x = 0.0) to 7.4 % (for x = 0.3) with addition of silver oxide. Moreover, the change in magnetic entropy(−ΔS M ) near the room temperature is slightly varying from 3.94 J/kg K−1 (for x = 0.0) to 3.59 J/kg K−1 (for x = 0.3) within the field of 6 T. A significant improvement of MR in presence of low magnetic field and enhancement in the TCR % have been observed, but the change in magnetic entropy varied slightly with addition of silver oxide to the pristine compound.

Hydrogenation studies on NdScSi and NdScGe

NdScSi and NdScGe were synthesized from the elements via arc-melting and subsequent annealing. Their ordered La2Sb type structures, with space group I4/mmm, were refined from single crystal X-ray diffractometer data: a=428.94(6) and b=1570.5(3)pm, wR2=0.0395, 309 F2 values for NdScSi and a=431.2(1) and c=1581.3(5)pm, wR2=0.1220, 227 F2 values for NdScGe, with 11 variables per refinement.Hydrogen insertion was performed on both Nd-based intermetallics by solid/gas reaction. Hydrogen uptake keeps the pristine compound space group but yields an anisotropic expansion of the unit cell with a large increase of c (≈+7%) and a slight decrease of a (≈−1.7%) parameters. Hydrogen absorption at 350°C and under 5bar of H2 pressure shows that the hydride NdScSiH1.48(5) is formed. An in-situ neutron diffraction study during the deuteration of NdScSi reveals for the first time in a CeScSi-type compound, the possibility to fill two interstitial sites with deuterium atoms, leading to the composition NdScSiD1.5 for the deuteride adopting then the La2Fe2Se2O3-type structure.From magnetization measurements, we evidence that hydrogenation strongly reduces the Curie temperature of NdScSi (TC=175K) and NdScGe (TC=194K) since NdScSiH1.5 and NdScGeHx undergo a magnetic transition at 4K and around 2K, respectively.

Charge/discharge Behavior of Triclinic LiTiOPO<sub>4</sub> Anode Materials for Lithium Secondary Batteries

Triclinic LiTiOPO4 fine powders were synthesized via low-temperature thermal treatment. First, amorphous fine powders were prepared by mechanical milling (MM) treatment of a mixture of the starting materials (Li2CO3, TiO2, and P2O5) at room temperature. The mechanically milled amorphous powder formed a triclinic LiTiOPO4 crystal below 700°C in air. The mechanically milled powders before heat treatment barely worked as an active material at ca. 0.1 C rate in the potential range of 1.0 to 3.0 V versus Li/Li+ in lithium cells. On the other hand, the triclinic LiTiOPO4 compounds obtained by the crystallization of the mechanically milled amorphous powders at 700°C in air worked as anode materials in lithium cells. The triclinic LiTiOPO4 electrode materials exhibited capacities of around 100 mAh g−1. The average operation potential was around 1.7 V (vs. Li/Li+). The triclinic LiTiOPO4 pristine compound when used as an anode caused a phase transition into an orthorhombic compound during lithium insertion (charge process). The orthorhombic compound changed into a triclinic phase during lithium extraction (discharge process). The triclinic LiTiOPO4 electrodes exhibited a good cycle performance in the potential range of 1.0 to 3.0 V versus Li/Li+. It is suggested that the crystalline phase changes reversibly during charge/discharge.

Effect of the Al-doping on the electrical and thermoelectric response of TbMnO3 polycrystalline samples: Evidence of polaronic transport

High-quality, polycrystalline Tb1−xAlxMnO3 (x = 0–0.2) samples were prepared by means of standard solid state reaction. The incorporation of the Al ions into the TbMnO3 lattice is verified by X-ray diffraction measurements. The zero-field electrical conductivity, thermopower, and thermal conductivity of these samples are carefully measured and analyzed. The pristine compound shows low electrical conductivity, high and positive thermopower values (∼300 μV/K at 300 K) in the whole temperature range measured, and rather low thermal conductivity (∼5 W m−1K−1 at 300 K). Al substitution leads to a dramatic reduction in resistivity and stabilization of the ferromagnetic phase at low temperatures. The low value of the electrical conductivity constitutes a major obstacle for thermoelectric applications of this material. Nevertheless, the incorporation of Al ions at the Tb site provokes a slight reduction in the value of the thermopower and a slight increase in the thermal conductivity. For the tested samples dκ/dT > 0 (the behavior of an amorphous solid) is verified in the whole temperature range (2–390 K). Nevertheless, dκ/dT > 0 here should be related not to quenched structural disorder but rather to unusually large dynamic lattice distortions accompanying charge transport. The lower values of κ at low-temperatures (as compared to those reported for single crystals) can be linked to the high concentration of grain boundaries. The variation in both the resistivity and thermopower with temperature is well described by the polaronic model, which, nevertheless, is not linked to the stabilization of a ferromagnetic phase in the compound. Although the values of the figure of merit ended up being too small to thermoelectric applications, it is noted that the addition of Al ions improve the values of this parameters by more than one order of magnitude. The improvement of the low electrical conductivity upon Al addition is behind this technical achievement.

Efficiency assessment of novel materials based flexible thermoelectric devices by a multiscale modeling approach

The presented work demonstrates a multiscale approach for evaluating novel materials for room temperature thermoelectric applications and provides some insights into the development of flexible devices composed of those materials. Tetrahedrite is studied as it is a promising p-type thermoelectric material that exhibits good thermoelectric properties at room temperature. Considering our target application, analysis of the theoretical results reveals that tetrahedrite is an interesting surrogate material to bismuth telluride for room temperature applications with a power factor ranging from 4.16μW/cmK2, for the pristine tetrahedrite compound, to around 9μW/cmK2, for a doped tetrahedrite. A single thermocouple made of p-type pristine tetrahedrite and n-type natural chalcopyrite has an optimum output power of 5.53nW/K. This output power can reach 7.47nW/K when optimally doping tetrahedrite.

An Investigation of Na1-XLi2x MnyNizOd Compounds for High Performance Sodium-Ion Batteries

Lithium ion batteries (LIBs) are the current energy storage technology of choice for numerous applications ranging from portable electronics to transportation and grid energy storage. The demand for LIBs production is predicted to considerably increase in the near future. The rising price of lithium and geopolitical problems associated with the lithium extraction urge us to look for alternative energy storage technologies. Sodium ion batteries (SIBs) are an attractive choice due to the natural abundance and lower cost, as compared to lithium, of sodium. However, due to the higher atomic mass of Na as compared to Li, SIBs have a lower energy density than LIBs and therefore current research efforts are focused on the development of high performance, low-cost, easy to manufacture, safe and non-toxic SIBs. Compounds of the type P2-NaxMO2 are intensively investigated due to their suitability for Na-ion intercalation [1]. However, a drawback of these compounds is the de-stabilization during cycling attributed to layer-gliding and phase transformations (often seen as steps and kinks in GCPL curves) [2]. Recently, C.S Johnson et al. has proposed that introduction of Li-ions in compounds of the type P2-NaLix MnyNizOδ and Na1-xLix MnyNizO δ prvents layer-gliding during cycling, stabilizing the P2 phase (for the former compound) and therefore enabling an improved power and rate performance [2-4]. In the pristine compounds, the transition metals are in the Mn (4+) and Ni (2+) states (implying values of δ > 2.0, i.e oxygen rich materials) [3]. The authors confirmed that during cycling, only the Ni (+2) provides redox activity whereas the manganese remains inactive providing stability to the compounds [2]. In the case of P2-NaLix MnyNizO δ , Li was found to reside on both the alkali and the transition metal layer and the lack of layer gliding was attributed to the presence of a Li2MnO3-like phase where Li remained immobile [2]. In the case of Na1-xLix MnyNizO δ , the stability was attributed to the inter-growth of P2/O3 phases. We are intrigued by the complex nature of these compounds and the associated stabilizing mechanism during Na-ion insertion/de-insertion processes. We are interested on exploring alternative stoichiometries, particularly those that perhaps will allow stability to a higher upper cut-off voltages enabling a higher energy density while maintaining a high power performance. We believe that besides adequate stoichiometry, the performance of these compounds can be improved by adequate electrolyte formulation. In this work, compounds of the type Na1-xLi2xMnyNizO δ were synthesized using a facile sol-gel technique The electrochemical performance of the compounds was investigated in a two-electrode cell using the metal oxide as working electrode, metallic sodium as pseudo-reference and counter electrodes and a 1 M NaClO4/EC/PC/additive as electrolyte. The main electrochemical techniques used were GCPL and EIS.The morphology and crystal structure were investigated by XRD, SEM and TEM. [1] J. Xu, D. H. Lee, and Y. S. Meng, Functional Materials Letters 06, 1330001 (2013). [2] N. K. Karan, M. D. Slater, F. Dogan, D. Kim, C. S. Johnson, and M. Balasubramanian, Journal of The Electrochemical Society 161, A1107 (2014). [3] D. Kim, S.-H. Kang, M. Slater, S. Rood, J. T. Vaughey, N. Karan, M. Balasubramanian, and C. S. Johnson, Advanced Energy Materials 1, 333 (2011). [4] E. Lee et al., Advanced Energy Materials 4, 1400458 (2014).