Tunable Properties of Mg-Doped V2O5 Thin Films for Energy

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Tunable Properties of Mg-doped VO Thin Films for Energy Applications: Li-ion Batteries and Electrochromics Marianthi Panagopoulou, Dimitra Vernardou, Emmanuel Koudoumas, Nikos Katsarakis, Dimitris Tsoukalas, and Yannis S. Raptis J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b09018 • Publication Date (Web): 16 Dec 2016 Downloaded from http://pubs.acs.org on December 20, 2016

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The Journal of Physical Chemistry

Tunable Properties of Mg-doped V2O5 Thin Films for Energy Applications: Li-ion Batteries and Electrochromics Marianthi Panagopoulou†*, Dimitra Vernardou‡, Emmanuel Koudoumas‡§, Nikos Katsarakis‡§!, Dimitris Tsoukalas†, Yannis S. Raptis† †

School of Applied Mathematical and Physical Sciences, National Technical University of

Athens, 157 80, Zografou Campus, Athens, Greece ‡

Center of Materials Technology and Photonics, School of Engineering, Technological

Educational Institute of Crete, 71004 Heraklion, Crete, Greece §

Electrical Engineering Department, Technological Educational Institute of Crete, 710 04

Heraklion, Crete, Greece !

Institute of Electronic Structure and Laser, Foundation for Research & Technology-Hellas, P.O.

Box 1527, Vassilika Vouton, 711 10 Heraklion, Crete, Greece

ACS Paragon Plus Environment

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ABSTRACT

Vanadium pentoxide (V2O5) is doped for the first time with Mg and the influence of Mg content on the films properties and functionality is investigated in detail, emphasis given on the electrochemical and electrochromic response. The Mg-doped V2O5 films exhibit characteristics suitable for lithium ion batteries and electrochromic window applications, the optimization of the functionality depending on the Mg content. Low Mg content (2 at. % Mg) appears to favor lithium ion batteries applications, the corresponding films exhibiting high specific discharge capacity, increased diffusion coefficient and high capacity retention. In contrast, high Mg content (15 at. % Mg) is more favorable for electrochromic windows, presenting fast switching response time, high coloration efficiency and high visible transmittance. In both cases, the determined characteristics are superior or at least equivalent to those reported for V2O5 doped with other transition metal. The obtained results clearly indicate that tuning of the Mg doping enables the growth of thin films with application-centered characteristics.

1. Introduction Nowadays, the research on electrical energy-storage devices has been focused, among others, on rechargeable lithium-ion batteries, which can be used in a wide range of applications due to their high energy density, long lifetime, safety and minimal environmental impact1, 2. Vanadium pentoxide (V2O5) is used in a great extend as an intercalation host for lithium ions and thus as a cathode material for this type of batteries. Instead of Li, it can be also used as an intercalation host for other polyvalent cations, like Mg2+, Zn2+, and Al3+, as it was early reported by Smyrl et al.3. Based on the same property, V2O5 has also been suggested for use in industrial applications, as an electrochromic device for controlling sunlight through windows and thus resulting in


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energy saving for buildings4, 5. This is because, upon charge insertion or extraction, it changes its optical transmittance between a clear and a color state, respectively. Orthorhombic crystalline V2O5 consists of a layered crystal structure and exhibits a high theoretical capacity (296 mAh/g), which originates from the intercalation of 2 Li ions6. On the other hand, amorphous V2O5, such as the one found in aerogels or xerogels, presents a bi-layer form7, further enhancing the intercalation property. It is considered safe, cheap with great stability, good intercalation capacity and cycling performance. However, crystalline V2O5 presents poor electrochemical performance during long term cycling8-11, a fact that introduces a limitation on its use as a cathode material (in Li+ batteries or electrochromic windows applications). This can be attributed to various reasons like low electronic and ionic conductivity8, 9, slow ion diffusion (slow electrochemical kinetics) and poor structural stability10, 11. In the past decade, several groups have proposed various approaches for the improvement of the Li ions intercalation properties (enhancing the rate of insertion) and the electrochemical performance of V2O5. Among them, its doping with transition metal ions (Ag12, Cu13, Mn14, Cr15, Al16, Fe17, Sn18, etc.) has been thoroughly investigated. As found out, the metallic dopant atoms replace one of the V atoms, forming V4+ cations, which results in a higher electronic conductivity. For instance, Cu or Ag doped V2O5 has been reported to have 2 -10 times higher electronic conductivity than the pure (intrinsic) material19, 20, a property that leads in an improvement of the electrochemical behavior21, 22. Additionally, doping with Mn has demonstrated to induce higher intercalation capacity and discharge voltage, both increasing with increasing Mn concentration14. At the same time, doped V2O5 exhibits excellent cyclic stability, a fading rate of about 0.06 % per cycle, a value significantly better than that of the pure V2O5 films (0.8 % per cycle) 23. In general, the metal dopant atoms form octahedral chains making the


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material structure more stable during electrochemical cycling, enhancing the system’s reversibility24. Finally, V2O5 /graphene nanocomposite films have been found to expand the optical modulatory range in the visible, by presenting enhanced intercalation properties of Li+ ions25. In this work, V2O5 has been doped, for the first time to the best of our knowledge, with Mg, so that the electrochemical and the electrochromic properties can be enhanced. The fabrication of V2O5 thin films, pure and doped with Mg at various concentrations, was carried out by RF magnetron reactive sputtering, and their intercalation properties, such as charge storage capability, capacity, switching response, coloration efficiency and stability, were studied in detail. Special attention was given to the conditions optimizing the doped films performance, regarding lithium-ion batteries and electrochromic windows. 2. Experimental Section 2.1. Materials preparation V2O5 thin films were prepared by RF magnetron reactive sputtering onto glass substrates precoated with SnO2 thin film (K-glass, Pilkington). All substrates had a surface of 1 cm x 2 cm and a thickness of 0.4 cm and were all cleaned before the deposition with acetone, isopropanol, water and then dried in pure nitrogen flow. The deposition was performed using a Kurt J. Lesker RF magnetron sputtering deposition system, employing metallic V and metallic Mg target (both of 99.95 % purity). Each one of them was functioning at a different RF power, in order to control the Mg concentration in the doped films. V target was functioning at 140 W, while Mg at a range of 3 to 25 W. Oxygen and argon were introduced in the chamber in a 0.06 ratio, resulting in a total chamber deposition pressure of 0.8 Pa. The substrate temperature was kept constant at 300


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o

C and the deposition time for all films was 180 min, resulting in a thickness of about 60 nm, as

measured by surface profilometry (Dektak 150 stylus profiler). 2.2. Materials characterization The structure and the surface morphology of all films were investigated by X-ray diffraction (XRD, Panalytical X’Pert Diffractometer operating with a continuous scan of Cu Ka1 radiation with λ = 1.54056 Å), Raman spectroscopy (Micro-Raman T64000 J-Y system with an Argon laser at 514.5 nm) and Field Emission Scanning Electron Microscopy (FESEM, FEI Nova NanoSEM 230). The detection of Mg dopant and the estimation of its at. % concentration was performed through the energy dispersive X-ray (EDS) component attached to FESEM. 2.3. Electrochemical measurements The electrochemical properties of all films were studied using a standard three-electrode system, which consists of counter (Pt), reference (Ag/AgCl) and working thin film of pure and doped V2O5 grown on SnO2 pre-coated glass substrate electrodes26-28. A solution of LiClO4 / propylene carbonate (1 M) acted as the electrolyte during all measurements. Cyclic voltammetry tests (CV) were carried out in the potential region -1.5 to +1 V vs. Ag/AgCl with a scan rate of 10 mV/s. The charge-discharge properties of the films were investigated by chronopotentiometric (CP) measurements with a constant current density of 150 µΑ cm-2. Furthermore, chronoamperometry at -1.5 V and +1 V for a step of 200 s and a total time period of 2000 s was performed to study the Li+ ion intercalation/deintercalation properties. The electrochemical impedance spectroscopy (EIS) of the films was also studied in the frequency range from 100 kHz to 10 mHz with an AC amplitude of 0.4 V and a set potential of -1 V. All the above-mentioned electrochemical measurements were performed using an AUTOLAB (PGSTAT302N potentiostat-galvanostat) instrument. Finally, ex-situ transmittance spectra were


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obtained using a Perkin-Elmer Lambda 950 UV-VIS spectrophotometer in the wavelength range of 300-1000 nm, for the determination of the coloration efficiency. 3. Results and Discussion 3.1. Morphological and Structural Characterization The field emission scanning electron microscopy (FESEM) images of pure and Mg-doped V2O5 films with different doping concentrations are presented in Figure 1. It can be clearly seen that the resulting films morphology is greatly affected by the inserted Mg atoms. In particular, the pure film consists of well-crystallized elongated grains, with a size of the order of 200 nm. Doping of Mg resulted in grains of different shape and size, the per case morphology depending on the dopant concentration. By increasing Mg content, the films appeared more smooth and dense, their grains became smaller, with a diameter of 75 nm for the case of the film with the highest doping. The energy-dispersive X-ray spectroscopy (EDS) spectra of the undoped and Mg-doped V2O5 thin films, shown in Figure 1(f), were used to reveal the presence and the atomic ratio of Mg in the films, which was calculated as Mg/V+Mg. The resulting Mg concentrations for the deposited films, using the EDS results, were estimated to be 0, 2, 6.7, 9.7 and 15 at. %.


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Figure 1. FESEM images of V2O5 films with a) Mg = 0 at. %, b) Mg = 2 at. %, c) Mg = 6.7 at. %, d) Mg = 9.7 at. %, e) Mg = 15 at. % and f) EDS spectra for the case of a), c) and e). X-ray diffraction (XRD) measurements were performed to investigate the phase structure of the deposited films, Figure 2(a) presenting the respecting XRD patterns of pure and Mg-doped V2O5. Except the highest concentration studied (15 at. %), they were all found crystalline in a typical single orthorhombic structure, with no detectable secondary phase. The major peak observed at 20.4o corresponds to the (001) preferred orientation of the V2O5 crystal structure29. By introducing Mg, the peak position exhibits a small shift to lower diffraction angles (Figure S1(a)), indicating that the presence of Mg atoms slightly affect the structure of V2O5. For the highest Mg concentration studied, the peak disappears, indicating an amorphous behavior. Furthermore, increasing doping results in a decrease of the diffraction peak intensity of the Mgdoped V2O5 films, which can be ascribed to their reduced crystal size, as calculated by Scherrer’s


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formula (dropping from 12.5 nm for the undoped film, to 9 nm for the 9.7 at. %). All the other diffraction peaks present in Figure 2(a) and noted with an asterisk, originate from the SnO2 buffer layer30.

Figure 2. a) XRD patterns and b) Raman spectra of the pure and Mg-doped V2O5 films for different doping concentrations. The respective Raman spectra of the films are shown in Figure 2(b). All spectra exhibit well resolved Raman lines, indicative of the high degree of crystallinity of the films, except the high Mg concentration case. All the nine peaks observed in the frequency range 100-1000 cm-1 correspond to nanocrystalline V2O59. In particular, the most evident peak at 145 cm-1 is attributed to the skeleton bent vibration31, peaks at 301 and 482 cm-1 are ascribed to bending modes of V– O–V bridging bonds, while those at 524 and 698 cm-1 are related with the stretching modes32. Additionally, peaks located at 282 and 402 cm-1 are assigned to the bending vibration of V=O bonds and the high frequency Raman peak at 991 cm-1 corresponds to the terminal oxygen (V=O) stretching mode, which results from unshared oxygen33. The peak at 145 cm-1 exhibits a shift to higher frequencies for increasing Mg doping (Figure S1(b)) combined with a decrease in the peak’s intensity, in an analogous way as in the XRD measurements. Finally, the Raman


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spectrum of the highest Mg content film is featureless, indicating an amorphous character, which is in agreement with the XRD findings. 3.2. Electrochemical Response The effect of Mg doping on the electrochemical properties of V2O5 thin films was firstly investigated by cyclic voltammetry (CV). All CV tests were carried out at a scan rate of 10 mV/s in the voltage range of -1.5 to +1 V vs. Ag/AgCl. Figure 3(a, b) present the CV profiles of the first and second cycles for the pure and the 2 at. % Mg-doped V2O5 films, respectively, while Figure 3(c) compares the 1st CV cycle profile of pure and doped V2O5 thin films at various Mg concentrations. As can be seen, in the first cycle pure V2O5 exhibits more redox peaks as compared to the 2 at. % Mg-doped film. Similar results have also been reported for Sn-doped V2O5 films, where less redox pairs indicate less or depressed phase transitions, thus enhanced cycling stability for the doped film34. In the case of the pure film, the reduction peaks are centered at 0.29, 0.007, -0.95 and -1.35 V and are indicative of multistep Li ion intercalation, corresponding to the formation of the α, ε, δ and finally γ phase, respectively23, 35. Accordingly, the four well-defined oxidation peaks at about 0.53, 0.37, -0.15 and -0.48 V correspond to the respective γ, δ, ε, and α phase transitions36.


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Figure 3. Cyclic voltammograms of a) pure and b) 2 at. % Mg-doped films (first and second scan), c) first scan for all samples and d) peak current vs. square root of scan rate for the pure and Mg-doped V2O5 films. Comparing the cyclic voltammograms presented in Figure 3(a, b), a permanent irreversible phase transition in the structure of pure V2O5 films during the first cycles is evident in agreement with previously reported results37, whereas the 2 at. % Mg-doped film exhibits a more stable CV profile, indicating better electrochemical stability. However, the existence of Mg leads to a small shift of the peaks depending on the dopant concentration (Figure 3(c)) 38, 39, as well as to enhanced current density values associated with cathodic/anodic reactions. The most doped film (Mg = 15 at. %), loses the well-defined redox peaks and presents very low current density in the same potential window. This indicates that a large concentration of Mg modifies significantly the V2O5 structure, in accordance with the structural (XRD, Raman) and morphological (FESEM) characterization, having a great impact in the electrochemical properties of the film. Generally, a decrease of the current density appears for increased doping content, probably associated to a difficulty of intercalation/deintercalation processes of the Li ions. As more Mg atoms are


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introduced in the V2O5 lattice and distort the original structure, the available space for the Li ions insertion is reduced. The dependence of the peak current (ip) with the square root of scan rate (ν1/2) for pure and Mg-doped V2O5 films is presented in Figure 3(d). The relation between peak currents and scan rates in CV curves can provide better insights on various electrochemical reaction characteristics, such as diffusion-controlled and charge-transfer processes40. An almost linear relationship is obtained from the plotted data, which indicates a diffusion-controlled process of Li ions intercalation and deintercalation in both pure and Mg-doped films34. The diffusion coefficient of Li+ can then be determined through this linear relationship, by employing the Randles - Sevcik equation40, 41: / =

2.72 ×

10

×

/ ×

× × /

(1)

where D is the diffusion coefficient of lithium ions, ip is the peak current (anodic/cathodic), n is the number of electrons, C0 is the concentration of active ions in the solution and v is the scan rate. Estimated values for D, for anodic and cathodic current respectively, are given as follows: a) pure film, D(a) = 2.05 x 10-10 cm2 s-1 and D(c) = 2.56 x 10-11 cm2 s-1 b) 2 at. % Mg-doped film, D(a) = 5.99 x 10-10 cm2 s-1 and D(c) = 9.33 x 10-11 cm2 s-1 It is obvious that the diffusion process of lithium is sensitive to the doping concentration, since both peak current and diffusion coefficient for lithium are higher for the 2 at. % Mg doping concentration. Similar behavior appears for the 6.7 at. % Mg doping concentration, while for greater Mg contents the recorded values are decreased, as is obvious in Figure 3(d). Therefore, by introducing a fair amount of Mg atoms in the V2O5 lattice, the cell volume is modified, enhancing diffusion of Li+ ions42. 3.3. Capacity evaluation and EIS analysis


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Galvanostatic charge/discharge measurements were performed for all films, and their specific capacity was calculated, based on the mass of the active material (V2O5 film). Figure 4(a) displays the charge and discharge potential profiles of the pure and the Mg-doped samples at a constant current density of 150 µA cm-2. As can be seen, the charge/discharge behavior of the films is significantly affected by the incorporation of Mg atoms. The initial discharge capacity of pure, 2 at. % and 6.7 at. % Mg-doped V2O5 films was found to be 458, 473 and 470 mAh g-1, respectively. The corresponding charge capacities were 433, 465 and 464 mAh g-1, accordingly. As the doping concentration increases further to 9.7 at. %, the specific capacity drops significantly to 332 mAh g-1, a behavior consistent with the CV curves, because Mg atoms distort the original structure, thus reducing the efficient Li ions insertion sites. A plot of the charge/discharge profiles of the 2 at. % Mg-doped V2O5 at different current densities is shown in Figure 4(b). As the current density increases, the discharge plateaus become more pronounced and a consistent drop in capacity is evident, as expected from the literature43, 44. The cycling performance of the Mg-doped V2O5 films is presented in Figure S4 (SI).


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Figure 4. a) Charge/discharge profiles for the pure and Mg-doped V2O5 films at a current density of 150 µA cm-2, b) charge-discharge profile of the 2 at. % Mg-doped film for different current densities. Furthermore, the capacitance fading has been calculated as the percentage difference of the specific discharge capacity between the first and the hundredth scan. Figure 5(a) shows the dependence of capacitance retention on the Mg content of the films. Both doped and pure V2O5 films showed gradual capacity fading upon cycling. However, the introduction of Mg results in a decrease of fading, the effect being more pronounced for high Mg content. To be more specific, the pure film exhibits an initial specific discharge capacity of 458 mAh g-1, which drops to 214 mAh g-1 after 100 cycles (54 % degradation). Regarding films doped with Mg, the 2 at. % film exhibits 50 % degradation, whereas for the case of the 9.7 at. % Mg content, the degradation is only 37 %. The inset in Figure 5(a) presents the galvanostatic discharge potential profiles of the pure the 2 at. % and the 9.7 at.% Mg-doped V2O5 films in the 1st (solid lines) and the 100th (dashed lines) discharge cycles at a current density of 150 µA cm-2. This graph indicates enhanced, chemical stability due to the presence of Mg atoms. Therefore, a compromise between the nominal specific capacity value and the stability of the film can be established. Although, the


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most doped films exhibit smaller specific capacity, they maintain this value almost constant or with a small fading for a large number of cycles, probably due to their amorphous-like nature45.

Figure 5. a) Capacity fading versus Mg content. (Inset: Discharge curves for the pure, the 2 at. % and the 9.7 at. % Mg-doped V2O5 at the 1st and 100th cycles), b) Fitted Nyquist plots for pure and the 2 at. % Mg-doped V2O5 samples along with the equivalent circuit. In order to understand the kinetics of Li ions intercalation/deintercalation process, electrochemical impedance spectroscopy (EIS) was employed as the best way to analyze the kinetic behavior and calculate the values of the circuit components. The study was performed in


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the frequency range of 100 kHz to 10 mHz with a signal amplitude of 0.4 V, at -1 V set potential. Figure 5(b) presents the Nyquist plots of the pure and 2 at. % Mg-doped V2O5 films. The impedance plots indicate two well-defined regions for both samples. The high to medium frequency region features a semicircle and the low frequency region an inclined straight line, which correspond to charge transfer and diffusion respectively22. The inset in Figure 5(b) shows the equivalent circuit used to fit the EIS data. In the equivalent circuit, there are three components Rs, Rct and CPE, regarding the high frequency response. Rs corresponds to the Ohmic resistance of the electrolyte, Rct is the charge transfer resistance and CPE is the constant phase-angle element that correlates with the double layer capacitance. W, in the low frequency case, is the Warburg impedance and indicates Li+ ions diffusion46, 47. As shown in Figure 5(b), the 2 at. % Mg-doped film exhibits smaller Rct resistance compared with that of the pure one. Smaller charge transfer resistance suggests higher specific capacitance. It has the smaller semicircle diameter, which implies improved electric conductivity, structural stability and smoother electrochemical reaction. The calculated charge transfer resistance of the 2 at. % Mgdoped V2O5 film was 75.1 Ω, while for the pure film was more than double, 184 Ω. The presence of Mg affects Rct, as it is observed elsewhere for the case of graphene and Cu doping48, 49. The starting position of the impedance curve corresponds to Rs. The displacement of this position, in the case of the pure film, can be attributed to an increased Rs value. The reduced Rs value of the 2 at. % Mg-doped sample, can be attributed to improved electrical conductivity and good bonding between the film and the substrate (electrons are being transferred more easily), as have been observed elsewhere50, 51. The slope of the inclined lines increases with the increase of the Mg concentration, demonstrating an improved lithium diffusion rate52.


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Regarding the use of Mg-doped V2O5 thin films as component in Li ion batteries, a 2 at. % Mg content can be considered as the optimum amount of doping, since it results in a slightly distorted crystalline structure which facilitates larger number of Li+ within the lattice, increasing the specific capacity and improving the lithium diffusion rate. Due to the valence difference between V and Mg, a small amount of Mg (2-7 at. %) atoms create oxygen vacancies in their vicinity, deforming the V2O5 structure and generating more free space for the Li ions to occupy. By increasing the Mg content (7-15 at. %), saturation is reached, the film becomes more dense and subsequently, there is no space for Li+ to insert the structure. On the other hand, electrochemical stability is enhanced for higher Mg content (9.7-15 at. %), due probably to the amorphous nature of the films as already mentioned above. Comparing with other results in the literature, such as those with Sn34 and Mn23 doping, our Mg-doped films exhibit higher initial discharge capacity than the corresponding pure film and maintain this relative behavior on further cycling. In contrast, Sn- and Mn-doped films present initially lower discharge capacity than their pure counterparts, while after a number of cycles the behavior is reversed. Regarding the capacity retention, Mg displays a value of 81.7 % after 50 cycles of continuous cycling, value similar to that observed in Cu53 and Mn54 doped films, which display 85 % and 79 % capacity retention, respectively, in contrast to Ag55, which presents a more pronounced fading. It should be emphasized at this point, that by increasing the Mg content, a capacity retention of 97.3 % after the 50th cycle can be reached. 3.4. Electrochromic Performance Chronoamperometric (CA) tests were conducted, switching the voltage between -1.5 to +1 V at an interval of 200 s, for a total time of 2000 s. The current density versus time curves of the pure and the 2 at. % Mg-doped film (Figure S5 (SI)) indicated that the maximum current density


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for the doped film is higher and there is no decreasing rate upon the total time of 2000 s, revealing a reproducible process. The response time tc, which can be extracted by CA measurements, is a quite important parameter for electrochromic devices and is defined as the time needed for excess current to reduce to 10 % of its absolute maximum value56. The tc value for the undoped film was estimated to be 19.5 s for the intercalation process and 20.5 s for the deintercalation, whereas for 2 at. % Mg concentration, tc decreases to 17 s and 15 s, respectively. Deintercalation (bleached state) was faster than intercalation (colored state), as expected from literature57, 58, while increased Mg content resulted in reduced tc values, this reaching 10 s (intercalation) and 4 s (de-intercalation) for the 15 at. % Mg-doped film.

Figure 6. a) Transmittance spectra of the as prepared doped and pure V2O5 films with b) their corresponding optical bandgap, assuming indirect allowed transitions. The optical and electrochromic properties of pure and doped V2O5 thin films with different Mg content were then investigated. Figure 6(a) displays the respective optical transmittance spectra of the films, in the range of 300 to 1000 nm. As can be seen, by increasing the Mg at. % content the luminous transmittance (Tlum) is progressively enhanced, from 73 % for the pure film to 90 % for the 12.5 at. % Mg-doped film. Since no significant fluctuations on the thickness of the films


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were found, the observed Tlum enhancement is solely attributed to the presence of Mg. Furthermore, a blue shift of the absorption edge is observed for the most doped films, which reflects a widening of the optical bandgap. The optical bandgap of the films has been calculated as a function of the doping content through the absorption coefficient. According to the interband absorption theory, the optical band of the films can be calculated using the following relation59: ℎ = (ℎ − ) (2) where A is a constant, Eg is the bandgap of the film, hv is the incident photon energy, and n is the transition coefficient. For the case of V2O5 we have considered n as 2, assuming an indirect bandgap25. The bandgap energy value is evaluated, as shown in Figure 6(b), by extrapolating the steepest linear part of the curve, (ℎ)/ to zero, which corresponds to the optical properties of V2O5 around the middle of the visible spectrum. The calculated values of the bandgap Eg rise as the Mg content increases, starting from a value of 2.18 eV for the pure V2O5 film to 2.45 eV for the 12.5 at. % Mg-doped sample, while for higher Mg concentration a marginal reversing is observed. This bandgap widening is in accord with the observed absorption edge blue shift60, 61. We can presume that Mg can have a similar effect in doping V2O5, as in VO262, causing an increase in Tlum values. In order to evaluate the applicability of Mg-doped films in electrochromic devices, their optical transmittance was recorded in the as prepared and the intercalated state. Figure 7 presents the exsitu optical transmittance of the pure, the 6.7 at. % and the 15 at. % Mg-doped V2O5 films, at initial state and at −1.5 V vs. Ag/AgCl. The films switch in all cases from a transparent yellow (bleached state) to a light blue/gray color (colored state), the difference in the transmittance being larger over the entire spectral region for both the Mg-doped films.


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Figure 7. Transmittance spectra of a) pure, b) 6.7 at.% Mg-doped and c) 15 at.% Mg-doped V2O5 film at different coloration states. The highest contrast value at a specific wavelength λ, can be expressed as ∆Τ % (λ) = Tmax (%) – Tmin (%) and it is exhibited by the 6.7 at. % Mg-doped film, followed by 15 at. % Mg-doped film as shown in Table 1. The ∆T % values are comparable with V2O5/graphene nanocomposite films where the maximal transmittance variation is 30.86 % at 664 nm wavelength25. Another important aspect for electrochromic application is the coloration efficiency (η), which can be calculated by the following equation63: =

1 '()*+,-*. = " # log " # (3) ! ',/)/0*. !

and is defined as the change in optical density (∆OD) divided by the inserted charge per unit area (q).Tbleached and Tcolored are the transmittance values of the film in the bleached and colored state, respectively. Li-ion charge transferred (q) can be calculated by integrating the chronoamperometric curves. The desirable behavior for an electrochromic device is the demonstration of large optical modulation with low charge insertion, resulting in high coloration efficiency. Coloration efficiency was studied as a function of Mg content in the films, at λ = 560 nm (Figure S6 (SI)). The highest coloration efficiency was found in the most doped film (15 at. % Mg) with a value of 44.5 cm2 C-1 at 750 nm and 71.3 cm2 C-1 at 560 nm. Table 1. Transmittance modulation and coloration efficiency of pure and Mg-doped films.


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Mg-content

Page 20 of 31

η (cm2 C-1)

∆Τ (%) 560 nm

750 nm

560 nm

750 nm

0 at. %

14.8

17.3

9

11.2

6.7 at. %

33.6

27

22

18.6

15 at. %

34.4

21.4

71.3

44.5

Regarding the application of Mg-doped V2O5 films in electrochromic smart windows, it seems that a small amount of Mg content is not enough to produce the desired properties, as it was in the case of Li+ batteries. Normally, in electrochromic windows, the desired characteristics are: fast switching time, high contrast between the coloration states, enhanced visible transmittance (to facilitate the comfort of the human eye) and high coloration efficiency. All these criteria are satisfied in the case of the film with the highest Mg content, 15 at. %. For this doping, Tlum significantly increases due to the bandgap widening induced by the Mg doping, while at the same time, owing to its amorphous character, it can provide less space for the Li ions to occupy, resulting in reduced specific capacity and thus enhanced color change ability with reduced power requirements. Therefore, there is an increase in the coloration efficiency of 297 % at 750 nm, and 690 % at 560 nm, between the undoped and the 15 at. % Mg-doped film, accordingly. To the best of our knowledge, this is the largest enhancement recorded for a doped V2O5 film. As an example, Özer et al.64 have presented a 117 % improvement of η (at 550 and 800 nm) between a pure and a Ti-doped V2O5 film. 4. Conclusions Mg-doped V2O5 thin films have been successfully fabricated for the first time, using RF sputtering in different at. % Mg concentrations, and their applicability in Li-ion batteries and electrochromic smart window applications was investigated. The structural, electrochemical and


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optical properties of the doped films were systematically studied compared to those of the undoped film. When used as a cathode material for a Li+ battery, the 2 at. % Mg content was found to deliver the best specific discharge capacity of 473 mAh g-1 at 150 µA cm-2 current density, with a large diffusion coefficient of 5.99 x 10-10 cm2 s-1, as compared to the other films. This enhanced electrochemical performance can be ascribed to the distorted crystalline structure due to the presence of a small amount of Mg atoms, which facilitates incorporation of larger number of Li+. As the Mg content increases, films lose their crystallinity and an amorphous phase is introduced, which favors the cycling stability. Regarding the use of the Mg-doped films as electrochromic components, the 15 at. % Mg-doped films displayed the fastest switching time tc = 10/4 s (intercalation/deintercalation), the best coloration efficiency with a value of 71.3 cm2 C-1 at 560 nm and the highest contrast value between the coloration states of ∆Τ % (560 nm) = 34.4 %. The 15 at. % Mg content also exhibits 85 % visible transmittance and a high transmittance variation through the entire spectrum. This enhanced electrochromic performance can be ascribed to the amorphous nature of this film, which reduces the occupied space of Li ions and thus decreases the energy requirements for the film to change color, as well as to a bandgap widening induced by the Mg doping. Concluding, Mg can be considered an excellent choice of dopant, as compared to the ones reported in the literature, because it can combine both enhanced electrochemical and electrochromic properties, depending on the Mg content.

ASSOCIATED CONTENT Supporting Information. Figures showing XRD and Raman peak shift and analysis, cycling performance of the electrodes, chronoamperometric (CA) measurements and coloration


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efficiency (η) as a function of Mg content. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * (Marianthi Panagopoulou) E-mail: [email protected], Tel: +30 210 772 3044 REFERENCES (1) Armand, M.; Tarascon, J. M. Building better batteries. Nature 2008, 451, 652-657. (2) Kang, K.; Meng, Y. S.; Bréger, J.; Grey, C. P.; Ceder, G. Electrodes with high power and high capacity for rechargeable lithium batteries. Science 2006, 311, 977-980. (3) Le, D. B.; Passerini, S.; Coustier, F.; Guo, J.; Soderstrom, T.; Owens, B. B.; Smyrl, W. H. Intercalation of polyvalent cations into V2O5 aerogels. Chem. Mater. 1998, 10, 682-684. (4) Andersson, A. M.; Granqvist, C. G.; Stevens, J. R. Electrochromic LixWO3/polymer laminate/LiyV2O5 device: toward an all-solid-state smart window. Appl. Opt. 1989, 28, 32953302. (5) Gillaspie, D. T.; Tenent, R. C.; Dillon, A. C. Metal-oxide films for electrochromic applications: present technology and future directions. J. Mater. Chem. 2010, 20, 9585-9592. (6) Tang, Y.; Rui, X., Zhang, Y.; Lim, T. M.; Dong, Z.; Hng, H. H., Chen X. D.; Yan Q. Y.; Chen, Z. Vanadium pentoxide cathode materials for high-performance lithium-ion batteries enabled by a hierarchical nanoflower structure via an electrochemical process. J. Mater. Chem. A 2013, 1, 82-88.


22

Page 23 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(7) Giorgetti, M.; Passerini, S.; Smyrl, W. H.; Berrettoni, M. Evidence of bilayer structure in V2O5 xerogel. Inorg. Chem. 2000, 39, 1514-1517. (8) Wang, J.; Curtis, C. J.; Schulz, D. L.; Zhang, J. G. Influences of treatment temperature and water content on capacity and rechargeability of V2O5 xerogel films. J. Electrochem. Soc. 2004, 151, A1-A7. (9) Baddour-Hadjean, R.; Pereira-Ramos, J. P.; Navone, C.; Smirnov, M. Raman microspectrometry study of electrochemical lithium intercalation into sputtered crystalline V2O5 thin films. Chem. Mater. 2008, 20, 1916-1923. (10) Muster, J.; Kim, G. T.; Krstić, V.; Park, J. G.; Park, Y. W.; Roth, S.; Burghard, M. Electrical transport through individual vanadium pentoxide nanowires. Adv. Mater. 2000, 12, 420-424. (11) Owens, B. B.; Passerini, S.; Smyrl, W. H. Lithium ion insertion in porous metal oxides. Electrochim. Acta 1999, 45, 215-224. (12) Xiong, C.; Aliev, A. E.; Gnade, B.; Balkus Jr, K. J. Fabrication of silver vanadium oxide and V2O5 nanowires for electrochromics. ACS Nano 2008, 2, 293-301. (13) Wei, Y.; Ryu, C. W.; Kim, K. B. Improvement in electrochemical performance of V2O5 by Cu doping. J. Power Sources 2007, 165, 386-392. (14) Park, H. K. Manganese vanadium oxides as cathodes for lithium batteries. Solid State Ionics 2005, 1, 307-312.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 31

(15) Zhan, S. Y.; Wang, C. Z.; Nikolowski, K.; Ehrenberg, H.; Chen, G.; Wei, Y. J. Electrochemical properties of Cr doped V2O5 between 3.8 V and 2.0 V. Solid State Ionics 2009, 180, 1198-1203. (16) Zhan, S.; Wei, Y.; Bie, X.; Wang, C.; Du, F.; Chen, G.; Hu, F. Structural and electrochemical properties of Al3+ doped V2O5 nanoparticles prepared by an oxalic acid assisted soft-chemical method. J. Alloys Compd. 2010, 502, 92-96. (17) Li, S. R.; Ge, S. Y.; Qiao, Y.; Chen, Y. M.; Feng, X. Y.; Zhu, J. F.; Chen, C. H. Threedimensional porous Fe

0.1V 2O5.15

thin film as a cathode material for lithium ion batteries.

Electrochim. Acta 2012, 64, 81-86. (18) Wang, H.; Tang, Z. Y.; Li, J. X. Study on the capacitance performance of Sn4+-doped V2O5. J. Solid State Electrochem. 2010, 14, 1525-1531. (19) Coustier, F.; Hill, J.; Owens, B. B.; Passerini, S.; Smyrl, W. H. Doped vanadium oxides as host materials for lithium intercalation. J. Electrochem. Soc. 1999, 146, 1355-1360. (20) Wei, Y.; Ryu, C. W.; Kim, K. B. Cu-doped V2O5 as a high-energy density cathode material for rechargeable lithium batteries. J. Alloys Compd. 2008, 459, L13-L17. (21) Giorgetti, M.; Berrettoni, M.; Smyrl, W. H. Doped V2O5-based cathode materials: where does the doping metal go? An X-ray absorption spectroscopy study. Chem. Mater. 2007, 19, 5991-6000. (22) Leger, C.; Bach, S.; Soudan, P.; Pereira-Ramos, J. P. Evaluation of the sol–gel mixed oxide Cr 0.11 V 2 O 5.16 as a rechargeable positive electrode working in the potential range 3.8/1.5 V vs. Li. Solid State Ionics 2005, 176, 1365-1369.


24

Page 25 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Yu, D. M.; Zhang, S. T.; Liu, D. W.; Zhou, X. Y.; Xie, S. H.; Zhang, Q. F.; Liu, Y. Y.; Cao, G. Z. Effect of manganese doping on Li-ion intercalation properties of V

2

O

5

films. J.

Mater. Chem. 2010, 20, 10841-10846. (24) Grégoire, G.; Baffier, N.; Kahn-Harari, A.; Badot, J. C. X-Ray powder diffraction study of a new vanadium oxide Cr 0.11 V 2 O 5.16 synthesized by a sol–gel process. J. Mater. Chem. 1998, 8, 2103-2108. (25) Zhang, X.; Sun, H.; Li, Z.; Xu, J.; Jiang, S.; Zhu, Q., Jin A.; Zakharova, G. S. Synthesis and electrochromic characterization of vanadium pentoxide/graphene nanocomposite films. J. Electrochem. Soc. 2013, 160, H587-H590. (26) Vernardou, D.; Apostolopoulou, M.; Louloudakis, D.; Katsarakis, N.; Koudoumas, E. Hydrothermally grown β-V2O5 electrode at 95° C. J. Colloid Interface Sci. 2014, 424, 1-6. (27) Vernardou, D.; Sapountzis, A.; Spanakis, E.; Kenanakis, G.; Koudoumas, E.; Katsarakis, N. Electrochemical activity of electrodeposited V2O5 coatings. J. Electrochem. Soc. 2013, 160, D6-D9. (28) Vernardou, D.; Louloudakis, D.; Spanakis, E.; Katsarakis, N.; Koudoumas, E. Electrochemical properties of vanadium oxide coatings grown by hydrothermal synthesis on FTO substrates. New J. Chem. 2014, 38, 1959-1964. (29) Wang, X. J.; Li, H. D.; Fei, Y. J.; Wang, X.; Xiong, Y. Y.; Nie, Y. X.; Feng, K. A. XRD and Raman study of vanadium oxide thin films deposited on fused silica substrates by RF magnetron sputtering. Appl. Surf. Sci. 2001, 177, 8-14.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

(30) Galazka, Z.; Uecker, R.; Klimm, D.; Irmscher, K.; Pietsch, M.; Schewski, R.; Albrecht, M.; Kwasniewski, A.; Ganschow, S.; Schulz, D. et al. Growth, characterization, and properties of bulk SnO2 single crystals. Phys. Status Solidi A 2014, 211, 66-73. (31) Julien, C.; Haro-Poniatowski, E.; Camacho-Lopez, M. A.; Escobar-Alarcon, L.; JımenezJarquın, J. Growth of V2O5 thin films by pulsed laser deposition and their applications in lithium microbatteries. Mater. Sci. Eng. B 1999, 65, 170-176. (32) Julien, C.; Nazri, G. A.; Bergström, O. Raman scattering studies of microcrystalline V6O13. Phys. Stat. Sol. B 1997, 201, 319-326. (33) Clark, R. J. H. The Chemistry of Titanium and Vanadium; Elsevier, New York, 1968. (34) Li, Y.; Yao, J.; Uchaker, E.; Zhang, M.; Tian, J.; Liu, X.; Cao, G. Sn-doped V2O5 film with enhanced lithium-ion storage performance. J. Phys. Chem. C 2013, 117, 23507-23514. (35) Leger, C.; Bach, S.; Soudan, P.; Pereira-Ramos, J. P. Structural and electrochemical properties of ω Li x V2O5 (0.4≤ x≤ 3) as rechargeable cathodic material for lithium batteries. J. Electrochem.Soc. 2005, 152, A236-A241. (36) Liu, Y.; Clark, M.; Zhang, Q.; Yu, D.; Liu, D.; Liu, J.; Cao, G. V2O5 Nano-Electrodes with High Power and Energy Densities for Thin Film Li-Ion Batteries. Adv. Energy Mater.2011, 1, 194-202. (37) Livage, J. Vanadium pentoxide gels. Chem. Mater. 1991, 3, 578-593.


26

Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(38) Mai, L.; Dong, F.; Xu, X.; Luo, Y.; An, Q.; Zhao, Y.; Pan, J.; Yang, J. Cucumber-like V2O5/poly (3, 4-ethylenedioxythiophene) &MnO2 nanowires with enhanced electrochemical cyclability. Nano Lett. 2013, 13, 740-745. (39) Lu, Y.; Liu, L.; Mandler, D.; Lee, P. S. High switching speed and coloration efficiency of titanium-doped vanadium oxide thin film electrochromic devices. J. Mater. Chem. C 2013, 1, 7380-7386. (40) Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamental and Applications; Wiley, New York, 2001. (41) Bathe, S. R.; Patil, P. S. Electrochromic characteristics of fibrous reticulated WO3 thin films prepared by pulsed spray pyrolysis technique. Sol. Energy Mater. Sol. Cells 2007, 91, 1097-1101. (42) Zhao, H.; Pan, L.; Xing, S.; Luo, J.; Xu, J. Vanadium oxides–reduced graphene oxide composite for lithium-ion batteries and supercapacitors with improved electrochemical performance. J. Power Sources 2013, 222, 21-31. (43) Navone, C.; Pereira-Ramos, J. P.; Baddour-Hadjean, R.; Salot, R. High-capacity crystalline V2O5 thick films prepared by RF sputtering as positive electrodes for rechargeable lithium microbatteries. J. Electrochem. Soc. 2006, 153, A2287-A2293. (44) Wang, Y.; Cao, G. Li+-intercalation electrochemical/electrochromic properties of vanadium pentoxide films by sol electrophoretic deposition. Electrochim. Acta 2006, 51, 48654872.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 31

(45) Benayad, A.; Martinez, H.; Gies, A.; Pecquenard, B.; Levasseur, A.; Gonbeau, D. Vanadium pentoxide thin films used as positive electrode in lithium microbatteries: An XPS study during cycling.J. Phys. Chem. Solids 2006, 67, 1320-1324. (46) Qin, J.; Lv, W.; Li, Z.; Li, B.; Kang, F.; Yang, Q. H. An interlaced silver vanadium oxide– graphene hybrid with high structural stability for use in lithium ion batteries. Chem. Commun. 2014, 50, 13447-13450. (47) Wu, Y.; Zhu, P.; Zhao, X.; Reddy, M. V.; Peng, S.; Chowdari, B. V. R.; Ramakrishna, S. Highly improved rechargeable stability for lithium/silver vanadium oxide battery induced via electrospinning technique. J. Mater. Chem. A 2013, 1, 852-859. (48) Liu, Q.; Li, Z. F.; Liu, Y.; Zhang, H.; Ren, Y.; Sun, C. J.; Lu, W.; Zhou, Y.; Stanciu, L.; Stach, E. A. et al. Graphene-modified nanostructured vanadium pentoxide hybrids with extraordinary electrochemical performance for Li-ion batteries. Nat. Commun. 2015, 6, 6127 (49) Coustier, F.; Jarero, G.; Passerini, S.; Smyrl, W. H. Performance of copper-doped V2O5 xerogel in coin cell assembly. J. Power Sources 1999, 83, 9-14. (50) Wu, M.; Lin, X.; Wang, T.; Qiu, J.; Ma, T. Low-cost dye-sensitized solar cell based on nine kinds of carbon counter electrodes. Energy Environ. Sci. 2011, 4, 2308-2315. (51) Chen, H.; Zou, Q.; Liang, Z.; Liu, H.; Li, Q.; Lu, Y. C. Sulphur-impregnated flow cathode to enable high-energy-density lithium flow batteries. Nat. Commun. 2015, 6. (52) Jia, X.; Zhang, L.; Zhang, R.; Lu, Y.; Wei, F. Carbon nanotube-penetrated mesoporous V2O5 microspheres as high-performance cathode materials for lithium-ion batteries. RSC Advances 2014, 4, 21018-21022.


28

Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(53) Yu, H.; Rui, X.; Tan, H.; Chen, J.; Huang, X.; Xu, C.; Liu, W.; Yu, D. Y. W.; Hng, H. H.; Hoster, H. E. et al. Cu doped V2O5 flowers as cathode material for high-performance lithium ion batteries. Nanoscale 2013, 5, 4937-4943. (54) Zeng, H.; Liu, D.; Zhang, Y.; See, K. A.; Jun, Y. S.; Wu, G.; Gerbec, J. A.; Ji. X.; Stucky, G. D. Nanostructured Mn-Doped V2O5 Cathode Material Fabricated from Layered Vanadium Jarosite. Chem. Mater. 2015, 27, 7331-7336. (55) Gies, A.; Pecquenard, B.; Benayad, A.; Martinez, H.; Gonbeau, D.; Fuess, H.; Levasseur, A. Effect of silver co-sputtering on V2O5 thin films for lithium microbatteries. Thin Solid Films 2008, 516, 7271-7281. (56) Vernardou, D.; Paterakis, P.; Drosos, H.; Spanakis, E.; Povey, I. M.; Pemble, M. E.; Koudoumas, E.; Katsarakis, N. A study of the electrochemical performance of vanadium oxide thin films grown by atmospheric pressure chemical vapour deposition. Sol. Energ. Mat. Sol. Cells 2011, 95, 2842-2847. (57) Benmoussa, M.; Outzourhit, A.; Bennouna, A.; Ameziane, E. L. Electrochromism in sputtered V 2 O 5 thin films: structural and optical studies. Thin Solid Films 2002, 405, 11-16. (58) Denesuk, M.; Cronin, J. P.; Kennedy, S. R.; Uhlmann, D. R. The Relation Between Coloring and Bleaching with Lithium in Tungsten Oxide Based Electrochromic Devices Step Current Analysis. J. Electrochem. Soc. 1997, 144, 1971-1979. (59) Tauc, J. Amorphous and liquid semiconductor; Plenum Press, New York, 1974.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 31

(60) Zhao, C.; Feng, S.; Chen, W.; Li, X.; Song, Y.; Cao, J. Preparation of Mesoporous V2O5@ TiO2 Composites with Enhanced Photoactivity for Gaseous Benzene Degradation. Phys. Procedia 2013, 48, 38-45. (61) Najdoski, M.; Koleva, V.; Samet, A. Effect of deposition conditions on the electrochromic properties of nanostructured thin films of ammonium intercalated vanadium pentoxide xerogel. J. Phys. Chem. C 2014, 118, 9636-9646. (62) Mlyuka, N.; Niklasson, G.; Granqvist, C. G. Mg doping of thermochromic VO2 films enhances the optical transmittance and decreases the metal-insulator transition temperature. Appl. Phys. Lett. 2009, 95, 171909. (63) Lin, Y. S.; Tsai, C. W.; Chen, P. W. Electrochromic properties of V2O5−z thin films sputtered onto flexible PET/ITO substrates. Solid State Ionics 2008, 179, 290-297. (64) Özer, N.; Sabuncu, S.; Cronin, J. Electrochromic properties of sol-gel deposited Ti-doped vanadium oxide film. Thin Solid Films 1999, 338, 201-206.


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TOC


31

Tunable Properties of Mg-Doped V2O5 Thin Films for Energy

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