Anomalous Conductivity Behavior of AgI-Vycor7930 Nanocomposites

Oct 8, 2010 - AgI was found to be in its β-form with nanometric crystallite size. Microstructure has also been investigated by scanning electron micr...
0 downloads 0 Views 2MB Size
Download PDF
18318

J. Phys. Chem. C 2010, 114, 18318–18322

Anomalous Conductivity Behavior of AgI-Vycor7930 Nanocomposites Pascal G. Yot,* Ste´phanie Albert, Nathalie Frolet, Michel Ribes, and Annie Pradel Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-ENSCM-UM1, UniVersite´ Montpellier 2, CC 1503, Place E. Bataillon, F-34095 Montpellier, Cedex 5, France ReceiVed: June 8, 2010; ReVised Manuscript ReceiVed: September 18, 2010

Using the electrocrystallization process, silver iodide particles were embedded into bulk Vycor7930 porous glass (VPG) to obtain ionic conductor composite. X-ray microdiffraction (µXRD) was carried out on the composite. AgI was found to be in its β-form with nanometric crystallite size. Microstructure has also been investigated by scanning electron microscopy (SEM). The ionic conductor was found to be embedded in the center of the VPG disk, into the 4 nm diameter pore network. Electron probe for micro analysis (EPMA) has shown the homogeneity of the silver iodide precipitate inside the VPG. Electrical conductivity was measured by complex impedance spectroscopy (CIS). A large hysteresis phenomenon in the conductivity versus temperature curve at a temperature close to the transition β T R-AgI was observed. At low temperature, the conductivity of the composite was found to be higher than that of pure β-AgI by 1 order of magnitude. 1. Introduction Ionic conductors are of great interest because their implications in batteries and sensors. Solid ionic conductors as for instance R-AgI have been found to exhibit an ionic conductivity comparable to that of the best liquid electrolytes. For the past ten years, several groups have been focused on solid ionic conductors and more particularly on a promising type, namely, the composite ionic conductors.1-3 In the early 70s, Liang has shown that the conductivity of LiI could be increased by several orders of magnitude when this compound is mixed with an insulating phase Al2O3.4 Since these pioneering works, recent investigations have been carried out on composite materials showing an improvement in conductivity correlated with the composition, the host matrix, and porosity.5-12 In the mean time, the physical properties of materials embedded in nanoporous solids were intensively studied. They emphasized a significant influence of the nanoconfinement on the properties of these materials including melting, freezing, phase transitions, diffusion.13-20 Regarding the field of ionic conductors, the effects of both nanostucturation and confinement on conductivity were investigated. The AgI-based systems are the most investigated ones. Silver iodide is an ionic conductor existing in three polymorphic phases: β (hexagonal), γ (fcc), and R (bcc) which are low and high temperature phases, respectively. The commonly first-order phase transition β/γ T R generally occurs at 147 °C (420 K) under atmospheric pressure. Recently, Guo et al. reported a relation between the shape of the AgI nanocrystallites and the type of crystalline phases.21-23 As a result, the phase transition leads to a change of the conductivity values that vary from one to another type of the nanocrystalline phase studied as a function of the disorder in the cation lattice.22 In all cases, an anomalous behavior was detected that consists of a more or less large hysteresis loop on the electrical conductivity curve, while only a step in conductivity is obtained for “pure β-AgI” at the phase transition temperature. The authors have demonstrated that both the shape and the temperature domain of the hysteresis are related to the crystalline phase and the shape * Author to whom correspondence should be addressed: Tel: +33-4 67 14 32 94. Fax: +33-4 67 14 42 90. E-mail: [email protected].

of AgI nanocrystals. More recently, other authors have evidenced the relation between the crystallite size of the silver iodide and its thermal behavior upon cooling and heating. Makiura et al.’s major finding is a size dependence of the phase transition temperature.24 When the particle is decreased from 50 to 10 nm, the phase transition temperature (i) shifts slightly upon heating from 147 °C (420 K) to 155 °C (428 K) and (ii) decreases dramatically upon cooling from 120 °C (393 K) to 40 °C (313 K). The combination of the two effects leads to a thermal hysteresis. Some authors have already reported thermal hysteresis on the conductivity.25-27 In the case of AgI-Al2O3 composites studied by Lee et al. the anomalous behavior of the conductivity results from the existence of 7H-AgI polytypes.26 Tatsumisago et al. have evidenced the effect of compression by the glassy matrix leading to freeze the R-AgI phase upon cooling.25 As a result, the R T β phase transition temperature (PTT) was observed at 110 °C (383 K) instead of the commonly observed temperature: 147 °C (420 K). In the case of the composite systems, where silver iodide is associated with an insulating phase and introduced within the porosity, some studies relate the effect of the nanoconfinement on the ionic conductivity.28-30 As reported by several authors, the phase transition temperature is strongly affected by the chemical composition of the host material and its porosity (i.e., the pore diameter). PTT β T R-AgI, was found to slightly increase and then decrease when the pore size varies from 50 to 10 nm31 in the case of porous silicate materials. In contrast, it was found that the PTT increases in the case of porous alumina used as host.32 To date, the majority of the studies were carried out using Al2O3 as the host system for the confinement of AgI. Two type of hosts can be distinguished for these composite systems: (i) the host is prepared from porous powder of alumina and sintered before ionic conductor insertion,32-34 (ii) the host is a “bulk” template like anodic alumina oxide (AAO).28 Recently, Baryshnikov et al.29,30 reported a study where silver iodide has been included in molecular sieves as silica MCM-41 and SBA-15 with pore diameter smaller than 10 nm. The effect of the nanoconfinement was evidenced by the presence of a shift of the phase transition temperature upon both heating and cooling which depends

10.1021/jp105252k  2010 American Chemical Society Published on Web 10/08/2010

Nanocomposite Ionic Conductors

J. Phys. Chem. C, Vol. 114, No. 43, 2010 18319

Figure 1. Schematic representation of the “electrocrystallization” process.

Figure 2. Comparison of classical and transverse methods used to measure electrical conductivity.

significantly on the pore size of the host matrix thus leading to a hysteresis in the evolution of the conductivity as a function of temperature. The present authors have demonstrated that it could be possible to introduce an ionic conductor with a weak solubility such as silver iodide into bulk Vycor7930 porous glass (VPG) using an electric field.35 At the difference of the host materials previously cited, porous alumina sintered powders, VPG is a bulk silica glass, with a 3-dimensional pore channel network with 4 nm pore diameter. It should be of interest to understand the influence of the nanoconfinement in such host. Herein, we report the preparation of AgI-Vycor7930 composites using the “electrocrystallization” process and their characterizations by scanning electron microscopy (SEM), analysis of the composition by electron probe for microanalysis (EPMA) and phase identification by micro X-rays diffraction (µXRD). The shape of the material requires us to adapt the classical electrical measurement method here called the “transverse mode”. Conductivity is measured parallel to the plane formed by the “SiO2-AgI” layer composite at the difference of the classical method where the measurement is carried out perpendicularly to this plane. We then report the results of the electrical characterization of the composites by complex impedance spectroscopy (CIS).

electric field of (≈13 V.m-1). Following “electrocrystallization”, the glassy disk was washed several times with distilled water and dried at 373 K for 12 h. The morphology of the samples was investigated by scanning electron microscopy (SEM) and the composition at different points of the composites was measured by SEM and electron probe for microanalysis (EPMA) using a S360 Cambridge Instrument and a KEVEX “DELTA” system with a 135 eV detector. The microdiffraction measurements were performed at “Laboratoire Pierre Su¨e” (CEA Saclay, France) using Mo KR radiation (λ ) 0.709 32 Å) at room temperature. The diffraction patterns I ) f(θ) were obtained by circularly integrating the pattern collected with a 2D-dimensional detector, using FIT2D software41 and indexed with the JCPDS database (X’Pert Highscore software). 2.2. Complex Impedance Spectroscopy. The conductivity measurements required a specific preparation of the sample. The method can be explained on the basis of the schema shown in Figure 2. The classical measurement of conductivity would require deposition of sputtered electrodes on the faces of the pellet. However, the AgI layer being only present in the center of the pellet, we had to use the “transverse method”. It required first cutting the sample in a parallelepipedic form and then depositing Pt electrodes on the cross section at the place where AgI was present. The electrode’s area was ≈1 mm2. Conductivity was measured using a Solartron SI-1620 and a homemade sealed conductivity cell with stainless steel electrodes within the frequency range 1 Hz to 10 MHz with an applied voltage of 100 mV. All measurements were carried out on a bar-shaped sample (≈0.8 × 0.5 × 3.5 mm3) under primary dynamic vacuum from room temperature to 453 K. The dc conductivity was calculated from the Cole-Cole plots of the ac impedance measurement using a nonlinear least-squares fitting program included in ZView software.

2. Experimental Methods 2.1. Synthesis and Characterization. AgI-based ionic conductor composites were prepared using Vycor7930 (VPG) as the host matrix. VPG is a commercial porous glass from Corning obtained by the process reported by Hood and Nordberg36,37 with the following composition 96.3 SiO2-2.95 B2O3-0.75 Na2O (wt %).38,39 VPG has a free porosity of 28%, an average pore diameter of 4 nm, and an internal surface area of approximately 250 m2/g.38,39 Commercial plates of porous Vycor7930 were first machined to obtain bulk disks of 13 mm in diameter and less than 2 mm in thickness as reported in a previous paper.35 The obtained disks were used as host for silver iodide, which was confined using a process developed by Nagai et al.33,34,40 Figure 1 gives a schematic representation of this “electrocrystallization” process. The VPG disk was placed in between two compartments filled with 0.1 mol · L-1 solutions of NaI (Aldrich 99.99%) and AgNO3 (99.99%), respectively. Synthesis was carried out at room temperature for 16.5 h with a voltage applied between the two solutions of 1.5 V giving an

3. Results and Discussion The composites were synthesized by “electrocrystallization” inspired by the process developed by Nagai et al.33 and has been detailed in a previous paper.35 Upon the influence of the electric field, Ag+ and I- ions penetrate through the pores and react, leading to a precipitation of AgI close to the middle of the Vycor disk. In a previous work, the formation of the precipitate was studied by applying the same voltage during different times.

18320

J. Phys. Chem. C, Vol. 114, No. 43, 2010

Yot et al.

Figure 4. Elemental distribution analysis: (left to right) SEM picture of the cross section, elemental distribution of silver (in green), and elemental distribution of iodine (in red). Figure 3. SEM observations of the cross section of the composite obtained after 6.5 h of “electrocrystallization”: (a)-(c) overview of the precipitate layer, (d) observation of the middle part, (e)-(f) observations of the lower and upper parts, respectively.

Increasing the time of reaction has allowed us to increase the AgI layer thickness and to reach a limit value of about 230 µm for 16.5 h. The thickness of the precipitate follows a power law d ) R × tβ where R and β were found to be equal to 0.81 and 0.52, respectively. According to Fick’s law a value of 0.52 for β suggests a growth of the thickness by diffusion.34 The 3-dimensional pore framework of Vycor7930 and the difference of mobility of the Ag+ and I- ions into the solutions and into the precipitate with an increasing thickness led to a remarkable microstructure of the silver iodide layer in the composite. Figure 3 provides an overview of the microstructure of the AgI layer for several magnifications (Figure 3a,b) and on various locations on the layer (Figure 3c-f) for a composite obtained after 6.5 h. The SEM images have evidenced the complex structure of the composite. The lower and the upper parts of the SEM pictures correspond to the side of VPG in regard to the AgNO3 and NaI solutions, respectively. The precipitation of AgI occurs close to the middle of the VPG (Figure 3a-d). The white line is a rich AgI zone at the origin of the formation of the crystallites during the formation of the layer. For the highest magnifications (Figure 3d,e) it could be seen that crystallization of silver iodide occurs during the process within the 4 nm diameter pores of Vycor7930 and that the porous framework remains fractal (Figure 3e). As evidenced in Figure 3a, the silver iodide layer is thicker on the upper part, which was close to the silver nitrate solution. The structure of the precipitate can be explained by taking into account that the mobility of silver is higher than that of iodine inside AgI. As the silver mobility is higher than

that of iodine, the pore filling is more efficient in the upper part than in the lower one, as seen in Figures 3e,f. This behavior can be explained by the existence of “nodules” pointed out by the SEM pictures, which correspond to high-filled pores zones. The composition of the layer containing both the conducting and the insulating phases has been derived from the SEM images and the thickness of the layer. The free porosity of the host was considered to be 28% and the pore filling assumed to be equal to unity. Whatever the deposition time, the composition was found to be 0.21AgI-0.79VPG (in molar fraction). EPMA analysis has confirmed XRD observations and evidenced the homogeneous partition of silver iodide into the porous glass for each considered zone (Figure 4). XRD was carried out to identify the crystalline phases obtained during the synthesis process. To elucidate the crystalline structure of the embedded phase within VPG, micro X-ray diffraction (µXRD) experiments on the composites have been performed. Figure 5 shows the pattern obtained by µXRD. All the peaks present in the pattern were indexed according to the low temperature phase of wu¨rtzite β-AgI.42 The so-extracted cell parameters were found to be a ) 4.5980(2) Å and c ) 7.5156(4) Å, close to the ones given in the Joint Committee on Powder Diffraction Standards (JCPDS) card 09-0374.42 Because of the divergence induced by Mo KR radiation in microdiffraction measurements, the estimation of the particle size was performed from a diffraction pattern obtained using Cu KR radiation (λ ) 1.540 56 Å). The crystallite apparent sizes were thus estimated by the Scherrer’s method, which provides a value of 11 nm, which is higher than the pore diameter of the host material.35 The porous glass host generates a continuous background, giving an underestimation of the fullwidth at half-maximum on the most intense Bragg peak. The result of this underestimation is an overestimation of the

Nanocomposite Ionic Conductors

J. Phys. Chem. C, Vol. 114, No. 43, 2010 18321 TABLE 1: Temperature of Transition and Activation Energies of AgI-Vycor Composites Obtained by “Electrocrystallisation” phase temperature transition (K)

Figure 5. Patterns of AgI-Vycor composites obtained by micro X-ray diffraction using Mo KR radiation.

Figure 6. Temperature dependence of the electrical conductivity of AgI-Vycor composites obtained by electrocrystallization (Arrhenius plots) compared to pure nanocrystalline β-AgI.22

apparent size of β-AgI nanocrystallites using Scherrer’s expression. We could reasonably estimate that the real crystallites size is less than 4 nm. When the classical method was used to measure electrical conductivity, conductivity of about 10-13 S cm-1 was observed due to the porous silica on each side of the “composite layer AgI-VPG”. Whatever the thickness of the two “pure” SiO2 layer surrounding the composite layer, it was not possible to detect conductivity because of their electrical insulating character. In contrast, when we used the above-described method, the conductivities were measured upon heating and cooling from room temperature to 453 K. Figure 6 displays the composite log(σT) as a function of the temperature upon heating and cooling compared to that of the pure nanocrystalline β-AgI presented by Guo et al.22 The conductivity plots for the composites show also a transition and a wide thermal hysteresis (≈44 K). Temperatures of transition and transition domains are summarized in Table 1. This trend evidenced an anomalous behavior of the conductivity of AgI embedded into the porous framework of Vycor 7930. Upon warming, the conductivity increased and the phase transition occurred at 425 K, which is somewhat higher than the usually β T R phase transition reported at 420 K. At the same time the increase of the slope for the Arrhenius plot most probably reveals a contribution of the intraparticle conductivity inside the pores.43 At the difference, upon cooling, the conductivity

Ea (eV)

upon heating β f R-AgI

upon cooling R f β-AgI

transition range (K)

before transition

after transition

425(1)

378(1)

≈47

0.35

0.07

decreased slightly, the phase transition occurred at about 378 K, a temperature much lower (by ≈44 K) than the temperature observed unpon heating. As a result, the phase with the highest conductivity (R-AgI) is stabilized down to 378 K when associated with the porous glass. These results are in good agreement with previous work carried out on nanocrystallites of AgI associated with porous molecular sieves with pore diameters from 2.0 to 5.2 nm:29,30 (i) upon heating, the phase transition shifts toward higher temperatures, and (ii) upon cooling, the phase transition temperature shifts toward lower temperatures. At room temperature, the composite presents a conductivity enhanced by more than 1 order of magnitude compared to that of pure β-AgI (≈1.37 × 10-5 S cm-1). The observed gain in conductivity is consistent with a percolation behavior. As reported above, VPG exhibits a porosity of 28%; therefore, the composition of the obtained composites in volume fraction is then “0.28AgI0.72VPG”. Such a composition is located in the first increasing part of the bell-shaped “conductivity vs volume fraction” curve characteristic of percolation behavior. Below the phase transition, the conductivities of the composite increase with temperature and were found to be higher than that of pure silver iodide. In addition, around 385 K a step of more than 1 order of magnitude was observed, leading to the maximum of conductivity above 425 K. At the difference, above the transition temperature, the measured conductivity is lower than that of pure R-AgI by about 2 orders of magnitude. It is admitted that the decrease in conductivity after the transition for the super ionic phase results from the blocking effect of the internal boundaries with respect to the superconductivity of the bulk material.44,45 Taking into account the size of the AgI crystallites, the grain boundaries increase strongly, giving a blocking effect enhanced compared to other composites (i.e., AgI-Al2O3,32-34,44,45 AgI-MCM41 or AgI-SBA1529,30). The two previous points are in agreement with observations reported elsewhere.28-30,34,45 The activation energies were estimated using the Nernst-Einstein equation (eq 2):

σ)

(

σ0 Ea exp T kB · T

)

(2)

where Ea is the activation energy, kB is the Boltzmann constant, T is the temperature, and σ0 is the pre-exponential factor. The soobtained activation energies are summarized in Table 1. They were determined using the linear parts of the conductivity curves below and above the phase transition. Below 423 K, Ea was found to be 0.35 eV, which is lower than the activation energy found in the case of nanocrystalline β-AgI.22 As seen in Figure 6, the slope of the Arrhenius plot increases slightly at the vicinity of the transition due to the increase of the contribution of intraparticle conductivity.43 Activation energy at room temperature was then found close to those obtained for confined AgI in several similar systems (AgI-Al2O3: Ea ) 0.31 eV34 and AgI-MCM-41: Ea ) 0.34 eV29,30). The decrease of the activation energy results from the charge transport occurring at the surface of the silver iodide crystallites.46

18322

J. Phys. Chem. C, Vol. 114, No. 43, 2010

Figure 7. Comparison of the dependences of the super ionic phase transition temperatures observed upon warming (Tcw) and cooling (Tcc) for several types of composites as a function of the inverse pore diameter d.29-31

At high temperature, Ea was found to be 0.07 eV, close to the value usually found for R-AgI (Ea ) 0.11 eV).22 The evolution of the conductivity as a function of temperature has revealed a nonreversible thermal behavior of the composites. Since the β T R-AgI phase transition temperature was found to shift to lower temperature when the pressure is increased,47 then the assumption of a pressure effect inside the pores can be discarded. The temperatures of transition upon warming and cooling (Table 1) were compared to the ones obtained in previous works and related to the pore size (Figure 7). Whatever the technique used to determine the phase transition, DSC or conductivity measurement for Hanaya et al.31 and Baryshnikov et al.,29,30 respectively, our results are consistent with the trends evidenced in the aforementioned works. Considering the difference of porous host, its nature and its form: “bulk” porous glass31 or powder,29,30 it is possible to assume that the anomalous behavior results from the confinement of the silver iodide nanocrystallites inside the pores. 4. Conclusion β-AgI nanocrystalites have been embedded within the 4 nm pores of a bulk silicate glass: Vycor7930 using the “electrocrystallization” process. The silver iodide layer was found to precipitate with a time dependent thickness in the center of the insulating matrix and shows a leveling off after ≈16 h. The ionic conductivity of the composite has been investigated. An enhancement in conductivity of about 1 order of magnitude was found and an anomalous behavior with a wide thermal hysteresis phenomenon related to the phase transition β T R-AgI has been evidenced. While upon heating the phase transition temperature was found to slightly increase (≈5 K), it was found to decrease drastically upon cooling. The thermal hysteresis range was found to be consistent with those found in the literature for AgI particle confined in nanoporous materials. The activation energy below the temperature transition temperature is close to 0.35 eV, which is consistent with the value found by other authors in similar confined systems and where the conductivity has been demonstrated to be related to surface transport. Acknowledgment. We thank Dr. Yves Brocheton (Corning Inc., France) for supplying the Vycor 7930. We also thank Ph. Dillmann and E. Foy (Laboratoire Pierre Su¨e, CEA Saclay, France) for their fruitful discussions and for their kind help in µXRD measurements. References and Notes (1) Owens, B. B. J. Power Sources 2000, 90, 2–8.

Yot et al. (2) Arico, A. S.; Bruce, P.; Scrosati, B.; Tarrascon, J.-M. Nat. Mater. 2005, 4, 366–377. (3) Guo, Y. G.; Hu, J. S.; Wan, L. J. AdV. Matter. 2008, 20, 2878–2887. (4) Liang, C. C. J. Electrochem. Soc. 1973, 120, 1289–1292. (5) Ardel, G.; Golonitsky, D.; Peled, E.; Wang, Y.; Wang, G.; Bajue, S.; Greenbaum, S. Solid State Ionics 1998, 113, 477–485. (6) Knauth, Ph. J. Electrochem. 2000, 5, 111–125. (7) Maekawa, H.; Tanaka, R.; Sato, T.; Fujimaki, Y.; Yamamura, T. Solid State Ionics 2004, 175, 281–285. (8) Maekawa, H.; Fujimaki, Y.; Shen, H.; Kawamura, J.; Yamamura, T. Solid State Ionics 2006, 177, 2711–2714. (9) Yamada, H.; Moriguchi, I.; Kudo, T. Solid State Ionics 2005, 176, 945– 953. (10) Kumar, B.; Nellutla, S.; Thokchom, J. S.; Chen, C. J. Power Sources 2006, 160, 1329–1335. (11) Albert, S.; Frolet, N.; Yot, P.; Pradel, A.; Ribes, M. Solid State Ionics 2006, 177, 3009–3013. (12) Albert, S.; Frolet, N.; Yot, P.; Pradel, A.; Ribes, M. Mater. Sci. Eng., B 2008, 150, 199–202. (13) Ka¨rger, J., Ruthven, D. M. Diffusion in zeolites and other microporous solids: Wiley: New York, 1992. (14) Crawford, G. P.; Zummer, S. Liquid crystals in complex geometries: Taylor and Francis: London, 1996. (15) Charnaya, E. V.; Tien, C.; Lin, K. J.; Kumzerov Yu, S. V.; Wur, C.-S. Phys. ReV. B 1998, 58, 467–472. (16) Christenson, H. K. J. Phys. Condens. Matter. 2001, 13, R95–R133. (17) Lopez, C. AdV. Matter. 2003, 15, 1679–1704. (18) Alcoutlabi, M.; McKenna, G. B. J. Phys. Condens. Matter. 2005, 17, R461–R524. (19) Tien, C.; Charnaya, E. V.; Lee, M. K.; Baryshnikov, S. V.; Sun, S. Y.; Michel, D.; Bo¨hlmann, W. Phys. ReV. B 2005, 72, 104105. (20) Charnaya, E. V.; Tien, C.; Lee, M. K.; Kumzerov Yu, A.; Wur, C.-S. Phys. ReV. B 2007, 75, 212202–212205. (21) Guo, Y.-G.; Lee, J.-S.; Maier, J. AdV. Matter. 2005, 17, 2815–2819. (22) Guo, Y.-G.; Lee, J.-S.; Maier, J. Solid State Ionics 2006, 177, 2467–2474. (23) Guo, Y.-G.; Hu, Y.-S.; Lee, J.-S.; Maier, J. Electrochem. Commun. 2006, 8, 1179–1184. (24) Makiura, R.; Yonemura, T.; Yamada, T.; Yamauchi, M.; Ikeda, R.; Kitagawa, H.; Kato, K.; Takata, M. Nat. Mater. 2009, 8, 476–480. (25) Tatsumisago, M.; Shinkuma, Y.; Minami, T. Nature 1991, 354, 217–218. (26) Lee, J.-S.; Adams, S.; Maier, J. Solid State Ionics 2000, 136-137, 1261– 1266. (27) Foltyn, M.; Wasiucionek, M.; Garbarczyk, J. E.; Nowinski, J. L.; Gierlotka, S.; Palosz, B. J. Power Sources 2007, 173, 795. (28) Liang, C.; Terabe, K.; Hasegawa, T.; Aono, M. J. Appl. Phys. 2007, 102, 124308–124312. (29) Baryshnikov, S. V.; Tien, C.; Charnaya, E. V.; Lee, M. K.; Michel, D.; Bo¨hlmann, W.; Andriyanova, N. P. J. Phys. Condens. Matter. 2008, 20, 025214-025218. (30) Baryshnikov, S. V.; Tien, C.; Charnaya, E. V.; Lee, M. K.; Michel, D.; Bo¨hlmann, W.; Andriyanova, N. P. Phys. Solid State 2008, 50, 1342–1346. (31) Hanaya, M.; Osawa, I.; Watanabe, K. J. Therm. Anal. Calorim. 2004, 76, 529–536. (32) Nagai, M.; Nishino, T. Solid State Ionics 1999, 117, 317–321. (33) Nagai, M.; Nishino, T. J. Electrochem. Soc. 1991, 138, L49–L51. (34) Nagai, M.; Nishino, T. Solid State Ionics 1992, 53-56, 63–67. (35) Albert, S.; Frolet, N.; Yot, P.; Pradel, A.; Ribes, M. Microporous Mesoporous Mater. 2007, 99, 56–61. (36) Hood, H. P.; Nordberg, M. E. Treated Borosilicate Glass: U.S. patent 2,106,744, Feb 1938. (37) Hood, H. P.; Nordberg, M. E. Method of Treating Borosilicate Glasses: U.S. patent 2,286,275, June 1942. (38) Elmer, T. H.: Engineered Materials Handbook, Porous and Reconstructed Glasses; Ceramics and Glasses, Vol. 4; ASM International: Materials Park, OH, U.S.A., 1992; p 427. (39) http://www.corning.com/lightingmaterials/images/Vycor_7930.pdf. (40) Nagai, M.; Nishino, T. Solid State Ionics 1995, 79, 319–324. (41) Hammersley, A. P.: FIT2D Reference Manual: ESRF International Report No. EXP/AH/93-02, 1993. (42) Powder Diffraction File No. 09-0374, Joint Committee on Powder Diffraction Santards, Swathmore, PA, U.S.A. (43) Cava, R. J.; Rietman, E. A. Phys. ReV. B 1984, 30, 6896–6902. (44) Lee, J.-S.; Adams, S.; Maier, J. J. Electrochem. Soc. 2000, 147, 2407–2418. (45) Baza´n, J. C.; Garcia´, N. J.; Dristas, J. A.; Spetter, C. V. Solid State Ionics 2004, 170, 57–61. (46) Maier, J. Solid State Ionics 1986, 18-9, 1141-1145. (47) Majumdar, A. J.; Roy, R. J. Phys. Chem. 1959, 63, 1858–1860.

JP105252K