Impedance spectroscopy is used to investigate the long-range ionic conductivity of the microporous, zincosilicate VPI-9 (Si/Zn = 4.0) (International Zeolite Association framework type VNI) containing the alkali cations Li^+, Na^+, K^+, Rb^+, and Cs^+, and the alkaline earth cations Mg^(2+), Ca^(2+), and Sr^(2+). Monovalent cation-exchanged samples Li- and Na-VPI-9 lose X-ray crystallinity upon vacuum dehydration at 450 °C, whereas K-, Rb-, and Cs-VPI-9 remain crystalline and exhibit conductivities of 1.7 × 10^(−4), 3.5 × 10^(−4), and 4.9 × 10^(−4) S/cm, respectively, at 450 °C and activation energies of 0.72, 0.64, and 0.69 eV, respectively, in the temperature range 150−450 °C. Divalent cation-exchanged sample Mg-VPI-9 also loses X-ray crystallinity, but Ca- and Sr-VPI-9 remain crystalline and exhibit conductivities of 2.3 × 10^(−6) S/cm and 7.7 × 10^(−7) S/cm, respectively, at 450 °C, and activation energies of 0.88 and 0.91 eV, respectively, over the temperature range 150−450 °C. When compared to aluminosilicate zeolite X (Si/Al = 1.25) exchanged with the same cations, all crystalline M-VPI-9 materials have greater conductivities than M-X, with the exception of K-X (1.6 × 10^(−3) S/cm at 450 °C), with the greatest differences arising between the divalent exchanged materials. Dense, crystalline zincosilicate samples with the compositions K_2ZnSi_xO_(2(x+1)) (x = 2−5), Rb_2ZnSi_5O_(12), and Cs_2ZnSi_5O_(12) are also prepared and characterized for comparison with the microporous materials and exhibit much lower conductivities than their microporous counterparts at the same composition

Davis, Mark E.

McKeen, John C.

English

Caltech Authors - Main

Supporting Information 
Experimental Apparatus. 
A photograph of the apparatus used for high temperature impedance characterization of 
pressed pellet samples is shown in Figure S1. The thermocouple passes through the 
bottom alumina disc and approaches the bottom platinum contact from the bottom up. 
Electrical connection to the bottom contact is made by the indicated Pt wire which was 
attached by welding. An internal Pt wire was welded to the Pt rod used to contact the 
top of the sample. A bushing (not visible) was used to load the visible spring to apply 
gentle force to the sample. 
To confirm the repeatability of measurements, multiple samples of sodium 
exchanged zeolite X (Aldrich) were investigated, as producing a large quantity of VPI-9 
is difficult. Figure S2 shows data from three Na-X samples prepared and characterized 
on different days (separated by weeks). Measured values of conductivity and observed 
trends are in accordance with other published literature.1 All VPI-9 used in this study 
was from a pool of as-made material, produced from many identical synthesis batches. 
Each batch was crystallized according to a previously published method and as stated 
in the main article2; the crystalline product of each was confirmed by powder X-ray 
diffraction. Every batch appeared the same visually and by powder X-ray diffraction.  
 
 
Figure S1. Experimental apparatus used for the high temperature characterization of 
pressed pellets. 
 
 
 
 
Pt rod used to contact top gold contact 
Pt wire for bottom contact Alumina shielded thermocouple that 
descends through the alumina disc and 
approaches the bottom contact from 
the below 
Spring used to apply gentle force to the 
disc
 
Figure S2. Conductivity data for three samples of Na-X. Pellets were all prepared 
following the same procedure described in the manuscript, but pellets were pressed on 
different days, contacts were sputtered in on different days, and characterization 
occurred on different days (separated in weeks, in fact).
A further discussion of impedance spectroscopy on zeolite samples. 
 In a series of papers on ionic motion in zeolites3-6, it was suggested the 
presentation of data in the modulus representation, equation 1, and in particular the 
imaginary part of the modulus, M” as a function of frequency, rather than traditional 
impedance (Z) data, allowed for more straight forward visualization of ionic conduction 
and local relaxations. In equation S1, i is the square root of -1, ω is the frequency in 
radians per second, C0 is the empty cell capacitance, M* is the complex modulus, and 
Z* is the complex impedance. 
      S1) 
 A further article on ion conductivity in ETS-10 also uses modulus representation, 
and presents data on sodium exchanged zeolite X and ETS-10.7 
 In our investigation of ionic conductivity in VPI-9, we began by first repeating 
literature results from the aforementioned papers on Na-X, but we found this to be a 
non-straightforward process. Figure S3 shows M” data from a pressed pellet of Na-X 
with sputtered gold contacts, recorded at 303 K.   
 
 
Figure S3. Imaginary part of the modulus as a function of frequency for a hydraulically pressed pellet of 
Na-X with sputtered gold contacts. 
 An intense peak at high frequency is clearly seen, which has been previously 
attributed to the local motion of a sodium ion within the large α cages in zeolite X.6 The 
peak (or hump, rather) at low frequency, however is not well resolved from the large 
high frequency peak, as in references 4 and 6. This was troubling at first, but further 
experimentation revealed the answer. Figure S4 shows M” spectra of Na-X powder, 
held between two platinum discs in vacuum, at various temperatures, and in this case 
two well resolved peaks are observed. The low frequency peak has been attributed to 
the long range ionic conduction process6, but the full interpretation is more complex, 
and will be discussed shortly. Finally, Figure S5 shows M” data for Na-X powder drop-
cast from an ethanol slurry onto an interdigitated electrode (IE) structure (Novocontrol). 
The sample was dehydrated in vacuum to remove water and ethanol, and contributions 
to the spectra from the IE substrate have been subtracted. Again, two well resolved 
peaks are observed, with nearly equal peak heights. Pressed pellets of NaX without 
sputtered contacts were also characterized by directly sandwiching them between two 
Pt electrodes, and spectra similar to those show in Figure S4, but with less peak 
separation, were observed.  
 
Figure S4. M” spectra of Na-X powder held between two circular Pt plates. 
 
 
Figure S5. M” spectra for Na-X powder drop case from ethanol onto interdigitated electrode structure. 
 
 Circuit models are often used to describe the physical processes occurring in 
ionic conduction and the most common element is the parallel combination of a resistor 
and a capacitor. The M” spectra for Na-X can be modeled using two of these elements 
in series, one element corresponding to the motion of a sodium ion in an α cage and 
one to represent the long range process (such as DC conduction).7  
 To illustrate how circuit model parameter values (Ri and Ci) influence the fitting of 
data, and to help elucidate the nature of the variation in shape and position of the low 
frequency peak, Mathematica was used to plot M” as a function of frequency. This is 
shown in Figure S6, along with the circuit model used to generate the appropriate 
equations (by taking the laplace transform of the appropriate transfer function). In the M” 
spectra, each RC parallel element corresponds to one of the peaks. 
C1
R1
C2
R2
 
Figure S6. M” spectra calculated and plotted using Mathematica. 
In both Figure S6 a) and b) R2 and C2 are held constant and correspond to the 
high frequency peak. In a), however, a smaller value of C1 and larger value of R1 are 
used than in b). The peak position in frequency is controlled by the value R1, larger 
a)  b)
values of R1 shifting the peak to lower frequencies. The height of the peak is controlled 
by the value C1, smaller values of C1 increasing the peak height.  
Recall that the M” spectra for a pressed pellet with sputtered contacts looks like 
Figure S6 b) while spectra of Na-X powder held between two Pt plates, Na-X powder 
drop cast onto IE electrodes, and pressed pellets of Na-X without sputtered electrodes 
more closely resemble Figure S6 a). Poor interparticle contact, particularly in the non-
hydraulically pressed powder samples and poor particle contact with the electrodes in 
all three latter cases significantly increase the value of R1, which can be thought of as 
an overall resistance of the sample (corresponding to long range ionic conductivity in 
the absence of these parasitic effects). The increase in R1 causes peak separation in 
frequency. In the latter three cases C1, some overall capacitance, decreases with the 
addition of more series capacitors arising from an increase in space between particles 
and poor interfacial contact with the gold or platinum electrodes. 
It should be noted that the high frequency peak in Na-X samples appears at the 
same frequency for a give temperature for all methods of characterization, indicating a 
true internal process, as was previously suggested.6 Interestingly, VPI-9 samples do not 
show multiple peaks at any temperature in the M” spectra when powder samples are 
sandwiched between Pt plates, suggesting the absence of internal relaxation 
processes. 
While presenting data in M” representation is useful for over emphasizing high 
frequency data and, therefore, studying internal processes that may occur very quickly, 
eliminating parasitic impedances by pressing pellets and forming intimate electrical 
contacts is more appropriate for extracting values of ionic conductivity. (Nearly all 
reviewed literature on solid electrolytes reports on sintering powders and either painting 
on metallic contacts from Pt paste or using a physical vapor deposition technique to 
apply intimate metallic contacts.) 
The characterization of powder samples between two circular Pt electrodes was 
accomplished by replacing the long Pt probe used to contact the top of pelltized 
samples (see Figure S1) with an alumina tube with a flat Pt disc attached to the bottom. 
A piece of quartz tube having an internal diameter the same as the external diameter of 
the Pt plates/alumina tube was used to hold the powder in place while sandwiching 
between Pt contacts. This is similar to what was done in reference 5. 
 
References 
(1) Kalogeras, I. M.; Vassilikou-Dova, A. Defect and Diffusion Forum 1998, 164, 1. 
(2) McCusker, L. B.; Grosse-Kunstleve, R. W.; Baerlocher, C.; Yoshikawa, M.; 
Davis, M. E. Microporous Materials 1996, 6, 295. 
(3) Franke, M. E.; Simon, U. Solid State Ionics 1999, 118, 311. 
(4) Franke, M. E.; Simon, U. ChemPhysChem 2004, 5, 465. 
(5) Franke, M. E.; Simon, U.; Moos, R.; Knezevic, A.; Muller, R.; Plog, C. Physical 
Chemistry Chemical Physics 2003, 5, 5195. 
(6) Simon, U.; Flesch, U. J. Porous Mater. 1999, 6, 33. 
(7) Wei, T.-C.; Hillhouse, H. W. J. Phys. Chem. B 2006, 110, 13728. 
 


Conductivity of Mono- and Divalent Cations in the Microporous Zincosilicate VPI-9

Supporting Information 
Experimental Apparatus. 
A photograph of the apparatus used for high temperature impedance characterization of 
pressed pellet samples is shown in Figure S1. The thermocouple passes through the 
bottom alumina disc and approaches the bottom platinum contact from the bottom up. 
Electrical connection to the bottom contact is made by the indicated Pt wire which was 
attached by welding. An internal Pt wire was welded to the Pt rod used to contact the 
top of the sample. A bushing (not visible) was used to load the visible spring to apply 
gentle force to the sample. 
To confirm the repeatability of measurements, multiple samples of sodium 
exchanged zeolite X (Aldrich) were investigated, as producing a large quantity of VPI-9 
is difficult. Figure S2 shows data from three Na-X samples prepared and characterized 
on different days (separated by weeks). Measured values of conductivity and observed 
trends are in accordance with other published literature.1 All VPI-9 used in this study 
was from a pool of as-made material, produced from many identical synthesis batches. 
Each batch was crystallized according to a previously published method and as stated 
in the main article2; the crystalline product of each was confirmed by powder X-ray 
diffraction. Every batch appeared the same visually and by powder X-ray diffraction.  
 
 Figure S1. Experimental apparatus used for the high temperature characterization of 
pressed pellets. 
 
 
 
 
Pt rod used to contact top gold contact 
Pt wire for bottom contact Alumina shielded thermocouple that 
descends through the alumina disc and 
approaches the bottom contact from 
the below 
Spring used to apply gentle force to the 
disc
 Figure S2. Conductivity data for three samples of Na-X. Pellets were all prepared 
following the same procedure described in the manuscript, but pellets were pressed on 
different days, contacts were sputtered in on different days, and characterization 
occurred on different days (separated in weeks, in fact).
A further discussion of impedance spectroscopy on zeolite samples. 
 In a series of papers on ionic motion in zeolites3-6, it was suggested the 
presentation of data in the modulus representation, equation 1, and in particular the 
imaginary part of the modulus, M” as a function of frequency, rather than traditional 
impedance (Z) data, allowed for more straight forward visualization of ionic conduction 
and local relaxations. In equation S1, i is the square root of -1, ω is the frequency in 
radians per second, C0 is the empty cell capacitance, M* is the complex modulus, and 
Z* is the complex impedance. 
      S1) 
 A further article on ion conductivity in ETS-10 also uses modulus representation, 
and presents data on sodium exchanged zeolite X and ETS-10.7 
 In our investigation of ionic conductivity in VPI-9, we began by first repeating 
literature results from the aforementioned papers on Na-X, but we found this to be a 
non-straightforward process. Figure S3 shows M” data from a pressed pellet of Na-X 
with sputtered gold contacts, recorded at 303 K.   
 
 Figure S3. Imaginary part of the modulus as a function of frequency for a hydraulically pressed pellet of 
Na-X with sputtered gold contacts. 
 An intense peak at high frequency is clearly seen, which has been previously 
attributed to the local motion of a sodium ion within the large α cages in zeolite X.6 The 
peak (or hump, rather) at low frequency, however is not well resolved from the large 
high frequency peak, as in references 4 and 6. This was troubling at first, but further 
experimentation revealed the answer. Figure S4 shows M” spectra of Na-X powder, 
held between two platinum discs in vacuum, at various temperatures, and in this case 
two well resolved peaks are observed. The low frequency peak has been attributed to 
the long range ionic conduction process6, but the full interpretation is more complex, 
and will be discussed shortly. Finally, Figure S5 shows M” data for Na-X powder drop-
cast from an ethanol slurry onto an interdigitated electrode (IE) structure (Novocontrol). 
The sample was dehydrated in vacuum to remove water and ethanol, and contributions 
to the spectra from the IE substrate have been subtracted. Again, two well resolved 
peaks are observed, with nearly equal peak heights. Pressed pellets of NaX without 
sputtered contacts were also characterized by directly sandwiching them between two 
Pt electrodes, and spectra similar to those show in Figure S4, but with less peak 
separation, were observed.  
 
Figure S4. M” spectra of Na-X powder held between two circular Pt plates. 
 
 
Figure S5. M” spectra for Na-X powder drop case from ethanol onto interdigitated electrode structure. 
 
 Circuit models are often used to describe the physical processes occurring in 
ionic conduction and the most common element is the parallel combination of a resistor 
and a capacitor. The M” spectra for Na-X can be modeled using two of these elements 
in series, one element corresponding to the motion of a sodium ion in an α cage and 
one to represent the long range process (such as DC conduction).7  
 To illustrate how circuit model parameter values (Ri and Ci) influence the fitting of 
data, and to help elucidate the nature of the variation in shape and position of the low 
frequency peak, Mathematica was used to plot M” as a function of frequency. This is 
shown in Figure S6, along with the circuit model used to generate the appropriate 
equations (by taking the laplace transform of the appropriate transfer function). In the M” 
spectra, each RC parallel element corresponds to one of the peaks. 
C1
R1
C2
R2
 
Figure S6. M” spectra calculated and plotted using Mathematica. 
In both Figure S6 a) and b) R2 and C2 are held constant and correspond to the 
high frequency peak. In a), however, a smaller value of C1 and larger value of R1 are 
used than in b). The peak position in frequency is controlled by the value R1, larger 
a)  b)
values of R1 shifting the peak to lower frequencies. The height of the peak is controlled 
by the value C1, smaller values of C1 increasing the peak height.  
Recall that the M” spectra for a pressed pellet with sputtered contacts looks like 
Figure S6 b) while spectra of Na-X powder held between two Pt plates, Na-X powder 
drop cast onto IE electrodes, and pressed pellets of Na-X without sputtered electrodes 
more closely resemble Figure S6 a). Poor interparticle contact, particularly in the non-
hydraulically pressed powder samples and poor particle contact with the electrodes in 
all three latter cases significantly increase the value of R1, which can be thought of as 
an overall resistance of the sample (corresponding to long range ionic conductivity in 
the absence of these parasitic effects). The increase in R1 causes peak separation in 
frequency. In the latter three cases C1, some overall capacitance, decreases with the 
addition of more series capacitors arising from an increase in space between particles 
and poor interfacial contact with the gold or platinum electrodes. 
It should be noted that the high frequency peak in Na-X samples appears at the 
same frequency for a give temperature for all methods of characterization, indicating a 
true internal process, as was previously suggested.6 Interestingly, VPI-9 samples do not 
show multiple peaks at any temperature in the M” spectra when powder samples are 
sandwiched between Pt plates, suggesting the absence of internal relaxation 
processes. 
While presenting data in M” representation is useful for over emphasizing high 
frequency data and, therefore, studying internal processes that may occur very quickly, 
eliminating parasitic impedances by pressing pellets and forming intimate electrical 
contacts is more appropriate for extracting values of ionic conductivity. (Nearly all 
reviewed literature on solid electrolytes reports on sintering powders and either painting 
on metallic contacts from Pt paste or using a physical vapor deposition technique to 
apply intimate metallic contacts.) 
The characterization of powder samples between two circular Pt electrodes was 
accomplished by replacing the long Pt probe used to contact the top of pelltized 
samples (see Figure S1) with an alumina tube with a flat Pt disc attached to the bottom. 
A piece of quartz tube having an internal diameter the same as the external diameter of 
the Pt plates/alumina tube was used to hold the powder in place while sandwiching 
between Pt contacts. This is similar to what was done in reference 5. 
 
References 
(1) Kalogeras, I. M.; Vassilikou-Dova, A. Defect and Diffusion Forum 1998, 164, 1. 
(2) McCusker, L. B.; Grosse-Kunstleve, R. W.; Baerlocher, C.; Yoshikawa, M.; 
Davis, M. E. Microporous Materials 1996, 6, 295. 
(3) Franke, M. E.; Simon, U. Solid State Ionics 1999, 118, 311. 
(4) Franke, M. E.; Simon, U. ChemPhysChem 2004, 5, 465. 
(5) Franke, M. E.; Simon, U.; Moos, R.; Knezevic, A.; Muller, R.; Plog, C. Physical 
Chemistry Chemical Physics 2003, 5, 5195. 
(6) Simon, U.; Flesch, U. J. Porous Mater. 1999, 6, 33. 
(7) Wei, T.-C.; Hillhouse, H. W. J. Phys. Chem. B 2006, 110, 13728. 
 


Conductivity of Mono- and Divalent Cations in the Microporous Zincosilicate VPI-9

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