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An investigation of modified AgI solid electrodes containing the homopiperazinium cation—I. Synthesis and characterization
Ema Acta, Vol. 38, No. 4, pp. 565-569.1993 Printed in Great Britain.
om-4w93~+o‘lm 81993.papmollPreuLtd.
AN INVESTIGATION OF MODIFIED AgI SOLID ELECTRODES CONTAINING THE HOMOPIPERAZINIUM CATION-I. SYNTHESIS AND CHARACTERIZATION JOSEPHJ. ROSENFBRG,*~M AI-LUANEFkmzou,~ OLIVIER CBRCLIER~ and JACQUJBE&IENNE$ tLaboratoire de Chimie des Matkriaux Inorganiques, U.R.A. C.N.RS. 1311, Universitk Paul Sabatier, 118 route de Narbonne, 31062 Toulouse cedex, France SLaboratoire de Chimie Organique Structurale, Universitk de Provence, Centre Saint-JkrSme,Case 542, Avenue Esadrille Normandie+Niemen, 13397 Marseille cedex, France &entre de Diffractomtirie, Universitk de Provence, Case 29,3, Place Victor-Hugo, 13331 Marseille a&x 3, France (Received 7 October 1991; in revisedform29 July 1992 Ahstraet-Homopiperazinium and N, N, N’, N’-tetramethylhomopiperazinium diiodide (briefly designated as HI, and TMHI,) have been synthesized and characterixed by Srared spectroscopy and proton magnetic rekance spe&oscopy. The-two diazonia diiodides were reacted withsilver tide in &&entrations ranging from 75 to 95 equivalent I- of AgI. In both HI,-AgI and TMHI,-AgI systems, the study of the total electrical conductivity with respect to temperature shows that the Arrhenius equation is obeyed. At 25”C, the maximal conductivity is reached for an equivalent content of 85% in the HI,-AgI system with a value of 0.003 (ohm cm)-‘. For the TMHI,&I system a dissymetric commsition deuen&nce of the ekctricd conduc&ty is &served around a n&in-m&mum at 90% AgI con&t corresp&ding to a 0.027 (ohm cm)-’ conductivity. Existence in this system of a second electrolyte phase around a 77.5-80% composition in AgI is swtained by electrochemical conductivity measurements and an independent X-ray powder di&ction study. Key words: silver iodide, silver solid electrolyte, homopiperazinium diiodide, total electrical conductivity, Fourier transformed infrared snectroscom IFTM uroton magnetic resonance spectroscopy (‘H NMR), X-ray power diffraction (XRP6). ‘. _
1. INTRODUCTION A survey of the literature indicates the good electrical conductivity of cationic organo-mineral electrolytes based on Ag+ ion conductors. Among them, the carbon cycles having one or many ammoniums have been studied in terms of their electrical conductivity. Owens[l] was the first to mention the good conductivity of axacyclic iodide (one ammonium in the carbon cycle) associated with AgI. Other authors have presented electrical conductivity of the systems N-alkyl hexamethylenetetraaminium iodide (with R = H, CH, or C,H,)-AgI[2]; N, N’-dimethyl triethylenediammonium diiodide-AgI[2, 33; and N, N, N’, N’-tetramethylpiperazinium diiodide-AgI[4]. In the present work based on homopiperazinium diiodide (HIJ and on N, N, N’, N’-tetramethyl- homopiperazinium diiodide (THMI,) the conductivity of the two electrolyte systems HI,-AgI and TMHI,-AgI is investigated. Previous synthesis and characterization of the organic and mineral starting materials are described.
earlier[4]. The N, N, N’, N’-tetramethyl homopiperazinium diiodide was prepared according to Rembaum et ar[S] in DMF-methanol (l-l in volume). The reaction was carried for 168 h, with tetramethyldiaminoethane and 1,3-diiodopropane in equal concentrations, at 25°C. The precipitated crystals are filtered, washed with acetone, recrystallized from ethanol, and dried in vacuum at 40°C (yield 73.6%). The reactants, organic salt and silver iodide in preweighed proportions (75-95% equivalent I- of A&) were intimately mixed, compacted and then annealed at 150°C for 5 days, to permit the system to come to equilibrium.
2. EXPERIMENTAL 2.1. Preparation of salts Agl and homopiperazinium diiodide were prepared and analysed in the same manner as described * Author to whom correspondence should be addressed. 565
2.2. NMR and ir characterization of the organic salts The ‘H NMR spectra are recorded on a VARIAN EM 36OA spectrometer operating at 60 MHz. All spectra are measured on solutions in 99.7% DzO obtained from Spectrometrie Spin et Techniques, at probe temperature of ca. 30°C. Samples are prepared in a 5 mm o.d. tube containing 5 mg of the sample in 0.4 ml of DzO; 2,2-dimethyl-2-silapentane-5-s& fonate sodium salt was used as an internal standard in all measurements. The vibrational spectra were recorded between 4000 and 400 cm- ’ on a NICOLET 5DX FTir spectrophotometer, at a resolution of 4 cm-’ with 100 interferograms added for each spectrum. KBr pellets (about 1 mg of sample for 150 mg KBr) were used as no peculiar effect on position and intensity of the
J. J. ROSENBERGet al.
566
vibration bands owing to Br- diffusion had been previously detected. 2.3. Total electrical conductivity measurements The total electrical conductivity was determined by tracing impedance diagrams (Radiometer 6 B 11 C). 2.4. Powder diffraction analysis 2.4.1. Preparation of powders. The specimens were ground manually for 5 min in an agate mortar and annealed for 24 h at 100°C. Since our main interest lay in the semi-quantitative measurement of peak intensities, the powder sample had to be prepared in such a way that preferred orientations were minimized, even if not avoided completely. For this purpose an excess of compound was powdered on the adhesive side of a piece of sellotape, the sample holder being placed in a horizontal position; the powder was uniformly distributed by a buzzer during 3 min and the excess thrown out. The sample holder consisted of a hole (10 mm in diameter) drilled in a sheet of aluminium (40 x 20 x 2 mm) fixed firmly on the axial rod of the goniometer: the coated tape overlapping the hole adhered to the face of the sheet, in coincidence with the vertical axis of the goniometer. Because AgI-based compounds are very absorbing, the choice of a powdered sample packed in a capillary was avoided and this sheet form-is adopted. 2.4.2. Data collection. The powder diffraction system is composed of: (i) a stabilized Sigma 2080 “Compagnie GCntrale de Radiologie, CGR” generator operating at 40 kV, 25 mA, with a fine focus copper target; (ii) an incident beam curved-crystal quartz monochromator with asymmetric focusing (short focal distance 130 mm, long focal distance 500 mm), producting a strictly monochromatized Cu-Kal, radiation (0.1540598 nm); (iii) a position sensitive curved detector (PSCD) (INEL CPS 120), fixed on a CGR goniometer, 500 mm distant of the monochromator, allowing the simultaneous data collection over a 120” 2 theta angular range with a resolution which compared the conventional powder diffraction systems, but with a shorter acquisition time (1200 s), (iv) a PC with Diffractinel software providing transfer of data from the multichannel analyser, calibration, peak search and analysis report (position, width and intensity of each peak). The sample was placed between the bent quartz monochromator and the PSCD in transmission mode. The sample holder was tixed and made a constant angle (25°C) with respect to the X-ray beam.
3
4
AND DISCUSSION
3.1. The HI,-AgI system 3.1.1. Infrared spectrum of HI,. Figure 1 shows the infrared spectrum of HI,. Between 2950 and 2800 cm- ‘, the characteristic stretching bands of CH bonds in the methylene groups were seen. Connected with the >NH, groups we noticed an absorption of
1.5 “/lOS (cm-‘)
1
0.5
Fig. 1. FTir spectrum of HI, between 400 and 4ooo em-‘. strong intensity at 3200 cm-‘. At 1620 cm-‘, the frequency, corresponded to a bending deformation. The strong stretching band at 1155 cm-t could be attributed to C-N bonds[6]. 3.1.2. ‘H NMR spectrum of HI,. ‘H NMR spectrum of HI, is shown in Fig 2. The peak at 4.66 ppm corresponds to H,O as impurity in D20. The protons of -NH; groups were rapidly replaced by D coming from D,O and so are not shown. The unscreening effect of the ammonium cation was the same for the protons of the four methylene groups in a-position and consequently the corresponding chemical shifts were very closed: a singlet absorption was observed at 3.23 ppm assigned to the +N-CHsCH2-N+ group and a triplet, not resolved, at 3.10 ppm, attributed to +N-CH#-CHs-N+ proton resonances. These values are in agreement with the corresponding 3.15 ppm shift observed in triethylenediammonium diiodide[3]. The signal at 2.10 ppm was assigned to the methylene C-CH,-C absorbing group. 3.1.3. Total electrical conductivity of the HI,-AgI system. We have represented the variation of conductivity vs. (l/T) for the compositions varying between 75 and 95% equivalent I- of silver iodide (Fig. 3). This electrical conductivity follows the Arrhenius type law with: u = u,, exp(-E/RT) where us is the pre-exponential term, E the activation energy of conduction, R the ideal gas constant, and T the absolute temperature. We obtained straight line curves. Maximum conductivity was noted for the composition 85% equivalent I- of AgI at 25°C viz C,H,,N,Ag,,I,,. The activation energy of conduction calculated between
“,&-3JH,,2lj
Solvent:
3. RESULTS
2
DzO
H20 I N-CH2-CH2-N I
6 bp.m.)
Fig. 2. ‘H NMR spectrum of HI,.
I
Modified AgI solid electrodes-1
567
i/X
100
50
25
I
CHJ-&2M 4
r-
VSI -CH,
V*t
-CH2-
1
v!, C-N 1 [C-&CH2)21
~.N”:[C&CH2)21
3
2
1.5 v/10’ (cm-‘)
1
0.5
Fig. 5. FW spectrum of TMHI, between 400 and 4000 cm-‘.
28
28
3x)
3.2
3A
lO’T->K-’
Fig. 3. Total electrical conductivity of the AgI-homopiperazinium diiodide system as a function of reciprocal absolute temperature.
25°C and 100°C for this composition has a value of 4.4 kcal mol-’ (or 0.19 ev). Figure 4 represents the variation of conductivity vs. the composition of the system. The maximum conductivity is, at all temperatures, observed for the same composition. We have 2.95 x 10-j (ohm cm)-’ at 25”C, 5.25 x lo-’ (ohm cm)-’ at 50°C and 0.013 (ohm cm)-’ at 100°C. 3.2. The TMHI,-AgI system 3.2.1. Infrmed spectrum of TMH12. Figure 5 shows the infrared spectrum of TMHI, . The substitution of hydrogen atoms in each quaternary ammonium group induced the disappearing of N-H absorption bands localised at 3220, 2350 and
1620 cm-’ in HI,. The existence of methyl groups gave rise to a new stretching 6ne band at 3008 cm-‘. The deformation mode of the CH, group attached to a nitrogen atom gave an absorption band at 1465 cm-’ and a 6ne and strong stretching band at 960 cm-‘. The stretching band of CH in -CH,- was weaker than in the preceding spectrum (Fig 1); its frequency was almost unchanged (2950-2900 cm-‘). 3.2.2. ‘H NMR sjwctrwn of TMHIz. ‘N NMR spectrum of TMHI, is shown in Fig. 6. As for HI,, the peak at 4.66 ppm corresponded to H20. The group C-CH,-C was responsible for the signal at 2.50 ppm. The absorption of +N-CHa-CH2-N+ and +N-CH2-C-CHI-N+ groups were, respectively, observed at 4.10 ppm and 3.80 ppm, a shifting to lower fields (comparing to HI,) meant a more unscreened quaternarized molecule with methyl radicals than with protons. The +N-CHs resonance occurred at 3.33 ppm These different shifts compared to the correspondent values found for N, N’dimethyltriethylenediammonium diiodide[3]. 3.2.3. Total electrical conductivityof the TMHI,AgI system. Figure 7 represents the curves log Q = f (l/T) of the system AgI-1,1,4&tetramethylhomopiperazinium diiodide for the compositions varying between 75 and 95% quivalent I- of silver iodide. The maximal conductivity was reached for an equivalent AgI content of 90%. The activation energy, for this composition, was 3.34 kcal mol-’ (or 0.145 ev). We plotted the total electrical conductivity at 25, 50 and 100°C as a function of the AgI content. We found, respectively, conductivity of 0.0269 (ohm cm)-‘; 0.037 (ohm cm)-’ and 0.083 (ohm cm)- ’ for this composition (Fig. 8). At difference with the observations in the HI,-AgI system, in the present one, the evolution of log Q vs. AgI content does not vary in a symmetrical way around the composition of the highest conductivity.
Hz0
R&H,
N-CH2
N-CHz-C-CH2-N ,_I’ DSS ‘C-CH2-C 75
50
95 90 %equi.Agl
“---G-A
95
Fig. 4. Isothermal conductivities of the AgIhomopiperazinium diiodide system as a function of the equivalent AgI content.
10
9
6
7
6
5
4
3
2
1
6 (iwm.)
Fig. 6. ‘H NMR spectrum of TMHI,
.
o
J. J. ROSBNBERG et al.
5
10
15
20
25
30
35
40
45 C
2.6
2.8
30 tO’T-!K-’
3.2
5
10
15
20
25
30
35
40
45
5
10
15
20
25
30
35
40
45
Fig. 7. Total electrical conductivity of the AgI-tetramethyl1,1,4,4 homopiperazinium diiodide system as a function of reciprocal absolute temperature.
3.2.4. XRPD study of the TMHI,-AgI system. The XRPD spectra for the same nine compositions ranging from 75 to 95% equivalent I- of AgI, matter of the conductivity study, were recorded. From the XRPD analysis it transpires that for every composition, sets of diffraction peaks could be related to silver iodide (Fig. 9a) and TMHI, (Fig. 9d). Yet a number of characteristic peaks, which were different from those of the starting materials, could be associated to another phase. These results indicate the formation of a conducting composition with a limited stability at room temperature. In Fig. 10 intensitycomposition plots A, B, C, D and E refer to five new
I
I
75
I
I
80
I
I
I
I
85 90 %mola Agl
I
I
26 Fig. 9. X-ray diffraction powder patterns in the system AgI-TMHI, (a) bAgI; (b) 87.5 eq./o AgI; (c) 80 eq./o AgI; (d) TMHI,
.
reflections, respectively, at 10.8, 10.5, 9.6, 8.6 and 7.6
A. Two maxima were observed for the 87.5 and 80 equivalent AgI compositions. In Fig. 9b and 9c are reported the corresponding XRPD spectra[7J The conducting phase apparently seems to be a mixture of two solid electrolytes with approximate
I
95
Fig. 8. Isothermal conductivities of the AgI-tetramethyl-1, 1,4,4 homopiperazinium diiodide system as a function of reciprocal absolute temperature.
70
80
90
1 0
yh mole Agl
Fig 10. Intensity-composition plots for the five intense new reflections in the svstem AnI-TMHI.
most
Modified AgI solid electrodes-I
569
ent phases (reported in Table 1) as HMED 66.7 CAgJ&HdVl~ HMED85.7 C4GG,H,,WI and HMED 88.6 [Ag,lIs9(C,H,,N3;1[8]. The first one was a nonconducting phase with I- edge-shared tetrahedra tilled with Ag+ ions. For the other conducting phases, as for those reported by Geller et al.[9-121, face sharing of the iodide polyhedra was observed, inducing pathways through which the silver ions moved. Moreover, the change carriers were distributed nonuniformly over different sets of crystallographically nonequivalent sites with no possibility for the ordering of the Ag+ ions among these sites. The direction and the number of pathways for the Ag+ ion diffusion inferred the one-, two- or three-dimensional nature of the solid electrolyte. I
L
75
90 95 90 % mole Agl
95
4. CONCLUSION
Fig 11. Schematic variation of the total electrical conductivity vs. composition for a two solid electrolytes system as observed in TMHI,-AgI association. stoichiometry AgsI,,C,H,,N2 (80% eq. I- of AgI) and Ag,,I,,CsH,,N, (87.5% eq. I- of AgI). According to this hypothesis, existence of a second electro-
lyte phase around 80% eq. I- of AgI is sustained by examination of Fig. 8 showing a dissymmetric composition dependence for the conductivity variation vs. AgI content around a main maximum at 90% eq. AgL Moreover, the observed quasi-linear evolution of the “mean and total” electric conductivity in the 8040% eq. AgI range between the two maxima is an elementary illustration of the lever rule. Figure 11 reports a schematic illustration of this. Diffusion-controlled solid reactions tend to produce mixtures of compounds, the relative ratio of which being related to their thermodynamic stability at the reaction temperature. Thackeray and Coetxer isolated in the HMED (N, N, N, N’, N’, N’hexamethyl-1,2ethylenediamine) system three differTable 1. Electrical conductivity of some A&based solid electrolytes Organic silver iodide
TMA Aa,,L PyAgsI, Py,A8&s HMED 66.7 HMED 85.7 HMED 88.6 DMMA&I, @MM)sA8,& @ENDM),Ag,sI,, C,Hi,NsA8,sI,, C,HssNsA&,I,, C,H,,N,A8sI,,
Conductivity (ohm-’ cm-‘) at2%K
0.04 0.077 0.008
Reference 9 9 9 8 a 8 10 11 12 this work this work this work
TMA = tetramethyl ammonium radical, Py = pyridinium radical, HMED = hesamethyl 1,2-ethylenediammonium radical, DMM = N, Ndimethylmorpholinium radical, DENDM = diethyldimethylammonium radical.
AgI association with analogous organic diiodides, homopiperaxinium and N, N, N’, N-tetramethylhomopiperaxinium leads to two fundamental different electrochemical behaviour. If, for the former case, a symmetrical curve log u vs. AgI content is observed, for the latter an asymmetrical one is determined. XRPD study confinns the existence of new conducting phases corresponding to the maximum of conductivity and corroborates the presence of more than one conducting composition when an asymmetrical curve for conductivity vs. AgI content is observed. The conductivity and the enthalpy of activation of motion for silver ions observed in the different solid electrolytes suggest for them iodide ions arranged such that they form polyhedra, mainly tetrahedra, which share faces forming a network of channels, pathways through which the silver ions can move by a hopping mechanism.
REFERENCES 1. B. B. Owens, J. electroc~. Sot. 118,1144 (1971). 2 T. Takahashi, Jpn Kokaf 7461697-CA al-180 369 f. (June 1974). 3. J. J. Rosenberg, A. Benchettara, A Nouacer and J. Estienne, J. appl. Electrochem. 20,701(1990). 4. G. Robert, 1. Faucheu and J. J. Rosenberg J. Power Sources 1,359 (1976-1977). 5. A. Rembaum and H. Noguchi, Macromolecules 5, 261 (1972). 6. L. J. Bellamy, The lnfiared Spectra of Complex Molecules, pp. 248-262. Methuen, London (1964). 7. J. J. Rosenberg 0. Cerclier, M. Bouzou and J. Estienne, Powder diffraction. Satellite Meeting (XVth ConSress of the International Union of Crystallography), Toulouse (1990). 8. M. M. Thackeray and J. Coetzer, Electroch. Acta 24, 495 (1979). 9. S. Geller, in “Solid Electrolytes”, (Edited by S. Geller) pp. 41-W Springer, Berlin (1977). 10. X. Sishen and S. Geller. J. solid state Gem. 68, 73 (1987).
11. J. M. Gaines and S. Geller, 1. Phys. Gem. Solids 4U, 12, 1159 (1987). 12. S. Gelkr and X. Siihen, 2. Kristallogr. 181, 11 (1987).
om-4w93~+o‘lm 81993.papmollPreuLtd.
AN INVESTIGATION OF MODIFIED AgI SOLID ELECTRODES CONTAINING THE HOMOPIPERAZINIUM CATION-I. SYNTHESIS AND CHARACTERIZATION JOSEPHJ. ROSENFBRG,*~M AI-LUANEFkmzou,~ OLIVIER CBRCLIER~ and JACQUJBE&IENNE$ tLaboratoire de Chimie des Matkriaux Inorganiques, U.R.A. C.N.RS. 1311, Universitk Paul Sabatier, 118 route de Narbonne, 31062 Toulouse cedex, France SLaboratoire de Chimie Organique Structurale, Universitk de Provence, Centre Saint-JkrSme,Case 542, Avenue Esadrille Normandie+Niemen, 13397 Marseille cedex, France &entre de Diffractomtirie, Universitk de Provence, Case 29,3, Place Victor-Hugo, 13331 Marseille a&x 3, France (Received 7 October 1991; in revisedform29 July 1992 Ahstraet-Homopiperazinium and N, N, N’, N’-tetramethylhomopiperazinium diiodide (briefly designated as HI, and TMHI,) have been synthesized and characterixed by Srared spectroscopy and proton magnetic rekance spe&oscopy. The-two diazonia diiodides were reacted withsilver tide in &&entrations ranging from 75 to 95 equivalent I- of AgI. In both HI,-AgI and TMHI,-AgI systems, the study of the total electrical conductivity with respect to temperature shows that the Arrhenius equation is obeyed. At 25”C, the maximal conductivity is reached for an equivalent content of 85% in the HI,-AgI system with a value of 0.003 (ohm cm)-‘. For the TMHI,&I system a dissymetric commsition deuen&nce of the ekctricd conduc&ty is &served around a n&in-m&mum at 90% AgI con&t corresp&ding to a 0.027 (ohm cm)-’ conductivity. Existence in this system of a second electrolyte phase around a 77.5-80% composition in AgI is swtained by electrochemical conductivity measurements and an independent X-ray powder di&ction study. Key words: silver iodide, silver solid electrolyte, homopiperazinium diiodide, total electrical conductivity, Fourier transformed infrared snectroscom IFTM uroton magnetic resonance spectroscopy (‘H NMR), X-ray power diffraction (XRP6). ‘. _
1. INTRODUCTION A survey of the literature indicates the good electrical conductivity of cationic organo-mineral electrolytes based on Ag+ ion conductors. Among them, the carbon cycles having one or many ammoniums have been studied in terms of their electrical conductivity. Owens[l] was the first to mention the good conductivity of axacyclic iodide (one ammonium in the carbon cycle) associated with AgI. Other authors have presented electrical conductivity of the systems N-alkyl hexamethylenetetraaminium iodide (with R = H, CH, or C,H,)-AgI[2]; N, N’-dimethyl triethylenediammonium diiodide-AgI[2, 33; and N, N, N’, N’-tetramethylpiperazinium diiodide-AgI[4]. In the present work based on homopiperazinium diiodide (HIJ and on N, N, N’, N’-tetramethyl- homopiperazinium diiodide (THMI,) the conductivity of the two electrolyte systems HI,-AgI and TMHI,-AgI is investigated. Previous synthesis and characterization of the organic and mineral starting materials are described.
earlier[4]. The N, N, N’, N’-tetramethyl homopiperazinium diiodide was prepared according to Rembaum et ar[S] in DMF-methanol (l-l in volume). The reaction was carried for 168 h, with tetramethyldiaminoethane and 1,3-diiodopropane in equal concentrations, at 25°C. The precipitated crystals are filtered, washed with acetone, recrystallized from ethanol, and dried in vacuum at 40°C (yield 73.6%). The reactants, organic salt and silver iodide in preweighed proportions (75-95% equivalent I- of A&) were intimately mixed, compacted and then annealed at 150°C for 5 days, to permit the system to come to equilibrium.
2. EXPERIMENTAL 2.1. Preparation of salts Agl and homopiperazinium diiodide were prepared and analysed in the same manner as described * Author to whom correspondence should be addressed. 565
2.2. NMR and ir characterization of the organic salts The ‘H NMR spectra are recorded on a VARIAN EM 36OA spectrometer operating at 60 MHz. All spectra are measured on solutions in 99.7% DzO obtained from Spectrometrie Spin et Techniques, at probe temperature of ca. 30°C. Samples are prepared in a 5 mm o.d. tube containing 5 mg of the sample in 0.4 ml of DzO; 2,2-dimethyl-2-silapentane-5-s& fonate sodium salt was used as an internal standard in all measurements. The vibrational spectra were recorded between 4000 and 400 cm- ’ on a NICOLET 5DX FTir spectrophotometer, at a resolution of 4 cm-’ with 100 interferograms added for each spectrum. KBr pellets (about 1 mg of sample for 150 mg KBr) were used as no peculiar effect on position and intensity of the
J. J. ROSENBERGet al.
566
vibration bands owing to Br- diffusion had been previously detected. 2.3. Total electrical conductivity measurements The total electrical conductivity was determined by tracing impedance diagrams (Radiometer 6 B 11 C). 2.4. Powder diffraction analysis 2.4.1. Preparation of powders. The specimens were ground manually for 5 min in an agate mortar and annealed for 24 h at 100°C. Since our main interest lay in the semi-quantitative measurement of peak intensities, the powder sample had to be prepared in such a way that preferred orientations were minimized, even if not avoided completely. For this purpose an excess of compound was powdered on the adhesive side of a piece of sellotape, the sample holder being placed in a horizontal position; the powder was uniformly distributed by a buzzer during 3 min and the excess thrown out. The sample holder consisted of a hole (10 mm in diameter) drilled in a sheet of aluminium (40 x 20 x 2 mm) fixed firmly on the axial rod of the goniometer: the coated tape overlapping the hole adhered to the face of the sheet, in coincidence with the vertical axis of the goniometer. Because AgI-based compounds are very absorbing, the choice of a powdered sample packed in a capillary was avoided and this sheet form-is adopted. 2.4.2. Data collection. The powder diffraction system is composed of: (i) a stabilized Sigma 2080 “Compagnie GCntrale de Radiologie, CGR” generator operating at 40 kV, 25 mA, with a fine focus copper target; (ii) an incident beam curved-crystal quartz monochromator with asymmetric focusing (short focal distance 130 mm, long focal distance 500 mm), producting a strictly monochromatized Cu-Kal, radiation (0.1540598 nm); (iii) a position sensitive curved detector (PSCD) (INEL CPS 120), fixed on a CGR goniometer, 500 mm distant of the monochromator, allowing the simultaneous data collection over a 120” 2 theta angular range with a resolution which compared the conventional powder diffraction systems, but with a shorter acquisition time (1200 s), (iv) a PC with Diffractinel software providing transfer of data from the multichannel analyser, calibration, peak search and analysis report (position, width and intensity of each peak). The sample was placed between the bent quartz monochromator and the PSCD in transmission mode. The sample holder was tixed and made a constant angle (25°C) with respect to the X-ray beam.
3
4
AND DISCUSSION
3.1. The HI,-AgI system 3.1.1. Infrared spectrum of HI,. Figure 1 shows the infrared spectrum of HI,. Between 2950 and 2800 cm- ‘, the characteristic stretching bands of CH bonds in the methylene groups were seen. Connected with the >NH, groups we noticed an absorption of
1.5 “/lOS (cm-‘)
1
0.5
Fig. 1. FTir spectrum of HI, between 400 and 4ooo em-‘. strong intensity at 3200 cm-‘. At 1620 cm-‘, the frequency, corresponded to a bending deformation. The strong stretching band at 1155 cm-t could be attributed to C-N bonds[6]. 3.1.2. ‘H NMR spectrum of HI,. ‘H NMR spectrum of HI, is shown in Fig 2. The peak at 4.66 ppm corresponds to H,O as impurity in D20. The protons of -NH; groups were rapidly replaced by D coming from D,O and so are not shown. The unscreening effect of the ammonium cation was the same for the protons of the four methylene groups in a-position and consequently the corresponding chemical shifts were very closed: a singlet absorption was observed at 3.23 ppm assigned to the +N-CHsCH2-N+ group and a triplet, not resolved, at 3.10 ppm, attributed to +N-CH#-CHs-N+ proton resonances. These values are in agreement with the corresponding 3.15 ppm shift observed in triethylenediammonium diiodide[3]. The signal at 2.10 ppm was assigned to the methylene C-CH,-C absorbing group. 3.1.3. Total electrical conductivity of the HI,-AgI system. We have represented the variation of conductivity vs. (l/T) for the compositions varying between 75 and 95% equivalent I- of silver iodide (Fig. 3). This electrical conductivity follows the Arrhenius type law with: u = u,, exp(-E/RT) where us is the pre-exponential term, E the activation energy of conduction, R the ideal gas constant, and T the absolute temperature. We obtained straight line curves. Maximum conductivity was noted for the composition 85% equivalent I- of AgI at 25°C viz C,H,,N,Ag,,I,,. The activation energy of conduction calculated between
“,&-3JH,,2lj
Solvent:
3. RESULTS
2
DzO
H20 I N-CH2-CH2-N I
6 bp.m.)
Fig. 2. ‘H NMR spectrum of HI,.
I
Modified AgI solid electrodes-1
567
i/X
100
50
25
I
CHJ-&2M 4
r-
VSI -CH,
V*t
-CH2-
1
v!, C-N 1 [C-&CH2)21
~.N”:[C&CH2)21
3
2
1.5 v/10’ (cm-‘)
1
0.5
Fig. 5. FW spectrum of TMHI, between 400 and 4000 cm-‘.
28
28
3x)
3.2
3A
lO’T->K-’
Fig. 3. Total electrical conductivity of the AgI-homopiperazinium diiodide system as a function of reciprocal absolute temperature.
25°C and 100°C for this composition has a value of 4.4 kcal mol-’ (or 0.19 ev). Figure 4 represents the variation of conductivity vs. the composition of the system. The maximum conductivity is, at all temperatures, observed for the same composition. We have 2.95 x 10-j (ohm cm)-’ at 25”C, 5.25 x lo-’ (ohm cm)-’ at 50°C and 0.013 (ohm cm)-’ at 100°C. 3.2. The TMHI,-AgI system 3.2.1. Infrmed spectrum of TMH12. Figure 5 shows the infrared spectrum of TMHI, . The substitution of hydrogen atoms in each quaternary ammonium group induced the disappearing of N-H absorption bands localised at 3220, 2350 and
1620 cm-’ in HI,. The existence of methyl groups gave rise to a new stretching 6ne band at 3008 cm-‘. The deformation mode of the CH, group attached to a nitrogen atom gave an absorption band at 1465 cm-’ and a 6ne and strong stretching band at 960 cm-‘. The stretching band of CH in -CH,- was weaker than in the preceding spectrum (Fig 1); its frequency was almost unchanged (2950-2900 cm-‘). 3.2.2. ‘H NMR sjwctrwn of TMHIz. ‘N NMR spectrum of TMHI, is shown in Fig. 6. As for HI,, the peak at 4.66 ppm corresponded to H20. The group C-CH,-C was responsible for the signal at 2.50 ppm. The absorption of +N-CHa-CH2-N+ and +N-CH2-C-CHI-N+ groups were, respectively, observed at 4.10 ppm and 3.80 ppm, a shifting to lower fields (comparing to HI,) meant a more unscreened quaternarized molecule with methyl radicals than with protons. The +N-CHs resonance occurred at 3.33 ppm These different shifts compared to the correspondent values found for N, N’dimethyltriethylenediammonium diiodide[3]. 3.2.3. Total electrical conductivityof the TMHI,AgI system. Figure 7 represents the curves log Q = f (l/T) of the system AgI-1,1,4&tetramethylhomopiperazinium diiodide for the compositions varying between 75 and 95% quivalent I- of silver iodide. The maximal conductivity was reached for an equivalent AgI content of 90%. The activation energy, for this composition, was 3.34 kcal mol-’ (or 0.145 ev). We plotted the total electrical conductivity at 25, 50 and 100°C as a function of the AgI content. We found, respectively, conductivity of 0.0269 (ohm cm)-‘; 0.037 (ohm cm)-’ and 0.083 (ohm cm)- ’ for this composition (Fig. 8). At difference with the observations in the HI,-AgI system, in the present one, the evolution of log Q vs. AgI content does not vary in a symmetrical way around the composition of the highest conductivity.
Hz0
R&H,
N-CH2
N-CHz-C-CH2-N ,_I’ DSS ‘C-CH2-C 75
50
95 90 %equi.Agl
“---G-A
95
Fig. 4. Isothermal conductivities of the AgIhomopiperazinium diiodide system as a function of the equivalent AgI content.
10
9
6
7
6
5
4
3
2
1
6 (iwm.)
Fig. 6. ‘H NMR spectrum of TMHI,
.
o
J. J. ROSBNBERG et al.
5
10
15
20
25
30
35
40
45 C
2.6
2.8
30 tO’T-!K-’
3.2
5
10
15
20
25
30
35
40
45
5
10
15
20
25
30
35
40
45
Fig. 7. Total electrical conductivity of the AgI-tetramethyl1,1,4,4 homopiperazinium diiodide system as a function of reciprocal absolute temperature.
3.2.4. XRPD study of the TMHI,-AgI system. The XRPD spectra for the same nine compositions ranging from 75 to 95% equivalent I- of AgI, matter of the conductivity study, were recorded. From the XRPD analysis it transpires that for every composition, sets of diffraction peaks could be related to silver iodide (Fig. 9a) and TMHI, (Fig. 9d). Yet a number of characteristic peaks, which were different from those of the starting materials, could be associated to another phase. These results indicate the formation of a conducting composition with a limited stability at room temperature. In Fig. 10 intensitycomposition plots A, B, C, D and E refer to five new
I
I
75
I
I
80
I
I
I
I
85 90 %mola Agl
I
I
26 Fig. 9. X-ray diffraction powder patterns in the system AgI-TMHI, (a) bAgI; (b) 87.5 eq./o AgI; (c) 80 eq./o AgI; (d) TMHI,
.
reflections, respectively, at 10.8, 10.5, 9.6, 8.6 and 7.6
A. Two maxima were observed for the 87.5 and 80 equivalent AgI compositions. In Fig. 9b and 9c are reported the corresponding XRPD spectra[7J The conducting phase apparently seems to be a mixture of two solid electrolytes with approximate
I
95
Fig. 8. Isothermal conductivities of the AgI-tetramethyl-1, 1,4,4 homopiperazinium diiodide system as a function of reciprocal absolute temperature.
70
80
90
1 0
yh mole Agl
Fig 10. Intensity-composition plots for the five intense new reflections in the svstem AnI-TMHI.
most
Modified AgI solid electrodes-I
569
ent phases (reported in Table 1) as HMED 66.7 CAgJ&HdVl~ HMED85.7 C4GG,H,,WI and HMED 88.6 [Ag,lIs9(C,H,,N3;1[8]. The first one was a nonconducting phase with I- edge-shared tetrahedra tilled with Ag+ ions. For the other conducting phases, as for those reported by Geller et al.[9-121, face sharing of the iodide polyhedra was observed, inducing pathways through which the silver ions moved. Moreover, the change carriers were distributed nonuniformly over different sets of crystallographically nonequivalent sites with no possibility for the ordering of the Ag+ ions among these sites. The direction and the number of pathways for the Ag+ ion diffusion inferred the one-, two- or three-dimensional nature of the solid electrolyte. I
L
75
90 95 90 % mole Agl
95
4. CONCLUSION
Fig 11. Schematic variation of the total electrical conductivity vs. composition for a two solid electrolytes system as observed in TMHI,-AgI association. stoichiometry AgsI,,C,H,,N2 (80% eq. I- of AgI) and Ag,,I,,CsH,,N, (87.5% eq. I- of AgI). According to this hypothesis, existence of a second electro-
lyte phase around 80% eq. I- of AgI is sustained by examination of Fig. 8 showing a dissymmetric composition dependence for the conductivity variation vs. AgI content around a main maximum at 90% eq. AgL Moreover, the observed quasi-linear evolution of the “mean and total” electric conductivity in the 8040% eq. AgI range between the two maxima is an elementary illustration of the lever rule. Figure 11 reports a schematic illustration of this. Diffusion-controlled solid reactions tend to produce mixtures of compounds, the relative ratio of which being related to their thermodynamic stability at the reaction temperature. Thackeray and Coetxer isolated in the HMED (N, N, N, N’, N’, N’hexamethyl-1,2ethylenediamine) system three differTable 1. Electrical conductivity of some A&based solid electrolytes Organic silver iodide
TMA Aa,,L PyAgsI, Py,A8&s HMED 66.7 HMED 85.7 HMED 88.6 DMMA&I, @MM)sA8,& @ENDM),Ag,sI,, C,Hi,NsA8,sI,, C,HssNsA&,I,, C,H,,N,A8sI,,
Conductivity (ohm-’ cm-‘) at2%K
0.04 0.077 0.008
Reference 9 9 9 8 a 8 10 11 12 this work this work this work
TMA = tetramethyl ammonium radical, Py = pyridinium radical, HMED = hesamethyl 1,2-ethylenediammonium radical, DMM = N, Ndimethylmorpholinium radical, DENDM = diethyldimethylammonium radical.
AgI association with analogous organic diiodides, homopiperaxinium and N, N, N’, N-tetramethylhomopiperaxinium leads to two fundamental different electrochemical behaviour. If, for the former case, a symmetrical curve log u vs. AgI content is observed, for the latter an asymmetrical one is determined. XRPD study confinns the existence of new conducting phases corresponding to the maximum of conductivity and corroborates the presence of more than one conducting composition when an asymmetrical curve for conductivity vs. AgI content is observed. The conductivity and the enthalpy of activation of motion for silver ions observed in the different solid electrolytes suggest for them iodide ions arranged such that they form polyhedra, mainly tetrahedra, which share faces forming a network of channels, pathways through which the silver ions can move by a hopping mechanism.
REFERENCES 1. B. B. Owens, J. electroc~. Sot. 118,1144 (1971). 2 T. Takahashi, Jpn Kokaf 7461697-CA al-180 369 f. (June 1974). 3. J. J. Rosenberg, A. Benchettara, A Nouacer and J. Estienne, J. appl. Electrochem. 20,701(1990). 4. G. Robert, 1. Faucheu and J. J. Rosenberg J. Power Sources 1,359 (1976-1977). 5. A. Rembaum and H. Noguchi, Macromolecules 5, 261 (1972). 6. L. J. Bellamy, The lnfiared Spectra of Complex Molecules, pp. 248-262. Methuen, London (1964). 7. J. J. Rosenberg 0. Cerclier, M. Bouzou and J. Estienne, Powder diffraction. Satellite Meeting (XVth ConSress of the International Union of Crystallography), Toulouse (1990). 8. M. M. Thackeray and J. Coetzer, Electroch. Acta 24, 495 (1979). 9. S. Geller, in “Solid Electrolytes”, (Edited by S. Geller) pp. 41-W Springer, Berlin (1977). 10. X. Sishen and S. Geller. J. solid state Gem. 68, 73 (1987).
11. J. M. Gaines and S. Geller, 1. Phys. Gem. Solids 4U, 12, 1159 (1987). 12. S. Gelkr and X. Siihen, 2. Kristallogr. 181, 11 (1987).