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Properties of the CuTeX solid conductors
Ekcrmhindca 0 _mon
Acta Vol. 23. pa. 805807. Press Ltd. 1978. Printed in Great
Britain.
SHORT PROPERT1ES
COMMUNICATION
OF THE CuTeX SOLID
CONDUCTORS
G. RAZZINI*, M. LAZZARI’ and B. SCR~SAT~~ + Centro Studio Processi Elettrodici de1 C.N.R., Istituto di Elettrochimica, Polytechnic of Milan, Milan t lstituto di Chimica Fisica, University of Rome, Rome, Italy (Received 1 October 1977)
It has been recently reported[l] that compounds of the type CuTeX, where X may be Cl, Br or I, exhibit a conductivity prevalently ionic in character which at 200°C becomes of the order of 10-3-10-2S/cm. ie ofpractical interest. On the other hand it was also reported that copper electrodes are not suitable to be used in connection with these electrolytes since they decompose in presence of copper. Due to the peculiarity of this aspect and the basic importance of copper solid conductors[2], it appeared to us of interest to further investigate the decomposition reaction induced by copper and toexamine theapplicability ofalternativeelectrodes with reduced copper activity. The CuTeX compounds have been prepared following the procedure indicated by Rabenau et af[3], TiS, has been prepared from the elements (Johnson and Matthey Specpure) in evacuated and sealed silica tubes at 600°C for several days. The X-ray powder patterns were in agreement with the literature (ASTM card 15-853). The intercalates Cu,TiS, have been prepared by reaction of Cu and TiS, at 8OO”C, according to I,eNagard et aI[4]. The conductivity studies have been carried out by sandwiching a compressed pellet of the electrolyte (1.2 cm in dia) between two pellets of the electrodic materials at a pressure of 2500 ks/cm2. The measurements were performed in Pyrex cell holders tluxed with inert gas. The ac bridge (Wayne and Kerr B331 MKII) operated at 1592Hz. For the calorimetric studies a Perkin-Elmer DSC Mod. I-B was used. X-ray powder patterns were registered by a JEOL diffractometer mod. JDX-85 with monocromator, using CuKcr radiation. The furnace temperature was regulated by a Herams Kelvitron TPG 2.2 programmer, with NiCrNi thermocouples. The electrochemical investigation was mainly devoted to chloride and bromide. The measurements of total conductivity as a function of temperature with copper and graphite electrodes are reported for CuTeCl in Fig. 1. The experiments were performed by keeping the cells for 2 h at each temperature: the aim was to get informations on the stability of the materials in connection with different electrodes. The thicknesses of the CuTeX pellets were in different runs 0.05,0.10,0.18 cm. The results reported in Figs 1-4 refer to 0.10 thick samples. The conductivity values were not corrected for the contact resistance. The cycle obtained with CuTeCl using copper electrodes (Fig. 1) shows a change in slope in the heating scan at about 100°C; at higher temperatures steady values were not reached, but conductivity continuously increased with time at constant temperature. The cooling scan is typical ofa metallic behaviour. The result is in agreement with a decomposition of CuTeCl in presence ofcopper[l] and indicates that probably the process becomes kinetically fast at about 100°C and originates compounds with metallic properties. In the ab-
T. “C
electrodes
’
10-a
’
’ n ’ ’ ’ 2.0
2.5 103/T.
’
’
’
’
DK -I
’
3.0
’
’
Fig. 1. Total electrical conductivity us reciprocal temperature for CuTeCl (copper and graphite electrodes; values not corrected for contact resistance).
805
CuTeCl
a A
I”v
E ?I =
-
CUT&L-Cu3:I
A
cv-mx-cu 3:l 46-C. 72hrs
c
s
I=d
-
-
.
CuTeCI-Cu 24hrs
60-C
CuTeCI-Cu 3rl 110°C 24hrs
c I 20
31
I 100 t.
I 180 QC
I 260
I
Fig. 2. DSC traces (16”C/min) of CuTeCl and CuTeCl-Cu mixtures as prepared and after annealing.
nealed at 46, 80 and 110°C respectively (curves c, d and e). Results qualitatively similar were obtained with CuTeBr, as shown in Fig. 3, where the critical role of copper is evidenced by comparison with the graphite cell. DSC measurements showed for the pure compound a thermal et&t at about 7O”C, probably related to a phase transition[l]; a freshly prepared mixture of CuTeBr and Cu showed a diffuse peak similar to that observed with CUT&I-Cu. The conductivity-time measurements at fixed temperatures, performed to trace the plot of Fig. 3, and the DSC scans on mixtures CuTeBr-Cu after annealing seem to indicate that the decomposition of CuTeBr is kinetically slower than for CuTeCl. The above results confirm the instability of the CuTeX compounds in the presence of copper, thus considerably reducing their possible applications. In the attempt of overcoming this, we have considered as possible alternative electrodes layered materials such as titanium disulphide, and their copper intercalates. In fact it has been ascertained[S] that copper can be reversibly incorporated into TiS, using cells completely in the solid state with cuprous solid elcctrolytes based on organic halides[6]. Considering that in the copper intercalate the metal is ‘stored’ in the bulk of the electrode, one may hope that the use of these materials would avoid massive contact of copper with CuTeX and then prevent the decomposition. To check this, cells of the type: Cu,TiS,/CuTeX/Cu,TiS, IO
"K-'
+T,
Fig. 3. Total electrical conductivity us reciprocal for CuTeBr (copper and graphite electrodes; corrected for contact resistance).
temperature values not
sence ofcopper, instead, the material is stable, as indicated by the cycle concerning a cell with graphite electrodes, also reported in Fig. 1. .The calorimetric scans (16”C/min) reported in Fig. 2 confirm the irreversible character of the decomposition of CuTeCl induced by copper and its fast evolution over 100°C. The trace a, related to pure CuTeCI, shows no them+ effect in the range of temperature 20-300°C. A freshly prepared CuTeCI-Cu mixture (3 :l weight ratio] shows a large,diffuseendothermicpeak between 180 and 240°C and no effect in the cooling curve. The peak progressively shifts towards higher temperatures and decreases in intensity, to finally disappear, for mixtures anT.
*c
(I)
with y = 0.7-0.9 were assembled and their conductivity measured. As shown in Fig. 4, where the conductivity-temperature cycle for a cell with CuO,sTiS, electrodes is reported, the shape of the plot is similar to that obtained by V. Alpen et al with Cu,Te elcctrodes[l], with the change in slope at about 70°C. Furthermore, steady values of conductivity were reached and indefinitely maintained at each temperature. This indeed indicates that the Cu,TiS, electrodes do not affect the CuTeX compounds, and may eventually be used for applications involving these solid conductors. To achieve this successfully, however, it is also necessary that the electronic conductivity of the electrolyte materials results a negligible fraction of their total conductivity. In the cases mider study, ie theCuTeX materials, theelectronicconductivity, determined with the Wagner’s method[7], is about IO-’ S/cm at 200°C for CuTeBr and CuTeCl, as quoted by V. Alpen et a/Cl] and also confirmed in our laboratory. Furthermore, from the shape of the current-voltage curve over about Cl.35 Vat 25°C. it was possible to ascertain[7] that this conductivity is due to holes. In a recent paper[S] Kennedy pointed out that in the case of a hole conductor, the electronic conductivity determined with blocking measurements has to be regarded as a minimum value. Under conditions such as in a galvanic cell, where the cathode is at a positive potential (us copper) greater than the value at which the hole conductivity of the electrolyte becomes significant, the electronic conductivity may be quite high and finally produceappreciable self-discharges. This seems to be confirmed in the case of the CuTeX materials. In fact, the open circuit voltage of cells of the type : Cu,T&/CuTeX/TiS, measured with a high impedance a rapid and constant decrease.
voltmeter,
(II) showed
at 200°C
REFERENCES 10-5
J
2.0
’
I
’
’
’
2.5
’
’
IO 3/T.
I
’
’
3-c
\ ’
’
1
I’
3.5
OK-’
Fig. 4. Total electrical conductivity DSreciprocal temperature for CuTeBr berwcen Cu,.,TiS, electrodes (values not corrected for contact resistance).
1. U. V. Alpen, J. Fenner, J. Marco11 and A. Rabenau, Elecrrochim. Acto 22, 801 (1977). 2. T. Matsui and J. Bruce Wagner’Jr., J. electrochem. SIX. 124,937 (1977). 3. A. Rabenau, H. Rau and G. Rosenstein, 2. anorg. ailg. Gem. 374.43 (1970).
SHORT COMMUNICATION
0. Gorochov and G. Collin, Mar. Res. 4. N. LeNagard, Bull. 10, 1269 (1975). 5. M. Lazzari, G. Razzini and B. Scrosati, to be published. 6. T. Takahashi, 0. Yamamoto and S. Ikeda, J. electrochem.
807
Sot. 120, 1431 (1973); T. Takahashi and 0. Yamamoto, ibid. 122, 83 (1975). 7. C. Wagner, Z. Elekrrochem. 60, 4 (1956). 8. J. H. Kennedy, J. elecrrockem. Sot. 124, 865 (1977).
Acta Vol. 23. pa. 805807. Press Ltd. 1978. Printed in Great
Britain.
SHORT PROPERT1ES
COMMUNICATION
OF THE CuTeX SOLID
CONDUCTORS
G. RAZZINI*, M. LAZZARI’ and B. SCR~SAT~~ + Centro Studio Processi Elettrodici de1 C.N.R., Istituto di Elettrochimica, Polytechnic of Milan, Milan t lstituto di Chimica Fisica, University of Rome, Rome, Italy (Received 1 October 1977)
It has been recently reported[l] that compounds of the type CuTeX, where X may be Cl, Br or I, exhibit a conductivity prevalently ionic in character which at 200°C becomes of the order of 10-3-10-2S/cm. ie ofpractical interest. On the other hand it was also reported that copper electrodes are not suitable to be used in connection with these electrolytes since they decompose in presence of copper. Due to the peculiarity of this aspect and the basic importance of copper solid conductors[2], it appeared to us of interest to further investigate the decomposition reaction induced by copper and toexamine theapplicability ofalternativeelectrodes with reduced copper activity. The CuTeX compounds have been prepared following the procedure indicated by Rabenau et af[3], TiS, has been prepared from the elements (Johnson and Matthey Specpure) in evacuated and sealed silica tubes at 600°C for several days. The X-ray powder patterns were in agreement with the literature (ASTM card 15-853). The intercalates Cu,TiS, have been prepared by reaction of Cu and TiS, at 8OO”C, according to I,eNagard et aI[4]. The conductivity studies have been carried out by sandwiching a compressed pellet of the electrolyte (1.2 cm in dia) between two pellets of the electrodic materials at a pressure of 2500 ks/cm2. The measurements were performed in Pyrex cell holders tluxed with inert gas. The ac bridge (Wayne and Kerr B331 MKII) operated at 1592Hz. For the calorimetric studies a Perkin-Elmer DSC Mod. I-B was used. X-ray powder patterns were registered by a JEOL diffractometer mod. JDX-85 with monocromator, using CuKcr radiation. The furnace temperature was regulated by a Herams Kelvitron TPG 2.2 programmer, with NiCrNi thermocouples. The electrochemical investigation was mainly devoted to chloride and bromide. The measurements of total conductivity as a function of temperature with copper and graphite electrodes are reported for CuTeCl in Fig. 1. The experiments were performed by keeping the cells for 2 h at each temperature: the aim was to get informations on the stability of the materials in connection with different electrodes. The thicknesses of the CuTeX pellets were in different runs 0.05,0.10,0.18 cm. The results reported in Figs 1-4 refer to 0.10 thick samples. The conductivity values were not corrected for the contact resistance. The cycle obtained with CuTeCl using copper electrodes (Fig. 1) shows a change in slope in the heating scan at about 100°C; at higher temperatures steady values were not reached, but conductivity continuously increased with time at constant temperature. The cooling scan is typical ofa metallic behaviour. The result is in agreement with a decomposition of CuTeCl in presence ofcopper[l] and indicates that probably the process becomes kinetically fast at about 100°C and originates compounds with metallic properties. In the ab-
T. “C
electrodes
’
10-a
’
’ n ’ ’ ’ 2.0
2.5 103/T.
’
’
’
’
DK -I
’
3.0
’
’
Fig. 1. Total electrical conductivity us reciprocal temperature for CuTeCl (copper and graphite electrodes; values not corrected for contact resistance).
805
CuTeCl
a A
I”v
E ?I =
-
CUT&L-Cu3:I
A
cv-mx-cu 3:l 46-C. 72hrs
c
s
I=d
-
-
.
CuTeCI-Cu 24hrs
60-C
CuTeCI-Cu 3rl 110°C 24hrs
c I 20
31
I 100 t.
I 180 QC
I 260
I
Fig. 2. DSC traces (16”C/min) of CuTeCl and CuTeCl-Cu mixtures as prepared and after annealing.
nealed at 46, 80 and 110°C respectively (curves c, d and e). Results qualitatively similar were obtained with CuTeBr, as shown in Fig. 3, where the critical role of copper is evidenced by comparison with the graphite cell. DSC measurements showed for the pure compound a thermal et&t at about 7O”C, probably related to a phase transition[l]; a freshly prepared mixture of CuTeBr and Cu showed a diffuse peak similar to that observed with CUT&I-Cu. The conductivity-time measurements at fixed temperatures, performed to trace the plot of Fig. 3, and the DSC scans on mixtures CuTeBr-Cu after annealing seem to indicate that the decomposition of CuTeBr is kinetically slower than for CuTeCl. The above results confirm the instability of the CuTeX compounds in the presence of copper, thus considerably reducing their possible applications. In the attempt of overcoming this, we have considered as possible alternative electrodes layered materials such as titanium disulphide, and their copper intercalates. In fact it has been ascertained[S] that copper can be reversibly incorporated into TiS, using cells completely in the solid state with cuprous solid elcctrolytes based on organic halides[6]. Considering that in the copper intercalate the metal is ‘stored’ in the bulk of the electrode, one may hope that the use of these materials would avoid massive contact of copper with CuTeX and then prevent the decomposition. To check this, cells of the type: Cu,TiS,/CuTeX/Cu,TiS, IO
"K-'
+T,
Fig. 3. Total electrical conductivity us reciprocal for CuTeBr (copper and graphite electrodes; corrected for contact resistance).
temperature values not
sence ofcopper, instead, the material is stable, as indicated by the cycle concerning a cell with graphite electrodes, also reported in Fig. 1. .The calorimetric scans (16”C/min) reported in Fig. 2 confirm the irreversible character of the decomposition of CuTeCl induced by copper and its fast evolution over 100°C. The trace a, related to pure CuTeCI, shows no them+ effect in the range of temperature 20-300°C. A freshly prepared CuTeCI-Cu mixture (3 :l weight ratio] shows a large,diffuseendothermicpeak between 180 and 240°C and no effect in the cooling curve. The peak progressively shifts towards higher temperatures and decreases in intensity, to finally disappear, for mixtures anT.
*c
(I)
with y = 0.7-0.9 were assembled and their conductivity measured. As shown in Fig. 4, where the conductivity-temperature cycle for a cell with CuO,sTiS, electrodes is reported, the shape of the plot is similar to that obtained by V. Alpen et al with Cu,Te elcctrodes[l], with the change in slope at about 70°C. Furthermore, steady values of conductivity were reached and indefinitely maintained at each temperature. This indeed indicates that the Cu,TiS, electrodes do not affect the CuTeX compounds, and may eventually be used for applications involving these solid conductors. To achieve this successfully, however, it is also necessary that the electronic conductivity of the electrolyte materials results a negligible fraction of their total conductivity. In the cases mider study, ie theCuTeX materials, theelectronicconductivity, determined with the Wagner’s method[7], is about IO-’ S/cm at 200°C for CuTeBr and CuTeCl, as quoted by V. Alpen et a/Cl] and also confirmed in our laboratory. Furthermore, from the shape of the current-voltage curve over about Cl.35 Vat 25°C. it was possible to ascertain[7] that this conductivity is due to holes. In a recent paper[S] Kennedy pointed out that in the case of a hole conductor, the electronic conductivity determined with blocking measurements has to be regarded as a minimum value. Under conditions such as in a galvanic cell, where the cathode is at a positive potential (us copper) greater than the value at which the hole conductivity of the electrolyte becomes significant, the electronic conductivity may be quite high and finally produceappreciable self-discharges. This seems to be confirmed in the case of the CuTeX materials. In fact, the open circuit voltage of cells of the type : Cu,T&/CuTeX/TiS, measured with a high impedance a rapid and constant decrease.
voltmeter,
(II) showed
at 200°C
REFERENCES 10-5
J
2.0
’
I
’
’
’
2.5
’
’
IO 3/T.
I
’
’
3-c
\ ’
’
1
I’
3.5
OK-’
Fig. 4. Total electrical conductivity DSreciprocal temperature for CuTeBr berwcen Cu,.,TiS, electrodes (values not corrected for contact resistance).
1. U. V. Alpen, J. Fenner, J. Marco11 and A. Rabenau, Elecrrochim. Acto 22, 801 (1977). 2. T. Matsui and J. Bruce Wagner’Jr., J. electrochem. SIX. 124,937 (1977). 3. A. Rabenau, H. Rau and G. Rosenstein, 2. anorg. ailg. Gem. 374.43 (1970).
SHORT COMMUNICATION
0. Gorochov and G. Collin, Mar. Res. 4. N. LeNagard, Bull. 10, 1269 (1975). 5. M. Lazzari, G. Razzini and B. Scrosati, to be published. 6. T. Takahashi, 0. Yamamoto and S. Ikeda, J. electrochem.
807
Sot. 120, 1431 (1973); T. Takahashi and 0. Yamamoto, ibid. 122, 83 (1975). 7. C. Wagner, Z. Elekrrochem. 60, 4 (1956). 8. J. H. Kennedy, J. elecrrockem. Sot. 124, 865 (1977).