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Structure and electrical properties of Cu+ ion-conducting oxyhalide glasses in the system CuI—CuPO3—Cu2MoO4
Solid State Ionics 45 ( 199 North-Holland
1) 123- 129
Structure and electrical properties of Cu + ion-conducting oxyhalide glasses in the system CuI-CuP03-Cu2Mo04 Nobuya
Machida,
Yoshikane
Shinkuma
and Tsutomu
Minami
Department ofApplied Chemistry, University of Osaka Prefecture, Mozu-Umemachi, Sakal-Shi, Osaka-Fu 591, Japan Received
17 September
1990; accepted
for publication
23 October
1990
Cu+ ion-conducting glasses were prepared in the pseudotemary system CuI-CuPOX-Cu2Mo04. Infrared spectra of the glasses with a constant CuI content suggested that non-bridging oxygens were more preferentially formed in the phosphate groups than in the molybdate groups. This preference order for non-bridging oxygen formation was consistent with the order of acidity, PzOs> MOO,, of the glass-forming oxides in melts. These glasses showed high ionic conductivities of 10m2 to IO0 Sm-’ at room temperature. For the glasses with a constant CuI content, the conductivity at 298 K of the glasses decreased non-linearly with an increase in the composition parameter x, which denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms included in the glasses, X= [P] / ( [P] + [MO] ). The activation energy for conduction increased non-linearly with an increase in X. These non-linear changes in the conductivity and in the activation energy were correlated with the structural change during melting of these glasses.
1. Introduction Glassy electrolytes or superionic conducting glasses with high ion conductivity have attracted much attention for a fundamental interest in their conduction mechanism and for their technological application to micro-electrochemical devices [ l-41. In particular, there are many investigations on Ag+ ionconducting glasses for the reason that these glasses have high ionic conductivities in the range of 10-l to 10’ Sm- ’ at room temperature. On the other hand, in recent years, Cu+ ion-conducting glasses were reported to be obtained in the systems CuI-Cu20-P205 [ 5 1, CuI-CuzO-MOO, [ 6 1, CuI-CuBr-Cu,MoO, [ 71, and CuCl-CuzO-Moos-Pz05 [ 81, and to exhibit higher ion conductivities than Ag+ ion-conducting glasses. Recently we reported the preparation of Cu+ ionconducting glasses in the pseudoternary system CuICuZMo04-Cu3P04 and their ion-conducting properties [ 9 1. In the previous study, the following results were obtained: (a) these glasses were composed of one type of cations, Cu+ ions, and three different types of anions, I-, monomer MoOd2-, and monomer POd3- ions; (b) the conductivity of these glasses 0 167-2738/9
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0 1991 - Elsevier Science Publishers
increased with an increase in the amount of Cu+ ions which were generated from the CuI component; and (c) the ortho-oxoanions existing in the glasses acted as traps of Cu+ mobile ions and the depth of the traps was varied with the valence of ortho-oxoanions. These results lead to the conclusion that the diffusion path model [3] is the most acceptable as the conduction mechanism of those Cu+ ion-conducting glasses [ 9 1. In this study, in order to clear the relation between oxo-salt ions present in the glasses and conductivities of the glasses, we have prepared Cu+ ion-conducting glasses in the pseudoternary system CuICuPO,-Cu2Mo0, and discuss the changes of the glass structure and Cu+ ion-conductivity.
2. Experimental Reagent-grade CuI, Cu20, Moo3 and P20s were used as starting materials for sample preparation. Desired amounts of raw materials were mixed in a glove box filled with dry nitrogen gas. In order to avoid oxidation of Cu+ ions and decomposition of CuI during melting, the mixtures were melted in a
B.V. ( North-Holland
)
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
124
silica tube under a dry nitrogen atmosphere of 1 atm at 923 K. The tube containing the melt was quenched with ice water. The glass compositions were shown by the starting batch composition in mol%. Further details of sample preparation have been reported previously [ lo]. The X-ray powder diffraction measurements, using Cu Ko radiation, were made for all the prepared samples to determine whether any crystalline phase was included. The infrared (IR) spectra were recorded on a Hitachi 260-50 IR spectrophotometer in the range 4000-250 cm-’ at room temperature; the measurements were carried out by use of the KRr pellet method. Ionic conductivity measurements were carried out for the bulk glasses with evaporated gold electrodes in a dry nitrogen atmosphere from 5 Hz to 500 kHz by use of a vector impedance meter (Hewlett-Packard 4800A) in the temperature range of 220 to 320 K. The conductivities were determined by employing the complex impedance analysis.
ples, respectively. The glass-forming region in the binary system CuI-CuP03 has been investigated by Liu and Angel1 [ 5 1, who reported that the glasses were obtained over the wide composition range of 0 to 50 mol% CuI by press quenching with brass plates. The glass-forming region reported by Liu and Angel1 was larger than that obtained in this study. This difference is caused by the difference of quenching rate during the glass formation. The glasses containing large amounts of CuP03 exhibit a slightly hygroscopic property, and the hygroscopic tendency decreases with a decrease in the CuP03 content. Fig. 2 shows the IR spectra of the glasses 4OCuI.yCuPO,* ( 60-y)CuzMoO,, which lie on the horizontal tie line in fig. 1, i.e. they have a constant CuI content and various mole ratios of molybdate to (a)-(e) are the spectra of phosphate:
3. Results and discussion 3.1. Glass .formation and structure The glass-forming region in the pseudoternary system CuI-CuP03-CuzMo04 is shown in fig. 1. In the figure open circles, open triangles and closed circles denote glassy, partial crystalline and crystalline sam-
1400liUOXXlO800600400 wavenumber I cm’ 80
mol%
CUP03
Cup03
Fig. 1. Glass-forming region in the system CuI-CuPOS-Cu2Mo0,; (0 ) glassy, ( A ) partially crystalline, (0 ) crystalline.
Fig. 2. IR spectra of the glasses in KBr pellets: (a) 40CuI~60Cu2M00,; (b) 40CuI~12CuP0,~48CuzMo0,; (c) 4OCuI. 15CuPO~~45Cu2~Mo0,; (d) 4OCuI.3OCuP0,. 30Cu2Mo0,; (e) 40CuI.45CuP03. 15Cu,MoO,; (f) 25CuI. 75CuPOI (mol%).
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
40CuI*yCuP03( 60-y)Cu2Mo04 glasses, of which the CuP03 content increases from (a) to (e). The 4OCuI-60CuP03 glass could not be obtained in this study, and instead the spectrum of the 25CuI-75CuP03 glass is shown as (f) for comparison. The assignment of each absorption band in the spectra was made by using the reference data for phosphates [ 111 and molybdates [ 121, and is summarized in table 1. The spectrum (a) is of the 40CuI-60CuzMo0, glass, which is expected from the composition to contain only ortho-molybdate as oxosalt ions. In the spectrum (a ), there are two absorption bands at 9 10 and 840 cm-‘, which are respectively assigned to the V, and the v3 modes of monomeric tetrahedral Mood*- ions. These results indicate that the active species in the 4OCuI. 60CuzMo0, glass are monomer MOO,*- ions only, and thus suggest that such a glass consists of only monomer Mo04*- ions, I- ions, and Cu+ ions. The spectrum (f) is of the 25CuI*75CuP03 glass, which is expected from the composition to contain meta-phosphates as main oxosalt ions. In the spectrum (f ), there are seven absorption bands at about 1260, 1140, 1080, 1020, 980, 760, and 520 cm-‘. The strong absorption bands at 1260 and 1080 cm-’ are respectively assigned to the v,, and the V, modes of PO; units in meta-phosphate groups, which have Table 1 Absorption
bands and their assignment
125
chain or ring structure. The absorption bands at 890 and 760 cm-’ are ascribed to the v,, and the v, modes of P-O-P stretching, and the bands at 1140 and 1020 cm-’ to the v,, and the v, modes of P032- units. The broad absorption band at about 520 cm- ’ is ascribed to the P-O-H stretching mode; the P-O-H units were probably caused by the reaction between the 25CuI-75Cu2P03 glass and a small amount of water contained in the KBr pellets. These results indicate that the active species in the 25CuI*75CuP03 glass are mainly meta-phosphate anions, and thus suggest that the phosphate groups in the glass mainly exist as the meta-phosphate anion form of linear chain or ring structure of PO, tetrahedra, as expected from the chemical composition. This glass is thus composed of the meta-phosphate anions, I- anions, and Cu+ cations. spectrum (b) is of The the 4OCuI- 12CuP03*48Cu2Mo04 glass. In this spectrum, there are live absorption bands at about 1100, 1040, 1000, 620 and 560 cm-‘, in addition to the two absorption bands at 9 10 and 840 cm-’ ascribed to the ortho-molybdate anions, MoOd2-. The absorption bands at 1040, 1000 and 620 cm-’ are ascribed to the vj, the v,, and the vq of the monomeric ortho-phosphate ions, POd3-, and the absorption band at 1100 cm- ’ is ascribed to the stretching mode of P03*- units, which exist in the pyro-phosphate
for the glasses in the system CuI-CUPO~-Cu,MoO,.
(a)
(b)
(c)
(d)
(e)
(f)
4OCuI 60CuzMo0,
4OCuI 12CuPO9 48CuzMo0,
4OCuI 1SCUPOX 45Cu,MoO,
4OCuI 3OCuP0, 30Cu2Mo0,
4OCuI 45CuPO4 1SCU~MOO.,
25CuI 75CuPO9
910(s) 84O(vs)
910(w) 840(s) 560(w) 990(w) 1040(s) 620(w) I 100(s)
910(w) 860(s) 560(w) 1000(w) 1040(s) 620(w) 1100(s)
540(w) 1000(w) 1050(s) 620(w)
9OO(vs) 700(w)
1140(w) 1040(w) 9OO(vs) 740(w) 1260(w)
1140(w) 1020(w) 890(s) 760(w) 126O(vs)
1100(s)
108O(vs)
530(w)
520(br)
Mode
w,MoO., v,Mo04 v.,Mo-O-MO v,P043v3P043v4P043v.,Po,z&PO,*v.,P-O-P u,P-O-P %SPG v,POr VP-O-H
N. Machida et al. /CIA+ ion-conducting oxyhalide glasses
126
anion, P20,4- , i.e. the dimer ions of PO, tetrahedra, or in the terminal units in the chain structural phosphate anions. The absorption band at 560 cm- ’ is assigned to the v,, mode of MO-O-MO bonds attributed to the formation of condensed ions of Moo4 tetrahedra. The absorption bands ascribed to monomeric ortho-phosphate ions, P043-, are weakened and the absorption bands ascribed to condensed units of PO4 tetrahedra are strengthened with an increase in the CuPO, content in the spectra (b)-(e). Observation of the absorption bands resulting from such monomeric ortho-phosphate anions, P043-, and the condensed units of MOO, can be explained by the occurrence of the reaction 2Mo04*- + PO, -+Mo207*- + POd3- in the melt as shown in the following scheme: 0 2 -O-&-otl
0 + +-;-+ &-
-
0 0 -o_&_&o-o6
6
0 + -o-;-oA-
The freezing of the melt through quenching causes the coexistence of these structural units in the glass. These results suggest that non-bridging oxygens were much more preferentially formed in the phosphate groups than in the molybdate groups. This preference order for non-bridging oxygen formation is consistent with the order of acidity, P205 > Mo03, of the oxides in the melts decided by the thermodynamic measurements [ 13 1.
4.5x10&
I
0
I
40CuI~45CuPO~~15Cu2MoOL
0
0
1.5X10h
30x10&
4.5x104
Fig. 3. Complex impedance 4OCuI*45CuPO,* I 5CuzMo0, (mol%)
60X1&
plots a glass for at various temperatures.
where A is the preexponential factor and E, the activation energy for conduction. Fig. 5 shows the composition dependence of the conductivity at 298 K, ~~298, of the glasses in the system CuI-CuPO3-CU~MOO~; the abscissa of this figure is a composition parameter X, which denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms includedintheglasses;x=[P]/([P]+[Mo]).Inthis
~~uI.(~O-~)CU~MO~*~CUI’~~ .
:y=
0
cl :y=15 . : y=30 0 :y=45
3.2. Electrical conducting properties Y 7
Examples of complex impedance plots for a glass 40CuI~45CuP0315Cu2Mo04 at various temperatures are shown in fig. 3. The bulk impedance is attributed to the semicircle observed at each temperature, and thus the bulk resistance is identified as the intersecting point of the semicircle with the real axis. Similar results were obtained for other glasses in the present system. Fig. 4 shows the temperature dependence of conductivity of the 4OCuI.yCuPO,(60 -y)CuzMo04 glasses. The conductivity data fit the Arrhenius equation; ~7T=A exp (-EJkT),
:
10’
I-
b
100
10-l 3m
4 .4 1OOOKIT
Fig. 4. Temperature dependence 4OCuI-yCuPOS. (60 - y)Cu2Mo04
of the conductivity glasses.
of the
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
30 mol % CuI
\
0
0.2
121
0.4
0.6
x = CPI I ([PI
0.8
1.0
+ CM03 1
Fig. 5. Conductivities at 298 K, u2ss, of the glasses in the system CuI-CuPOr-CuZMoO, as a function of the composition parameter x, x denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms includedinthegIasses,x=[P]/([P]+[Mo]).
figure, the conductivities for three series of glass compositions with a constant CuI content (50, 40 and 30 mol%) are shown by open circles, open triangles, and open squares, respectively. At a given composition parameter x, the conductivity of these glasses increases with an increase in the CuI content. The conductivity of each series of glass composition with 50, 40 and 30 mol% CuI decreases with an increase in the composition parameter x. However, this conductivity decrease with an increase in x is not linear. The conductivity decreases steeply in the range ~~0.3, and then decreases gradually in the range x> 0.5 for each series of glass compositions with 50, 40 and 30 mol% CuI. In order to elucidate the non-linear change of conductivity of the glasses with a constant CuI content, the conductivities of the glasses in the system CuICuP03-CuzMo04, which is the combination of metaand ortho-salts, are compared to those of the glasses in the system CuI-CuJP04-Cu2Mo04, which is the combination of two ortho-salts and consists of only Cu+ ions, I- ions, monomeric ortho-phosphate, POe3-, and monomeric ortho-molybdate, MOO,‘-, anions [ 91. Fig. 6 shows the conductivities at 298 K, 0298, of the 4OCuI.yCuP03( 60-y)Cu2Mo04 glasses
I 0
I
I
I
I
0.2 0.4 0.6 0.8 x =IP1/(CPI+CMo3)
I 1.0
Fig. 6. Comparison of conductivities at 298 K, uzs8, between the 4OCuI~yCuPO,* (60 - y)Cu2Mo0, glasses and the 4OCuI. zCu3P0.,* ( 60 - z)Cu,MoO, glasses [ 91.
and of the 4OCuI.zCu,PO,* (60 - z)Cu2M004 glasses by open triangles and closed circles, respectively, as a function of the composition parameter x. Although 0298 Of the ‘tocUI-~UPo,(60-J’)CU,MO0, glasses decreases non-linearly, 0298 Of the 4OCuI. zCu3P04. (60 -z) CuzMoO, glasses, which was cited from ref. [ 91, decreases linearly with an increase in X. In the range ~~0.3, 029g of the 4OCuI*yCuPO,(60-y)Cu,MoO, glasses is almost the same as that of the 4OCuI.zCu3P04- ( 6O-z)CU~MOO, glasses. However, in the range of x>O.6, the 0298 of the 40CuI~~CuPo,( ~O-~)CU~MOO, glasses is three times or more larger than that of the 4OCuI. ZCU,PO~* (60 - z)CU~MOO,. In the range ~~0.3, the phosphorus atoms in the 4OCuI.yCuPO,(60 -JJ) CuzMoO, glasses mainly exist as the monomeric ortho-phosphate anion, P0.,3-, as shown in the previous section. The orthophosphate anion is a trivalent oxoanion and the local electric field around the trivalent oxoanion is stronger than the field around the meta-phosphate anion, PO,, and also than that around the divalent orthomolybdate anion, Moo,‘-. Accordingly, the electrostatic interaction between the mobile Cu+ ions and the ortho-phosphate anions is stronger than that between the Cu+ ions and the meta-phosphate anions,
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
128
and between the Cu+ ions and the ortho-molybdate anions. Hence the ortho-phosphate anions are the strongest as traps of mobile Cu+ ions among the anion species existing in the glasses in the system CuICuP03Cu2Mo04. These results suggest that the steep decrease of @9g in the range x < 0.3 is probably caused by the Cu+ ion-trapped effects by POd3- anions present in these glasses. On the other hand, in the range x>O.6, the phosphorus 40CuI.yCuP03. atoms in the ( 60-y)CuzMo04 glasses mainly exist as meta-phosphate anions, PO,, as shown in the previous section. The Cu+ ion-trapping ability of the meta-phosphate anion is smaller as compared to that of the ortho-phosphate anion. Hence, the conductivity of the glasses decreases much gradually with an increase in x in the range x> 0.6. The activation energies for conduction, E,, of the glasses in the system CuI-CuP03-CuzMo04 are plotted in fig. 7 as a function of the composition parameter x. In this figure, E, for three series of glass compositions with a constant CuI content (50, 40 and 30 mol%) is shown by open circles, open triangles, and open squares, respectively. At a given composition parameter x, E, of these glasses decreases with an increase in the CuI content. The E, of each series of glass compositions with a constant CuI content increases non-linearly with an increase in x. The E, increases steeply in the range
1
50
I
30 mol%
5
I
I
CuI /--
I
50 _
I
I
1
4ocuI*zcu3~4-
(60-z)CuzMoo4
30; 0
, I I I 0.2 0.4 0.6 0.8 x=IPl/(CPl+CMol)
1.0
Fig. 8. Comparison of the activation energy for conduction, E,, between the 4OCuI~yCuP0,~ (60- y)CuzMo04 glasses and the 40 CuI~zCusPO,~ ( 60-z)CuZMoO, glasses [ 91.
~~0.3 and gradually in the range x>O.6 for each series. In order to clarify the non-linear behavior of E, the comparison of E, between the 40CuI~yCuP03~ ( 60-y)Cu2M00, glasses, which are the combination of meta-salts and ortho-salts, and the 40 CuI.zCu3P04. ( 60-z)Cu2Mo04 glasses, which are the combination of two ortho-salts [ 9 1, is shown in fig. 8. Although E, of the 40CuI~yCuP03~ (60 - y) Cu2Mo04 glasses increases non-linearly, E, of the 40CuI.zCu3P04. ( 60 - z)Cu2Mo04 glasses, which was cited from ref. [ 91, increases linearly with an increase in x. In the range ~~0.3, E, Of the ~OCUI~JCUPO~. ( ~O-~)CU~MOO~ glasses is almost the same as that of the 4OCuI-zCu3P04. (60-z)Cu,MoO, glasses. However, in the range x>O.6, E, of the 4OCuI* yCuP03* ( 60-y)Cu2Mo04 glasses is smaller than that of 4OCuI~zCu,PO,~ (60 -z) Cu2Mo04 glasses by 5 kJ mol-’ or more. These behaviors of the activation energy can be explained similarly to the case of the conductivity behavior mentioned above.
4. Summary 0
0.2
0.4
0.6
0.8
1.0
x = CPl/(CPl+CMol) Fig. 7. Activation energy for conduction, E., of the glasses in the system CuI-CuPO,-Cu,MoO, as a function of the composition parameterx;x=[P]/([P]+[Mo]).
Cu+ ion-conducting glasses were prepared in the pseudoternary system GUI-CuPO3-CU~MOO~. Infrared spectra of the glasses with a constant CuI content suggested that non-bridging oxygens were more
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
preferentially formed in the phosphate groups than in the molybdate groups. This preference order for non-bridging oxygen formation was consistent with the order of acidity, Pz05 > Mo03, of the glass-forming oxides in melts. These glasses showed high ionic conductivities of 10e2 to 10’ Sm- I at room temperature. For the glasses with a constant CuI content, in the range x< 0.3 a198 of the glasses decreased and E, increased steeply with an increase in x, whereas in the range x>O.6 @9g decreased and E, increased much gradually with an increase in x. These non-linear changes in the conductivity and in the activation energy were correlated with the structural change during melting of these glasses. In the range x 0.6, the phosphorus atoms in the glasses mainly exist as meta-phosphate anions, which have chain or ring structure, and the Cu+ iontrapping ability of the meta-phosphate anions is smaller than that of the ortho-phosphate anions. Hence, in the range x> 0.6 the a298 decreased and E, increased gradually with an increase in x.
129
Acknowledgement This work was partly supported by a Grant-in-Aid for Scientific Research on Priority Areas, New Functionality Materials - Design, Preparation and Control, the Ministry of Education, Science and Culture of Japan (No. 02204015).
References [ 1 ] M.D. Ingram, Phys. Chem. Glasses 28 (1987) 215. [ 2 ] C.A. Angell, Solid State Ionics 18/ 19 ( 1986) 72. [3] T. Minami, J. Non-Cryst. Solids 95/96 (1987) 107. [4] T. Minami, J. Non-Cryst. Solids 73 (1985) 273. [ 51 C. Liu and C.A. Angell, Solid State lonics 13 ( 1984) 105. [ 6 ] N. Machida and T. Minami, J. Am. Ceram. Sot. 7 1 ( 1988) 784. [ 71 T. Minami and N. Machida, Mat. Chem. Phys. 23 (1989) 63. [8] X. Pan, H. Zhao and Y. Bao, Solid State Ionics 28-30 ( 1988) 1470. [ 91 N. Machida, Y. Shinkuma and T. Minami, J. Ceram. Sot. Japan 97 (1989) 1104. [ lo] N. Machida, M. Chusho and T. Minami, J. Non-(&t. Solids 101 (1988) 70. [ 111 D.E.C. Corbridge, in: Topics in phosphorus chemistry, eds. M. Grayson and E.J. Griffith, Vol. 6 (Wiley, New York, 1969) p. 235. [ 121 F.A. Miller and C. Welkins, Anal. Chem. 24 (1952) 1253. [ 13 ] T. Yokokawa and S. Kohsaka, J. Chem. Eng. Data 24 ( 1979) 1671.
1) 123- 129
Structure and electrical properties of Cu + ion-conducting oxyhalide glasses in the system CuI-CuP03-Cu2Mo04 Nobuya
Machida,
Yoshikane
Shinkuma
and Tsutomu
Minami
Department ofApplied Chemistry, University of Osaka Prefecture, Mozu-Umemachi, Sakal-Shi, Osaka-Fu 591, Japan Received
17 September
1990; accepted
for publication
23 October
1990
Cu+ ion-conducting glasses were prepared in the pseudotemary system CuI-CuPOX-Cu2Mo04. Infrared spectra of the glasses with a constant CuI content suggested that non-bridging oxygens were more preferentially formed in the phosphate groups than in the molybdate groups. This preference order for non-bridging oxygen formation was consistent with the order of acidity, PzOs> MOO,, of the glass-forming oxides in melts. These glasses showed high ionic conductivities of 10m2 to IO0 Sm-’ at room temperature. For the glasses with a constant CuI content, the conductivity at 298 K of the glasses decreased non-linearly with an increase in the composition parameter x, which denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms included in the glasses, X= [P] / ( [P] + [MO] ). The activation energy for conduction increased non-linearly with an increase in X. These non-linear changes in the conductivity and in the activation energy were correlated with the structural change during melting of these glasses.
1. Introduction Glassy electrolytes or superionic conducting glasses with high ion conductivity have attracted much attention for a fundamental interest in their conduction mechanism and for their technological application to micro-electrochemical devices [ l-41. In particular, there are many investigations on Ag+ ionconducting glasses for the reason that these glasses have high ionic conductivities in the range of 10-l to 10’ Sm- ’ at room temperature. On the other hand, in recent years, Cu+ ion-conducting glasses were reported to be obtained in the systems CuI-Cu20-P205 [ 5 1, CuI-CuzO-MOO, [ 6 1, CuI-CuBr-Cu,MoO, [ 71, and CuCl-CuzO-Moos-Pz05 [ 81, and to exhibit higher ion conductivities than Ag+ ion-conducting glasses. Recently we reported the preparation of Cu+ ionconducting glasses in the pseudoternary system CuICuZMo04-Cu3P04 and their ion-conducting properties [ 9 1. In the previous study, the following results were obtained: (a) these glasses were composed of one type of cations, Cu+ ions, and three different types of anions, I-, monomer MoOd2-, and monomer POd3- ions; (b) the conductivity of these glasses 0 167-2738/9
l/$03.50
0 1991 - Elsevier Science Publishers
increased with an increase in the amount of Cu+ ions which were generated from the CuI component; and (c) the ortho-oxoanions existing in the glasses acted as traps of Cu+ mobile ions and the depth of the traps was varied with the valence of ortho-oxoanions. These results lead to the conclusion that the diffusion path model [3] is the most acceptable as the conduction mechanism of those Cu+ ion-conducting glasses [ 9 1. In this study, in order to clear the relation between oxo-salt ions present in the glasses and conductivities of the glasses, we have prepared Cu+ ion-conducting glasses in the pseudoternary system CuICuPO,-Cu2Mo0, and discuss the changes of the glass structure and Cu+ ion-conductivity.
2. Experimental Reagent-grade CuI, Cu20, Moo3 and P20s were used as starting materials for sample preparation. Desired amounts of raw materials were mixed in a glove box filled with dry nitrogen gas. In order to avoid oxidation of Cu+ ions and decomposition of CuI during melting, the mixtures were melted in a
B.V. ( North-Holland
)
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
124
silica tube under a dry nitrogen atmosphere of 1 atm at 923 K. The tube containing the melt was quenched with ice water. The glass compositions were shown by the starting batch composition in mol%. Further details of sample preparation have been reported previously [ lo]. The X-ray powder diffraction measurements, using Cu Ko radiation, were made for all the prepared samples to determine whether any crystalline phase was included. The infrared (IR) spectra were recorded on a Hitachi 260-50 IR spectrophotometer in the range 4000-250 cm-’ at room temperature; the measurements were carried out by use of the KRr pellet method. Ionic conductivity measurements were carried out for the bulk glasses with evaporated gold electrodes in a dry nitrogen atmosphere from 5 Hz to 500 kHz by use of a vector impedance meter (Hewlett-Packard 4800A) in the temperature range of 220 to 320 K. The conductivities were determined by employing the complex impedance analysis.
ples, respectively. The glass-forming region in the binary system CuI-CuP03 has been investigated by Liu and Angel1 [ 5 1, who reported that the glasses were obtained over the wide composition range of 0 to 50 mol% CuI by press quenching with brass plates. The glass-forming region reported by Liu and Angel1 was larger than that obtained in this study. This difference is caused by the difference of quenching rate during the glass formation. The glasses containing large amounts of CuP03 exhibit a slightly hygroscopic property, and the hygroscopic tendency decreases with a decrease in the CuP03 content. Fig. 2 shows the IR spectra of the glasses 4OCuI.yCuPO,* ( 60-y)CuzMoO,, which lie on the horizontal tie line in fig. 1, i.e. they have a constant CuI content and various mole ratios of molybdate to (a)-(e) are the spectra of phosphate:
3. Results and discussion 3.1. Glass .formation and structure The glass-forming region in the pseudoternary system CuI-CuP03-CuzMo04 is shown in fig. 1. In the figure open circles, open triangles and closed circles denote glassy, partial crystalline and crystalline sam-
1400liUOXXlO800600400 wavenumber I cm’ 80
mol%
CUP03
Cup03
Fig. 1. Glass-forming region in the system CuI-CuPOS-Cu2Mo0,; (0 ) glassy, ( A ) partially crystalline, (0 ) crystalline.
Fig. 2. IR spectra of the glasses in KBr pellets: (a) 40CuI~60Cu2M00,; (b) 40CuI~12CuP0,~48CuzMo0,; (c) 4OCuI. 15CuPO~~45Cu2~Mo0,; (d) 4OCuI.3OCuP0,. 30Cu2Mo0,; (e) 40CuI.45CuP03. 15Cu,MoO,; (f) 25CuI. 75CuPOI (mol%).
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
40CuI*yCuP03( 60-y)Cu2Mo04 glasses, of which the CuP03 content increases from (a) to (e). The 4OCuI-60CuP03 glass could not be obtained in this study, and instead the spectrum of the 25CuI-75CuP03 glass is shown as (f) for comparison. The assignment of each absorption band in the spectra was made by using the reference data for phosphates [ 111 and molybdates [ 121, and is summarized in table 1. The spectrum (a) is of the 40CuI-60CuzMo0, glass, which is expected from the composition to contain only ortho-molybdate as oxosalt ions. In the spectrum (a ), there are two absorption bands at 9 10 and 840 cm-‘, which are respectively assigned to the V, and the v3 modes of monomeric tetrahedral Mood*- ions. These results indicate that the active species in the 4OCuI. 60CuzMo0, glass are monomer MOO,*- ions only, and thus suggest that such a glass consists of only monomer Mo04*- ions, I- ions, and Cu+ ions. The spectrum (f) is of the 25CuI*75CuP03 glass, which is expected from the composition to contain meta-phosphates as main oxosalt ions. In the spectrum (f ), there are seven absorption bands at about 1260, 1140, 1080, 1020, 980, 760, and 520 cm-‘. The strong absorption bands at 1260 and 1080 cm-’ are respectively assigned to the v,, and the V, modes of PO; units in meta-phosphate groups, which have Table 1 Absorption
bands and their assignment
125
chain or ring structure. The absorption bands at 890 and 760 cm-’ are ascribed to the v,, and the v, modes of P-O-P stretching, and the bands at 1140 and 1020 cm-’ to the v,, and the v, modes of P032- units. The broad absorption band at about 520 cm- ’ is ascribed to the P-O-H stretching mode; the P-O-H units were probably caused by the reaction between the 25CuI-75Cu2P03 glass and a small amount of water contained in the KBr pellets. These results indicate that the active species in the 25CuI*75CuP03 glass are mainly meta-phosphate anions, and thus suggest that the phosphate groups in the glass mainly exist as the meta-phosphate anion form of linear chain or ring structure of PO, tetrahedra, as expected from the chemical composition. This glass is thus composed of the meta-phosphate anions, I- anions, and Cu+ cations. spectrum (b) is of The the 4OCuI- 12CuP03*48Cu2Mo04 glass. In this spectrum, there are live absorption bands at about 1100, 1040, 1000, 620 and 560 cm-‘, in addition to the two absorption bands at 9 10 and 840 cm-’ ascribed to the ortho-molybdate anions, MoOd2-. The absorption bands at 1040, 1000 and 620 cm-’ are ascribed to the vj, the v,, and the vq of the monomeric ortho-phosphate ions, POd3-, and the absorption band at 1100 cm- ’ is ascribed to the stretching mode of P03*- units, which exist in the pyro-phosphate
for the glasses in the system CuI-CUPO~-Cu,MoO,.
(a)
(b)
(c)
(d)
(e)
(f)
4OCuI 60CuzMo0,
4OCuI 12CuPO9 48CuzMo0,
4OCuI 1SCUPOX 45Cu,MoO,
4OCuI 3OCuP0, 30Cu2Mo0,
4OCuI 45CuPO4 1SCU~MOO.,
25CuI 75CuPO9
910(s) 84O(vs)
910(w) 840(s) 560(w) 990(w) 1040(s) 620(w) I 100(s)
910(w) 860(s) 560(w) 1000(w) 1040(s) 620(w) 1100(s)
540(w) 1000(w) 1050(s) 620(w)
9OO(vs) 700(w)
1140(w) 1040(w) 9OO(vs) 740(w) 1260(w)
1140(w) 1020(w) 890(s) 760(w) 126O(vs)
1100(s)
108O(vs)
530(w)
520(br)
Mode
w,MoO., v,Mo04 v.,Mo-O-MO v,P043v3P043v4P043v.,Po,z&PO,*v.,P-O-P u,P-O-P %SPG v,POr VP-O-H
N. Machida et al. /CIA+ ion-conducting oxyhalide glasses
126
anion, P20,4- , i.e. the dimer ions of PO, tetrahedra, or in the terminal units in the chain structural phosphate anions. The absorption band at 560 cm- ’ is assigned to the v,, mode of MO-O-MO bonds attributed to the formation of condensed ions of Moo4 tetrahedra. The absorption bands ascribed to monomeric ortho-phosphate ions, P043-, are weakened and the absorption bands ascribed to condensed units of PO4 tetrahedra are strengthened with an increase in the CuPO, content in the spectra (b)-(e). Observation of the absorption bands resulting from such monomeric ortho-phosphate anions, P043-, and the condensed units of MOO, can be explained by the occurrence of the reaction 2Mo04*- + PO, -+Mo207*- + POd3- in the melt as shown in the following scheme: 0 2 -O-&-otl
0 + +-;-+ &-
-
0 0 -o_&_&o-o6
6
0 + -o-;-oA-
The freezing of the melt through quenching causes the coexistence of these structural units in the glass. These results suggest that non-bridging oxygens were much more preferentially formed in the phosphate groups than in the molybdate groups. This preference order for non-bridging oxygen formation is consistent with the order of acidity, P205 > Mo03, of the oxides in the melts decided by the thermodynamic measurements [ 13 1.
4.5x10&
I
0
I
40CuI~45CuPO~~15Cu2MoOL
0
0
1.5X10h
30x10&
4.5x104
Fig. 3. Complex impedance 4OCuI*45CuPO,* I 5CuzMo0, (mol%)
60X1&
plots a glass for at various temperatures.
where A is the preexponential factor and E, the activation energy for conduction. Fig. 5 shows the composition dependence of the conductivity at 298 K, ~~298, of the glasses in the system CuI-CuPO3-CU~MOO~; the abscissa of this figure is a composition parameter X, which denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms includedintheglasses;x=[P]/([P]+[Mo]).Inthis
~~uI.(~O-~)CU~MO~*~CUI’~~ .
:y=
0
cl :y=15 . : y=30 0 :y=45
3.2. Electrical conducting properties Y 7
Examples of complex impedance plots for a glass 40CuI~45CuP0315Cu2Mo04 at various temperatures are shown in fig. 3. The bulk impedance is attributed to the semicircle observed at each temperature, and thus the bulk resistance is identified as the intersecting point of the semicircle with the real axis. Similar results were obtained for other glasses in the present system. Fig. 4 shows the temperature dependence of conductivity of the 4OCuI.yCuPO,(60 -y)CuzMo04 glasses. The conductivity data fit the Arrhenius equation; ~7T=A exp (-EJkT),
:
10’
I-
b
100
10-l 3m
4 .4 1OOOKIT
Fig. 4. Temperature dependence 4OCuI-yCuPOS. (60 - y)Cu2Mo04
of the conductivity glasses.
of the
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
30 mol % CuI
\
0
0.2
121
0.4
0.6
x = CPI I ([PI
0.8
1.0
+ CM03 1
Fig. 5. Conductivities at 298 K, u2ss, of the glasses in the system CuI-CuPOr-CuZMoO, as a function of the composition parameter x, x denotes the ratio of the number of phosphorus atoms to the total number of phosphorus and molybdenum atoms includedinthegIasses,x=[P]/([P]+[Mo]).
figure, the conductivities for three series of glass compositions with a constant CuI content (50, 40 and 30 mol%) are shown by open circles, open triangles, and open squares, respectively. At a given composition parameter x, the conductivity of these glasses increases with an increase in the CuI content. The conductivity of each series of glass composition with 50, 40 and 30 mol% CuI decreases with an increase in the composition parameter x. However, this conductivity decrease with an increase in x is not linear. The conductivity decreases steeply in the range ~~0.3, and then decreases gradually in the range x> 0.5 for each series of glass compositions with 50, 40 and 30 mol% CuI. In order to elucidate the non-linear change of conductivity of the glasses with a constant CuI content, the conductivities of the glasses in the system CuICuP03-CuzMo04, which is the combination of metaand ortho-salts, are compared to those of the glasses in the system CuI-CuJP04-Cu2Mo04, which is the combination of two ortho-salts and consists of only Cu+ ions, I- ions, monomeric ortho-phosphate, POe3-, and monomeric ortho-molybdate, MOO,‘-, anions [ 91. Fig. 6 shows the conductivities at 298 K, 0298, of the 4OCuI.yCuP03( 60-y)Cu2Mo04 glasses
I 0
I
I
I
I
0.2 0.4 0.6 0.8 x =IP1/(CPI+CMo3)
I 1.0
Fig. 6. Comparison of conductivities at 298 K, uzs8, between the 4OCuI~yCuPO,* (60 - y)Cu2Mo0, glasses and the 4OCuI. zCu3P0.,* ( 60 - z)Cu,MoO, glasses [ 91.
and of the 4OCuI.zCu,PO,* (60 - z)Cu2M004 glasses by open triangles and closed circles, respectively, as a function of the composition parameter x. Although 0298 Of the ‘tocUI-~UPo,(60-J’)CU,MO0, glasses decreases non-linearly, 0298 Of the 4OCuI. zCu3P04. (60 -z) CuzMoO, glasses, which was cited from ref. [ 91, decreases linearly with an increase in X. In the range ~~0.3, 029g of the 4OCuI*yCuPO,(60-y)Cu,MoO, glasses is almost the same as that of the 4OCuI.zCu3P04- ( 6O-z)CU~MOO, glasses. However, in the range of x>O.6, the 0298 of the 40CuI~~CuPo,( ~O-~)CU~MOO, glasses is three times or more larger than that of the 4OCuI. ZCU,PO~* (60 - z)CU~MOO,. In the range ~~0.3, the phosphorus atoms in the 4OCuI.yCuPO,(60 -JJ) CuzMoO, glasses mainly exist as the monomeric ortho-phosphate anion, P0.,3-, as shown in the previous section. The orthophosphate anion is a trivalent oxoanion and the local electric field around the trivalent oxoanion is stronger than the field around the meta-phosphate anion, PO,, and also than that around the divalent orthomolybdate anion, Moo,‘-. Accordingly, the electrostatic interaction between the mobile Cu+ ions and the ortho-phosphate anions is stronger than that between the Cu+ ions and the meta-phosphate anions,
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
128
and between the Cu+ ions and the ortho-molybdate anions. Hence the ortho-phosphate anions are the strongest as traps of mobile Cu+ ions among the anion species existing in the glasses in the system CuICuP03Cu2Mo04. These results suggest that the steep decrease of @9g in the range x < 0.3 is probably caused by the Cu+ ion-trapped effects by POd3- anions present in these glasses. On the other hand, in the range x>O.6, the phosphorus 40CuI.yCuP03. atoms in the ( 60-y)CuzMo04 glasses mainly exist as meta-phosphate anions, PO,, as shown in the previous section. The Cu+ ion-trapping ability of the meta-phosphate anion is smaller as compared to that of the ortho-phosphate anion. Hence, the conductivity of the glasses decreases much gradually with an increase in x in the range x> 0.6. The activation energies for conduction, E,, of the glasses in the system CuI-CuP03-CuzMo04 are plotted in fig. 7 as a function of the composition parameter x. In this figure, E, for three series of glass compositions with a constant CuI content (50, 40 and 30 mol%) is shown by open circles, open triangles, and open squares, respectively. At a given composition parameter x, E, of these glasses decreases with an increase in the CuI content. The E, of each series of glass compositions with a constant CuI content increases non-linearly with an increase in x. The E, increases steeply in the range
1
50
I
30 mol%
5
I
I
CuI /--
I
50 _
I
I
1
4ocuI*zcu3~4-
(60-z)CuzMoo4
30; 0
, I I I 0.2 0.4 0.6 0.8 x=IPl/(CPl+CMol)
1.0
Fig. 8. Comparison of the activation energy for conduction, E,, between the 4OCuI~yCuP0,~ (60- y)CuzMo04 glasses and the 40 CuI~zCusPO,~ ( 60-z)CuZMoO, glasses [ 91.
~~0.3 and gradually in the range x>O.6 for each series. In order to clarify the non-linear behavior of E, the comparison of E, between the 40CuI~yCuP03~ ( 60-y)Cu2M00, glasses, which are the combination of meta-salts and ortho-salts, and the 40 CuI.zCu3P04. ( 60-z)Cu2Mo04 glasses, which are the combination of two ortho-salts [ 9 1, is shown in fig. 8. Although E, of the 40CuI~yCuP03~ (60 - y) Cu2Mo04 glasses increases non-linearly, E, of the 40CuI.zCu3P04. ( 60 - z)Cu2Mo04 glasses, which was cited from ref. [ 91, increases linearly with an increase in x. In the range ~~0.3, E, Of the ~OCUI~JCUPO~. ( ~O-~)CU~MOO~ glasses is almost the same as that of the 4OCuI-zCu3P04. (60-z)Cu,MoO, glasses. However, in the range x>O.6, E, of the 4OCuI* yCuP03* ( 60-y)Cu2Mo04 glasses is smaller than that of 4OCuI~zCu,PO,~ (60 -z) Cu2Mo04 glasses by 5 kJ mol-’ or more. These behaviors of the activation energy can be explained similarly to the case of the conductivity behavior mentioned above.
4. Summary 0
0.2
0.4
0.6
0.8
1.0
x = CPl/(CPl+CMol) Fig. 7. Activation energy for conduction, E., of the glasses in the system CuI-CuPO,-Cu,MoO, as a function of the composition parameterx;x=[P]/([P]+[Mo]).
Cu+ ion-conducting glasses were prepared in the pseudoternary system GUI-CuPO3-CU~MOO~. Infrared spectra of the glasses with a constant CuI content suggested that non-bridging oxygens were more
N. Machida et al. / Cu+ ion-conducting oxyhalide glasses
preferentially formed in the phosphate groups than in the molybdate groups. This preference order for non-bridging oxygen formation was consistent with the order of acidity, Pz05 > Mo03, of the glass-forming oxides in melts. These glasses showed high ionic conductivities of 10e2 to 10’ Sm- I at room temperature. For the glasses with a constant CuI content, in the range x< 0.3 a198 of the glasses decreased and E, increased steeply with an increase in x, whereas in the range x>O.6 @9g decreased and E, increased much gradually with an increase in x. These non-linear changes in the conductivity and in the activation energy were correlated with the structural change during melting of these glasses. In the range x
129
Acknowledgement This work was partly supported by a Grant-in-Aid for Scientific Research on Priority Areas, New Functionality Materials - Design, Preparation and Control, the Ministry of Education, Science and Culture of Japan (No. 02204015).
References [ 1 ] M.D. Ingram, Phys. Chem. Glasses 28 (1987) 215. [ 2 ] C.A. Angell, Solid State Ionics 18/ 19 ( 1986) 72. [3] T. Minami, J. Non-Cryst. Solids 95/96 (1987) 107. [4] T. Minami, J. Non-Cryst. Solids 73 (1985) 273. [ 51 C. Liu and C.A. Angell, Solid State lonics 13 ( 1984) 105. [ 6 ] N. Machida and T. Minami, J. Am. Ceram. Sot. 7 1 ( 1988) 784. [ 71 T. Minami and N. Machida, Mat. Chem. Phys. 23 (1989) 63. [8] X. Pan, H. Zhao and Y. Bao, Solid State Ionics 28-30 ( 1988) 1470. [ 91 N. Machida, Y. Shinkuma and T. Minami, J. Ceram. Sot. Japan 97 (1989) 1104. [ lo] N. Machida, M. Chusho and T. Minami, J. Non-(&t. Solids 101 (1988) 70. [ 111 D.E.C. Corbridge, in: Topics in phosphorus chemistry, eds. M. Grayson and E.J. Griffith, Vol. 6 (Wiley, New York, 1969) p. 235. [ 121 F.A. Miller and C. Welkins, Anal. Chem. 24 (1952) 1253. [ 13 ] T. Yokokawa and S. Kohsaka, J. Chem. Eng. Data 24 ( 1979) 1671.