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On the coexistence of copper–molybdenum bronzes: CuxMoO3 (0.2 < x < 0.25; typically x ∼ 0.23) and CuyMoO3−z (0.1 < y < 0.2; typically y ∼ 0.15) in the Cu–MoO2–O quasi-ternary system
Materials Research Bulletin 45 (2010) 1635–1640
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On the coexistence of copper–molybdenum bronzes: CuxMoO3 (0.2 < x < 0.25; typically x 0.23) and CuyMoO3z (0.1 < y < 0.2; typically y 0.15) in the Cu–MoO2–O quasi-ternary system T.E. Warner *, E.M. Skou Institute of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark, Niels Bohrs Alle´ 1, DK-5230 Odense M, Denmark
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 January 2010 Received in revised form 24 June 2010 Accepted 16 July 2010 Available online 23 July 2010
Two copper–molybdenum bronzes: CuyMoO3z (0.1 < y < 0.2; typically y 0.15) and CuxMoO3 (0.2 < x < 0.25; typically x 0.23) were prepared as glistening black polycrystalline materials by the solid state reaction of Cu and MoO3 at 600 8C under argon in Pt crucibles. Powder XRD showed that the material with global composition ‘0.1CuMoO3’ comprises Cu0.15MoO3 and MoO3; whilst ‘0.2CuMoO3’ comprises Cu0.15MoO3 and Cu0.23MoO3. DTA performed on ‘0.2CuMoO3’ reveals a reversible solid state phase transition 520 8C under argon. Reacting equimolar amounts of Cu2O and MoO2 at 600 8C in a Cu crucible under argon yields: Cu6Mo5O18, Cu and MoO2. A tentative subsolidus Cu–MoO2–O isothermal (25 8C) phase diagram under argon is drawn from these data. Oxidation states of Cu and Mo within this system are discussed. ß 2010 Elsevier Ltd. All rights reserved.
Keyword: D. Phase equilibria
1. Introduction There is an interest in exploring new copper(I) containing early transition metal oxide compounds as potential candidates for alkali metal intercalation compounds. These have technological applications as electrode materials in solid state secondary lithium batteries, electrochemical sensors and electrochromic devices. In 1965, Casalot et al. [1] reported a new copper–vanadium bronze, e-CuyV2O5 (0.85 y 1), prepared by the direct chemical reaction of elemental copper with vanadium(V) oxide. Later in 1992 Garcia-Alvarado et al. [2] successfully de-intercalated the copper content in e-CuyV2O5 (to the extent that, y < 0.006) and performed a series of lithium intercalation experiments on this copper deficient phase. In 1991, Takeda et al. [3] investigated the solid solution CuV2xMoxO6 (0 x 1) which crystallizes with the brannerite-type structure, as suitable materials for lithium cathodes. Other copper(I) mixed, or low valence, group VIa/VIIa ternary oxides reported in the literature are the copper bronzes; Cu0.25ReO3 [4], Cu0.5WO3 [5], Cu0.26WO3 and Cu0.77WO3 [6], together with the minerals; delafossite CuICrIIIO2 and crednerite CuIMnIIIO2. The first reference in the literature to the existence of a copper– molybdenum bronze (i.e., a compound within the Cu–MoO3 quasibinary system) was in 1992 by Tian et al. [7]. They described the
* Corresponding author. Tel.: +45 6550 2575; fax: +45 6615 8780. E-mail address: [email protected] (T.E. Warner). 0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2010.07.004
results of a series of chemical reactions between, presumably, Cu and MoO3 in quartz glass ampoules at 400 8C. However, a lack of explicit detail in their experimental description makes the interpretation of the preparative procedure unclear. Nevertheless, they report a set of ten powder X-ray diffraction patterns for the product materials corresponding to various initial copper contents; but with little attempt to identify any of the phases contained within them. They note that Cu and MoO3 are absent in all these product materials; thus indicating that copper has intercalated into MoO3, with the result that the crystal structure of the product phase(s) becomes complex. Interestingly, there is an abrupt increase in the electrical conductivity between the materials ‘Cu0.1MoO3’ and ‘Cu0.2MoO3’ within this series, with the values; 2.66 106 S cm1 and 2.96 103 S cm1, respectively. Tian et al. did not comment on the significance of this feature with regards to the phase relationships within this system. No indication of colour is reported for any of these CuxMoO3 product materials. In the light of this work, Steiner et al. in 1994 [8] prepared a copper–molybdenum bronze, with the composition CuxMoO3 (x = 0.185 0.005). They reacted elemental copper with MoO3 in evacuated quartz glass ampoules for 120 h at 500 8C in order to investigate the preparation of CuxMoO3 in the compositional range; x = 0.15–0.20. The product materials were analysed by powder X-ray diffractometry which indicated an absence of MoO3; thus implying that MoO3 had reacted completely with the elemental copper. A crystal was selected from the product material for analysis by single crystal X-ray diffractometry. Their results showed that it belongs to
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the monoclinic space group, C2/2. Crystal structure data pertaining to this phase, as described by the chemical formula Cu1.49Mo8O24, is published in the ‘Inorganic Crystal Structure Database’ (ICSD) file; 74893. A calculated powder X-ray diffraction pattern as derived from these data is published in the ‘International Center for Diffraction Data’ (ICDD), Powder Diffraction File; PDF 82-843. Cu0.185MoO3 can be described as a tunnel structure in which the crystallographic sites for copper are significantly under occupied as revealed through the site occupation factors; Cu(1) = 0.148(4) and Cu(2) = 0.224(5). Most interestingly, an electron microprobe analysis of the same compound indicated a slightly higher copper content of x = 0.21, corresponding to Cu0.21MoO3. In 1996, Steiner et al. [9] published a sequel to this work in which they report (as part of a much larger survey of the Cu–Mo–O system) an additional phase within this system, namely; CuyMoO3z (y < 0.185). The material was analysed allegedly by electron microprobe analysis (EMPA), but the authors do not report a value for the copper content of this phase. They do not ascribe a value to the oxygen non-stoichiometry z, but they do mention that CuyMoO3z (in which, y < 0.185) coexists with Cu0.185MoO3 and MoO2 at 500 8C; thus implying that z > 0. In 1998, Kinomura et al. [10] prepared the copper–molybdenum bronze, Cu0.21MoO3, by reacting elemental copper with MoO3 in the molar ratio of 0.21:1 in an evacuated quartz glass ampoule at 500 8C for 120 h. Although the authors state that their preparative procedure is based upon the work by Tian et al. [7]; they fail to mention why they chose to prepare this specific composition (i.e., x = 0.21), which uncannily coincides with the composition (as determined by electron microprobe analysis) of the material prepared by Steiner et al. [8]. Nevertheless, the identity of the product was confirmed with X-ray powder diffractometry; although no details of this are given. The main purpose of their investigation was to study the reactions between Cu0.21MoO3 and n-alkylamines in various media. Besides this, no information is given regarding other compositions or phase relationships within the Cu–MoO3 system. But the fact that they managed to produce a copper–molybdenum bronze with the composition, Cu0.21MoO3, is pertinent to the work presented in this present article. Intrigued by the above observations, a further study of phase relationships in the Cu–MoO3 quasi-binary system was initiated by the present authors in an attempt to resolve these differences in copper stoichiometry within the copper–molybdenum bronze, CuxMoO3 (x = 0.185 vis-a`-vis 0.21) and explore its relationship with CuyMoO3z (y < 0.185) in more detail. The results of our preliminary findings are reported here for a series of reactions between elemental copper and MoO3 at the higher temperature of 600 8C under a gently flowing argon atmosphere.
product was then retrieved from the furnace at ambient temperature. The product materials were analysed by powder X-ray diffractometry using a Siemens D5000 powder diffractometer using Cu Ka1 radiation (l = 1.5405 A˚) with an associated data capture/treatment system. Differential thermal analysis (DTA) were performed on the above series of initial reaction mixtures (xCuMoO3) and on the corresponding product materials, in small platinum crucibles under an argon atmosphere using a Setaram TG-DTA 92 analyser. Alumina powder was used as the reference state for the purpose of internal thermal compensation. An additional reaction to prepare the copper-rich composition, 2CuMoO3, was performed by the alternative approach of reacting together equimolar quantities of Cu2O (99.5%) and MoO2 (99%), both supplied by Johnson Matthey GmbH, in a rectangular-shaped copper crucible (10 mm 10 mm 30 mm, fabricated in house) at 600 8C for 6 h under a flowing argon atmosphere. The copper crucible enabled the chemical reactions to be carried out in an environment in which the copper activity was fixed at unity, and under an atmosphere in which the partial pressure of oxygen is defined by the Cu2O/Cu couple (which acts as an in site oxygen buffer) at a given temperature; assuming the system is at a state of equilibrium. Nota bene, metallic copper cannot reduce the reactants (Cu2O and MoO2) under these conditions by any significant degree. Heating and cooling rates were at 300 8C/h. 3. Results and discussion All the compositions prepared in this work yielded a glistening black polycrystalline sintered product. A set of powder X-ray diffraction patterns corresponding to these product materials are shown in Figs. 1–6. A listing of the observed d-values with their relative intensities and assigned phases (with the PDF numbers) are shown for each of these product materials in the set of corresponding Tables 1–6. From the above powder diffraction data it was possible to assign all the peaks to previously known phases through comparisons with the PDFs as reported in the ICDD. Interestingly, the only exceptions were certain peaks appearing in Figs. 1 and 2. Fig. 1 shows the powder X-ray diffraction pattern regarding the product material with a global composition, ‘0.1CuMoO3’. None of the peaks correspond to elemental copper; its absence therefore, clearly implies that all the copper has reacted with the MoO3 within the charge. This is further evidenced by the drastic change in colour from the white/red colour of the reactants to the formation of a glistering black polycrystalline product. However,
[(Fig._1)TD$IG]
2. Experimental Appropriate amounts of finely divided elemental copper powder (copper bronze for organic synthesis, BDH) and molybdenum(VI) oxide powder (99.5%, Merck GmbH) were weighed to form a set of initial compositions; xCuMoO3 (with x = 0.1, 0.2, 0.25, 0.3 and 0.5), with each charge being typically, 7 g. Each preparation was mixed intimately and then placed in a rectangular-shaped platinum crucible (10 mm 10 mm 30 mm, fabricated in house). This was inserted inside a quartz glass tube with ‘vacuum greased’ quick-fitTM joints at both ends to facilitate a gentle flow of argon (99.995%, with PO2 105 bar), and placed inside a tube furnace such that both ends of the glass tube protruded from the furnace work tube. The contents were heated at a rate of 300 8C/h to 600 8C, and then held there for 1 h, before being cooled to ambient temperature at a rate of 300 8C/h. The product was reground and annealed under similar conditions for 6 h at 600 8C, with a heating and cooling rate of 300 8C/h. The
Fig. 1. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.1CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
[(Fig._2)TD$IG]
[(Fig._5)TD$IG]
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Fig. 2. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.2CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
[(Fig._3)TD$IG]
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Fig. 5. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.5CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
many of the peaks correspond to MoO3 indicating that significant quantities of this phase remain unconsumed. Interestingly, several peaks in the powder pattern (three of which have significantly high relative intensities) do not appear to correspond with any known phase within the Cu–Mo–O system as reported in the ICDD database. These peaks are therefore attributed here, to the formation of a copper–molybdenum bronze. An approximate
mass balance suggests that this bronze has the composition, CuyMoO3z (0.1 < y < 0.2; typically y 0.15) and shall be referred to in this article, simply as, Cu0.15MoO3z. Fig. 2 shows the powder X-ray diffraction pattern regarding the product material with a global composition, ‘0.2CuMoO3’. In this material, many of the peaks correspond to Cu0.185MoO3 (PDF 82843). All of the remaining peaks match precisely with those assigned to Cu0.15MoO3z in Fig. 1. Their relative intensities indicate that Cu0.15MoO3z and Cu0.185MoO3 are present in roughly equal amounts. Therefore, Cu0.15MoO3z and Cu0.185MoO3 appear to coexist within this material with the global composition, ‘0.2CuMoO3’. Furthermore, this interpretation reinforces the original assignment made in Fig. 1, as to the existence of Cu0.15MoO3z. Due to the uncertainties regarding the copper stoichiometry for the compound Cu0.15MoO3z, as prepared in this more copper-rich environment (0.2CuMoO3), these peaks are assigned to the phase expressed more generally, as, CuyMoO3z (0.1 < y < 0.185). The reader shall have noticed that none of the possible binary combinations of the phases CuyMoO3z (0.1 < y < 0.185) and Cu0.185MoO3 can ever summate to the global composition: 0.2CuMoO3. Nota bene, by application of the Lever rule, the phase CuxMoO3 as prepared in this present work cannot be of the composition Cu0.185MoO3; irrespective to any plausible composition that one may wish to ascribe to CuyMoO3z. This observation is used as evidence here, to suggest that the composition CuxMoO3 (x = 0.185 0.005) as determined by single crystal diffractometry by
Fig. 4. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.3CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
Fig. 6. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘Cu2OMoO2’ reacted at 600 8C for 6 h under a flowing argon atmosphere.
Fig. 3. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.25CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
[(Fig._4)TD$IG]
[(Fig._6)TD$IG]
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Table 1 Powder X-ray diffraction data for the annealed products of initial composition: 0.1CuMoO3 (corresponding with Fig. 1).
Table 3 Powder X-ray diffraction data for the annealed products of initial composition: 0.25CuMoO3 (corresponding with Fig. 3).
dobs. (A˚)
I/I1 obs.
Assigned phase
dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
6.9547 4.0999 3.8120 3.5514 3.4825 3.4642 3.4400 3.3312 3.2614 3.2339 3.1464 3.0067 2.8804 2.7028 2.6607 2.6082 2.5281 2.3215 2.3099 2.2710 2.2284 2.2116 2.1318
93 4 22 14 95 100 12 8 13 7 5 5 4 3 6 2 3 44 57 10 6 3 2
CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z
8.1487 6.3256 5.6246 4.6842 4.3441 4.0753 3.9483 3.9101 3.7480 3.6282 3.5042 3.4220 3.4044 3.2408 3.2205 3.1459 3.0771 3.0580 3.0250 2.9942 2.9433 2.9225 2.9032 2.8812
100 1 2 1 1 60 2 6 1 2 11 8 41 4 24 5 68 9 2 5 3 1 1 2
Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17
PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF
(y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185)
Steiner et al. [8] is perhaps inaccurate. The results of this present work are more compatible with Steiner et al. [8] alternative composition (viz. Cu0.21MoO3) as determined by electron microprobe analysis. The disparity in the two analyses as reported by Steiner et al. [8] are possibly a result of analytical uncertainties, rather than real differences in chemical composition between the various crystallites as analysed; although the effects of temperature dependency and phase inhomogeneity may also play a role. Furthermore, the phase CuxMoO3 as prepared in this present work is in terms of composition more consistent with Cu0.21MoO3 as prepared at 500 8C by Kinomura Table 2 Powder X-ray diffraction data for the annealed products of initial composition: 0.2CuMoO3 (corresponding with Fig. 2). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
8.1680 6.9712 4.6830 4.0766 3.9074 3.5065 3.4814 3.4040 3.2235 3.0772 3.0601 2.9419
94 19 1 59 7 14 25 67 29 100 12 4
Cu1.49Mo8O24 CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24
PDF 82-843
2.7154 2.7006 2.6670 2.6502 2.4849 2.4482 2.3704 2.3474 2.3354 2.3202 2.3060 2.2594 2.1958 2.0046
3 4 2 2 5 5 2 5 3 11 5 13 3 2
Cut-off point in Tables 1 and 2 Cu1.49Mo8O24 Cu1.49Mo8O24 CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 CuyMoO3z (y < 0.185) CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24
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82-843 82-843 82-843 82-843
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82-843 39-181 39-181 82-843 39-181 82-843 39-181 82-843 39-181 39-181 82-843 32-671 82-843 39-181 82-843 39-181 82-843 82-843 39-181 39-181 82-843 39-181 39-181 39-181
et al. [10]. In the work presented here, it is suggested that this phase is perhaps more correctly described as, CuxMoO3 (0.2 < x < 0.25), with the composition Cu0.23MoO3 being very realistic. Nevertheless, since the crystal structure can accommodate variable copper stoichiometry, this phase may be more appropriately described as a solidsolution with relatively narrow compositional limits, which may display a certain degree of temperature dependency. Interestingly, the abrupt change in the electrical conductivity between the materials ‘Cu0.1MoO3’ and ‘Cu0.2MoO3’ as prepared and measured by Tian et al. [7] (as discussed in Section 1), is further
Table 4 Powder X-ray diffraction data for the annealed products of initial composition: 0.3CuMoO3 (corresponding with Fig. 4). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
8.1610 6.3232 5.6269 4.6833 4.4282 4.3454 4.0774 3.9499 3.9108 3.7511 3.6301 3.5062 3.4269 3.4068 3.2434 3.2213 3.1472 3.0776 3.0595 3.0412 2.9939 2.9443 2.9257 2.9046 2.8819
100 3 7 2 2 2 44 7 9 3 6 12 20 73 9 33 14 87 17 5 10 4 3 5 7
Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17
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82-843 39-181 39-181 82-843 39-181 39-181 82-843 39-181 82-843 39-181 39-181 82-843 32-671 82-843 39-181 82-843 39-181 82-843 82-843 39-181 39-181 82-843 39-181 39-181 39-181
[(Fig._7)TD$IG]
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Table 5 Powder X-ray diffraction data for the annealed products of initial composition: 0.5CuMoO3 (corresponding with Fig. 5). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
8.1664 6.3151 5.6265 5.2134 4.8125 4.6722 4.4260 4.3496 4.0759 3.9479 3.9077 3.7506 3.6312 3.5030 3.4786 3.4259 3.4037 3.2414 3.2219 3.1477 3.0771 3.0580 3.0392 2.9930 2.9440 2.9263 2.9025 2.8799
60 12 19 5 3 4 5 7 33 19 5 12 24 7 6 100 25 19 17 89 51 9 17 42 7 6 57 31
Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17
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82-843 39-181 39-181 39-181 32-671 82-843 39-181 39-181 82-843 39-181 82-843 39-181 39-181 82-843 39-181 32-671 82-843 39-181 82-843 39-181 82-843 82-843 39-181 39-181 82-843 39-181 39-181 39-181
evidence of an immiscibility gap between Cu0.15MoO3 and Cu0.23MoO3. From the above discussion, the chemical reactions taking place between elemental copper and MoO3 at 600 8C under a flowing
Fig. 7. Differential thermal analysis (DTA) trace of ‘0.2CuMoO3’ in flowing argon. Platinum crucible with alumina powder as the thermal reference.
argon atmosphere are summarized by the following qualitative expressions:
0:1Cu þ MoO3 ! Cu0:15 MoO3 þ MoO3
0:2Cu þ MoO3 ! Cu0:23 MoO3 þ Cu0:15 MoO3z
0:25Cu þ MoO3 ! major Cu0:23 MoO3 þ traceCu4 Mo5 O17 þ traceMoO2
0:3Cu þ MoO3 ! major Cu0:23 MoO3 þ minorCu4 Mo5 O17 þ minorMoO2 Table 6 Powder X-ray diffraction data for the annealed products of initial composition: ‘Cu2OMoO2’ (corresponding with Fig. 6). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
5.7880 4.8155 4.6952 3.6398 3.4217 3.2177 3.1909 3.0261 2.9775 2.9505 2.9138 2.8892 2.8116 2.6963 2.5376 2.4885 2.4727 2.4545 2.4429 2.4288 2.4053 2.3811 2.2201 2.1834 2.1560 2.0873 2.0701 1.9361 1.9167 1.8075
13 2 5 15 100 7 33 15 17 20 29 16 4 16 9 5 7 7 15 33 21 7 9 3 5 41 5 5 5 13
Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 MoO2 MoO2 MoO2 Cu6Mo5O18 Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu
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40-865 32-671 40-865 40-865 32-671 40-865 40-865 40-865 40-865 40-865 40-865 40-865 32-671 40-865 40-865 40-865 40-865 40-865 32-671 32-671 32-671 40-865 40-865 32-671 40-865 85-1326 40-865 40-865 40-865 85-1326
0:5Cu þ MoO3 ! minor Cu0:23 MoO3 þ majorCu4 Mo5 O17 þ majorMoO2 The results of the differential thermal analysis (DTA) as performed on the product material ‘Cu0.2MoO3’ under a flowing argon atmosphere are shown in Fig. 7. On the forward scan (increasing temperature) there is an endothermic peak at 545 8C which corresponds to the exothermic peak at 500 8C on the return scan (decreasing temperature). The areas beneath these peaks are similar to each other and lie in close proximity, which suggests that they relate to a reversible phase transition at 520 8C. Since there is no evidence of melting taking place within the sample (up to 650 8C) this feature corresponds presumably to a solid state phase transition, most likely involving the phase approximating to, Cu0.21MoO3. It is interesting to note, that this transition occurs at a temperature above the temperatures 400 8C and 500 8C as deployed in the syntheses by Tian et al. [7], Steiner et al. [8] and Kinomura et al. [10] but, below the temperature (600 8C), deployed in the synthesis here. However, because this transition is reversible, it is unlikely to have affected the events leading to the preparation of the materials reported in this present work. In the product materials with a higher copper content (global compositions: 0.25CuMoO3; 0.3CuMoO3; and 0.5CuMoO3), the phases Cu4Mo5O17 [11] and MoO2 were identified as coexisting with the phase Cu0.23MoO3 throughout this compositional range. The two phases Cu4Mo5O17 and MoO2 become more predominate at the expense of Cu0.23MoO3 with increases in the global copper content. No other phases were observed. This indicates that
[(Fig._8)TD$IG]
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Fig. 8. A tentative subsolidus Cu–MoO2–O isothermal (25 8C) phase diagram under an argon atmosphere (with P O2 105 bar). Ternary phases are marked: 1 = (0.1 < y < 0.2; typically y 0.15); 2 = CuxMoO3 (0.2 < x < 0.25; typically x 0.23); 3 = Cu4Mo5O17; 4 = Cu6Mo5O18.
elemental copper can reduce molybdenum(VI) (within MoO3) to yield molybdenum(IV) (within Cu0.23MoO3). In an attempt to prepare the copper-rich composition, 2CuMoO3, equimolar amounts of Cu2O and MoO2 were reacted together at 600 8C in a copper crucible. A copper crucible was used in order to fix the copper activity at unity and thereby provide a socalled, ‘copper-anchor’ within the Cu–MoO2–O system. The powder X-ray diffraction pattern revealed the sole presence of the phases: MoO2, Cu6Mo5O18 and elemental copper within the product material (see Fig. 6). This indicates that copper(I) oxide can oxidise molybdenum(IV) (within MoO2) to molybdenum(VI) (within Cu6Mo5O18), and in doing so, is reduced to elemental copper. Cu2 O þ MoO2 ! majorMoO2 þ minorCu6 Mo5 O18 þ minorCu A tentative subsolidus Cu–MoO2–O isothermal (25 8C) phase diagram under an argon atmosphere (with P O2 105 bar) based on these results is shown in Fig. 8. 4. Conclusions A material with a global composition ‘0.1CuMoO3’ has been prepared at 600 8C and shown in this work to comprise; CuyMoO3z (0.1 < y < 0.2; typically y 0.15) and MoO3. This copper–molybdenum bronze, Cu0.15MoO3z relates to the phase CuyMoO3z (y < 0.185) as prepared at 500 8C by Steiner et al. [9] and to the material ‘Cu0.1MoO3’ as prepared at 400 8C by Tian et al. [6]. A material with a global composition ‘0.2CuMoO3’ has been prepared at 600 8C and shown in this work to comprise; Cu0.23MoO3 and Cu0.1MoO3z. As a consequence of this, the Cu0.23MoO3 phase prepared in this present work is more appropriately compared with the compound Cu0.21MoO3 as prepared at 500 8C by Kinomura et al. [10] and also with the composition Cu0.21MoO3 as determined by EMPA (rather than the alternative composition Cu0.185MoO3 as determined by single crystal diffractometry) for the material reported by Steiner et al. [8].
Some interesting features concerning the oxidation states of copper and molybdenum within the Cu–MoO2–O quasi-ternary system (600 8C) have arisen from this study. With reference to Fig. 8, and more specifically, the Cu–MoO2–Cu6Mo5O18 quasi-ternary system contained therein, the relative oxidative abilities of the phases Cu2O and MoO3, together with the reductive abilities of elemental copper and MoO2, become apparent, and lead to the following inferences. Reacting Cu2O and MoO2 in the molar ratio 7:10 will result in the formation of Cu6Mo5O18 and elemental copper. Hence copper(I) within Cu2O can oxidise molybdenum(IV) (within MoO2) to molybdenum(VI) (within Cu6Mo5O18), with itself being reduced to elemental copper. Reacting Cu2O and MoO3 in the molar ratio 6:10 will result in the formation of single phase Cu6Mo5O18 [12] whereby, both copper and molybdenum have retained their initial oxidation states of copper(I) and molybdenum(VI), respectively. Reacting equimolar (1:1) amounts of elemental copper and MoO3 will result in the formation of Cu6Mo5O18 and MoO2. Hence, elemental copper can reduce molybdenum(VI) (within MoO3) to molybdenum(IV) (within MoO2), with itself being oxidised to copper(I) (within Cu6Mo5O18). But, reacting elemental copper and MoO3 in the molar ratio 1:5 at 600 8C will result in the formation of Cu0.23MoO3 and Cu0.15MoO3z. In terms of formal oxidation states within these two phases, copper is present presumably as copper(I). This presents the possibility, by way of charge balance, for the existence of molybdenum(V); although the existence of mixed molybdenum(IV) and molybdenum(VI), or indeed, an averaged (i.e., non-integral) oxidation state are other possibilities [13–15]. This system therefore illustrates an interesting balance between the oxidation states of copper and molybdenum in the solid state, and presents an important comparison with the copper–molybdenum sulfide (Chevrel) phase, CuxMo2S8. The authors are presently attempting to prepare the copper– molybdenum bronzes, Cu0.23MoO3 and Cu0.15MoO3z, as single phase materials in order to characterize there properties in more detail. These findings will be reported in due course. Acknowledgements Assistance with powder X-ray diffractometry by Anne-Marie Krogh Andersen and Inger-Grethe Krogh Andersen and are gratefully acknowledged. References [1] A. Casalot, A. Deschanvres, P. Hagenmuller, B. Raveau, Bull. Soc. Chim. Fr. 6 (1965) 1730. [2] F. Garcia-Alvarado, J.M. Tarascon, B. Wilkens, J. Electrochem. Soc. 139 (1992) 3206. [3] Y. Takeda, K. Itoh, R. Kanno, T. Icikawa, N. Imanishi, O. Yamamoto, J. Electrochem. Soc. 138 (1991) 2566. [4] A. Deschanvres, B. Raveau, C.R. Acad. Sci. 264 (1967) 1841. [5] B. Broyde, J. Catal. 10 (1968) 13. [6] L.E. Conroy, M.J. Sienko, J. Am. Chem. Soc. 79 (1957) 4048. [7] S.B. Tian, F. Zhou, J.C. Yang, Z.C. Li, Solid State Ionics 57 (1992) 109. [8] U. Steiner, T. Morgenstern, W. Reichelt, H. Borrmann, A. Simon, Z. Anorg. Allg. Chem. 620 (1994) 1905–1908. [9] U. Steiner, W. Reichelt, T. Morgenstern, Z. Anorg. Allg. Chem. 622 (1996) 1428– 1434. [10] N. Kinomura, K. Mizumoto, N. Kumada, in: S. Sa¯miya, R.P.H. Chang, M. Doyama, R. Roy (Eds.), Materials Science and Engineering Serving Society, Proceedings of the Third Okinaga Symposium on Materials Science and Engineering Serving Society, Chiba, Japan, September 3–5, 1997, (1998), pp. 239–242. [11] E.M. McCarron, J.C. Calabrese, J. Solid State Chem. 65 (1986) 215. [12] E.M. McCarron, J.C. Calabrese, J. Solid State Chem. 62 (1986) 64. [13] P. Gall, P. Gougeon, Acta Crystallogr. C 48 (1992) 1915–1917. [14] C.C. Torardi, C. Fecketter, W.H. McCarroll, F.J. DiSalvo, J. Solid State Chem. 60 (1985) 332–342. [15] H. Leligny, M. Ledesert, P. Labbe, B. Raveau, W.H. McCarroll, J. Solid State Chem. 87 (1990) 35–43.
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Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu
On the coexistence of copper–molybdenum bronzes: CuxMoO3 (0.2 < x < 0.25; typically x 0.23) and CuyMoO3z (0.1 < y < 0.2; typically y 0.15) in the Cu–MoO2–O quasi-ternary system T.E. Warner *, E.M. Skou Institute of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark, Niels Bohrs Alle´ 1, DK-5230 Odense M, Denmark
A R T I C L E I N F O
A B S T R A C T
Article history: Received 25 January 2010 Received in revised form 24 June 2010 Accepted 16 July 2010 Available online 23 July 2010
Two copper–molybdenum bronzes: CuyMoO3z (0.1 < y < 0.2; typically y 0.15) and CuxMoO3 (0.2 < x < 0.25; typically x 0.23) were prepared as glistening black polycrystalline materials by the solid state reaction of Cu and MoO3 at 600 8C under argon in Pt crucibles. Powder XRD showed that the material with global composition ‘0.1CuMoO3’ comprises Cu0.15MoO3 and MoO3; whilst ‘0.2CuMoO3’ comprises Cu0.15MoO3 and Cu0.23MoO3. DTA performed on ‘0.2CuMoO3’ reveals a reversible solid state phase transition 520 8C under argon. Reacting equimolar amounts of Cu2O and MoO2 at 600 8C in a Cu crucible under argon yields: Cu6Mo5O18, Cu and MoO2. A tentative subsolidus Cu–MoO2–O isothermal (25 8C) phase diagram under argon is drawn from these data. Oxidation states of Cu and Mo within this system are discussed. ß 2010 Elsevier Ltd. All rights reserved.
Keyword: D. Phase equilibria
1. Introduction There is an interest in exploring new copper(I) containing early transition metal oxide compounds as potential candidates for alkali metal intercalation compounds. These have technological applications as electrode materials in solid state secondary lithium batteries, electrochemical sensors and electrochromic devices. In 1965, Casalot et al. [1] reported a new copper–vanadium bronze, e-CuyV2O5 (0.85 y 1), prepared by the direct chemical reaction of elemental copper with vanadium(V) oxide. Later in 1992 Garcia-Alvarado et al. [2] successfully de-intercalated the copper content in e-CuyV2O5 (to the extent that, y < 0.006) and performed a series of lithium intercalation experiments on this copper deficient phase. In 1991, Takeda et al. [3] investigated the solid solution CuV2xMoxO6 (0 x 1) which crystallizes with the brannerite-type structure, as suitable materials for lithium cathodes. Other copper(I) mixed, or low valence, group VIa/VIIa ternary oxides reported in the literature are the copper bronzes; Cu0.25ReO3 [4], Cu0.5WO3 [5], Cu0.26WO3 and Cu0.77WO3 [6], together with the minerals; delafossite CuICrIIIO2 and crednerite CuIMnIIIO2. The first reference in the literature to the existence of a copper– molybdenum bronze (i.e., a compound within the Cu–MoO3 quasibinary system) was in 1992 by Tian et al. [7]. They described the
* Corresponding author. Tel.: +45 6550 2575; fax: +45 6615 8780. E-mail address: [email protected] (T.E. Warner). 0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2010.07.004
results of a series of chemical reactions between, presumably, Cu and MoO3 in quartz glass ampoules at 400 8C. However, a lack of explicit detail in their experimental description makes the interpretation of the preparative procedure unclear. Nevertheless, they report a set of ten powder X-ray diffraction patterns for the product materials corresponding to various initial copper contents; but with little attempt to identify any of the phases contained within them. They note that Cu and MoO3 are absent in all these product materials; thus indicating that copper has intercalated into MoO3, with the result that the crystal structure of the product phase(s) becomes complex. Interestingly, there is an abrupt increase in the electrical conductivity between the materials ‘Cu0.1MoO3’ and ‘Cu0.2MoO3’ within this series, with the values; 2.66 106 S cm1 and 2.96 103 S cm1, respectively. Tian et al. did not comment on the significance of this feature with regards to the phase relationships within this system. No indication of colour is reported for any of these CuxMoO3 product materials. In the light of this work, Steiner et al. in 1994 [8] prepared a copper–molybdenum bronze, with the composition CuxMoO3 (x = 0.185 0.005). They reacted elemental copper with MoO3 in evacuated quartz glass ampoules for 120 h at 500 8C in order to investigate the preparation of CuxMoO3 in the compositional range; x = 0.15–0.20. The product materials were analysed by powder X-ray diffractometry which indicated an absence of MoO3; thus implying that MoO3 had reacted completely with the elemental copper. A crystal was selected from the product material for analysis by single crystal X-ray diffractometry. Their results showed that it belongs to
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the monoclinic space group, C2/2. Crystal structure data pertaining to this phase, as described by the chemical formula Cu1.49Mo8O24, is published in the ‘Inorganic Crystal Structure Database’ (ICSD) file; 74893. A calculated powder X-ray diffraction pattern as derived from these data is published in the ‘International Center for Diffraction Data’ (ICDD), Powder Diffraction File; PDF 82-843. Cu0.185MoO3 can be described as a tunnel structure in which the crystallographic sites for copper are significantly under occupied as revealed through the site occupation factors; Cu(1) = 0.148(4) and Cu(2) = 0.224(5). Most interestingly, an electron microprobe analysis of the same compound indicated a slightly higher copper content of x = 0.21, corresponding to Cu0.21MoO3. In 1996, Steiner et al. [9] published a sequel to this work in which they report (as part of a much larger survey of the Cu–Mo–O system) an additional phase within this system, namely; CuyMoO3z (y < 0.185). The material was analysed allegedly by electron microprobe analysis (EMPA), but the authors do not report a value for the copper content of this phase. They do not ascribe a value to the oxygen non-stoichiometry z, but they do mention that CuyMoO3z (in which, y < 0.185) coexists with Cu0.185MoO3 and MoO2 at 500 8C; thus implying that z > 0. In 1998, Kinomura et al. [10] prepared the copper–molybdenum bronze, Cu0.21MoO3, by reacting elemental copper with MoO3 in the molar ratio of 0.21:1 in an evacuated quartz glass ampoule at 500 8C for 120 h. Although the authors state that their preparative procedure is based upon the work by Tian et al. [7]; they fail to mention why they chose to prepare this specific composition (i.e., x = 0.21), which uncannily coincides with the composition (as determined by electron microprobe analysis) of the material prepared by Steiner et al. [8]. Nevertheless, the identity of the product was confirmed with X-ray powder diffractometry; although no details of this are given. The main purpose of their investigation was to study the reactions between Cu0.21MoO3 and n-alkylamines in various media. Besides this, no information is given regarding other compositions or phase relationships within the Cu–MoO3 system. But the fact that they managed to produce a copper–molybdenum bronze with the composition, Cu0.21MoO3, is pertinent to the work presented in this present article. Intrigued by the above observations, a further study of phase relationships in the Cu–MoO3 quasi-binary system was initiated by the present authors in an attempt to resolve these differences in copper stoichiometry within the copper–molybdenum bronze, CuxMoO3 (x = 0.185 vis-a`-vis 0.21) and explore its relationship with CuyMoO3z (y < 0.185) in more detail. The results of our preliminary findings are reported here for a series of reactions between elemental copper and MoO3 at the higher temperature of 600 8C under a gently flowing argon atmosphere.
product was then retrieved from the furnace at ambient temperature. The product materials were analysed by powder X-ray diffractometry using a Siemens D5000 powder diffractometer using Cu Ka1 radiation (l = 1.5405 A˚) with an associated data capture/treatment system. Differential thermal analysis (DTA) were performed on the above series of initial reaction mixtures (xCuMoO3) and on the corresponding product materials, in small platinum crucibles under an argon atmosphere using a Setaram TG-DTA 92 analyser. Alumina powder was used as the reference state for the purpose of internal thermal compensation. An additional reaction to prepare the copper-rich composition, 2CuMoO3, was performed by the alternative approach of reacting together equimolar quantities of Cu2O (99.5%) and MoO2 (99%), both supplied by Johnson Matthey GmbH, in a rectangular-shaped copper crucible (10 mm 10 mm 30 mm, fabricated in house) at 600 8C for 6 h under a flowing argon atmosphere. The copper crucible enabled the chemical reactions to be carried out in an environment in which the copper activity was fixed at unity, and under an atmosphere in which the partial pressure of oxygen is defined by the Cu2O/Cu couple (which acts as an in site oxygen buffer) at a given temperature; assuming the system is at a state of equilibrium. Nota bene, metallic copper cannot reduce the reactants (Cu2O and MoO2) under these conditions by any significant degree. Heating and cooling rates were at 300 8C/h. 3. Results and discussion All the compositions prepared in this work yielded a glistening black polycrystalline sintered product. A set of powder X-ray diffraction patterns corresponding to these product materials are shown in Figs. 1–6. A listing of the observed d-values with their relative intensities and assigned phases (with the PDF numbers) are shown for each of these product materials in the set of corresponding Tables 1–6. From the above powder diffraction data it was possible to assign all the peaks to previously known phases through comparisons with the PDFs as reported in the ICDD. Interestingly, the only exceptions were certain peaks appearing in Figs. 1 and 2. Fig. 1 shows the powder X-ray diffraction pattern regarding the product material with a global composition, ‘0.1CuMoO3’. None of the peaks correspond to elemental copper; its absence therefore, clearly implies that all the copper has reacted with the MoO3 within the charge. This is further evidenced by the drastic change in colour from the white/red colour of the reactants to the formation of a glistering black polycrystalline product. However,
[(Fig._1)TD$IG]
2. Experimental Appropriate amounts of finely divided elemental copper powder (copper bronze for organic synthesis, BDH) and molybdenum(VI) oxide powder (99.5%, Merck GmbH) were weighed to form a set of initial compositions; xCuMoO3 (with x = 0.1, 0.2, 0.25, 0.3 and 0.5), with each charge being typically, 7 g. Each preparation was mixed intimately and then placed in a rectangular-shaped platinum crucible (10 mm 10 mm 30 mm, fabricated in house). This was inserted inside a quartz glass tube with ‘vacuum greased’ quick-fitTM joints at both ends to facilitate a gentle flow of argon (99.995%, with PO2 105 bar), and placed inside a tube furnace such that both ends of the glass tube protruded from the furnace work tube. The contents were heated at a rate of 300 8C/h to 600 8C, and then held there for 1 h, before being cooled to ambient temperature at a rate of 300 8C/h. The product was reground and annealed under similar conditions for 6 h at 600 8C, with a heating and cooling rate of 300 8C/h. The
Fig. 1. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.1CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
[(Fig._2)TD$IG]
[(Fig._5)TD$IG]
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Fig. 2. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.2CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
[(Fig._3)TD$IG]
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Fig. 5. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.5CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
many of the peaks correspond to MoO3 indicating that significant quantities of this phase remain unconsumed. Interestingly, several peaks in the powder pattern (three of which have significantly high relative intensities) do not appear to correspond with any known phase within the Cu–Mo–O system as reported in the ICDD database. These peaks are therefore attributed here, to the formation of a copper–molybdenum bronze. An approximate
mass balance suggests that this bronze has the composition, CuyMoO3z (0.1 < y < 0.2; typically y 0.15) and shall be referred to in this article, simply as, Cu0.15MoO3z. Fig. 2 shows the powder X-ray diffraction pattern regarding the product material with a global composition, ‘0.2CuMoO3’. In this material, many of the peaks correspond to Cu0.185MoO3 (PDF 82843). All of the remaining peaks match precisely with those assigned to Cu0.15MoO3z in Fig. 1. Their relative intensities indicate that Cu0.15MoO3z and Cu0.185MoO3 are present in roughly equal amounts. Therefore, Cu0.15MoO3z and Cu0.185MoO3 appear to coexist within this material with the global composition, ‘0.2CuMoO3’. Furthermore, this interpretation reinforces the original assignment made in Fig. 1, as to the existence of Cu0.15MoO3z. Due to the uncertainties regarding the copper stoichiometry for the compound Cu0.15MoO3z, as prepared in this more copper-rich environment (0.2CuMoO3), these peaks are assigned to the phase expressed more generally, as, CuyMoO3z (0.1 < y < 0.185). The reader shall have noticed that none of the possible binary combinations of the phases CuyMoO3z (0.1 < y < 0.185) and Cu0.185MoO3 can ever summate to the global composition: 0.2CuMoO3. Nota bene, by application of the Lever rule, the phase CuxMoO3 as prepared in this present work cannot be of the composition Cu0.185MoO3; irrespective to any plausible composition that one may wish to ascribe to CuyMoO3z. This observation is used as evidence here, to suggest that the composition CuxMoO3 (x = 0.185 0.005) as determined by single crystal diffractometry by
Fig. 4. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.3CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
Fig. 6. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘Cu2OMoO2’ reacted at 600 8C for 6 h under a flowing argon atmosphere.
Fig. 3. Powder X-ray diffraction pattern (Cu Ka1 radiation) obtained for the global composition ‘0.25CuMoO3’ annealed at 600 8C for 6 h under a flowing argon atmosphere.
[(Fig._4)TD$IG]
[(Fig._6)TD$IG]
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Table 1 Powder X-ray diffraction data for the annealed products of initial composition: 0.1CuMoO3 (corresponding with Fig. 1).
Table 3 Powder X-ray diffraction data for the annealed products of initial composition: 0.25CuMoO3 (corresponding with Fig. 3).
dobs. (A˚)
I/I1 obs.
Assigned phase
dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
6.9547 4.0999 3.8120 3.5514 3.4825 3.4642 3.4400 3.3312 3.2614 3.2339 3.1464 3.0067 2.8804 2.7028 2.6607 2.6082 2.5281 2.3215 2.3099 2.2710 2.2284 2.2116 2.1318
93 4 22 14 95 100 12 8 13 7 5 5 4 3 6 2 3 44 57 10 6 3 2
CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z CuyMoO3z
8.1487 6.3256 5.6246 4.6842 4.3441 4.0753 3.9483 3.9101 3.7480 3.6282 3.5042 3.4220 3.4044 3.2408 3.2205 3.1459 3.0771 3.0580 3.0250 2.9942 2.9433 2.9225 2.9032 2.8812
100 1 2 1 1 60 2 6 1 2 11 8 41 4 24 5 68 9 2 5 3 1 1 2
Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17
PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF
(y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185) (y < 0.185)
Steiner et al. [8] is perhaps inaccurate. The results of this present work are more compatible with Steiner et al. [8] alternative composition (viz. Cu0.21MoO3) as determined by electron microprobe analysis. The disparity in the two analyses as reported by Steiner et al. [8] are possibly a result of analytical uncertainties, rather than real differences in chemical composition between the various crystallites as analysed; although the effects of temperature dependency and phase inhomogeneity may also play a role. Furthermore, the phase CuxMoO3 as prepared in this present work is in terms of composition more consistent with Cu0.21MoO3 as prepared at 500 8C by Kinomura Table 2 Powder X-ray diffraction data for the annealed products of initial composition: 0.2CuMoO3 (corresponding with Fig. 2). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
8.1680 6.9712 4.6830 4.0766 3.9074 3.5065 3.4814 3.4040 3.2235 3.0772 3.0601 2.9419
94 19 1 59 7 14 25 67 29 100 12 4
Cu1.49Mo8O24 CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24
PDF 82-843
2.7154 2.7006 2.6670 2.6502 2.4849 2.4482 2.3704 2.3474 2.3354 2.3202 2.3060 2.2594 2.1958 2.0046
3 4 2 2 5 5 2 5 3 11 5 13 3 2
Cut-off point in Tables 1 and 2 Cu1.49Mo8O24 Cu1.49Mo8O24 CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24 CuyMoO3z (y < 0.185) CuyMoO3z (y < 0.185) Cu1.49Mo8O24 Cu1.49Mo8O24 Cu1.49Mo8O24
PDF PDF PDF PDF
82-843 82-843 82-843 82-843
PDF PDF PDF PDF PDF
82-843 82-843 82-843 82-843 82-843
PDF 82-843 PDF 82-843 PDF PDF PDF PDF PDF PDF
82-843 82-843 82-843 82-843 82-843 82-843
PDF 82-843 PDF 82-843 PDF 82-843
82-843 39-181 39-181 82-843 39-181 82-843 39-181 82-843 39-181 39-181 82-843 32-671 82-843 39-181 82-843 39-181 82-843 82-843 39-181 39-181 82-843 39-181 39-181 39-181
et al. [10]. In the work presented here, it is suggested that this phase is perhaps more correctly described as, CuxMoO3 (0.2 < x < 0.25), with the composition Cu0.23MoO3 being very realistic. Nevertheless, since the crystal structure can accommodate variable copper stoichiometry, this phase may be more appropriately described as a solidsolution with relatively narrow compositional limits, which may display a certain degree of temperature dependency. Interestingly, the abrupt change in the electrical conductivity between the materials ‘Cu0.1MoO3’ and ‘Cu0.2MoO3’ as prepared and measured by Tian et al. [7] (as discussed in Section 1), is further
Table 4 Powder X-ray diffraction data for the annealed products of initial composition: 0.3CuMoO3 (corresponding with Fig. 4). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
8.1610 6.3232 5.6269 4.6833 4.4282 4.3454 4.0774 3.9499 3.9108 3.7511 3.6301 3.5062 3.4269 3.4068 3.2434 3.2213 3.1472 3.0776 3.0595 3.0412 2.9939 2.9443 2.9257 2.9046 2.8819
100 3 7 2 2 2 44 7 9 3 6 12 20 73 9 33 14 87 17 5 10 4 3 5 7
Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17
PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF PDF
82-843 39-181 39-181 82-843 39-181 39-181 82-843 39-181 82-843 39-181 39-181 82-843 32-671 82-843 39-181 82-843 39-181 82-843 82-843 39-181 39-181 82-843 39-181 39-181 39-181
[(Fig._7)TD$IG]
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Table 5 Powder X-ray diffraction data for the annealed products of initial composition: 0.5CuMoO3 (corresponding with Fig. 5). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
8.1664 6.3151 5.6265 5.2134 4.8125 4.6722 4.4260 4.3496 4.0759 3.9479 3.9077 3.7506 3.6312 3.5030 3.4786 3.4259 3.4037 3.2414 3.2219 3.1477 3.0771 3.0580 3.0392 2.9930 2.9440 2.9263 2.9025 2.8799
60 12 19 5 3 4 5 7 33 19 5 12 24 7 6 100 25 19 17 89 51 9 17 42 7 6 57 31
Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 MoO2 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu1.49Mo8O24 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu1.49Mo8O24 Cu4Mo5O17 Cu4Mo5O17 Cu4Mo5O17
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82-843 39-181 39-181 39-181 32-671 82-843 39-181 39-181 82-843 39-181 82-843 39-181 39-181 82-843 39-181 32-671 82-843 39-181 82-843 39-181 82-843 82-843 39-181 39-181 82-843 39-181 39-181 39-181
evidence of an immiscibility gap between Cu0.15MoO3 and Cu0.23MoO3. From the above discussion, the chemical reactions taking place between elemental copper and MoO3 at 600 8C under a flowing
Fig. 7. Differential thermal analysis (DTA) trace of ‘0.2CuMoO3’ in flowing argon. Platinum crucible with alumina powder as the thermal reference.
argon atmosphere are summarized by the following qualitative expressions:
0:1Cu þ MoO3 ! Cu0:15 MoO3 þ MoO3
0:2Cu þ MoO3 ! Cu0:23 MoO3 þ Cu0:15 MoO3z
0:25Cu þ MoO3 ! major Cu0:23 MoO3 þ traceCu4 Mo5 O17 þ traceMoO2
0:3Cu þ MoO3 ! major Cu0:23 MoO3 þ minorCu4 Mo5 O17 þ minorMoO2 Table 6 Powder X-ray diffraction data for the annealed products of initial composition: ‘Cu2OMoO2’ (corresponding with Fig. 6). dobs. (A˚)
I/I1 obs.
Assigned phase
Ref.
5.7880 4.8155 4.6952 3.6398 3.4217 3.2177 3.1909 3.0261 2.9775 2.9505 2.9138 2.8892 2.8116 2.6963 2.5376 2.4885 2.4727 2.4545 2.4429 2.4288 2.4053 2.3811 2.2201 2.1834 2.1560 2.0873 2.0701 1.9361 1.9167 1.8075
13 2 5 15 100 7 33 15 17 20 29 16 4 16 9 5 7 7 15 33 21 7 9 3 5 41 5 5 5 13
Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 MoO2 MoO2 MoO2 Cu6Mo5O18 Cu6Mo5O18 MoO2 Cu6Mo5O18 Cu Cu6Mo5O18 Cu6Mo5O18 Cu6Mo5O18 Cu
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40-865 32-671 40-865 40-865 32-671 40-865 40-865 40-865 40-865 40-865 40-865 40-865 32-671 40-865 40-865 40-865 40-865 40-865 32-671 32-671 32-671 40-865 40-865 32-671 40-865 85-1326 40-865 40-865 40-865 85-1326
0:5Cu þ MoO3 ! minor Cu0:23 MoO3 þ majorCu4 Mo5 O17 þ majorMoO2 The results of the differential thermal analysis (DTA) as performed on the product material ‘Cu0.2MoO3’ under a flowing argon atmosphere are shown in Fig. 7. On the forward scan (increasing temperature) there is an endothermic peak at 545 8C which corresponds to the exothermic peak at 500 8C on the return scan (decreasing temperature). The areas beneath these peaks are similar to each other and lie in close proximity, which suggests that they relate to a reversible phase transition at 520 8C. Since there is no evidence of melting taking place within the sample (up to 650 8C) this feature corresponds presumably to a solid state phase transition, most likely involving the phase approximating to, Cu0.21MoO3. It is interesting to note, that this transition occurs at a temperature above the temperatures 400 8C and 500 8C as deployed in the syntheses by Tian et al. [7], Steiner et al. [8] and Kinomura et al. [10] but, below the temperature (600 8C), deployed in the synthesis here. However, because this transition is reversible, it is unlikely to have affected the events leading to the preparation of the materials reported in this present work. In the product materials with a higher copper content (global compositions: 0.25CuMoO3; 0.3CuMoO3; and 0.5CuMoO3), the phases Cu4Mo5O17 [11] and MoO2 were identified as coexisting with the phase Cu0.23MoO3 throughout this compositional range. The two phases Cu4Mo5O17 and MoO2 become more predominate at the expense of Cu0.23MoO3 with increases in the global copper content. No other phases were observed. This indicates that
[(Fig._8)TD$IG]
1640
T.E. Warner, E.M. Skou / Materials Research Bulletin 45 (2010) 1635–1640
Fig. 8. A tentative subsolidus Cu–MoO2–O isothermal (25 8C) phase diagram under an argon atmosphere (with P O2 105 bar). Ternary phases are marked: 1 = (0.1 < y < 0.2; typically y 0.15); 2 = CuxMoO3 (0.2 < x < 0.25; typically x 0.23); 3 = Cu4Mo5O17; 4 = Cu6Mo5O18.
elemental copper can reduce molybdenum(VI) (within MoO3) to yield molybdenum(IV) (within Cu0.23MoO3). In an attempt to prepare the copper-rich composition, 2CuMoO3, equimolar amounts of Cu2O and MoO2 were reacted together at 600 8C in a copper crucible. A copper crucible was used in order to fix the copper activity at unity and thereby provide a socalled, ‘copper-anchor’ within the Cu–MoO2–O system. The powder X-ray diffraction pattern revealed the sole presence of the phases: MoO2, Cu6Mo5O18 and elemental copper within the product material (see Fig. 6). This indicates that copper(I) oxide can oxidise molybdenum(IV) (within MoO2) to molybdenum(VI) (within Cu6Mo5O18), and in doing so, is reduced to elemental copper. Cu2 O þ MoO2 ! majorMoO2 þ minorCu6 Mo5 O18 þ minorCu A tentative subsolidus Cu–MoO2–O isothermal (25 8C) phase diagram under an argon atmosphere (with P O2 105 bar) based on these results is shown in Fig. 8. 4. Conclusions A material with a global composition ‘0.1CuMoO3’ has been prepared at 600 8C and shown in this work to comprise; CuyMoO3z (0.1 < y < 0.2; typically y 0.15) and MoO3. This copper–molybdenum bronze, Cu0.15MoO3z relates to the phase CuyMoO3z (y < 0.185) as prepared at 500 8C by Steiner et al. [9] and to the material ‘Cu0.1MoO3’ as prepared at 400 8C by Tian et al. [6]. A material with a global composition ‘0.2CuMoO3’ has been prepared at 600 8C and shown in this work to comprise; Cu0.23MoO3 and Cu0.1MoO3z. As a consequence of this, the Cu0.23MoO3 phase prepared in this present work is more appropriately compared with the compound Cu0.21MoO3 as prepared at 500 8C by Kinomura et al. [10] and also with the composition Cu0.21MoO3 as determined by EMPA (rather than the alternative composition Cu0.185MoO3 as determined by single crystal diffractometry) for the material reported by Steiner et al. [8].
Some interesting features concerning the oxidation states of copper and molybdenum within the Cu–MoO2–O quasi-ternary system (600 8C) have arisen from this study. With reference to Fig. 8, and more specifically, the Cu–MoO2–Cu6Mo5O18 quasi-ternary system contained therein, the relative oxidative abilities of the phases Cu2O and MoO3, together with the reductive abilities of elemental copper and MoO2, become apparent, and lead to the following inferences. Reacting Cu2O and MoO2 in the molar ratio 7:10 will result in the formation of Cu6Mo5O18 and elemental copper. Hence copper(I) within Cu2O can oxidise molybdenum(IV) (within MoO2) to molybdenum(VI) (within Cu6Mo5O18), with itself being reduced to elemental copper. Reacting Cu2O and MoO3 in the molar ratio 6:10 will result in the formation of single phase Cu6Mo5O18 [12] whereby, both copper and molybdenum have retained their initial oxidation states of copper(I) and molybdenum(VI), respectively. Reacting equimolar (1:1) amounts of elemental copper and MoO3 will result in the formation of Cu6Mo5O18 and MoO2. Hence, elemental copper can reduce molybdenum(VI) (within MoO3) to molybdenum(IV) (within MoO2), with itself being oxidised to copper(I) (within Cu6Mo5O18). But, reacting elemental copper and MoO3 in the molar ratio 1:5 at 600 8C will result in the formation of Cu0.23MoO3 and Cu0.15MoO3z. In terms of formal oxidation states within these two phases, copper is present presumably as copper(I). This presents the possibility, by way of charge balance, for the existence of molybdenum(V); although the existence of mixed molybdenum(IV) and molybdenum(VI), or indeed, an averaged (i.e., non-integral) oxidation state are other possibilities [13–15]. This system therefore illustrates an interesting balance between the oxidation states of copper and molybdenum in the solid state, and presents an important comparison with the copper–molybdenum sulfide (Chevrel) phase, CuxMo2S8. The authors are presently attempting to prepare the copper– molybdenum bronzes, Cu0.23MoO3 and Cu0.15MoO3z, as single phase materials in order to characterize there properties in more detail. These findings will be reported in due course. Acknowledgements Assistance with powder X-ray diffractometry by Anne-Marie Krogh Andersen and Inger-Grethe Krogh Andersen and are gratefully acknowledged. References [1] A. Casalot, A. Deschanvres, P. Hagenmuller, B. Raveau, Bull. Soc. Chim. Fr. 6 (1965) 1730. [2] F. Garcia-Alvarado, J.M. Tarascon, B. Wilkens, J. Electrochem. Soc. 139 (1992) 3206. [3] Y. Takeda, K. Itoh, R. Kanno, T. Icikawa, N. Imanishi, O. Yamamoto, J. Electrochem. Soc. 138 (1991) 2566. [4] A. Deschanvres, B. Raveau, C.R. Acad. Sci. 264 (1967) 1841. [5] B. Broyde, J. Catal. 10 (1968) 13. [6] L.E. Conroy, M.J. Sienko, J. Am. Chem. Soc. 79 (1957) 4048. [7] S.B. Tian, F. Zhou, J.C. Yang, Z.C. Li, Solid State Ionics 57 (1992) 109. [8] U. Steiner, T. Morgenstern, W. Reichelt, H. Borrmann, A. Simon, Z. Anorg. Allg. Chem. 620 (1994) 1905–1908. [9] U. Steiner, W. Reichelt, T. Morgenstern, Z. Anorg. Allg. Chem. 622 (1996) 1428– 1434. [10] N. Kinomura, K. Mizumoto, N. Kumada, in: S. Sa¯miya, R.P.H. Chang, M. Doyama, R. Roy (Eds.), Materials Science and Engineering Serving Society, Proceedings of the Third Okinaga Symposium on Materials Science and Engineering Serving Society, Chiba, Japan, September 3–5, 1997, (1998), pp. 239–242. [11] E.M. McCarron, J.C. Calabrese, J. Solid State Chem. 65 (1986) 215. [12] E.M. McCarron, J.C. Calabrese, J. Solid State Chem. 62 (1986) 64. [13] P. Gall, P. Gougeon, Acta Crystallogr. C 48 (1992) 1915–1917. [14] C.C. Torardi, C. Fecketter, W.H. McCarroll, F.J. DiSalvo, J. Solid State Chem. 60 (1985) 332–342. [15] H. Leligny, M. Ledesert, P. Labbe, B. Raveau, W.H. McCarroll, J. Solid State Chem. 87 (1990) 35–43.