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Raman scattering in tellurium-metal oxyde glasses
Journal of MOLECULAR STRUCTURE Journal
Raman Scattering M. Mazzucaa,
of Molecular
Structure
in Tellurium-Metal
349 (1995)
413-416
Oxyde Glasses
J. Portierb, B. Tanguyb, F Romaina, A. Fadlia and S. Turrella*
aLaboratoire de Spectrochimie Infrarouge et Raman (CNRS, UPR A2631L), Universite des Sciences et Technologies de Lille,Bat. C-5, 59655 Villeneuve d’Ascq; 2 rue Henri Dunant, 94320 Thiais, France bLaboratoire de Chimie du Solide du CNRS, Universite de Bordeaux I, 351 tours de la Liberation, 33405, Talence, France Abstract Structural studies were undertaken of glasses in the (1-x)TeOz- xZn0 system. The glass domain (0,09 c x > 0,40) was verified and variations observed in the Raman spectra were correlated with changes induced on the Te02 polyhedra Spectra were upon glass formation with the addition of the metal oxyde. recorded as these glasses were heated through T, and recrystallized. The spectral profiles observed in the recrystallized systems closely resemble those of the broad bands in the initial glasses. The sharp bands in the final spectra, characteristic of a more ordered phase, are interpreted (by correlation with neutron diffraction data) on the basis of chains of Te03-TeO4 polyhedra interlaced with chains of Zn06 groups. 1. INTRODUCTION It is well known that tellurium oxyde, in combination with certain metal oxydes, forms stable glasses (1). The choice of the heavy metal, be it modifier or former, serves to vary the physical properties of the system and yields stable glasses formed at cooling rates typical of standard glass preparation (c l”K/min). The resultant glasses are characterized as having relatively low transition temperatures, high refractive indices and a broad transmittance range which extends from the visible to 6.6pm in the infrared (2). However, there is still a limited knowledge of the structure of these glasses. In the present work, Raman data are presented for the ZnO-Te02 glass system, as well as for the corresponding recrystallized glasses. A correlation will be made of spectral variations as a function of temperature and of composition. These results will be compared to those for related crystalline and glass systems. The interpretation of the ensemble of results will be made in terms of a model for short-range interactions. *Authorto
whom correspondence
0022-2860/95/$09.50 0 1995 Elsevier SSDI 0022-2860(95)08797-4
should be adressed Science
B.V
All rights reserved
414 2.
MATERIALS AND METHODS
2.1.Preparation of glasses TeOz-ZnO glasses were prepared from 99.99% purity grade oxydes (Aldrich) in alumina in amounts of about 5 g. Melting of the powders was performed crucibles in a tubular furnace with the temperature maintained between 600 and 750°C. Care was taken to avoid working at higher temperatures because TGA measurements showed that a great mass loss occurs at temperatures above 735°C. Transition Quenching was done by pouring the melt onto carbon plates. temperatures were determined by DTA while X-ray analyses were used for structural verfication. In order to reduce strains, the glasses were annealed at a temperature just below Tg, and then slowly cooled to room temperature. 2.2. Spectral measurements Room-temperature Raman spectra were obtained with a Dilor T800, triple monochromator spectrometer using the 514,5 nm argon ion-laser exciting line. High-temperature Raman spectra were obtained of samples contained in quartz capillary tubes heated in an oven coupled to an electronic P.I.D. regulator. This system, which was designed in our laboratory, uses a K-type thermocouple for the control of temperature.
3. RESULTS AND DISCUSSION Raman spectra of the initial crystalline presented in Figure 1. Analyses of our products L
compounds (Te02 and ZnO) are allowed us to verify that the
3 ‘g Y =
2 if ._ f
7 Y
100 Figure 1. crystalline
500
1000
Raman spectra of starting compounds and of systems obtained in the TeOz-ZnO system
100
500
1000
Figure 2. Room-temperature Raman spectra of glasses in the binary (I-x)TeOz - x ZnO system
415
glass-forming range lies between 9% and 40% in ZnO and, in addition, that two crystalline phases are formed: ZnTe03 et Zn2Te308 (4). The Raman spectra for these two compounds are also presented in Figure 1. The structure of Te02 is a three-dimensional network of TeOq trigonal bipyramids linked in infinite chains by shared vertices. Upon glass formation, some of the Te-0 bonds are broken, thus forming Te03 groups. It has been established that the introduction of metal oxydes contributes to the Te04 --> Te03 structural transition (5), under which stable glasses are obtained. This transition is reflected in the position and intensity variations of the bands in the 900600 cm-l range. In the Raman spectra of Figure 1, the Boson peak characteristic of the vitreous state is observed at 45 cm- 1. In addition to the broad shoulder observed around 120 cm-l, whose intensity increases with ZnO content, we observe a medium-intensity band at about 450 cm-l, which is assigned to Te-0-Te bending modes. By analogy with work done by Wang and Osaka (6-8), the last two bands observed at higher wavenumbers are assigned to Te-0 stretching vibrations in Te03 ( around 600 cm-l) or Te04 ( around 700 cm-l) groups. Accordingly, it can be observed that as the percentage of ZnO increases, the number of Te03 groups also increases, reflected by an increase in the intensity of the ’ Te03 ’ band with respect to that of the ’ Te04 ’ band. Hence, it seems clear that chain-breaking is fundamental in the glass-forming process. However, the role of ZnO remains to be clarified. If one assumes that the glass phase of these systems results from slight orientational disorder in a framework of polyhedra, heating the system just past the T, temperature should enable the polyhedra to reassume a certain order, while maintaining their coordination. A decrease in temperature at this point would result in blocking the groups in a crystalline framework. The short-range order in this new framework might be expected to resemble closely the order existing in the parent glass phase. With this in mind, we recrystallized the glasses in the binary Te02-ZnO systems. An example is given in Figure 3 for the composition 0.7 Te02 - 0.3 ZnO. The spectral modifications observed when the temperature passes Tg are mainly band broadening due to thermal agitation. Continued heating past the T, temperature results in the disappearance of the low-frequency Boson peak (thus affirming the absence of glass structure) and in a splitting of the broad bands associated with the Te-0 stretching modes. It is noted that at around 630 K, the crystalline ordering appears to begin. However, we were not able to obtain a clear transition before 669 K. Quenching at this point produces a phase whose spectrum is very similar to that oberved near T,, with the same sharp bands typical of an ordered structure. Hence it appears that the system has been blocked in some sort of a crystalline-type structure. It can be observed in the final spectrum of the recrystallized glass that the spectral contour is very similar to that observed in the parent glass. The only differences are the absence of a band in the range of the Boson peak, and an inversion of intensity of the Te03/Te04 stretching-mode bands in the 650 cm-l
416 1
Return to room temperature
region. The predominance of the Te03 groups which had existed in the glass structure, has apparently now been inversed. This result is very similar to that obtained for other binary glasses composed with ‘forming’ oxydes. On the other hand, when the second component is a modifier, as in the case of Mg, the final spectral contour does not reflect that of the parent glass. In this case, even though the system is blocked in a crystalline arrangement, it is not the same as in the intial glass. Further comparison of the spectrum of Figure 3 with those of the crystalline compounds in Figure 1, indicates that the spectrum of the recrystallized Te02 -ZnO system is nearly a superposition of the spectra of Te02 and ZnTe03 This observation is in agreement with the results obtained by neutron diffraction by Kozhukharov (9), showing that the glass framework in this system is built up of TeOq - ZnO - Te03 sequences. Moreover, since ZnO is an intermediary forming oxyde, it is natural that the zinc atoms should occupy a place in the glass network.
Fig. 3 Raman spectra of the CK7Te02-0.3 ZnO glass showing the evolution as the system is heated through its Tg and T, transitions and then retooled.
5. REFERENCES 1.
2. 3. 4. 5. 6. 7. 8. 9.
V. Kozhukharov, H. Burger, S. Neov and B. Sidzhimov, Polyhedron 5 (1986), 771. M. J. Redman and J. H. Chen, J. Am. Ceram. Sot. 50 (1967), 523. Khatir, S., These de Doctorat, Universite de Lille I, 1992. V. Kozhukharov, M. Marinov and G. Grigorova, J. Non Cryst. Solids 28 (1978), 429. Y. Dimitriev, V. Dimitrov and M Arnaudov, J. Mater. Sci. 18 (1983), 1353. Y. Wang and A. Osaka, Mater. Sci. For., 32 (1988), 161. M. Arnaudov, V. Dimitrov, Y. Dimitrov, and L. Markova, Mater. Res. Bull., 17 (1982), 1121. S. Khatir, F. Romain, J. Portier, J. Videau, S. Turrell, Journal Mol. Struct. 298 (1993) 13. V. Kozhukharov and H. Burger, J. Mater. Sci., 18 (1983) 1557.
Raman Scattering M. Mazzucaa,
of Molecular
Structure
in Tellurium-Metal
349 (1995)
413-416
Oxyde Glasses
J. Portierb, B. Tanguyb, F Romaina, A. Fadlia and S. Turrella*
aLaboratoire de Spectrochimie Infrarouge et Raman (CNRS, UPR A2631L), Universite des Sciences et Technologies de Lille,Bat. C-5, 59655 Villeneuve d’Ascq; 2 rue Henri Dunant, 94320 Thiais, France bLaboratoire de Chimie du Solide du CNRS, Universite de Bordeaux I, 351 tours de la Liberation, 33405, Talence, France Abstract Structural studies were undertaken of glasses in the (1-x)TeOz- xZn0 system. The glass domain (0,09 c x > 0,40) was verified and variations observed in the Raman spectra were correlated with changes induced on the Te02 polyhedra Spectra were upon glass formation with the addition of the metal oxyde. recorded as these glasses were heated through T, and recrystallized. The spectral profiles observed in the recrystallized systems closely resemble those of the broad bands in the initial glasses. The sharp bands in the final spectra, characteristic of a more ordered phase, are interpreted (by correlation with neutron diffraction data) on the basis of chains of Te03-TeO4 polyhedra interlaced with chains of Zn06 groups. 1. INTRODUCTION It is well known that tellurium oxyde, in combination with certain metal oxydes, forms stable glasses (1). The choice of the heavy metal, be it modifier or former, serves to vary the physical properties of the system and yields stable glasses formed at cooling rates typical of standard glass preparation (c l”K/min). The resultant glasses are characterized as having relatively low transition temperatures, high refractive indices and a broad transmittance range which extends from the visible to 6.6pm in the infrared (2). However, there is still a limited knowledge of the structure of these glasses. In the present work, Raman data are presented for the ZnO-Te02 glass system, as well as for the corresponding recrystallized glasses. A correlation will be made of spectral variations as a function of temperature and of composition. These results will be compared to those for related crystalline and glass systems. The interpretation of the ensemble of results will be made in terms of a model for short-range interactions. *Authorto
whom correspondence
0022-2860/95/$09.50 0 1995 Elsevier SSDI 0022-2860(95)08797-4
should be adressed Science
B.V
All rights reserved
414 2.
MATERIALS AND METHODS
2.1.Preparation of glasses TeOz-ZnO glasses were prepared from 99.99% purity grade oxydes (Aldrich) in alumina in amounts of about 5 g. Melting of the powders was performed crucibles in a tubular furnace with the temperature maintained between 600 and 750°C. Care was taken to avoid working at higher temperatures because TGA measurements showed that a great mass loss occurs at temperatures above 735°C. Transition Quenching was done by pouring the melt onto carbon plates. temperatures were determined by DTA while X-ray analyses were used for structural verfication. In order to reduce strains, the glasses were annealed at a temperature just below Tg, and then slowly cooled to room temperature. 2.2. Spectral measurements Room-temperature Raman spectra were obtained with a Dilor T800, triple monochromator spectrometer using the 514,5 nm argon ion-laser exciting line. High-temperature Raman spectra were obtained of samples contained in quartz capillary tubes heated in an oven coupled to an electronic P.I.D. regulator. This system, which was designed in our laboratory, uses a K-type thermocouple for the control of temperature.
3. RESULTS AND DISCUSSION Raman spectra of the initial crystalline presented in Figure 1. Analyses of our products L
compounds (Te02 and ZnO) are allowed us to verify that the
3 ‘g Y =
2 if ._ f
7 Y
100 Figure 1. crystalline
500
1000
Raman spectra of starting compounds and of systems obtained in the TeOz-ZnO system
100
500
1000
Figure 2. Room-temperature Raman spectra of glasses in the binary (I-x)TeOz - x ZnO system
415
glass-forming range lies between 9% and 40% in ZnO and, in addition, that two crystalline phases are formed: ZnTe03 et Zn2Te308 (4). The Raman spectra for these two compounds are also presented in Figure 1. The structure of Te02 is a three-dimensional network of TeOq trigonal bipyramids linked in infinite chains by shared vertices. Upon glass formation, some of the Te-0 bonds are broken, thus forming Te03 groups. It has been established that the introduction of metal oxydes contributes to the Te04 --> Te03 structural transition (5), under which stable glasses are obtained. This transition is reflected in the position and intensity variations of the bands in the 900600 cm-l range. In the Raman spectra of Figure 1, the Boson peak characteristic of the vitreous state is observed at 45 cm- 1. In addition to the broad shoulder observed around 120 cm-l, whose intensity increases with ZnO content, we observe a medium-intensity band at about 450 cm-l, which is assigned to Te-0-Te bending modes. By analogy with work done by Wang and Osaka (6-8), the last two bands observed at higher wavenumbers are assigned to Te-0 stretching vibrations in Te03 ( around 600 cm-l) or Te04 ( around 700 cm-l) groups. Accordingly, it can be observed that as the percentage of ZnO increases, the number of Te03 groups also increases, reflected by an increase in the intensity of the ’ Te03 ’ band with respect to that of the ’ Te04 ’ band. Hence, it seems clear that chain-breaking is fundamental in the glass-forming process. However, the role of ZnO remains to be clarified. If one assumes that the glass phase of these systems results from slight orientational disorder in a framework of polyhedra, heating the system just past the T, temperature should enable the polyhedra to reassume a certain order, while maintaining their coordination. A decrease in temperature at this point would result in blocking the groups in a crystalline framework. The short-range order in this new framework might be expected to resemble closely the order existing in the parent glass phase. With this in mind, we recrystallized the glasses in the binary Te02-ZnO systems. An example is given in Figure 3 for the composition 0.7 Te02 - 0.3 ZnO. The spectral modifications observed when the temperature passes Tg are mainly band broadening due to thermal agitation. Continued heating past the T, temperature results in the disappearance of the low-frequency Boson peak (thus affirming the absence of glass structure) and in a splitting of the broad bands associated with the Te-0 stretching modes. It is noted that at around 630 K, the crystalline ordering appears to begin. However, we were not able to obtain a clear transition before 669 K. Quenching at this point produces a phase whose spectrum is very similar to that oberved near T,, with the same sharp bands typical of an ordered structure. Hence it appears that the system has been blocked in some sort of a crystalline-type structure. It can be observed in the final spectrum of the recrystallized glass that the spectral contour is very similar to that observed in the parent glass. The only differences are the absence of a band in the range of the Boson peak, and an inversion of intensity of the Te03/Te04 stretching-mode bands in the 650 cm-l
416 1
Return to room temperature
region. The predominance of the Te03 groups which had existed in the glass structure, has apparently now been inversed. This result is very similar to that obtained for other binary glasses composed with ‘forming’ oxydes. On the other hand, when the second component is a modifier, as in the case of Mg, the final spectral contour does not reflect that of the parent glass. In this case, even though the system is blocked in a crystalline arrangement, it is not the same as in the intial glass. Further comparison of the spectrum of Figure 3 with those of the crystalline compounds in Figure 1, indicates that the spectrum of the recrystallized Te02 -ZnO system is nearly a superposition of the spectra of Te02 and ZnTe03 This observation is in agreement with the results obtained by neutron diffraction by Kozhukharov (9), showing that the glass framework in this system is built up of TeOq - ZnO - Te03 sequences. Moreover, since ZnO is an intermediary forming oxyde, it is natural that the zinc atoms should occupy a place in the glass network.
Fig. 3 Raman spectra of the CK7Te02-0.3 ZnO glass showing the evolution as the system is heated through its Tg and T, transitions and then retooled.
5. REFERENCES 1.
2. 3. 4. 5. 6. 7. 8. 9.
V. Kozhukharov, H. Burger, S. Neov and B. Sidzhimov, Polyhedron 5 (1986), 771. M. J. Redman and J. H. Chen, J. Am. Ceram. Sot. 50 (1967), 523. Khatir, S., These de Doctorat, Universite de Lille I, 1992. V. Kozhukharov, M. Marinov and G. Grigorova, J. Non Cryst. Solids 28 (1978), 429. Y. Dimitriev, V. Dimitrov and M Arnaudov, J. Mater. Sci. 18 (1983), 1353. Y. Wang and A. Osaka, Mater. Sci. For., 32 (1988), 161. M. Arnaudov, V. Dimitrov, Y. Dimitrov, and L. Markova, Mater. Res. Bull., 17 (1982), 1121. S. Khatir, F. Romain, J. Portier, J. Videau, S. Turrell, Journal Mol. Struct. 298 (1993) 13. V. Kozhukharov and H. Burger, J. Mater. Sci., 18 (1983) 1557.