- Email: [email protected]
Glass formation study in the Bi2O3-TeO2-WO3 system
Glass formation
in the Bi203-Te02-W03
GLASS
FORMATION
system
STUDY
J.-C. CHAMPARNAUD-MESJAFW,
Ann. Chim. Sci. Mat, 1998,23,
IN THE Bi,O,-TeO,-WO, P. THOMAS,
A. CHAGRAOUI*,
P. MARCHET,
pp. 289-292
SYSTEM B. FRIT
A. TAIRI*
Laboratoire de Mattiaux Chmiques et Traitements de Surface, URA 320 CNRS, 123 avenue Albert-Thomas, 87060 Limoges Cedex, France. * JXpartement de Chimie, Facult6 des Sciences Ben M’Sik Sidi-Othman, Universiti Hassan II-
MohammBdia, Casablanca, Maroc.
Summary : Glass formation regions in the Biz03-TeOz-WOj system have been determined at 65O”C, 700°C and 800°C. Physical characteristics of some vitreous samples have been measured.
R&urn& : Etude des verres dans le syst&ne Bi201-TeO,-WO1. Les domaines d’existence si 650°C, 700°C et 8OO’C des verres appartenant au systeme Biz03-Te02-W03 ont BtB dkterminks. Les caractkristiques physiques de certains Cchantillons vitreux ont &te mesudes.
1. INTRODUCTION The increasing interest for materials presenting nonlinear optical properties has been induced by the important industrial request for lall optical< devices. As a matter of fact glasses are ideal potential candidates for such applications due to their malleability, their homonogeneity in a wide range of compositions and their chemical stability. Tellurium oxide based glasses are of technical interest due to both the high values of their linear and nonlinear refractive indices and their good transmittance of visible and infrared lights (up to about 7pm). The aim of this study is to determine the glass formation regions, at 65O”C, 700°C and SOO”C,within the Bi203-Te02-W03 system. The variations of the glass transition, the crystallization and melting temperatures along with density and refractive index arc also given. Reprints : J.C. CHAMPARNAUD-MESJARD, Thomas, 87060 Limoges Cedex, France.
LMCTS, Facultk Des Sciences, 123 avenue Albert-
J.-C. Champamaud-Mesjard
et al.
2. EXPERTMENTAL PROCEDURE All investigated samples were obtained by melting appropriate quantities of reagent-grade Bi,O, TeOz and W03 in a platinum crucible at 650°C 7OO’C or 8OO’C for 1 hour. The melts were then quenched between two preheated brass plates (cooling rate about 104”C/s). All manipulations were carried out in air as it was previously found that W03 prevented the possible oxydation of Te@V) into Te(VI) (1). Glass formation regions were determined using X ray diffraction (GuinierDe Wolff camera, Cu Kal radiation) for the analysis of many samples with neighbouring compositions close to the glass-crystal separating line. Thermal evolutions of glasses were followed by in-situ X ray diffraction at various temperature at a heating rate of S”C/mn, under atmospheric conditions, using a Siemens D5000 diffractometer (0/S, Cu Ka radiation) fitted out with a high temperature furnace (Anton Parr HTRlO), a platinum heating sample holder and an Elphyse Position Detector (14” aperture). Each diffraction diagram was recorderd after an annealing time of 10 minutes at the given temperature in the 28 range 14-90” (step size: 0.029, time range: 15mn). Glass transition (Tg), crystallization (Tc) and melting (Tf) temperatures were measured using differential scanning calorimetry (Netzsch STA 409 apparatus). Glasses densities were measured using an Accupyc 1330 helium pycnometer. Refractive index measurements were performed on perfectly polished and parrallel faces pellets.
3. RESULTS Glass formation region is obviously dependent on temperature and so increases between 600 and 800°C (figure 1). At 8OO’C the glass formation region observed in the Te02-WOs binary system confirms previously reported results (2). Pure TeO, glass (very diffkult to vitrify in the conditions of this study) was obtained after a fast quenching of the melt in a mixture of ice, ethanol and NaCl (temperature about -15’C). Characteristics of some glasses are shown in table 1. A refractive index of 2.2 to 2.3 has been measured on these glasses. These values are much higher than that obtained with SiOZ based glasses (1.5). Nonlinear optical indice measurement performed on one sample, n2* 18 lo-l9 m’/W, indicates that such TeO, based glasses are certainly good candidates for nonlinear optical applications.
3.1. m,-WO,
binary system
Thermal analysis of glasses in the composition ranging from 10 to 30% WOs (mol%) clearly shows three exotherms. The glass crystallization process was followed thanks to in situ X ray diffraction diagrams, recorded at the corresponding temperatures. These three exotherms are correlated to: (i) the crystallization at about 385-44O“C (temperature increasing with higher W03 content) of a new TeO, polymorph (called y-Te02 and previously reported (1)) (ii) WO:, crystallization at 455-460°C and (iii) the progressive transformation of y-Te02 into a-Te& between 480-510°C. For compositions containing more than 30 mol % WOs, only one exotherm is observed at 460-48O’C. The latter attributed to the simultaneous crystallization of a-TeG, and WO,. Glass transition temperature and density were found to increase with the augmentation of W03 content.
Glass formation
in the Bis03-TeO*-WO,
system
291
These glasses, when annealed below their melting temperature, crystallize into phases of the ternary system (fiwre 1). For example, crystallization of a glass with 5% Bi01.5-85%Te02lO%WO, composition (sample n”8) gives first the BizTQ019 fluorite phase at about 370°C (l), then y-TeOz at 450°C and a-TeOz at 500°C. At 55O”C, cx-TeOz and Bi2T%W3016 compounds are obtained. For a constant BiOl.5 content, glass density increases with the augmentation of WOJTeO, ratio (table 1). In the same manner, for a constant W03 content glass density increases with increasing BiO&TeO, ratio. This augmentation is obviously due to the difference of Bi, Te and W atomic weights.
TeO, L 8OOOC
mm-
.
Bi2Te80,y;
/I
.
.
.
++++++
.
.
7oooc
65O’C
121.
Bi2
FIG. 1 .- Crystalline phases and glass formation regions (at 650°C 700°C and 800°C) in the Bi,03Te&-W03 system (see table 1 for correspondance between the sample number and its composition).
292
J.-C. Champarnaud-Mesjard
et al.
TABLE 1 - Characteristics (glass-transition temperature Tg, crystallization temperature Tc, melting temperature Tf, density and refractive index) of some glasses in the Biz03-Te02-W03 system.
4. REFERENCES (1) CHAGRAOUI (A.), Mat&iaux cristallis&s et amorphes appartenant au syst&me B&OS-Te02-W03: structures et pro i&s, Thbe d’Etat, Casablanca, 1996. nP(2) VOGEL (W.), Glass Chemistry, 2 edition, Springer Verlag, 1994.
in the Bi203-Te02-W03
GLASS
FORMATION
system
STUDY
J.-C. CHAMPARNAUD-MESJAFW,
Ann. Chim. Sci. Mat, 1998,23,
IN THE Bi,O,-TeO,-WO, P. THOMAS,
A. CHAGRAOUI*,
P. MARCHET,
pp. 289-292
SYSTEM B. FRIT
A. TAIRI*
Laboratoire de Mattiaux Chmiques et Traitements de Surface, URA 320 CNRS, 123 avenue Albert-Thomas, 87060 Limoges Cedex, France. * JXpartement de Chimie, Facult6 des Sciences Ben M’Sik Sidi-Othman, Universiti Hassan II-
MohammBdia, Casablanca, Maroc.
Summary : Glass formation regions in the Biz03-TeOz-WOj system have been determined at 65O”C, 700°C and 800°C. Physical characteristics of some vitreous samples have been measured.
R&urn& : Etude des verres dans le syst&ne Bi201-TeO,-WO1. Les domaines d’existence si 650°C, 700°C et 8OO’C des verres appartenant au systeme Biz03-Te02-W03 ont BtB dkterminks. Les caractkristiques physiques de certains Cchantillons vitreux ont &te mesudes.
1. INTRODUCTION The increasing interest for materials presenting nonlinear optical properties has been induced by the important industrial request for lall optical< devices. As a matter of fact glasses are ideal potential candidates for such applications due to their malleability, their homonogeneity in a wide range of compositions and their chemical stability. Tellurium oxide based glasses are of technical interest due to both the high values of their linear and nonlinear refractive indices and their good transmittance of visible and infrared lights (up to about 7pm). The aim of this study is to determine the glass formation regions, at 65O”C, 700°C and SOO”C,within the Bi203-Te02-W03 system. The variations of the glass transition, the crystallization and melting temperatures along with density and refractive index arc also given. Reprints : J.C. CHAMPARNAUD-MESJARD, Thomas, 87060 Limoges Cedex, France.
LMCTS, Facultk Des Sciences, 123 avenue Albert-
J.-C. Champamaud-Mesjard
et al.
2. EXPERTMENTAL PROCEDURE All investigated samples were obtained by melting appropriate quantities of reagent-grade Bi,O, TeOz and W03 in a platinum crucible at 650°C 7OO’C or 8OO’C for 1 hour. The melts were then quenched between two preheated brass plates (cooling rate about 104”C/s). All manipulations were carried out in air as it was previously found that W03 prevented the possible oxydation of Te@V) into Te(VI) (1). Glass formation regions were determined using X ray diffraction (GuinierDe Wolff camera, Cu Kal radiation) for the analysis of many samples with neighbouring compositions close to the glass-crystal separating line. Thermal evolutions of glasses were followed by in-situ X ray diffraction at various temperature at a heating rate of S”C/mn, under atmospheric conditions, using a Siemens D5000 diffractometer (0/S, Cu Ka radiation) fitted out with a high temperature furnace (Anton Parr HTRlO), a platinum heating sample holder and an Elphyse Position Detector (14” aperture). Each diffraction diagram was recorderd after an annealing time of 10 minutes at the given temperature in the 28 range 14-90” (step size: 0.029, time range: 15mn). Glass transition (Tg), crystallization (Tc) and melting (Tf) temperatures were measured using differential scanning calorimetry (Netzsch STA 409 apparatus). Glasses densities were measured using an Accupyc 1330 helium pycnometer. Refractive index measurements were performed on perfectly polished and parrallel faces pellets.
3. RESULTS Glass formation region is obviously dependent on temperature and so increases between 600 and 800°C (figure 1). At 8OO’C the glass formation region observed in the Te02-WOs binary system confirms previously reported results (2). Pure TeO, glass (very diffkult to vitrify in the conditions of this study) was obtained after a fast quenching of the melt in a mixture of ice, ethanol and NaCl (temperature about -15’C). Characteristics of some glasses are shown in table 1. A refractive index of 2.2 to 2.3 has been measured on these glasses. These values are much higher than that obtained with SiOZ based glasses (1.5). Nonlinear optical indice measurement performed on one sample, n2* 18 lo-l9 m’/W, indicates that such TeO, based glasses are certainly good candidates for nonlinear optical applications.
3.1. m,-WO,
binary system
Thermal analysis of glasses in the composition ranging from 10 to 30% WOs (mol%) clearly shows three exotherms. The glass crystallization process was followed thanks to in situ X ray diffraction diagrams, recorded at the corresponding temperatures. These three exotherms are correlated to: (i) the crystallization at about 385-44O“C (temperature increasing with higher W03 content) of a new TeO, polymorph (called y-Te02 and previously reported (1)) (ii) WO:, crystallization at 455-460°C and (iii) the progressive transformation of y-Te02 into a-Te& between 480-510°C. For compositions containing more than 30 mol % WOs, only one exotherm is observed at 460-48O’C. The latter attributed to the simultaneous crystallization of a-TeG, and WO,. Glass transition temperature and density were found to increase with the augmentation of W03 content.
Glass formation
in the Bis03-TeO*-WO,
system
291
These glasses, when annealed below their melting temperature, crystallize into phases of the ternary system (fiwre 1). For example, crystallization of a glass with 5% Bi01.5-85%Te02lO%WO, composition (sample n”8) gives first the BizTQ019 fluorite phase at about 370°C (l), then y-TeOz at 450°C and a-TeOz at 500°C. At 55O”C, cx-TeOz and Bi2T%W3016 compounds are obtained. For a constant BiOl.5 content, glass density increases with the augmentation of WOJTeO, ratio (table 1). In the same manner, for a constant W03 content glass density increases with increasing BiO&TeO, ratio. This augmentation is obviously due to the difference of Bi, Te and W atomic weights.
TeO, L 8OOOC
mm-
.
Bi2Te80,y;
/I
.
.
.
++++++
.
.
7oooc
65O’C
121.
Bi2
FIG. 1 .- Crystalline phases and glass formation regions (at 650°C 700°C and 800°C) in the Bi,03Te&-W03 system (see table 1 for correspondance between the sample number and its composition).
292
J.-C. Champarnaud-Mesjard
et al.
TABLE 1 - Characteristics (glass-transition temperature Tg, crystallization temperature Tc, melting temperature Tf, density and refractive index) of some glasses in the Biz03-Te02-W03 system.
4. REFERENCES (1) CHAGRAOUI (A.), Mat&iaux cristallis&s et amorphes appartenant au syst&me B&OS-Te02-W03: structures et pro i&s, Thbe d’Etat, Casablanca, 1996. nP(2) VOGEL (W.), Glass Chemistry, 2 edition, Springer Verlag, 1994.