Journal of Non-Crystalline Solids 379 (2013) 145–149
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Journal of Non-Crystalline Solids
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Free volume and structure of Gd2O3 and Y2O3 co-doped silicate glasses
Mitang Wang a,b,⁎, Mei Li a, Jinshu Cheng b, Feng He b, Zhaogang Liu a, Yanhong Hu a
a School of Material and Metallurgy, Inner Mongolia University of Science and Technology, Baotou, 014010, Chinab State key Laboratory of Silicate Materials for Architecture, Wuhan University of Technology, Wuhan, 430070, China
⁎ Corresponding author at: School of Material andMetalof Science and Technology, Baotou, 014010, China. Tel./fax
Viscosity andmelting temperature of soda lime silicate glasses co-dopedwith Gd2O3 and Y2O3measured using therotating crucible viscometer, and derived on the basis of theArrhenius Equationhave been reported inour previouspaper. To reveal the effect of substituting Y2O3 for Gd2O3 on the performance of soda lime silicate glass at hightemperature, the free volume fraction and structure of soda lime silicate glass co-doped with Y2O3 and Gd2O3
were investigated. The results show that a small amount of Gd2O3 decrease the fraction of free volume of sodalime silicate melt, and then increase when the content above 0.5 mol%, while Y2O3 addition decrease the fractionof free volume. For FTIR spectra, doping of Gd2O3 and Y2O3 into glass causes the peak position of bands assignedto Si–O–Si asymmetric and symmetric stretching vibration move to lower wavenumber, and broadens thedistribution of structural units. Raman spectra results show that Gd2O3 and Y2O3 result in the structural unitswith more bridging oxygen depolymerize to species with more non-bridging oxygen, consequently provide withmore non-bridging oxygen and decrease the rigidity of glass structure. The behavior of soda lime silicate glassesdopedwith Gd2O3 and Y2O3 at high temperature can be elucidated by the change of the free volume and structure.
Rare earth doped glasses play a very significant role in the develop-ment of lasers and fiber amplifiers for optical telecommunication dueto their unusual physical properties given by the specific ‘f ’ electron ofrare earth elements. They possess high glass transition and softeningtemperature, high hardness and elastic modulus, and excellent chemicalstability. Thereby, a lot of efforts have been devoted to studying rareearth bearing glasses with special properties, and relationship betweentheir structures and properties.
Physical properties of elevated temperature melts is a cornerstone ofhigh temperature related industries, such as iron and steelmaking, glassmelting, ceramics sintering, controlling the rate of various reactions andthe fluid flows. Thus, numerous measurements of the physico-chemicalproperties have been investigated in the last half a century [1]. Glass-viscosity is one of the key properties for melt, fining, conditionprocessing optimization, glass formulation and annealing process [2].However, to our best knowledge, there are very little reports on thephysical properties of rare earth doped glasses at high temperature andthe relationship between the physical properties of elevated tempera-ture melts and their structure relative to other properties. The physicalproperties at high temperature of glass melts are very important toboth the glass technologist and glass scientists. In our previous investiga-tion about the effect of rare earth oxides (La, Ce, Pr, Nd, Eu, Gd, Yb, Y) on
the performance of the soda lime silicate glass at high temperature, theresults show that, except for Nd2O3, introduction of other rare earthoxides (La, Ce, Pr, Eu, Gd, Yb, Y) decreases viscosity of soda–lime–silicateglass, and the most evident effect of Gd2O3 on the viscosity and meltingtemperature of silicate glass was also observed [3–5]. Addition of Nd2O3
increases the viscosity of the investigated glass in the testing tempera-ture ranges can be attributed to the effect of Nd2O3 on the soda–lime–silicate glass network structure, which is evidently different fromother rare earth oxides studied, in FTIR spectra, the shift of peak positionat around 1050 cm−1 to move towards high wavenumber, up to1090 cm−1 when doping Nd2O3 into silicate glass [6]. The relationshipbetween performances of silicate glass doped singly with different con-tent of Gd2O3 or Y2O3 at high temperature has also been investigatedwith Fourier transform infrared spectrometer using the KBr disc methodand the INVIA confocal microRaman spectrometer [7]. Moreover, the be-havior of soda lime silicate glasses co-doped with Gd2O3 and Y2O3 at el-evated temperature was also researched in our previous paper [8], theresults showed that the viscosity, melting temperature and coefficientof thermal expansion of soda–lime–silica glasses co-doped with Gd2O3
and Y2O3 are larger than those of glasses doped solely with Gd2O3 orY2O3, and the effect of co-doping with Gd2O3 and Y2O3 on thermalexpansion and viscosity properties of soda–lime–silica glass observedseem to be similar with the mixed-alkali effect in silicate glasses.
This work is a part of our ongoing program to investigate therelationship between structure and properties of soda lime silicateglasses doped with rare earths ions. In this work, in order to elucidatethe effect of co-doping Gd2O3 and Y2O3 on the physical properties ofsoda lime silicate glass at high temperature, therefore, the free volume
146 M. Wang et al. / Journal of Non-Crystalline Solids 379 (2013) 145–149
fraction of melts and structure of soda lime silicate glass co-doped withGd2O3 and Y2O3 are studied by relation between the free volume andviscosity, FTIR and Raman spectroscopy.
2. Experimental procedures
Rare earth Gd2O3 and Y2O3 doped soda–lime–silica glasses weresynthesized and investigated in this work, glass samples co-doped withGd2O3 and Y2O3 were labeled with FGGY0-4. The chemical compositionsof glasses were listed in ref. [8]. Fusion was carried out in corundumcrucibles by means of an electric furnace in the 1500–1580 °C tempera-ture range for 3 h. The melt was quenched in a few seconds from hightemperature by pouring the melt into water and dried for 24 h at120 °C in the oven to obtain glass frit for testing viscosity and structure.The viscosity of glass frit quenched in water was measured with arotating crucible viscometer (Model Rheotronic II) in the temperaturerange from 1100 °C to 1500 °C under atmospheric conditions, control-ling the temperature within ±1 °C. However, the maximum error onthe temperature is ±5 °C due to the accuracy of the thermal elementsand measurement equipment. The standard measurement error is lessthan 0.05 log units. The part of melt was poured into a pre-heatingstainless steel model to form, and then annealed for 1 h at below 50 °Cthe glass transition temperature Tg determined by dilatometry. Regularbulk glass samples were prepared for test of glass transition temperatureTg and dilatometric softening temperature Tf. The dilatometric experi-ments were performed in a horizontal dual-rod dilatometer (Model DIL402) at heating rate of 1 °C/min and quartz glass standard. Thedilatometric experiments of the pre-annealed samples were performedto yield final values. Tg was determined as the intersection of the linearextrapolation of the slope of thermal expansion curve of the solid glassand that of the glass “melt.” The dilatometric softening point Tf can bedetermined from themaximumof the dilatometric curve. Themeasuringprocedure of glass viscosity, glass transition temperature and dilatomet-ric softening temperature has been reported in detail in refs. [3–5,8].
FTIR absorption spectra of Gd2O3 doped soda lime silicate glass fritswere also measured on a Fourier transform infrared spectrometer(Nexus) using the KBr disc method, resolution of the instrument was2 cm−1, in 400–4000 cm−1 region. Raman spectra of Gd2O3 doped sodalime silicate glasses quenched in water were recorded with the INVIAconfocal microRaman spectrometer (RENISHAW) equipped with a CCDdetector. The 514.5 nm light from Ar+ laser was chosen for sample exci-tation. Spectral resolution of the Raman spectrometer was 1–2 cm−1, themeasurement frequency range is in 100–1500 cm−1.
3. Results and discussion
3.1. Viscosity and melting temperature
Results on the viscosity and melting temperature of Gd and Y co-doped silicate glasses showed that [8], when the doping totalcontent of Gd and Y keep constant of 1.00 mol%, substituting Y for Gdgradually, the viscosity of soda–lime–silicate glass co-doped withGd2O3 and Y2O3 at high temperature is seen to decrease in the series:FGGY1 N FGGY2 N FGGY3 N FGGY4 N FGGY0. It needs to note that theglass sample FGGY0 corresponding to soda lime silicate glass dopedwith Gd2O3 of 1.00 mol% and Y2O3 of 0 mol%, and FGGY4 with Gd2O3 of0 mol% and Y2O3 of 1.00 mol%. It suggests that viscosity of soda limesilicate glasses at high temperature rise firstly and then decrease withreplacing the Gd2O3 by same amount of Y2O3, namely, the viscosity ofsoda–lime–silica glasses co-doped with Gd2O3 and Y2O3 are larger thanthat of glass doped singly with Gd2O3 or Y2O3 of 1.00 mol%. Moreover,the same change tendency in melting temperature of the studied glassesco-dopedwith Gd2O3 and Y2O3 was also observed, themelting tempera-ture of soda–lime–silica glass does not monotonously increase ordecrease, while obtaining a extreme value at Gd2O3 of 0.75 mol% and
Y2O3 of 0.25 mol%, as Gd2O3 was replaced by the same amount of Y2O3
(total content of 1.00 mol%).Viscosity at high temperature and melting temperature of soda–
lime–silica glasses co-doped with Gd2O3 and Y2O3 are larger than thatof glass doped singly with Gd2O3 or Y2O3 of 1.00 mol%, which may beresulted from the different effect of Gd2O3 and Y2O3 on the free volumeof silicate melt and structure change of studied glasses.
3.2. Free volume fraction
Within the framework of the free volume concept, the lower viscosityof silicate at high temperature is directly related to the larger free volumein silicatemelts. Numerous study results have shown that the viscosity ofliquid is closely correlated with free volume. The theoretical modelsproposed by Doolittle suggest a close correlation between free volumeand viscosity [9]. According toDoolittle, the viscosity of glass forming sub-stances is determined in terms of the fraction of free volume f = vf/vm,
η ¼ η0 expbvm
.v f
� �ð1Þ
where vf is the average free volume per atom of the liquid, parameter b isa material-specific constant of order unity, the term bvm represents thecritical volume necessary for viscous flow, the pre-exponential factor η0is nearly constant according to the relation η0 ¼ h
.vm
, where h is the
Planck constant and vm the specific volume of the substance extrapolatedto absolute zero without change of phase.
Based on the Doolittle equation, the temperature dependence of theviscosity of glass forming liquid can be transformed to a dependence ofthe free volume of liquid on the temperature. The model of Cohenet al. gives the linear relation between the fraction of free volume andtemperature [10],
f ¼ α f T−T0ð Þ ð2Þ
where αf is the temperature coefficient of the fraction of free volume,which can be approximated by the difference between the volumetricthermal expansion coefficients of the liquid and the glass. In thismodel, the viscous flow is attributed not to energy barriers, but ratherto the redistribution of free volume. As the temperature equals to T0,the viscous flow no longer occurs due to the free volume of liquidsvanishes.
Another model of relation between the fraction of free volume ofliquid and temperature [11], that is,
f ¼ f g þ α f T−Tg
� �ð3Þ
where Tg is glass transition temperature, as T = Tg, the fraction of freevolume of glass forming substances reaches to a constant value fg.
By substituting the relation between fraction of free volume andtemperature (Eqs. (2) or (3)) for the fraction of free volume in Eq. (1),we can obtain the known empirical relationship describing the correla-tion between viscosity of glass forming melt and temperature, theVogel–Fulcher–Tamann equation,
η ¼ η0 expB.
T−T0
� �ð4Þ
the parameters of the Vogel–Fulcher–Tamann (VFT) equation are relatedto the αf and fg through the following expressions,
147M. Wang et al. / Journal of Non-Crystalline Solids 379 (2013) 145–149
Then we can obtain the same expression between fraction of freevolume of glass forming substances and VFT parameters T0 and B forboth Eqs. (2) and (3),
f ¼ T−T0ð Þb.B
ð7Þ
This equation can be used to describe the dependence of the fractionof free volume of glass forming liquids on the temperature if knowingthe Doolittle parameter b, and VFT parameters T0 and B, as a result, theeffect of chemical composition on the free volume of glass formingsubstances can be estimated. Sanditov et al. [11] measured and calculat-ed the viscosity and free volume of eight optical glasses with Doolittleparameter b as a constant close to unity (b ≈1). And the b is verysmall relative to the VFT parameters B, to be simple, b approximatelyview as 1 in this paper. It seems to be reliable for estimation of the effectsof chemical compositions and temperature on the free volume of glassforming substances, although the value of parameter b can influencethe temperature dependences of the free volume fraction of the glassforming substances to a small extent. In this work, the relationshipbetween viscosity of soda lime silicate glasses doped with Gd2O3 orY2O3 singly and temperature in the range between the glass transitiontemperature and melting temperature was fitted by using of the VFTempirical equation. The viscosity of studied silicate glasses at hightemperature was obtained from the rotating crucible viscometer, theglass transition temperature Tg and dilatometric softening temperatureTf determined by dilatometry (detailed data were listed in ref. [8])correspond to the viscosity data of 1012 Pa s and 1010 Pa s respectively[12,13]. Dependence of logarithmic viscosities (Pa s) on the temperaturefor soda lime silicate glass fitted with VFT equation is typically shown inFig. 1. And theVFT parametersA, B and T0 used to calculate the fraction offree volume of soda lime silicate glasses doped with and without Gd2O3
or Y2O3 are also listed in Table 1. It seems the suitable fitting with VFTequation in this work as shown all R2 is more than 0.99.
The fraction of free volume for soda lime silicate glasses doped withdifferent mol% content of Gd2O3 or Y2O3 as a function of temperaturewas calculated using Eq. (7) and is shown in Figs. 2 and 3. All the exper-imental curves display the same tendency, the fraction of free volumeincreases with elevating the temperature. It also can be observed thatthere is obvious variation in the fraction of free volume for the glassesdoped with various content of Gd2O3 or Y2O3. Obviously, Gd2O3 andY2O3 content play a crucible role on the fraction of free volume of thesoda lime silicate glass. Compared to the base soda lime silicate glass,Gd2O3 doping first leads to a decrease in the fraction of free volume,and then increases as the doping content above 0.50 mol%, while theY2O3 addition decreases the fraction of free volume of soda lime silicateglass. However, the different effect of Gd2O3 and Y2O3 on the fraction of
Fig. 1.Dependence of logarithmic viscosities (Pa s) on the temperature for glassfittedwithVFT equation.
free volume of soda lime silicate glass is clearly illustrated. This differenteffect of Gd2O3 (increase effect as the content of Gd2O3 more than0.25 mol%) and Y2O3 (decrease effect) is supposed to be related withthe different accumulation effect given by the different field strength ofGd (3.410 A−2) and Y (3.874 A−2) ions on the silicate glass structure.
According to the free volume theories [9–11,14,15], viscous flowmight be viewed as a coordinated series of jumps of flow elementsto voids. Therefore, only voids larger than that of critical size mayparticipate in the flow process. Moreover, the void size strongly dependson the free volume, that is, more free volume, larger voids consequentlyfacilitate to viscous flow. The viscosity of glass sample FGGY4 (Gd2O3 of0 mol% and Y2O3 of 1.00 mol%) larger than the sample FGGY0 (Gd2O3
of 1.00 mol% and Y2O3 of 0 mol%), therefore, can be attributed to the in-crease and decrease effects of Gd2O3 and Y2O3 on the free volume of sodalime silicate glass respectively. Additionally, substituting Y2O3 for Gd2O3
(samples FGGY1, FGGY2 and FGGY3) results in an increase in viscositycompared with Y2O3 free glass sample FGGY0, also may be as a resultof the different influence of Gd2O3 and Y2O3 on the free volume.
The viscosity of soda lime silicate glass decreased gradually asGd2O3 was replaced by Y2O3, namely, viscosity (FGGY3) b viscosity(FGGY2) b viscosity (FGGY1), and the viscosity of glass sample FGGY4is lower compared to base glass FG. Unexpectedly, these experimentalresults are reverse to the free volume theory. Generally, the networkmodifier ions would enter the free volume provided by the glassnetwork former, as a result, the free volume decreases [16]. However,network modifier ions break and expand the glass network throughproviding non-bridging oxygen. This effect can also lead to a decreasein viscosity and melting temperature (see next section).
3.3. Depolymerization of network
FTIR absorption spectral curves in 400–4000 cm−1 region of soda–lime–silicate glasses co-doped with Y2O3 and Gd2O3 are illustrated inFig. 4. And the data on peak position (470, 780 and 1050 cm−1) and
Fig. 2. Dependence of free volume fraction on temperature of glasses doped with Gd2O3.
148 M. Wang et al. / Journal of Non-Crystalline Solids 379 (2013) 145–149
the full-width at half-maximum in the 950–1200 cm−1 frequencyregion are summarized and listed in Table 2. The effect of co-dopingY2O3 and Gd2O3 on the change in FTIR spectral curve profiles is veryslight, however, it can be observed that the presence of rare earth oxidesin soda–lime–silicate leads to a clear shift of the peak position at around1050 cm−1 assigned to Si–O–Si asymmetric stretching and 780 cm−1
assigned to Si–O–Si symmetric stretching vibration, not to visiblechange of the peak position at about 470 cm−1 assigned to Si–O–Sibending vibration. Compared with the rare earth oxide free glass FG,addition of Y2O3 and Gd2O3 to base glass leads to the peak position atabout 1050 and 780 cm−1 shift towards lower wavenumber, as substi-tute Y2O3 for Gd2O3 from 0 to 1.00 mol%, the peak position assignedto Si–O–Si asymmetric stretching vibration shift from 1050 to1040 cm−1, while the peak position assigned to Si–O–Si symmetricstretching vibration shift firstly from 779 cm−1 to 771 cm−1, andthen to high wavenumber of 779 cm−1. On the basis of the relationshipbetween Si–O bond strength and effective frequency [6,17] FSi − O =4π2c2μveff2 , where c is the speed of light, μ the reduced mass of cationsite, the change of Si–O bond strength in the soda lime silicate glassesdoped with Y2O3 and Gd2O3 can be assessed. It has been observed thataddition of Y2O3 and Gd2O3 into soda lime silicate glass causes the effec-tive frequencymove to lowerwavenumber, as a result decreases the Si–O bond strength. Furthermore, it also can be assumed that the Si–Obond strength becomes a weaker result from the elongation of Si–Obond length caused by the larger polarizing force of Gd and Y ions [17].
It has been reported that the rare earth ions cause the silicate glassto form a broad distribution of Qn units [6,18–22], where Qn refers to a
Fig. 4. FTIR spectra of glasses co-doped with Y2O3 and Gd2O3.
silica tetrahedron with n bridging oxygen atoms. In this work, the full-width at half-maximum (FWHM) of FTIR absorption spectrum in 950–1200 cm−1 was used to characterize quantitatively the broadeningeffect of rare earth elements on the distribution of structural unitsQn in silicate glass [6]. Table 2 shows that doping Gd2O3 and Y2O3
into base glass widens the FWHM in the 950–1200 cm−1 region, it sug-gests that the glass doped with Y2O3 and Gd2O3 becomes moredepolymerized and disordered comparing with the base glass. TheFWHM values of glass samples FGGY1, FGGY2 and FGGY3 co-dopedwith Y2O3 and Gd2O3 are almost equal (about 340), however, thesevalues are evidently lower than the glass samples FGGY0 doped singlywith Gd2O3 (407) and FGGY4 doped with Y2O3 (381), which indicatesco-doping Y2O3 and Gd2O3 into soda lime silicate glass provides morenon-bridging oxygen atoms for network structure and broadens the dis-tribution of Qn units, but the depolymerized effect of co-doping of Y2O3
and Gd2O3 on the soda lime silicate glass is less than that of single dop-ing of Y2O3 or Gd2O3.
Raman spectra for soda lime silicate glasses doped with Y2O3 andGd2O3 are shown in Fig. 5. Raman spectra of the studied glasses in250–1300 cm−1 region contain three main bands at around 510–660 cm−1, 710–860 cm−1 and 900–1200 cm−1 range, assignment ofthese bands has been reported in our previous paper [6,23]. Bydeconvoluting the 850–1300 cm−1 high frequency region assigned tothe Si–O stretching vibration of [SiO4] structural units Qn with differentnon-bridging oxygen (n = 0, 1, 2, 3, 4), and based on some expressionscharacterizing the structure of aluminosilicate glass given in our previ-ous paper by combining andmodifying themethods reported by ShelbyandUmesaki [6,23], the content of structure unitsQn (n = 1, 2, 3, 4), thefraction of non-bridging oxygen (NBO/(NBO + BO)), average numberof NBO per tetrahedron (NBO/Tetrahedron), average number of bridg-ing corners per tetrahedron (Bridges/Tetrahedron) for base and rareearth oxides doped soda lime silicate glasses were calculated and listedin Table 3.
It can be observed that from Table 3, there is obvious variation in thecontent of structure units Qn, NBO/(NBO + BO), NBO/Tetrahedron andBridges/Tetrahedron for the studied glasses. Obviously, Gd2O3 andY2O3 have an important role on the structure of the soda lime silicateglass. It can be observed that [SiO4] tetrahedron with three bridging
Fig. 5. Raman spectra of glasses co-doped with Y2O3 and Gd2O3.
Table 3Amount of Qn (mol), oxygens per tetrahedron, fraction of non-bridging oxygen, averagenumber of NBO per tetrahetron, average number of bridging corners per tetrahedron ofGd2O3 and Y2O3 co-doped glasses.
149M. Wang et al. / Journal of Non-Crystalline Solids 379 (2013) 145–149
oxygen and one NBO (Q3) and with two NBO and two BO per tetrahe-dron (Q2) are main structural units in this glass system, and smallamount of Q1 with three non-bridging oxygen and Q4 fully polymerizedspecies. Compared to the base soda lime silicate glass, Q1 and Q3 speciesfor glass samples FGGY0, FGGY1, FGGY2 and FGGY3 decrease, and Q2
increases, however, Q2 and Q3 species of glass sample FGGY4 decrease,Q1 evidently increases. In the case of structure unit Q4, the content ofglass samples doped singly with Y2O3 or Gd2O3 increases, but thesamples co-doped with Y2O3 and Gd2O3 decrease. It is evidentlyshown that presenting the Y2O3 and Gd2O3 in the silicate glass compo-sition has a significant effect on the conversion of structure units Qn
(n = 1, 2, 3, 4) to more depolymerized structure units, although theconversion tendency of each species is not consistent for all studiedglass, meaning that doping Y2O3 and Gd2O3 in silicate glass depolymer-izes the [SiO4] structural units due to breaking of Si–O–Si bonds in thenetwork caused by the rare earth ions acting as network modifier, andcauses the structure of glasses more disorder.
Besides, the fraction of non-bridging oxygen (NBO/NBO + BO),average number of NBO per tetrahedron (NBO/tetrahedron) in sodalime silicate glasses doped with Y2O3 and Gd2O3 increase relative torare earth free glass, and the average number of bridging corners pertetrahedron (connectivity number) decreases, it is considerably shownthat the increasing and decreasing degree of NBO/NBO + BO, NBO/tetrahedron and connectivity number for the glasses doped singly withY2O3 or Gd2O3 is greater compared with glasses co-doped with Y2O3
and Gd2O3, namely, Y2O3 and Gd2O3 act as network modifier in silicateglass providing more NBO, and depolymerize the network structure,and that the depolymerization effect of co-doping with Y2O3 andGd2O3 on silicate glass is less than that of doping singly with Y2O3 orGd2O3, this result is well consisted with the FWHM of FTIR.
The experimental results show that viscosity of soda lime silicateglass decreases as Gd2O3 is replaced by Y2O3, and is lower than theviscosity of glasses doped singly with Y2O3 or Gd2O3, and the viscosityof glass sample FGGY4 is lower compared to the base glass FG, whichcan be attributed to the shift of band peak position and broad ofFWHM in 950–1200 cm−1 for FTIR absorption spectra, whichconsequently result in an elongation of the Si–O bond length and adecrease in Si–O bond strength, and also to the converse between Qn
species, an increase in fraction of NBO and decrease in structural con-nectivity, meaning more depolymerized and disordered network struc-tures, consequently cause the decrease in viscosity at high temperatureof silicate glass to occur, although there is a decrease effect of Y2O3 onthe free volume of soda lime silicate melt.
4. Conclusions
The effect of co-doping Gd2O3 and Y2O3 on the viscosity at hightemperature and melting temperature of soda lime silicate glass was
elucidated by the free volume fraction of melts and structure of sodalime silicate glass co-dopedwith Gd2O3 and Y2O3. Results on free volumefraction show that Gd2O3 and Y2O3 play a crucible role on the fraction offree volume of the soda lime silicate glass, compared to the Gd2O3 andY2O3 free soda lime silicate glass, Gd2O3 doping first leads to a slightdecrease in the fraction of free volume, and then increases the dopingcontent above 0.50 mol%, while the Y2O3 addition decreases the fractionof free volume of soda lime silicate glass. Results of FTIR spectra showthat the presence of Gd2O3 and Y2O3 in soda–lime–silicate leads to aclear shift towards lower wavenumber of the peak position at round1050 cm−1 assigned to Si–O–Si asymmetric stretching and 780 cm−1
assigned to Si–O–Si symmetric stretching vibration, and widens theFWHM in the 950–1200 cm−1 region. Raman results show that Y2O3
and Gd2O3 in the silicate glass composition has a significant effect onthe conversion of structure unitsQn (n = 1, 2, 3, 4), increases the fractionof non-bridging oxygen (NBO/NBO + BO) and average number of NBOper tetrahedron (NBO/tetrahedron) and decreases the average numberof bridging corners per tetrahedron (connectivity number). It also canbe concluded that the depolymerization effect of co-doping with Y2O3
and Gd2O3 on silicate glass structure is less than that of doping singlywith Y2O3 or Gd2O3. The effect of doping Gd2O3 and Y2O3 on the viscosityat high temperature and melting temperature of soda lime silicate glasscan be attributed to the change of free volume and structure.
Acknowledgments
This project was supported by National Natural Science Funds forDistinguishedYoung Scholar (51025416), Young Scientist Fundof theNa-tional Nature Science Foundation of China (51202104), Natural ScienceFoundation of the Inner Mongolia Autonomous Region (2012MS0807),and School Funds of InnerMongolia University of Science and Technology(2010NC022, 2010NC019 and PY-201006).
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