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The effects of La2O3 on the early stages of crystallization for MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramics
Solid State Sciences 70 (2017) 6e12
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The effects of La2O3 on the early stages of crystallization for MgOAl2O3-SiO2-TiO2-La2O3 glass-ceramics Hui-Juan Wang a, b, c, *, Christian Bocker c, Bo-Tao Li a, Hui-Xing Lin a, Christian Rüssel c, Lan Luo a a b c
Key Laboratory of Inorganic Functional Material and Device, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China University of Chinese Academy of Sciences, Beijing 100049, China Otto-Schott-Institut, Jena University, 07743 Jena, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 February 2017 Received in revised form 21 May 2017 Accepted 25 May 2017 Available online 26 May 2017
The early stages of crystallization for MgO-Al2O3-SiO2-TiO2-La2O3 glasses with different La2O3 concentrations were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The glass transition temperature (Tg) of the glass decreases at first and then increases again with increasing La2O3 concentration. This indicates that the structure of the glass becomes weaker at first and then stronger again. Lanthanum acts in glasses as network modifier and will usually decrease the network connectivity of the glass structure. Nevertheless, if the La2O3 concentration is high enough, the oxygen and other ions start to agglomerate around La, resulting in a more closely packed structure. Heat-treatment of the sample with x ¼ 0.1 at 770e810 C results in the precipitation of a droplet phase with higher mean atomic weight embedded in a matrix with lower mean atomic weight. The initial crystalline phase magnesium aluminum titanate (MAT) precipitates from the droplet phase. Nevertheless, for the sample with x ¼ 0.4, dendrite-like structure could be observed after heat-treatment of the glass at 810 C. Furthermore, the crystalline phase first precipitated is the lanthanum containing perrierite, which could be attributed to the rearrangement of the glass structure as an effect of La3þ incorporation. © 2017 Elsevier Masson SAS. All rights reserved.
Keywords: Glass-ceramic Crystallization La2O3
1. Introduction Cordierite (Mg2Al4Si5O18) based glass-ceramics have received considerable attention in the area of millimeter-wave dielectrics, dentistry and microelectronics due to their excellent properties such as low dielectric loss, low coefficient of thermal expansion as well as high mechanical strength [1e4]. The phase transformation of the glass-ceramics, which deviate from those of a stoichiometric cordierite compound, are greatly dependent on the compositions of the starting glasses. A glass with excesses both of SiO2 and Al2O3 has a higher activation energy for crystallization [5]. Compositions richer in MgO or (MgO,SiO2) than the stoichiometric cordierite compound suppress the formation of m-cordierite [6,7]. The addition of TiO2 [8], ZrO2 [9], P2O5 [10], B2O3 [11] or CeO2 [12] also has significant effects on the nucleation and crystallization process of
* Corresponding author. Key Laboratory of Inorganic Functional Material and Device, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China. E-mail address: [email protected] (H.-J. Wang). http://dx.doi.org/10.1016/j.solidstatesciences.2017.05.012 1293-2558/© 2017 Elsevier Masson SAS. All rights reserved.
the glass. For example, three-phase immiscibility was detected in the MgO-Al2O3-SiO2-TiO2 system on the basis of Raman scattering, small-angle X-ray scattering (SAXS), and X-ray powder diffraction (XRD) data [13,14]. In many cases, three phases emerge after the process of glass liquid phase separation: magnesium aluminum titanate, magnesium-aluminate containing a small amount of SiO2, and the residual glassy phase enriched in silica [15]. The crystallization proceeding in these regions leads to the precipitation of nanocrystals of two phases, namely, x(MgO$2TiO2)$y(Al2O3$TiO2) solid solution in a magnesium/aluminum/titanate-rich regions as well as spinel (MgAl2O4) in magnesium/aluminate-rich regions. In our previous studies, glass-ceramics from the MgO-Al2O3SiO2-TiO2-La2O3 (MASTL) system with excellent microwave dielectric properties have been reported [16e18]. In the studies concerning the compositions 1MgO$1.2Al2O3$2.8SiO2$1.2TiO2$xLa2O3 (x ¼ 0.1, 0.2, 0.3, 0.4 in molar ratio), the La2O3 concentration proves to have a significant effect on the crystallization behavior and the dielectric properties [17]. However, no further analysis was conducted on the initial stage of the crystallization as a function of La2O3 concentration, which is an
H.-J. Wang et al. / Solid State Sciences 70 (2017) 6e12
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important part of the crystallization mechanism. In this paper, a special focus is laid on the first stage of the crystallization process for MASTL glasses with different La2O3 concentrations by X-ray diffraction (XRD) studies in combination with the transmission electron microscopy (TEM). 2. Experimental procedure Glasses with the compositions 1MgO$1.2Al2O3$2.8SiO2$1.2TiO2$xLa2O3 (x ¼ 0.1, 0.2, 0.3 and 0.4) in molar ratio were prepared as already described in Ref. [17] and denoted as L1, L2, L3 and L4. The samples were crystallized by a one-step heattreatment at temperatures between 770 and 950 C and kept for 2e16 h. For all the samples, a heating rate of 5 K min1 was used. Dilatometric measurements (NETZSCH DIL 402 C) were performed at glass samples, which were shaped into rectangular bars of about 5 5 25 mm3. The used heating rate was also 5 K min1. From crystallized and powdered samples, X-ray diffraction (XRD) patterns were recorded using CuKa radiation in a 2q-range between 10 and 70 (Rigaku Miniflex 300, Rigaku, Tokyo, Japan). The microstructure and selected area electron diffraction (SAED) of the thin sections produced from both the parent glass and the samples heated at 770e810 C from samples, heat-treated at 770e810 C were detected using Hitachi-H8100 TEM. The sample preparation was done as follows: first, the samples were mechanically thinned to make slices 100e200 mm thick and then disks with a diameter of 3 mm were cut from the slices. The central region of the disk was dimpled to a residual thickness of 10e15 mm. Then, double-sided ion-beam etching with Arþ-ions under a small angle incidence (±5 ) and low ion beam energy (3 kV, 1.5 mA) was applied until the samples became electron transparent (Baltec RES010). As the samples are non-conductive, carbon coating was carried out using Edwards AUTO 306 at 103 Pa. TEM was done at 200 kV and some samples proved to react very sensitively to the electron beam in terms of both contamination and degradation. The measured dhkl values for the crystalline phases were calculated based on the SAED patterns and camera length. The theoretical dhkl values and relative intensities (I/Imax) were calculated according to the crystal structures of the Al2TiO5 (ICSD 002759) and perrierite (ICSD 043798) for the electron diffraction using the software Materials Studio. The relative intensities for Al2TiO5 and perrierite were obtained when dhkl changes from 4.818 to 0.532 Å and 5.62 to 0.532 Å respectively.
Fig. 1. Dilatometric curves of the glass samples L1-L4.
Fig. 2. XRD patterns of samples L1-L4 heat-treated at 850 C for 2 h.
3. Results and discussions Fig. 1 shows the dilatometric curves of the glass samples L1, L2, L3 and L4. With increasing La2O3 concentration, the glass transition temperature (Tg) as determined by the tangents (see Fig. 1) shifts to lower temperature from 746 to 739 C, then rises again from 739 to 752 and finally to 756 C. The lowest value is reached for sample L2. The temperature attributed to the maximum value in the dilatometric curve (marked by the arrows in Fig. 1) is the dilatometric softening temperature Td. Similar to Tg, Td also decreases at first and then increases with increasing La2O3 concentration. During heat treatment of the glasses, the appearances of the glass-ceramics change from translucent to opaque. Fig. 2 shows the XRD patterns of samples L1-L4 heat-treated at 850 C for 2 h. The peaks in the XRD patterns for sample L1 and L2 after heat treatment at 850 C could be assigned to magnesium aluminum titanate (MAT, MgxAl2(1x)Ti(1þx)O5). MAT (space group Cmcm) is orthorhomic and a solid solution of Al2TiO5 and MgTi2O5. However, if the La2O3 concentration is further increased, i.e. for samples L3 and L4, monoclinic perrierite appears instead of MAT. The idealized structural formula of perrierite is speculated to be
Fig. 3. XRD patterns of the parent glass L1 and the samples heat-treated at various temperatures between 770 and 950 C for different periods of time.
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Fig. 4. XRD patterns of the parent glass L4 and the samples heat-treated at various temperatures between 770 and 900 C for different periods of time.
[A3þ4B2þC3þ2Ti4þ2O8(Si2O7)2] (with A ¼ rare-earths from La to Sm; B¼Fe, Co, Ni, Mg; and C¼Al, Fe3þ, Ga or (Me2þTi4þ)) [19] and the chemical formula of the perrierite in this research is close to La4MgAl2Ti2Si4O22. As shown in Fig. 2, the crystalline phases detected in glassceramic L1 and L2, L3 and L4 are similar to each other. Thus, two typical compositions 1MgO$1.2Al2O3$2.8SiO2$1.2TiO2$xLa2O3 (x ¼ 0.1, 0.4) in molar ratio are chosen for the further studies to clarify the effects of La2O3 on the first stage of the crystallization. Fig. 3 shows the XRD patterns of the parent glass L1 and the samples heat-treated at various temperatures and time. The parent glass is X-ray amorphous and shows a broad diffraction halos centered at 25.7. Two diffraction peaks at about 26.2 and 66.3 appear after heat treatment at 770 C (24 K above Tg) for 4 h, giving a hint at the existence of some Al2TiO5 crystals. While increasing the crystallization time to 16 h, the two peaks are slightly shifted to lower 2q angles of 25.9 and 65.9 , which indicates the formation of
MAT as a result of the incorporation of MgTi2O5 into Al2TiO5. At the same time, the intensities of these two peaks increase and hence the concentration of the MAT crystal phase. No significant changes are observed in the sample after heat treatment at 790 C for 16 h or 810 C for 4 h. Peaks attributable to perrierite are detected in the sample after heat treated at 810 C for 16 h. Furthermore, the XRD pattern exhibits more peaks attributed to MAT. Nevertheless, peaks attributed to perrierite are not found in the XRD-patterns after heat treatment at 850 C for 4 h. For a crystallization temperature at 950 C, distinct peaks due to MAT and perrierite are observed while the formation of spinel is also detected. Fig. 4 shows XRD patterns of the parent glass L4 and samples heat-treated at various temperatures between 770 and 900 C. The parent glass is also X-ray amorphous. But for the sample after heat treatment at 770 C, a well resolved diffraction peak is not detected after a crystallization time of 4 h and only a weak diffraction peak at about 66.3 is detected after a longer crystallization time of 16 h. The intensity of the peak increases after heat treatment at higher temperatures up to 790 and 810 C for 16 h. Additionally, a broad peak at about 42 is detected. However, the intensity of the diffraction peak at 66.3 for the sample heat-treated at 810 C for 4 h is still comparatively low while a peak at 42 is not observed. These results show that the effect of the longer crystallization time is more pronounced than that of a higher crystallization temperature, if the latter is 810 C. The softening temperature (Td) for L4 is 815 C as shown in Fig. 1. When the temperature is below Td, the viscosity of the glass is large and the crystal growth velocity comparatively small due to small diffusion coefficients. To achieve a high degree volume concentration of crystals, a longer crystallization time is needed. By contrast, significant changes are observed if the crystallization temperature is further increased to temperatures T 850 C. The peak at about 30.2 , which is attributed to perrierite, is first observed after thermal treatment at 850 C; its intensity obviously increases if the temperature is further increased to 900 C. Moreover, the XRD pattern of the sample heat-treated at 900 C exhibits further peaks attributed to perrierite. Fig. 5 shows TEM micrographs of the sample L1 after heattreatment at 770 C for 16 h and the corresponding selected area electron diffraction (SAED) patterns. There is a large number of
Fig. 5. (a) TEM micrographs of the glass L1 after heat-treatment at 770 C for 16 h; (bec) the SAED patterns of an area with 2.6 mm and 500 nm in diameter, respectively.
H.-J. Wang et al. / Solid State Sciences 70 (2017) 6e12 Table 1 The measured dhkl values in Fig. 5 and the theoretical dhkl values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Al2TiO5
Table 2 The measured dhkl values in Fig. 6 and the theoretical dhkl values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Perrierite
9
Al2TiO5
Perrierite
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
3.36 2.09 1.8 1.39
101 420 002 242
100 10.37 26.22 3.85
3.356 2.117 1.796 1.377
31e2 420 22e5 82e5
11.07 4.11 8.1 2.8
3.36 2.088 1.793 1.39
4.58 3.34 2.67 2.39 2.09 1.92 1.81 1.49 1.38
200 101 230 301 420 430 002 232 242
49.27 100 58.02 5.11 10.37 21.31 26.22 9.78 3.85
4.715 3.356 2.654 2.365 2.117 1.9 1.796 1.487 1.377
111 31e2 004 221 420 223 22e5 514 82e5
3.75 11.07 34.88 4.16 4.11 9.87 8.1 0.43 2.8
4.35 3.36 2.676 2.404 2.088 1.936 1.793 1.489 1.39
small dark particles about 10 nm in size embedded in a brighter matrix in the parent glass (Fig. 5a). Diffraction spots and rings could be observed in the SAED patterns proving the poly-crystallinity of the sample. The measured dhkl values from the SAED patterns are 3.36, 2.09, 1.92, 1.8 and 1.39 Å as listed in Table 1. The measured dhkl values fit better to the theoretical values of Al2TiO5 (ICSD 002759) than to that of perrierite (ICSD 043798), which is in agreement with the XRD results (Fig. 3). Since Al2TiO5 and MAT are hard to distinguish by electron diffraction due to the same space group Cmcm, Al2TiO5 is chosen as a typical example for the following structure analysis. It is worth emphasizing that the d101 value in the SAED pattern could be found while the 100% diffraction peak for (101) plane at about 26 for MAT in the XRD pattern is also observed. Besides, the peaks corresponding to MAT show up earlier in the XRD patterns than those of perrierite (Fig. 3). Thus, MAT is the most probable initial phase in sample L1. Fig. 6 shows TEM micrographs of the sample L1 after heattreatment at 810 C for 16 h and the corresponding SAED
patterns. The structure is similar to that in Fig. 5a, however, the average size of small dark particles increases to about 15 nm. More diffraction rings were observed in the SAED pattern, which is readily explained by the increased crystal size. Furthermore, the lattice fringes of a nanocrystal could be observed (Fig. 6ced). The dhkl values calculated from the SAED patterns are 4.58, 3.34, 2.67, 2.39, 2.09, 1.92, 1.81, 1.49 and 1.38 Å as listed in Table 2. The measured dhkl could fit to both MAT (Al2TiO5) and perrierite, which is in good agreement with the XRD results in Fig. 3. Fig. 7 shows the TEM micrographs of the parent glass L4 after heat treatment at 770 C for 16 h and the corresponding SAED patterns. The structure is also similar to that in Figs. 5a and 6a with the dark particles with a size of about 15 nm embedded in the brighter matrix. These nanoparticles might show a preferred
Fig. 6. (a, c) TEM micrographs of the glass L1 after heat-treatment at 810 C for 16 h; (b) the SAED patterns and (d) a magnification of the selected area in the TEM micrograph are also shown.
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Fig. 7. (a) TEM micrographs of the glass L4 after heat treatment at 770 C for 16 h; (b) attributed SAED patterns.
Table 3 The measured dhkl values in Fig. 7 and the theoretical dhkl values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Al2TiO5
Perrierite
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
2.12 1.4
321 630
1.78 0.94
2.123 1.412
313 040
7.71 12.33
2.124 1.405
orientation or texture as indicated by only 2 strong rings in the SAED pattern. The dhkl values calculated from the SAED patterns are 2.12 and 1.4 Å as listed in Table 3. Although no specific phase could be confirmed based on the only two peaks observed in the XRD patterns (Fig. 4), the measured dhkl values better fit to perrierite in comparison to Al2TiO5. Fig. 8 shows the TEM micrographs of the parent glass L4 after heat treatment at 810 C for 16 h and the corresponding SAED patterns. There are many dendrite-like, dark appearing structures that are not single crystalline but are composed of crystals with
Fig. 8. Top: TEM micrographs of the glass L4 after heat treatment at 810 C for 16 h; Bottom: attributed SAED patterns of an area with 2.6 mm and 500 nm in diameter, respectively.
H.-J. Wang et al. / Solid State Sciences 70 (2017) 6e12
different orientations. The size of the dendrite-like structure is about 200 nm while the smaller, single crystalline particles are about 20 nm in size. The brighter matrix in the parent glass (Fig. 8b) is not uniform but shows a substructure with a large number of light droplets that are supposed to be enriched in Si. Diffraction rings of the dendrite-like structure were analyzed. The dhkl values calculated from the SAED patterns are 2.13, 1.4, 1.17, 1.13 and 0.88 Å as listed in Table 4. Similar to that in Table 3, the measured dhkl values better fit to perrierite than Al2TiO5. In addition, more peaks that could be assigned to perrierite appear after heat treatment at higher temperatures in the XRD patterns (see Fig. 4). Hence, the initial phase in sample L4 is most likely to be perrierite. The cationic field strength can be calculated from Z/a2 (Z is the valence and a is the metal-oxygen bond length) [20]. According to the relation between the field strength and the roles in glass structure, La3þ, for which the field strength is 0.43 [21], is assigned as a network modifier. The role of La3þ as network modifier has been well established both by experiment and simulations [22,23]. According to the literature [22], a silicate glass network contains more non-bridging oxygen (NBO) if the La2O3 concentration is increased. Besides, it is well known that high-field strength rareearth (RE) ions with high coordination numbers tend to cluster in silicate glasses regardless of their concentration [23]. Evidence for La clustering was found to occur over a range from 1 to 10 mol% La2O3 [23,24]. In lanthanum containing glasses, La3þ ions either bond to SiO4 tetrahedra forming Si-O-La bonds or, however, they link with other La-O bonds forming La-O-La units, which were reported to be energetically favorable in Refs. [22,25,26]. Thus, the change in Tg with the La2O3 concentration is a comprehensive result from the network-modifying effect and clustering of La3þ ions in the glass structure. The decrease in Tg from L1 to L2 might be related to the decrease of the network connectivity. Nevertheless, the further increase in the La2O3 concentration from L2 to L4 increases the glass transition temperature Tg since the effect of the La clustering is more prominent than that of the increasing number of NBO. As a result from clustering, above a certain threshold, a higher La2O3 concentration results in a more rigid glass, which is in agreement with existing literature [27,28]. La ions tend to cluster, forming La-O-La linkages, which results in oxygen atoms that are no longer linked to the silica network [23]. In other words, clustering of the La cations would lead to a structure in which aggregates are inhomogeneously dispersed throughout the glass. These clustering should not be an effect of percolation, but should be a thermodynamically preferred state. The small, isolated, La-containing, phase-ordered domains may act as nucleation sites favoring the devitrification of glass. With increasing La2O3 concentration in the parent glass, the number of the domains would increase, thus promoting the precipitation of perrierite and the first phase that can be detected in the XRD changed from MAT to perrierite. The dendrite-like structure, which is formed in dependence of heat treatment temperature and the La2O3 concentration, may also relate to the formation of the La-containing domains.
Table 4 The measured dhkl values in Fig. 8 and the dhkl theoretical values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Al2TiO5
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
2.13 1.4 1.17 1.13 0.88
321 630 810 181 723
1.78 0.94 0.06 0.12 0.48
2.123 1.412 1.17 1.134 0.879
313 040 42e9 715 827
7.71 12.33 1.48 1.41 0.2
2.124 1.405 1.177 1.137 0.877
Perrierite
11
4. Conclusions In glasses with the molar compositions 1.0MgO-1.2Al2O32.8SiO2-1.2TiO2-xLa2O3 (x ¼ 0.1, 0.2, 0.3, 0.4), the addition of La2O3 produces more non-bridging oxygens, which break the connectivity of the glass network and soften the structure of glass at first. However, with the further increasing concentration of La2O3, clustering of the La cations leads to a more rigid structure. Thus, the transition temperature of the glass (Tg) decreases at first and then increases again with increasing La2O3 concentration. Furthermore, small, La-containing, phase-ordered domains in the glass might form and act as nucleation sites. Thus, higher La2O3 concentration would promote the precipitation of perrierite that is the only La2O3-containing crystalline phase in the glass-ceramic. Then, the change of the initial phase that could be detected by XRD from MAT to perrierite is closely related with the effect of La2O3 on the structural rearrangement in glass during heat treatment due to its high field-strength and strong gathering effect. References [1] S.H. Wang, H.P. Zhou, L.H. Luo, Sintering and crystallization of cordierite glass ceramics for high frequency multilayer chip inductors, Mater. Res. Bull. 38 (8) (2003) 1367e1374. [2] H. Ohsato, J.-S. Kim, A.-Y. Kim, C. Cheon II, Ki-Woong Chae, Millimeter-wave dielectric properties of cordierite/indialite glass ceramics, Jpn. J. Appl. Phys. 50 (9) (2011), 09NF01-1-09NF01-5. [3] Z. Li, J. Wu, L. Song, Y. Huang, Effect of composition on sinter-crystallization and properties of low temperature co-fired a-cordierite glass-ceramics, J. Eur. Ceram. Soc. 34 (2014) 3981e3991. [4] B.K. Choi, E.S. Kim, Microwave dielectric properties of cordierite-diopside glass-ceramics, J. Electroceramics 33 (1e2) (2014) 89e95. [5] Y. Hu, H.-T. Tsai, Compositional effect on the crystallization of the cordieritetype glasses, J. Mater. Sci. 36 (1) (2001) 123e129. [6] J. Banjuraizah, H. Mohamad, Z.A. Ahmad, Effect of excess MgO mole ratio in a stoichiometric cordierite (2MgO$2Al2O3$5SiO2) composition on the phase transformation and crystallization behavior of magnesium aluminum silicate phases, Int. J. Appl. Ceram. Technol. 8 (3) (2011) 637e645. [7] S.-P. Hwang, J.-M. Wu, Effect of composition on microstructural development in MgO-Al2O3-SiO2 glass-ceramics, J. Am. Ceram. Soc. 84 (5) (2001) 1108e1112. €che, C. Rüssel, J. Dieter Schnapp, Microstructure-property [8] P. Wange, T. Ho relationship in high-strength MgO-Al2O3-SiO2-TiO2 glass-ceramics, J. NonCrystalline Solids 298 (2e3) (2002) 137e145. € land, C. Rüssel, Effect of the ZrO2 [9] S. Seidel, M. Dittmer, W. Wisniewski, W. Ho concentration on the crystallization behavior and the mechanical properties of high-strength MgO-Al2O3-SiO2 glasseceramics, J. Mater. Sci. 52 (2016) 1955e1968. [10] S. Mei, J. Yang, J.M.F. Ferreira, Microstructural evolution in sol-gel derived P2O5-doped cordierite powders, J. Eur. Ceram. Soc. 20 (12) (2000) 2191e2197. [11] J.-M. Wu, S.-P. Hwang, Effects of (B2O3, P2O5) additives on microstructural development and phase-transformation kinetics of stoichiometric cordierite glasses, J. Am. Ceram. Soc. 83 (5) (2000) 1259e1265. [12] S.-B. Sohn, S.-Y. Choi, Crystallization behavior in the glass system MgO-Al2O3SiO2: influence of CeO2 addition, J. Non-Crystalline Solids 282 (2e3) (2001) 221e227. [13] O.S. Dymshits, A.A. Zhilin, V.I. Petrov, M.Ya Tsenter, T.I. Chuvaevav, et al., A Raman spectroscopic study of phase transformations in titanium-containing magnesium aluminosilicate glasses, Glass Phys. Chem. 28 (2) (2002) 66e78. [14] V.V. Golubkov, O.S. Dymshits, A.A. Zhilin, T.I. Chuvaeva, A.V. Shashkin, On the phase separation and crystallization of glasses in the MgO-Al2O3-SiO2-TiO2 system, Glass Phys. Chem. 29 (3) (2003) 254e266. [15] I.P. Alekseeva, O.S. Dymshits, A.A. Zhilin, M.D. Mikhailov, A.A. Khubetsov, Phase transformations in glass of the MgO-Al2O3-SiO2-TiO2 system doped with yttrium oxide, Glass Phys. Chem. 41 (6) (2015) 597e606. [16] H.-J. Wang, B.-T. Li, H.-X. Lin, W. Chen, L. Luo, Effects of MgO on crystallization and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramics, Int. J. Appl. Glass Sci. 5 (4) (2014) 436e442. [17] H.-J. Wang, B.-T. Li, H.-X. Lin, W. Chen, L. Luo, Effects of La2O3 on crystallization, microstructure, and properties of MgO-Al2O3-SiO2-TiO2-La2O3 glassceramics, Int. J. Appl. Glass Sci. 7 (1) (2016) 80e87. [18] H.-J. Wang, B.-T. Li, H.-X. Lin, L. Luo, Phase separation, crystallization, and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramic, Int. J. Appl. Glass Sci. 7 (3) (2016) 328e336. [19] I. Jon, A study of chevkinite and perrierite, Am. Mineral. 52 (7e8) (1967) 1094e1104. €rken und ihre Beziehungen zu Entgla[20] A. Dietzel, Die Kationenfeldsta €ngen, zur Verbindungsbildung und zu den Schmelzpunkten von sungsvorga
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Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
The effects of La2O3 on the early stages of crystallization for MgOAl2O3-SiO2-TiO2-La2O3 glass-ceramics Hui-Juan Wang a, b, c, *, Christian Bocker c, Bo-Tao Li a, Hui-Xing Lin a, Christian Rüssel c, Lan Luo a a b c
Key Laboratory of Inorganic Functional Material and Device, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China University of Chinese Academy of Sciences, Beijing 100049, China Otto-Schott-Institut, Jena University, 07743 Jena, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 February 2017 Received in revised form 21 May 2017 Accepted 25 May 2017 Available online 26 May 2017
The early stages of crystallization for MgO-Al2O3-SiO2-TiO2-La2O3 glasses with different La2O3 concentrations were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The glass transition temperature (Tg) of the glass decreases at first and then increases again with increasing La2O3 concentration. This indicates that the structure of the glass becomes weaker at first and then stronger again. Lanthanum acts in glasses as network modifier and will usually decrease the network connectivity of the glass structure. Nevertheless, if the La2O3 concentration is high enough, the oxygen and other ions start to agglomerate around La, resulting in a more closely packed structure. Heat-treatment of the sample with x ¼ 0.1 at 770e810 C results in the precipitation of a droplet phase with higher mean atomic weight embedded in a matrix with lower mean atomic weight. The initial crystalline phase magnesium aluminum titanate (MAT) precipitates from the droplet phase. Nevertheless, for the sample with x ¼ 0.4, dendrite-like structure could be observed after heat-treatment of the glass at 810 C. Furthermore, the crystalline phase first precipitated is the lanthanum containing perrierite, which could be attributed to the rearrangement of the glass structure as an effect of La3þ incorporation. © 2017 Elsevier Masson SAS. All rights reserved.
Keywords: Glass-ceramic Crystallization La2O3
1. Introduction Cordierite (Mg2Al4Si5O18) based glass-ceramics have received considerable attention in the area of millimeter-wave dielectrics, dentistry and microelectronics due to their excellent properties such as low dielectric loss, low coefficient of thermal expansion as well as high mechanical strength [1e4]. The phase transformation of the glass-ceramics, which deviate from those of a stoichiometric cordierite compound, are greatly dependent on the compositions of the starting glasses. A glass with excesses both of SiO2 and Al2O3 has a higher activation energy for crystallization [5]. Compositions richer in MgO or (MgO,SiO2) than the stoichiometric cordierite compound suppress the formation of m-cordierite [6,7]. The addition of TiO2 [8], ZrO2 [9], P2O5 [10], B2O3 [11] or CeO2 [12] also has significant effects on the nucleation and crystallization process of
* Corresponding author. Key Laboratory of Inorganic Functional Material and Device, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China. E-mail address: [email protected] (H.-J. Wang). http://dx.doi.org/10.1016/j.solidstatesciences.2017.05.012 1293-2558/© 2017 Elsevier Masson SAS. All rights reserved.
the glass. For example, three-phase immiscibility was detected in the MgO-Al2O3-SiO2-TiO2 system on the basis of Raman scattering, small-angle X-ray scattering (SAXS), and X-ray powder diffraction (XRD) data [13,14]. In many cases, three phases emerge after the process of glass liquid phase separation: magnesium aluminum titanate, magnesium-aluminate containing a small amount of SiO2, and the residual glassy phase enriched in silica [15]. The crystallization proceeding in these regions leads to the precipitation of nanocrystals of two phases, namely, x(MgO$2TiO2)$y(Al2O3$TiO2) solid solution in a magnesium/aluminum/titanate-rich regions as well as spinel (MgAl2O4) in magnesium/aluminate-rich regions. In our previous studies, glass-ceramics from the MgO-Al2O3SiO2-TiO2-La2O3 (MASTL) system with excellent microwave dielectric properties have been reported [16e18]. In the studies concerning the compositions 1MgO$1.2Al2O3$2.8SiO2$1.2TiO2$xLa2O3 (x ¼ 0.1, 0.2, 0.3, 0.4 in molar ratio), the La2O3 concentration proves to have a significant effect on the crystallization behavior and the dielectric properties [17]. However, no further analysis was conducted on the initial stage of the crystallization as a function of La2O3 concentration, which is an
H.-J. Wang et al. / Solid State Sciences 70 (2017) 6e12
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important part of the crystallization mechanism. In this paper, a special focus is laid on the first stage of the crystallization process for MASTL glasses with different La2O3 concentrations by X-ray diffraction (XRD) studies in combination with the transmission electron microscopy (TEM). 2. Experimental procedure Glasses with the compositions 1MgO$1.2Al2O3$2.8SiO2$1.2TiO2$xLa2O3 (x ¼ 0.1, 0.2, 0.3 and 0.4) in molar ratio were prepared as already described in Ref. [17] and denoted as L1, L2, L3 and L4. The samples were crystallized by a one-step heattreatment at temperatures between 770 and 950 C and kept for 2e16 h. For all the samples, a heating rate of 5 K min1 was used. Dilatometric measurements (NETZSCH DIL 402 C) were performed at glass samples, which were shaped into rectangular bars of about 5 5 25 mm3. The used heating rate was also 5 K min1. From crystallized and powdered samples, X-ray diffraction (XRD) patterns were recorded using CuKa radiation in a 2q-range between 10 and 70 (Rigaku Miniflex 300, Rigaku, Tokyo, Japan). The microstructure and selected area electron diffraction (SAED) of the thin sections produced from both the parent glass and the samples heated at 770e810 C from samples, heat-treated at 770e810 C were detected using Hitachi-H8100 TEM. The sample preparation was done as follows: first, the samples were mechanically thinned to make slices 100e200 mm thick and then disks with a diameter of 3 mm were cut from the slices. The central region of the disk was dimpled to a residual thickness of 10e15 mm. Then, double-sided ion-beam etching with Arþ-ions under a small angle incidence (±5 ) and low ion beam energy (3 kV, 1.5 mA) was applied until the samples became electron transparent (Baltec RES010). As the samples are non-conductive, carbon coating was carried out using Edwards AUTO 306 at 103 Pa. TEM was done at 200 kV and some samples proved to react very sensitively to the electron beam in terms of both contamination and degradation. The measured dhkl values for the crystalline phases were calculated based on the SAED patterns and camera length. The theoretical dhkl values and relative intensities (I/Imax) were calculated according to the crystal structures of the Al2TiO5 (ICSD 002759) and perrierite (ICSD 043798) for the electron diffraction using the software Materials Studio. The relative intensities for Al2TiO5 and perrierite were obtained when dhkl changes from 4.818 to 0.532 Å and 5.62 to 0.532 Å respectively.
Fig. 1. Dilatometric curves of the glass samples L1-L4.
Fig. 2. XRD patterns of samples L1-L4 heat-treated at 850 C for 2 h.
3. Results and discussions Fig. 1 shows the dilatometric curves of the glass samples L1, L2, L3 and L4. With increasing La2O3 concentration, the glass transition temperature (Tg) as determined by the tangents (see Fig. 1) shifts to lower temperature from 746 to 739 C, then rises again from 739 to 752 and finally to 756 C. The lowest value is reached for sample L2. The temperature attributed to the maximum value in the dilatometric curve (marked by the arrows in Fig. 1) is the dilatometric softening temperature Td. Similar to Tg, Td also decreases at first and then increases with increasing La2O3 concentration. During heat treatment of the glasses, the appearances of the glass-ceramics change from translucent to opaque. Fig. 2 shows the XRD patterns of samples L1-L4 heat-treated at 850 C for 2 h. The peaks in the XRD patterns for sample L1 and L2 after heat treatment at 850 C could be assigned to magnesium aluminum titanate (MAT, MgxAl2(1x)Ti(1þx)O5). MAT (space group Cmcm) is orthorhomic and a solid solution of Al2TiO5 and MgTi2O5. However, if the La2O3 concentration is further increased, i.e. for samples L3 and L4, monoclinic perrierite appears instead of MAT. The idealized structural formula of perrierite is speculated to be
Fig. 3. XRD patterns of the parent glass L1 and the samples heat-treated at various temperatures between 770 and 950 C for different periods of time.
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Fig. 4. XRD patterns of the parent glass L4 and the samples heat-treated at various temperatures between 770 and 900 C for different periods of time.
[A3þ4B2þC3þ2Ti4þ2O8(Si2O7)2] (with A ¼ rare-earths from La to Sm; B¼Fe, Co, Ni, Mg; and C¼Al, Fe3þ, Ga or (Me2þTi4þ)) [19] and the chemical formula of the perrierite in this research is close to La4MgAl2Ti2Si4O22. As shown in Fig. 2, the crystalline phases detected in glassceramic L1 and L2, L3 and L4 are similar to each other. Thus, two typical compositions 1MgO$1.2Al2O3$2.8SiO2$1.2TiO2$xLa2O3 (x ¼ 0.1, 0.4) in molar ratio are chosen for the further studies to clarify the effects of La2O3 on the first stage of the crystallization. Fig. 3 shows the XRD patterns of the parent glass L1 and the samples heat-treated at various temperatures and time. The parent glass is X-ray amorphous and shows a broad diffraction halos centered at 25.7. Two diffraction peaks at about 26.2 and 66.3 appear after heat treatment at 770 C (24 K above Tg) for 4 h, giving a hint at the existence of some Al2TiO5 crystals. While increasing the crystallization time to 16 h, the two peaks are slightly shifted to lower 2q angles of 25.9 and 65.9 , which indicates the formation of
MAT as a result of the incorporation of MgTi2O5 into Al2TiO5. At the same time, the intensities of these two peaks increase and hence the concentration of the MAT crystal phase. No significant changes are observed in the sample after heat treatment at 790 C for 16 h or 810 C for 4 h. Peaks attributable to perrierite are detected in the sample after heat treated at 810 C for 16 h. Furthermore, the XRD pattern exhibits more peaks attributed to MAT. Nevertheless, peaks attributed to perrierite are not found in the XRD-patterns after heat treatment at 850 C for 4 h. For a crystallization temperature at 950 C, distinct peaks due to MAT and perrierite are observed while the formation of spinel is also detected. Fig. 4 shows XRD patterns of the parent glass L4 and samples heat-treated at various temperatures between 770 and 900 C. The parent glass is also X-ray amorphous. But for the sample after heat treatment at 770 C, a well resolved diffraction peak is not detected after a crystallization time of 4 h and only a weak diffraction peak at about 66.3 is detected after a longer crystallization time of 16 h. The intensity of the peak increases after heat treatment at higher temperatures up to 790 and 810 C for 16 h. Additionally, a broad peak at about 42 is detected. However, the intensity of the diffraction peak at 66.3 for the sample heat-treated at 810 C for 4 h is still comparatively low while a peak at 42 is not observed. These results show that the effect of the longer crystallization time is more pronounced than that of a higher crystallization temperature, if the latter is 810 C. The softening temperature (Td) for L4 is 815 C as shown in Fig. 1. When the temperature is below Td, the viscosity of the glass is large and the crystal growth velocity comparatively small due to small diffusion coefficients. To achieve a high degree volume concentration of crystals, a longer crystallization time is needed. By contrast, significant changes are observed if the crystallization temperature is further increased to temperatures T 850 C. The peak at about 30.2 , which is attributed to perrierite, is first observed after thermal treatment at 850 C; its intensity obviously increases if the temperature is further increased to 900 C. Moreover, the XRD pattern of the sample heat-treated at 900 C exhibits further peaks attributed to perrierite. Fig. 5 shows TEM micrographs of the sample L1 after heattreatment at 770 C for 16 h and the corresponding selected area electron diffraction (SAED) patterns. There is a large number of
Fig. 5. (a) TEM micrographs of the glass L1 after heat-treatment at 770 C for 16 h; (bec) the SAED patterns of an area with 2.6 mm and 500 nm in diameter, respectively.
H.-J. Wang et al. / Solid State Sciences 70 (2017) 6e12 Table 1 The measured dhkl values in Fig. 5 and the theoretical dhkl values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Al2TiO5
Table 2 The measured dhkl values in Fig. 6 and the theoretical dhkl values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Perrierite
9
Al2TiO5
Perrierite
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
3.36 2.09 1.8 1.39
101 420 002 242
100 10.37 26.22 3.85
3.356 2.117 1.796 1.377
31e2 420 22e5 82e5
11.07 4.11 8.1 2.8
3.36 2.088 1.793 1.39
4.58 3.34 2.67 2.39 2.09 1.92 1.81 1.49 1.38
200 101 230 301 420 430 002 232 242
49.27 100 58.02 5.11 10.37 21.31 26.22 9.78 3.85
4.715 3.356 2.654 2.365 2.117 1.9 1.796 1.487 1.377
111 31e2 004 221 420 223 22e5 514 82e5
3.75 11.07 34.88 4.16 4.11 9.87 8.1 0.43 2.8
4.35 3.36 2.676 2.404 2.088 1.936 1.793 1.489 1.39
small dark particles about 10 nm in size embedded in a brighter matrix in the parent glass (Fig. 5a). Diffraction spots and rings could be observed in the SAED patterns proving the poly-crystallinity of the sample. The measured dhkl values from the SAED patterns are 3.36, 2.09, 1.92, 1.8 and 1.39 Å as listed in Table 1. The measured dhkl values fit better to the theoretical values of Al2TiO5 (ICSD 002759) than to that of perrierite (ICSD 043798), which is in agreement with the XRD results (Fig. 3). Since Al2TiO5 and MAT are hard to distinguish by electron diffraction due to the same space group Cmcm, Al2TiO5 is chosen as a typical example for the following structure analysis. It is worth emphasizing that the d101 value in the SAED pattern could be found while the 100% diffraction peak for (101) plane at about 26 for MAT in the XRD pattern is also observed. Besides, the peaks corresponding to MAT show up earlier in the XRD patterns than those of perrierite (Fig. 3). Thus, MAT is the most probable initial phase in sample L1. Fig. 6 shows TEM micrographs of the sample L1 after heattreatment at 810 C for 16 h and the corresponding SAED
patterns. The structure is similar to that in Fig. 5a, however, the average size of small dark particles increases to about 15 nm. More diffraction rings were observed in the SAED pattern, which is readily explained by the increased crystal size. Furthermore, the lattice fringes of a nanocrystal could be observed (Fig. 6ced). The dhkl values calculated from the SAED patterns are 4.58, 3.34, 2.67, 2.39, 2.09, 1.92, 1.81, 1.49 and 1.38 Å as listed in Table 2. The measured dhkl could fit to both MAT (Al2TiO5) and perrierite, which is in good agreement with the XRD results in Fig. 3. Fig. 7 shows the TEM micrographs of the parent glass L4 after heat treatment at 770 C for 16 h and the corresponding SAED patterns. The structure is also similar to that in Figs. 5a and 6a with the dark particles with a size of about 15 nm embedded in the brighter matrix. These nanoparticles might show a preferred
Fig. 6. (a, c) TEM micrographs of the glass L1 after heat-treatment at 810 C for 16 h; (b) the SAED patterns and (d) a magnification of the selected area in the TEM micrograph are also shown.
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Fig. 7. (a) TEM micrographs of the glass L4 after heat treatment at 770 C for 16 h; (b) attributed SAED patterns.
Table 3 The measured dhkl values in Fig. 7 and the theoretical dhkl values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Al2TiO5
Perrierite
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
2.12 1.4
321 630
1.78 0.94
2.123 1.412
313 040
7.71 12.33
2.124 1.405
orientation or texture as indicated by only 2 strong rings in the SAED pattern. The dhkl values calculated from the SAED patterns are 2.12 and 1.4 Å as listed in Table 3. Although no specific phase could be confirmed based on the only two peaks observed in the XRD patterns (Fig. 4), the measured dhkl values better fit to perrierite in comparison to Al2TiO5. Fig. 8 shows the TEM micrographs of the parent glass L4 after heat treatment at 810 C for 16 h and the corresponding SAED patterns. There are many dendrite-like, dark appearing structures that are not single crystalline but are composed of crystals with
Fig. 8. Top: TEM micrographs of the glass L4 after heat treatment at 810 C for 16 h; Bottom: attributed SAED patterns of an area with 2.6 mm and 500 nm in diameter, respectively.
H.-J. Wang et al. / Solid State Sciences 70 (2017) 6e12
different orientations. The size of the dendrite-like structure is about 200 nm while the smaller, single crystalline particles are about 20 nm in size. The brighter matrix in the parent glass (Fig. 8b) is not uniform but shows a substructure with a large number of light droplets that are supposed to be enriched in Si. Diffraction rings of the dendrite-like structure were analyzed. The dhkl values calculated from the SAED patterns are 2.13, 1.4, 1.17, 1.13 and 0.88 Å as listed in Table 4. Similar to that in Table 3, the measured dhkl values better fit to perrierite than Al2TiO5. In addition, more peaks that could be assigned to perrierite appear after heat treatment at higher temperatures in the XRD patterns (see Fig. 4). Hence, the initial phase in sample L4 is most likely to be perrierite. The cationic field strength can be calculated from Z/a2 (Z is the valence and a is the metal-oxygen bond length) [20]. According to the relation between the field strength and the roles in glass structure, La3þ, for which the field strength is 0.43 [21], is assigned as a network modifier. The role of La3þ as network modifier has been well established both by experiment and simulations [22,23]. According to the literature [22], a silicate glass network contains more non-bridging oxygen (NBO) if the La2O3 concentration is increased. Besides, it is well known that high-field strength rareearth (RE) ions with high coordination numbers tend to cluster in silicate glasses regardless of their concentration [23]. Evidence for La clustering was found to occur over a range from 1 to 10 mol% La2O3 [23,24]. In lanthanum containing glasses, La3þ ions either bond to SiO4 tetrahedra forming Si-O-La bonds or, however, they link with other La-O bonds forming La-O-La units, which were reported to be energetically favorable in Refs. [22,25,26]. Thus, the change in Tg with the La2O3 concentration is a comprehensive result from the network-modifying effect and clustering of La3þ ions in the glass structure. The decrease in Tg from L1 to L2 might be related to the decrease of the network connectivity. Nevertheless, the further increase in the La2O3 concentration from L2 to L4 increases the glass transition temperature Tg since the effect of the La clustering is more prominent than that of the increasing number of NBO. As a result from clustering, above a certain threshold, a higher La2O3 concentration results in a more rigid glass, which is in agreement with existing literature [27,28]. La ions tend to cluster, forming La-O-La linkages, which results in oxygen atoms that are no longer linked to the silica network [23]. In other words, clustering of the La cations would lead to a structure in which aggregates are inhomogeneously dispersed throughout the glass. These clustering should not be an effect of percolation, but should be a thermodynamically preferred state. The small, isolated, La-containing, phase-ordered domains may act as nucleation sites favoring the devitrification of glass. With increasing La2O3 concentration in the parent glass, the number of the domains would increase, thus promoting the precipitation of perrierite and the first phase that can be detected in the XRD changed from MAT to perrierite. The dendrite-like structure, which is formed in dependence of heat treatment temperature and the La2O3 concentration, may also relate to the formation of the La-containing domains.
Table 4 The measured dhkl values in Fig. 8 and the dhkl theoretical values with the corresponding relative intensities (I/Imax) of Al2TiO5 and perrierite for the electron diffraction. Measured dhkl (±0.04 Å)
Al2TiO5
in Å
hkl
I/Imax
dhkl in Å
hkl
I/Imax
dhkl in Å
2.13 1.4 1.17 1.13 0.88
321 630 810 181 723
1.78 0.94 0.06 0.12 0.48
2.123 1.412 1.17 1.134 0.879
313 040 42e9 715 827
7.71 12.33 1.48 1.41 0.2
2.124 1.405 1.177 1.137 0.877
Perrierite
11
4. Conclusions In glasses with the molar compositions 1.0MgO-1.2Al2O32.8SiO2-1.2TiO2-xLa2O3 (x ¼ 0.1, 0.2, 0.3, 0.4), the addition of La2O3 produces more non-bridging oxygens, which break the connectivity of the glass network and soften the structure of glass at first. However, with the further increasing concentration of La2O3, clustering of the La cations leads to a more rigid structure. Thus, the transition temperature of the glass (Tg) decreases at first and then increases again with increasing La2O3 concentration. Furthermore, small, La-containing, phase-ordered domains in the glass might form and act as nucleation sites. Thus, higher La2O3 concentration would promote the precipitation of perrierite that is the only La2O3-containing crystalline phase in the glass-ceramic. Then, the change of the initial phase that could be detected by XRD from MAT to perrierite is closely related with the effect of La2O3 on the structural rearrangement in glass during heat treatment due to its high field-strength and strong gathering effect. References [1] S.H. Wang, H.P. Zhou, L.H. Luo, Sintering and crystallization of cordierite glass ceramics for high frequency multilayer chip inductors, Mater. Res. Bull. 38 (8) (2003) 1367e1374. [2] H. Ohsato, J.-S. Kim, A.-Y. Kim, C. Cheon II, Ki-Woong Chae, Millimeter-wave dielectric properties of cordierite/indialite glass ceramics, Jpn. J. Appl. Phys. 50 (9) (2011), 09NF01-1-09NF01-5. [3] Z. Li, J. Wu, L. Song, Y. Huang, Effect of composition on sinter-crystallization and properties of low temperature co-fired a-cordierite glass-ceramics, J. Eur. Ceram. Soc. 34 (2014) 3981e3991. [4] B.K. Choi, E.S. Kim, Microwave dielectric properties of cordierite-diopside glass-ceramics, J. Electroceramics 33 (1e2) (2014) 89e95. [5] Y. Hu, H.-T. Tsai, Compositional effect on the crystallization of the cordieritetype glasses, J. Mater. Sci. 36 (1) (2001) 123e129. [6] J. Banjuraizah, H. Mohamad, Z.A. Ahmad, Effect of excess MgO mole ratio in a stoichiometric cordierite (2MgO$2Al2O3$5SiO2) composition on the phase transformation and crystallization behavior of magnesium aluminum silicate phases, Int. J. Appl. Ceram. Technol. 8 (3) (2011) 637e645. [7] S.-P. Hwang, J.-M. Wu, Effect of composition on microstructural development in MgO-Al2O3-SiO2 glass-ceramics, J. Am. Ceram. Soc. 84 (5) (2001) 1108e1112. €che, C. Rüssel, J. Dieter Schnapp, Microstructure-property [8] P. Wange, T. Ho relationship in high-strength MgO-Al2O3-SiO2-TiO2 glass-ceramics, J. NonCrystalline Solids 298 (2e3) (2002) 137e145. € land, C. Rüssel, Effect of the ZrO2 [9] S. Seidel, M. Dittmer, W. Wisniewski, W. Ho concentration on the crystallization behavior and the mechanical properties of high-strength MgO-Al2O3-SiO2 glasseceramics, J. Mater. Sci. 52 (2016) 1955e1968. [10] S. Mei, J. Yang, J.M.F. Ferreira, Microstructural evolution in sol-gel derived P2O5-doped cordierite powders, J. Eur. Ceram. Soc. 20 (12) (2000) 2191e2197. [11] J.-M. Wu, S.-P. Hwang, Effects of (B2O3, P2O5) additives on microstructural development and phase-transformation kinetics of stoichiometric cordierite glasses, J. Am. Ceram. Soc. 83 (5) (2000) 1259e1265. [12] S.-B. Sohn, S.-Y. Choi, Crystallization behavior in the glass system MgO-Al2O3SiO2: influence of CeO2 addition, J. Non-Crystalline Solids 282 (2e3) (2001) 221e227. [13] O.S. Dymshits, A.A. Zhilin, V.I. Petrov, M.Ya Tsenter, T.I. Chuvaevav, et al., A Raman spectroscopic study of phase transformations in titanium-containing magnesium aluminosilicate glasses, Glass Phys. Chem. 28 (2) (2002) 66e78. [14] V.V. Golubkov, O.S. Dymshits, A.A. Zhilin, T.I. Chuvaeva, A.V. Shashkin, On the phase separation and crystallization of glasses in the MgO-Al2O3-SiO2-TiO2 system, Glass Phys. Chem. 29 (3) (2003) 254e266. [15] I.P. Alekseeva, O.S. Dymshits, A.A. Zhilin, M.D. Mikhailov, A.A. Khubetsov, Phase transformations in glass of the MgO-Al2O3-SiO2-TiO2 system doped with yttrium oxide, Glass Phys. Chem. 41 (6) (2015) 597e606. [16] H.-J. Wang, B.-T. Li, H.-X. Lin, W. Chen, L. Luo, Effects of MgO on crystallization and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramics, Int. J. Appl. Glass Sci. 5 (4) (2014) 436e442. [17] H.-J. Wang, B.-T. Li, H.-X. Lin, W. Chen, L. Luo, Effects of La2O3 on crystallization, microstructure, and properties of MgO-Al2O3-SiO2-TiO2-La2O3 glassceramics, Int. J. Appl. Glass Sci. 7 (1) (2016) 80e87. [18] H.-J. Wang, B.-T. Li, H.-X. Lin, L. Luo, Phase separation, crystallization, and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramic, Int. J. Appl. Glass Sci. 7 (3) (2016) 328e336. [19] I. Jon, A study of chevkinite and perrierite, Am. Mineral. 52 (7e8) (1967) 1094e1104. €rken und ihre Beziehungen zu Entgla[20] A. Dietzel, Die Kationenfeldsta €ngen, zur Verbindungsbildung und zu den Schmelzpunkten von sungsvorga
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