Properties and Structures of Bi 2 O 3 eb 2 O 3 eteo 2 Glass

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1 Available online at SciVerse ScienceDirect J. Mater. Sci. Technol., 2013, 29(3), 209e214 Properties and Structures of Bi 2 O 3 eb 2 O 3 eteo 2 Glass Guoying Zhao 1,2)*, Ying Tian 1,2), Huiyan Fan 3), Junjie Zhang 1), Lili Hu 1) 1) Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai , China 2) Graduate School of Chinese Academy of Sciences, Beijing , China 3) SCHOTT Glass Technologies (Suzhou) Co., Ltd, Suzhou , China [Manuscript received January 12, 2012, in revised form March 23, 2012, Available online 24 December 2012] Glass formation range of Bi 2 O 3 eb 2 O 3 eteo 2 system has been investigated (B 2 O 3 40 mol%). Four glasses with compositions xbi 2 O 3 e30b 2 O 3 e(70ex)teo 2 (x ¼ 40, 50, 60 and 70 mol%) have been prepared by using melt quenching technique. The effect of Bi 2 O 3 content on thermal stability, optical properties and structures of these four Bi 2 O 3 eb 2 O 3 eteo 2 glasses is systematically investigated by inductive coupled plasma emission spectrometer (ICP), differential scanning calorimetry (DSC), Raman spectra and X-ray photoelectron spectroscopy (XPS). It is found that the density, refractive index and optical basicity increase with increasing Bi 2 O 3. The Raman spectra and XPS spectra show that the glass network is mainly constituted by the [BiO 6 ] octahedron, [TeO 4 ] trigonal bipyramidal, [TeO 3 ] trigonal pyramid, [BO 3 ] trigonal pyramid and [BO 4 ] tetrahedron structural units. With increasing Bi 2 O 3, the coordination number around B atom changes from 3 to 4 and [TeO 4 ] units are converted to [TeO 3 ] units. Bi 5þ ions may exist in Bi 2 O 3 eb 2 O 3 eteo 2 (BBT) system and their amount grows with increasing Bi 2 O 3 content. KEY WORDS: Bismuth glass; Glass forming region; Raman and X-ray photoelectron spectroscopy (XPS) spectra 1. Introduction Recently, considerable effort has been contributed to the leadfree bismuth glass which is considered to be a promising candidate for linear and non-linear optics applications, fast ion conducting glass and glass ceramic superconductor material [1e3]. The large polarizability and small field strength of Bi 3þ in oxide glasses make bismuth glasses suitable for optical devices such as ultra fast all-optical switches, optical isolators, optical Kerr shutter (OKS) and environmental guidelines [4]. Furthermore, bismuth glass has a long infrared cut-off wavelength, which makes it an ideal candidate for infrared radiation (IR) optical transmission [5]. TeO 2 is characterized by high refractive index and high optical non-linearity, the low melting temperature and good transmission in the infrared region [6,7]. Thus, it is expected that the introduction of TeO 2 into the bismuth glass matrix can modify the physical properties, such as density, refractive index and optical transmittance. According to the report of Hasegawa [8],theBi 2 O 3 eb 2 O 3 eteo 2 (BBT) glass system showed high transmittance in visible and near- * Corresponding author. Tel.: þ ; Fax: þ ; address: zhaogy135@126.com.cn (G. Zhao) /$ e see front matter Copyright Ó 2013, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved. IR wavelength, high refractive index and optical non-linearity. However, the atomic level structure of bismuth glass and its correlation with macroscopic properties of BBT system are less understood. Moreover, to our knowledge, there are no systematic reports in the literature on structural properties in BBTsystem. Thus, it is prime importance to know the glass network structure and understand how bismuth oxide influences the physical and optical properties of BBT system. The aim of the present work is to study the effect of Bi 2 O 3, B 2 O 3 and TeO 2 on glass formation property and the local structure of Bi 2 O 3 eb 2 O 3 eteo 2 glasses. The physical and optical properties of glasses have been established by the structure features from Raman and X-ray photoelectron spectroscopy (XPS) spectra. In order to get high non-linear refractive index, glass formation region with B 2 O 3 40 mol% was investigated in Bi 2 O 3 eb 2 O 3 eteo 2 system. 2. Experimental All the glasses were prepared by conventional melt quenching method with analytical reagent Bi 2 O 3,H 3 BO 3 and TeO 2 as raw materials. In order to determine the glass forming region, mixed batches of 5 g were melted in alumina crucibles at 1000e1100 C for about 30 min and then poured into preheated stainless-steel molds. Glasses with composition xbi 2 O 3 e30b 2 O 3 e(70ex)teo 2 (x ¼ 40, 50, 60 and 70 mol%) were selected (simply named as BBT1e4) to investigate the structures and properties. 30 g well mixed raw material was melted in alumina crucibles at 1000e1100 C using an electric furnace for 30 min and annealed

2 210 G. Zhao et al.: J. Mater. Sci. Technol., 2013, 29(3), 209e214 around 2.74 wt%. The highest concentration of Bi 2 O 3 is 70 mol% in ternary Bi 2 O 3 eb 2 O 3 eteo 2 system, which is beneficial to high non-linear optical properties Density, refractive index, optical basicity and thermal properties Fig. 1 Glass-forming region of the ternary Bi 2 O 3 eb 2 O 3 eteo 2 system (B 2 O 3 40 mol%). for 2 h near glass transition temperature. All samples were polished to 1.0 mm thickness for optical measurements. The density (r) was measured by the Archimedes method with distilled water as immersion liquid (error limit 2%). The differential scanning calorimetry (DSC) curve was detected from room temperature to 700 C with a NETZSCH STA 409 PC/PG apparatus under Ar atmosphere at a heating rate of 10 K/min. The glass transition temperature (T g ) and crystallization beginning temperature (T x ) were determined from DSC curves (error limits 5 C). The refractive index of glass was measured using Metricon Model 2010/M Prism Coupler (error limits 0.05%). The Raman spectra of the glasses were measured with a Renishaw InVia Raman spectrophotometer in 150e2000 cm 1 spectrum range using the 488 nm excitation line from a spectra physics laser. The XPS measurements were carried out with a Kratos AXIS Ultra DLD electron spectrometer which has Al conical anode for charge control. Non-monochromatic 150 W MgKa X-ray provides the excitation radiation. During experiments the pressure inside the analyzer chamber was about Pa (10 9 torr). The drift of the electron binding energy due to surface charge effect was calibrated by utilizing C1s peak of the contamination of adsorption from air (E b ¼ ev). 3. Results and Discussion 3.1. Glass-forming region The glass forming region of BBT glass is shown in Fig. 1. The graph is plotted in mol%. Only the glass forming property in B 2 O 3 40% region was investigated because the main intent was to get a glass with high content of heavy metal oxide. The glasses formed in ternary BBT system are mainly focused in TeO 2 rich area. It should be noted that the glass-forming region is larger than that of literature [8]. This difference may come from the effect of Al 2 O 3 content which is from alumina crucible. The average Al 2 O 3 content in glass determined by inductive coupled plasma emission spectrometer (ICP) is From the glass formation range, four glasses BBT1e4 with compositions of xbi 2 O 3 e30b 2 O 3 e(70ex)teo 2 (x ¼ 40, 50, 60 and 70 mol%) were chosen for further research. They have constant B 2 O 3 content of 30 mol%. All BBT1e4 glass samples are optically transparent with light yellow color. The measured density in Table 1 ranges from 5.98 to 6.92 g/cm 3 when TeO 2 is replaced by Bi 2 O 3, which is easily understood from the molecular weights of TeO 2 ( g/mol) and Bi 2 O 3 ( g/mol). The molar volume of glass is calculated by the following formula [9] : V m;exp ¼ M=d (1) where M is the average molar weight of the glass composition and d is the glass density. The data obtained for the prepared glass compositions are given in Table 1. It can be observed that the molar volume and density increase with the Bi 2 O 3 content. This is mainly due to the fact that the addition of Bi 2 O 3 produces more structural free volume [10,11]. The refractive indices (at 632.8, 1064 and 1552 nm) listed in Table 1 increase with increasing Bi 2 O 3 content. The BBT system presents very high refractive indices, even at 1552 nm. It is found that the refractive indices of BBT glasses are improved compared to previous reports [8]. The high refractive indices are associated with high concentration of Bi 2 O 3. It is well known that there are important relationships between the refractive index and the cation polarizability, oxide polarizability and density. In this case, the refractive indices increase with increasing Bi 2 O 3 content since the introduction of Bi 2 O 3 increases both oxide polarizability and density although the cation polarizability of Te 4þ is larger than that of Bi 3þ (a Bi ¼ nm 3 and a Te ¼ nm 3 ). The optical basicity (L) of an oxide medium is a numerical expression of the average electron donor capability of the oxide species in glass. According to literature [12], the theoretical optical basicity (L th ) is calculated and given in Table 2. The optical basicity can be calculated from the state of polarization of oxide ions in a glass matrix on the basis of refraction data as well as polarization state of oxide ions in a glass matrix as follows [13] : L ¼ 1:67ð1 1=a O 2 Þ (2) According to Dimitrov and Komatsu theory [14], for the general oxide glasses with formula xa p O q yb r O s (1exey)C m O n, the Table 1 Composition, refractive index, density and molar volume of BBT glasses Sample Bi 2 O 3 /mol% B 2 O 3 /mol% TeO 2 /mol% Refractive index Density /(g/cm 3 ) Molar volume /cm nm 1064 nm 1552 nm BBT BBT BBT BBT

3 G. Zhao et al.: J. Mater. Sci. Technol., 2013, 29(3), 209e Table 2 Electronic polarizability of oxide ion a O 2, optical basicity L and L th of BBT glasses Sample a O 2 /10 3 nm 3 L L th nm 1064 nm 1552 nm nm 1064 nm 1552 nm BBT BBT BBT BBT polarizability of the oxide ion can be calculated by the following equation [13] : a O 2 ðnþ ¼ Vm;exp 2:52 n 2 1 n 2 X a I ðn þ 2 O 2 Þ 1 (3) where V m,exp is the molar volume of a given composition, n is the refractive index, P a I is the total polarizability of the cation given by xpa A þ yra B þ (1exey)ma C (a Bi ¼ nm 3, a B ¼ nm 3, a Te ¼ nm 3 ) [15], and N O 2 is the number of oxygen ions in the chemical formula given by xq þ ys þ (1e xey)m. The calculated polarizability of the oxide ion (a O 2 at 632.8, 1064 and 1552 nm) and optical basicity (L at 632.8, 1064 and 1552 nm and L th ) are shown in Table 2. It can be seen that the values of oxide polarizability, theoretical and the calculated optical basicity based on the refractive index of BBT glasses increase with Bi 2 O 3 content due to the higher polarizability and heavier mass of Bi 3þ ion. In all glasses, the values of oxide polarizability a O 2 are quite high at three wavelengths. It means that the Lewis basicity of oxide ions increases due to the higher effective charge provided by Bi 2 O 3. The results are coincident with those in literature [15]. As can be seen in Fig. 2, the values of three thermal parameters (the glass transition temperature (T g ), the onset crystallization temperature (T x ) and the glass stability (characterize by T x et g )) first decrease and then increase with increasing Bi 2 O 3 in BBT1e4 glasses. It has been reported that T g is related to the density of cross-linking, tightness of the network formers, as well as the coordination number of the network-forming atoms, etc [5]. The change of thermal parameters can be explained by the structural change in ternary Bi 2 O 3 e B 2 O 3 eteo 2 glass system, especially the content of nonbridging oxygen which can be detected by Raman and XPS spectra. It will be discussed in the following section Raman spectra Fig. 3 shows the Raman spectra of BBT1e4 glasses in the range of 100e2000 cm 1 and the inset illustrates the deconvoluted Raman spectra of BBT2 glass. The Raman shift peaks are listed in Table 3. The spectrum is normalized and superimposed. The broad peaks are deconvoluted into seven peaks using Gaussian distribution to distinguish the exact mode of vibrations. The bands are peaked at 138, 188, 370, 560, 665, 702, 740, 930 and 1250 cm 1. The observed first high intense peak at 138 cm 1 and very weak shoulder at 188 cm 1 are due to the fact that Bi 3þ vibrations act as network former in the glasses [16]. The 370 cm 1 band is associated with BieOeBi bridged-anion (BA) bonds in the basal plane with different bond lengths [17], and the band shifts from 372 cm 1 in BBT1 to 321 cm 1 in BBT4 glass. The similar trend has been found in Bi 2 O 3 eb 2 O 3 ega 2 O 3 glass [18]. It may be correlated with the difference in cationic ion field strength f Bi3þ < f Te4þ < f Bi5þ. The covalent property of BieOe(A) bonds is affected by the linked cation. And the covalent degree changes in the order of Bi 3þ eoe(bi 3þ )> Bi 3þ eoe(te 4þ )>Bi 3þ eoe(bi 5þ ). Therefore, the BBT4 sample shows the lowest vibration wavenumber around 370 cm 1. At the same time, the shift of 370 cm 1 band toward lower wavenumber suggests the existence of Bi 5þ in the glasses. Bi 5þ is confirmed to exist in the bismuthate glass by other researchers [18e21]. The 560 cm 1 band is assigned to the vibration of [BO 4 ] tetrahedral [22] and its intensity increases with increasing Bi 2 O 3 content, which indicates an increase in the concentration of [BO 4 ] units and the transformation of [BO 3 ] triangle into Fig. 2 Composition dependence of T g, T x and T x et g of BBT1e4 glasses. Fig. 3 Raman spectra of BBT1e4 glasses. Inset: the deconvoluted Raman spectra of BBT2 glass.

4 212 G. Zhao et al.: J. Mater. Sci. Technol., 2013, 29(3), 209e214 Table 3 Numerical results of Gaussian fitting of Raman spectra Peak wave numbers of deconvoluted bands/cm BBT BBT BBT BBT Vibrational modes Bi 3 ions act as network former in the glasses [19] Stretching BieOeBi vibration of the distorted [BiO 6 ] octahedral units [20] Vibration of [BO 4 ] tetrahedral [22] Stretching vibrations of [TeO 4 ] tbp [23] Bending vibration of BeOeB in [BO 3 ] [25] Stretching vibrations of [TeO 3 ]tp [24] Tetrahedral [BO 4 ] groups [26] Triangular [BO 3 ] units [26] [BO 4 ] tetrahedra. The weak shoulder around 665 cm 1 is ascribed to stretching modes of the [TeO 4 ] trigonal bipyramids (tbp) with two non-equivalent oxygen atoms [23]. This vibration mode intensity is so weak that it is hardly detected in the Raman spectra of BBT3 sample. The band around 740 cm 1 can be ascribed to the stretching modes of the [TeO 3 ] trigonal units (tp) [24]. The intensity of the two bands decreases with reducing TeO 2 content. By comparing the intensity of 665 cm 1 band to 740 cm 1 band of BBT1 to BBT3 samples, it can be concluded that there is a transformation from [TeO 4 ] trigonal bipyramid into [TeO 3 ] trigonal unit. The 702 cm 1 band of the BBT4 sample can be ascribed to BeOeB bridges bending vibration of [BO 3 ] trigonal groups [25]. The 930 cm 1 band of this sample is assigned to isolated orthoborate [BO 4 ] group [22,26]. The band at 1250 cm 1 is due to stretching vibration of the terminal BeO bonds of triangular [BO 3 ] groups for all samples [26]. From the above attribution, it is reasonable to conclude that the conversion from [BO 3 ] triangular units into [BO 4 ] tetrahedral units with an increase of Bi 2 O 3 strengthens the glass network XPS spectra Fig. 4 shows the XPS spectra near the O1s core level region for BBT1e4 samples. The observed binding energy of O1s is around 530 ev, which is consistent with the binding energy of O1s in Bi 2 O 3 eb 2 O 3 system [27]. In BBT1e3 glasses, the binding energy of O1s reduced from to ev with increasing Bi 2 O 3 content, which results from the weaker covalence of BieO bands than that of TeeO bands. But with further increase of Bi 2 O 3 content, the binding energy of O1s in BBT4 glass is much larger than that of others. This may be because the electron density around oxygen atom is averaged by the hybridization of Bi6s and O2p in BBT4 glass. In order to further interpret this variation, the O1s spectra are fitted to decompose the asymmetric peaks by a sum of Gaussian curves by means of least square method. Each spectrum can be deconvoluted into two peaks according to the asymmetry of the shoulders and peaks shown in Fig. 5. The peak positions of O1s(1), O1s(2), Bi4f 7/2, Bi4f 5/2,Te3d 5/2 and Te3d 3/2 are given in Table 4. The low binding energy peak of O1s spectra referred as O1s(2) is attributed to the oxygen atom linked to the cations with low electronegativity (such as BieOeBi) and non-bridging oxygen. And the high binding energy peak of O1s spectra referred as O1s(1) is attributed to the oxygen atom linked to the cations with high electronegativity (such as BeOeB and TeeOeTe) and bridging oxygen [28,29]. In BBT1e 3 samples, it is obvious that the intensity of O1s(2) increases with increasing Bi 2 O 3 and the peak area ratio (R) ofo1s(2) to O1s(1) also increases from 0.31 to 0.61, which is due to the low band energy of BieO to form non-bridging oxygen. The intensity of O1s(2) decreases dramatically and the R value decreases from 0.61 to 0.20 with the further increasing Bi 2 O 3 content. This change may be caused by the disappearance of [TeO 3 ] trigonal units and the transformation from [BO 3 ] triangular units to [BO 4 ] tetrahedral units. These two processes will decrease the number Fig. 4 O1s core level photoelectron spectra of BBT1e4 glasses. Fig. 5 Experimental and decomposed peaks of O1s photoelectron spectra of BBT1e4 glasses.

5 G. Zhao et al.: J. Mater. Sci. Technol., 2013, 29(3), 209e Table 4 Binding energies of O1s, Bi4f and Te3d peaks and the area ratios (R) ofo1s(2) to O1s(1) in XPS spectra Sample O1s(2)/eV O1s(1)/eV Bi4f 7/2 /ev Bi4f 5/2 /ev Te3d 5/2 /ev Te3d 3/2 /ev R BBT BBT BBT BBT of non-bridging oxygen. This is also supported well by the change of T x et g in Fig. 2. The Bi4f XPS spectra of BBT1e4 glasses are shown in Fig. 6. The peak positions of binding energy of Bi4f are similar to those of other reports of bismuth oxide compound [30,31]. The shift of binding energy of Bi4f photoelectron peaks increases with Bi 2 O 3 content. It indicates that the polarization of Bi depends on the concentration of bismuth. As can be seen from Fig. 6, the XPS spectrum of BBT4 glass is different from BBT1e3 glasses with respect to peak position and band asymmetry. This result shows both Bi 3þ and Bi 5þ may co-exist in BBT4 glass, and the conversion of partial Bi 3þ ions into Bi 5þ ions reduces the electronic density 6S 2 shell around bismuth ions [21]. It is coincident with the Raman spectra of BBT system. As shown in Fig. 7, the intensity of Te3d decreases with decreasing TeO 2 but the peak position of Te3d 5/2 shifts to higher energy. The conversion from [TeO 4 ] to [TeO 3 ] configuration may be responsible for this phenomenon. It is in agreement with the Raman spectra at 665 cm 1 band to 740 cm 1 band. 4. Conclusion Glass formation region in Bi 2 O 3 eb 2 O 3 eteo 2 ternary system with B 2 O 3 40 mol% is determined. The thermal, optical properties and structures of xbi 2 O 3 e30b 2 O 3 e(70ex)teo 2 (x ¼ 40, 50, 60 and 70 mol%) glasses are investigated. The density, refractive index (2.011e2.114), optical basicity and molar volume increase with increasing Bi 2 O 3 content. Raman spectra and XPS spectra show that the glass network is mainly constituted by the [BiO 6 ] octahedron, [TeO 4 ] trigonal bipyramidal, [TeO 3 ] trigonal pyramid, [BO 3 ] trigonal pyramid and [BO 4 ] tetrahedron. [TeO 4 ] trigonal bipyramidals are converted into [TeO 3 ] trigonal pyramids and [BO 3 ] units are converted into [BO 4 ] units with increasing Bi 2 O 3 content. The existence of Bi 5þ has been proved by Raman and XPS spectra in the high Bi 2 O 3 content glass. The variations of thermal stability can be explained by the change of non-bridging oxygen in glass. Acknowledgment This research was financially supported by the National Natural Science Foundation of China (No ). REFERENCES Fig. 6 Bi4f photoelectron spectra of BBT1e4 glasses. Fig. 7 Te3d photoelectron spectra for BBT1e3 samples. [1] D.W. Hall, M.A. Newhouse, N.F. Borrelli, W.H. Dumbaugh, D.L. Weidman, Appl. Phys. Lett. 54 (1989) 1293e1295. [2] Y.G. Choi, K.H. Kim, V.A. Chernov, J. Heo, J. Non-Cryst. Solids 259 (1999) 205e211. [3] A. Pan, A. Ghosh, Phys. Rev. B 66 (2002) [4] S. Bale, S. Rahman, Opt. Mater. 31 (2008) 333e337. [5] A. Dutta, A. Ghosh, J. Non-Cryst. Solids 353 (2007) 1333e1336. [6] Y. Chen, Q. Nie, T. Xu, S. Dai, X. Wang, X. Shen, J. Non-Cryst. Solids 354 (2008) 3468e3472. [7] M. Udovic, P. Thomas, A. Mirgorodsky, O. Durand, M. Soulis, O. Masson, T. Merle-Mejean, J.C. Champarnaud-Mesjard, J. Solid State Chem. 179 (2006) 3252e3259. [8] T. Hasegawa, J. Non-Cryst. Solids 357 (2011) 2857e2862. [9] F. El-Diasty, F.A. Abdel Wahab, M. Abdel-Baki, J. Appl. Phys. 100 (2006) [10] V. Simon, R. Pop, S.G. Chiuzbaian, M. Neumann, M. Coldea, S. Simon, Mater. Lett. 57 (2003) 2044e2048. [11] A. Pan, A. Gosh, J. Non-Cryst. Solids 271 (2000) 157e161. [12] J.A. Duffy, M.D. Ingram, in: D. Uhlman, N. Kreidl (Eds.), Optical Properties of Glass, American Ceramic Society, Westerville, 1991, p [13] J. Duffy, Phys. Chem. Glasses 320 (1989) 1e4. [14] V. Dimitrov, T. Komatsu, J. Non-Cryst. Solids 249 (1999) 160e179. [15] V. Dimitrov, S. Sakka, J. Appl. Phys. 79 (1996) 1736e1740. [16] A. Chahine, M. Et-tabirou, J.L. Pascal, Mater. Lett. 58 (2004) 2776e2780. [17] A.A. Kharlamov, R.M. Almeida, J. Heo, J. Non-Cryst. Solids 202 (1996) 233e240. [18] H. Fan, L. Hu, K. Yang, Y. Fang, J. Non-Cryst. Solids 356 (2010) 1814e1818. [19] H. Fan, G. Wang, L. Hu, Solid State Sci. 11 (2009) 2065e2070.

6 214 G. Zhao et al.: J. Mater. Sci. Technol., 2013, 29(3), 209e214 [20] H. Fan, G. Gao, G. Wang, L. Hu, Solid State Sci. 12 (2010) 541e545. [21] Y. Shimizugawa, N. Sugimoto, K. Hirao, J. Non-Cryst. Solids 22 (1997) 208e212. [22] G.D. Chryssikos, M.S. Bitsis, J.A. Kapoutsis, E.I. Kamitsos, J. Non-Cryst. Solids 217 (1997) 278e290. [23] M. Arnaudov, V. Dimitrov, Y. Dimitriev, L. Markova, Mater. Res. Bull. 17 (1982) 1121e1129. [24] A.G. Kalmapounias, G.N. Papatheodorou, S.N. Yannopoulos, J. Phys. Chem. Solids 68 (2007) 1029e1034. [25] G. Gao, L. Hu, H. Fan, G. Wang, K. Li, S. Feng, S. Fan, H. Chen, Opt. Mater. 32 (2009) 159e163. [26] G.D. Chryssikos, E.I. Kamitsos, A.P. Patsis, M.S. Bitsis, M.A. Karakassides, J. Non-Cryst. Solids 126 (1990) 42e51. [27] V. Dimitrov, T. Komatsu, Phys. Chem. Glasses 44 (2003) 357e364. [28] B.V.R. Chowdari, Z. Rong, Solid State Ion. 90 (1996) 151e160. [29] T. Honma, R. Sato, Y. Benino, T. Komatsu, V. Dimitrov, J. Non- Cryst. Solids 272 (2000) 1e13. [30] C.D. Wagner, W.M. Riggs, L.E. Davis, J.F. Moulder, G.E. Mullenberg, Handbook of X-ray Photoelectron Spectroscopy, Perkin- Elmer Corp. Press, Eden Prairie, MN, USA, 1979, p. 91. [31] V.I. Nefedov, D. Gati, B.F. Dzurinskii, N.P. Sergushin, Y.V. Salyn, Russ. J. Inorg. Chem. 20 (1975) 2307.