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EPR and FT-IR spectroscopic studies of B2O3Bi2O3MnO glasses
Solid State Sciences 7 (2005) 1438–1442 www.elsevier.com/locate/ssscie
EPR and FT-IR spectroscopic studies of B2O3–Bi2O3 –MnO glasses I. Ardelean ∗ , Simona Cora, Raluca Ciceo Lucacel, Octavia Hulpus Faculty of Physics, Babes-Bolyai University, 400084, Cluj-Napoca, Romania Received 27 April 2004; received in revised form 8 August 2005; accepted 8 August 2005 Available online 20 October 2005
Abstract EPR and FT-IR absorption measurements performed on xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses with 0 x 50 mol% are reported. The EPR spectra of all investigated samples exhibit resonance signals that are characteristic for the Mn2+ ions. For x 20 mol% the spectra consists of two resonance lines centered at geff ∼ = 4.3 and geff ∼ = 2.0, their relative intensity depending on the manganese content of the sample. For x 3 mol%, ∼ the line from geff = 4.3 has a resolved hyperfine structure characteristic for isolated Mn2+ ions disposed in distorted sites of an octahedral symmetry. The resonance line centered at geff ∼ = 2.0 has not hyperfine structure and is attributed to coupled Mn2+ ions by dipolar (x 5 mol%) or/and superexchange interactions (x > 5 mol%). The FT-IR data indicate the presence in the glasses of the BO3 , BO4 , BiO6 and BiO3 units and its dependence on the MnO content. 2005 Elsevier SAS. All rights reserved. Keywords: Structure; EPR; FT-IR absorption; B2 O3 ·Bi2 O3 glass matrix; Manganese ions
1. Introduction Structural properties of the vitreous systems were frequently studied by means of the EPR and the FT-IR spectroscopy [1]. The borate glasses are very often investigated by a lot of methods because they are relatively easy to obtain and moreover because in their structure appears a large variety of structural units over a wide range of modifier concentration [2, 3]. Glasses that contain nonconventional network formers like Bi2 O3 , so-called heavy metal oxide glasses, are intensively studied because of their special properties such as high refractive index, high density, high nonlinear optical susceptibility and excellent infrared transmission [4,5]. Recently, interest in bismuthate glasses has increased because their suitability to synthesize high-temperature ceramic superconductors [6]. Manganese ions have been frequently used as paramagnetic probes for exploring the structure and properties of vitreous systems. Many oxide glasses such as borate [7–9], silicate [10,11], phosphate [11], tellurite [12], bismuthate [13, 14] and also chalcogenide [15,16] or halide [17,18] glasses doped with MnO ions have been investigated by means of EPR. * Corresponding author.
E-mail address: [email protected] (I. Ardelean). 1293-2558/$ – see front matter 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2005.08.017
A special effort was made to elaborate the theoretical support for explained the resonance lines at geff ∼ = 4.3 and geff ∼ = 2.0 2+ values for Mn ions absorption spectra [7–11,17–19]. Information concerning the structural details of the vitreous matrix revealed by the Mn2+ distribution on different structural units building the network, their coordination, etc., was obtained. This paper aim is to present our results concerning the structural details of the B2 O3 ·Bi2 O3 vitreous matrix containing manganese ions over a large concentration range. Investigations were made by EPR and FT-IR spectroscopy. 2. Experimental details Glasses of the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] system were prepared using pure reagent grade chemicals, i.e., H3 BO3 , MnCO3 and Bi(NO3 )3 ·5H2 O in suitable proportions. The mixtures were mechanically homogenized and melted in sintered corundum crucibles in an electric furnace. The mixtures were introduced directly at 1250 ◦ C in the pre-heated furnace. After 5 minutes the molten materials were quenched to room temperature by pouring on the stainless-steel plates. The structure of samples was analyzed by means of X-ray diffraction. The patterns obtained did not reveal any crystalline phases up to
I. Ardelean et al. / Solid State Sciences 7 (2005) 1438–1442
x = 50 mol%. The obtained glasses are transparent and become darker when the MnO content increase. EPR measurements were performed at room temperature using an ADANI Portable EPR PS 8400-type spectrometer, in the X frequency band (9.4 GHz) and a field modulation of 100 KHz. The microwave power used was 5 mW. To avoid the alteration of the glass structure due to the ambient condition, samples of equal quantities were enclosed immediately after preparation in the tubular holders of the same caliber. The FT-IR absorption spectra of studied glasses, in the 400–1500 cm−1 wave-number range, were obtained with on Equinox 55Bruker spectrometer using the KBr pellet technique. In order to obtain good quality spectra the samples were crushed in an agate mortar to obtain articles of micrometer size. This procedure was applied every time to fragments of bulk glass to avoid structural modifications due to ambient moisture. 3. Results and discussion 3.1. EPR data Recorded EPR spectra show resonance lines due to Mn2+ (3d5 , 6 S5/2 ) paramagnetic ions for all investigated concentrations. As can be observed in Fig. 1 the structure of the spectra
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strongly depends on the MnO content of the samples. The spectra consist mainly of resonance lines centered at geff ∼ = 4.3 and geff ∼ = 2.0 values, their relative intensity depending on the manganese content of the samples. For 0.3 x 3 mol%, the absorption line at geff ∼ = 4.3 is prevalent in the spectrum and shows the hyperfine structure (hfs) characteristic to the 55 Mn (I = 5/2) isotope. The resolution depends on the Mn2+ ion concentration as may be seen in Fig. 1(a) and is loosing with the increasing of the concentration due to the ligand field fluctuation in the Mn2+ ion surrounding. Superimposed on this absorption line, the narrow line corresponding to accidental impurities of Fe3+ (3d5 , 6 S5/2 ) ions was also detected (Fig. 1(a)). For 5 x 20 mol% the EPR resonance line centered at geff ≈ 4.3, had not hfs (Figs. 1(a) and (b)). The hfs sextet superimposes on a large absorption line, the envelope of all contributions at this absorption having geff ≈ 4.3. The concentration dependence of the peak-to-peak line width, B, and intensity, J , obtained as an integral of the area under the corresponding EPR signal, are presented in Fig. 2 for the absorption near geff ≈ 4.3. At lower values of manganese content (x 1 mol%) these parameters have been obtained approximately, taking account by the presence of a
(a) (a)
(b)
(b)
Fig. 1. The EPR spectra of Mn2+ in xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses for 0.3 x 5 mol% (a) and 10 x 50 mol% (b).
Fig. 2. Concentration dependence of the line intensity (a) and line-width (b) of the geff ≈ 4.3 EPR absorption.
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small Fe3+ ions quantity in the glasses. Up to 3 mol% MnO the intensity of the geff ≈ 4.3 lines increases (Fig. 2(a)) and for higher concentrations it decreases. Similar evolution was observed for B4.3 (Fig. 2(b)). According to the previous experimental and theoretic studies concerning the 3d5 paramagnetic ions in vitreous systems [1,17,18] the geff ≈ 4.3 resonance lines are due to magnetically isolated Mn2+ ions, in distorted sites of octahedral symmetry. The features of these resonance lines and their evolution when Mn2+ ions accumulates in the studied matrix, pointed out a great similarity in structure and symmetry of the local units involving manganese. The structural stability of the glass matrix with the progressive accumulation of manganese in its composition, through a wide range of concentration, reveals itself a distinct characteristic of the investigated glass system. The absorption line at geff ≈ 2.0 is prevalent in the spectrum for x 10 mol% and for this line no hfs was detected. This EPR line also depends on the MnO content of the samples. The concentration dependence of intensity and line-width of this resonance are presented in Fig. 3. Contrary to the evolution of geff ≈ 4.3-line intensity, the intensity of the resonance line centered at geff ≈ 2.0 increases very slowly in the x 5 mol% concentration ranges. The increasing character is more pronounced after 20 mol% MnO and appreciable for x > 35 mol% as may
be seen in Fig. 3(a). The evolution of the line-width vs. MnO content (Fig. 3(b)) is increasing almost linear until 5 mol%, which suggests that the Mn2+ ions are involved in dipolar interaction responsible for the EPR line broadening. At higher MnO content, the line-width vs. MnO content graphics reduced its slope. Therefore, the dipolar broadening is balanced, for higher concentrations, by narrowing mechanisms due to superexchange type interactions between the manganese ions. But, for x > 10 mol% the narrowing of the EPR signal centered at geff ≈ 2.0, can be balanced by the broadening effects due the interaction between manganese ions with mixed valance states or the progressive disordering of the vitreous structure. So that, at high MnO content, besides the Mn2+ ions species, the only ones giving rise to EPR absorption in our experiment, superior valence state of manganese ions may occur in the samples. In vitreous oxide matrices, Mn3+ ions have been frequently reported as progressively involved when increasing the MnO content [20–23] but the proportion of these ions depend on both glass matrix composition [24] and preparation conditions [25]. The geff ≈ 2.0 absorption line was generally attributed to isolated Mn2+ ions in octahedral symmetric sites slightly tetragonally distorted, to the Mn2+ ions participating at the dipolar interactions or/and to superexchange coupled pairs of these ions [26,27]. The vitreous structure of our glasses show an evolution with the MnO content from structural units involving Mn2+ ions in well-defined vicinities having certain symmetry, to structural units containing clustered magnetic ions. The change in the geff ≈ 4.3 and geff ≈ 2.0 absorption lines when increasing the MnO content revealed this evolution. 3.2. Infrared data The experimental FT-IR spectra for the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] with 0 x 50 mol% are presented in Fig. 4.
(a)
(b) Fig. 3. Concentration dependence of the line intensity (a) and line-width (b) of the geff ≈ 2.0 EPR absorption.
Fig. 4. FT-IR spectra of the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses.
I. Ardelean et al. / Solid State Sciences 7 (2005) 1438–1442
Table 1 Frequencies and their assignments for FT-IR spectra of xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses Wavenumber (cm−1 ) ∼ 490 ∼ 610 ∼ 713 ∼ 875 ∼ 1012 ∼ 1174 ∼ 1400
Assignment Bi–O bending vibrations in BiO6 units Specific vibrations of Mn–O bonds Bi-O− stretching vibrations (of non-bridging oxygen) in BiO6 units Specific vibrations of Mn–O bonds B–O–B symmetrical bending vibrations Bi–O stretching vibrations in BiO3 units B–O stretching vibrations in BO4 units from tri-, tetra- and pentaborate groups B–O− stretching vibrations in BO3 units from pyro- and ortoborate groups B–O− stretching vibrations in BO3 units from varied types of borate rings
The FT-IR spectral bands of the glasses investigated in this paper and their assignments are summarized in Table 1. These data have been discussed on the basis of the method given by Tarte [28,29] and Condrate [30,31] by comparing the experimental data of glasses with those of related crystalline compounds. In our study we made use of the characteristic absorption lines for the crystalline MnO2 and Mn3 O4 [32] and the vitreous B2 O3 [3,32–34] and Bi2 O3 [33,35,36]. The FT-IR absorption band obtained for our glasses are centered at ∼ 490, ∼ 610, ∼ 713, ∼ 875, ∼ 1012, ∼ 1174 and ∼ 1400 cm−1 . The band at ∼ 490 cm−1 is assigned to the Bi–O bending vibrations in BiO6 units [33,35,36]. For x > 0, at this band may also contribute specific vibration of Mn–O bonds [32]. The band at ∼ 610 cm−1 is ascribed to the stretching vibrations of Bi–O− bonds (of non-bridging oxygen) in BiO6 pyramidal units [35,36] and has approximately the same amplitude for all the compositional range. For x > 0 at this band may also contribute specific vibration of Mn–O bonds [32]. At the ∼ 713 cm−1 the FT-IR spectra present a relatively strong absorption band assigned to the B–O–B bending vibrations [33,34]. This band is increasing for x 0.3 mol% up to x = 10 mol% and then remains the same. The absorption band situated at ∼ 875 cm−1 is ascribed to the symmetrical stretching vibrations in the BiO3 pyramidal units and has approximately the same intensity for all the compositional range. At the ∼ 1012 cm−1 a weak absorption band assigned to the B–O stretching vibrations in BO4 units from tri-, tetra- and pentaborate groups [3,33,34], which remain the same as intensity in all study concentration range. Absorption at ∼ 1174 cm−1 can be attributed to the B–O asymmetric stretching vibrations in BO3 units from pyroborate and ortoborate groups [3, 34]. The intensity of this band is maximum for the samples with x = 10 mol%. For higher concentration of manganese ions, the intensity of this band remains the same. The band at ∼1400 cm−1 is assigned to B–O− stretching vibrations in BO3 units in varied borate rings [3,34]. The intensity of this band remains approximately the same in all concentration range studied. The presence of BiO3 and BiO6 units in the glass all over the compositional range and the preponderance of the three co-
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ordinated boron atoms all over the compositional range is probably due to the reciprocal influence of these two glass formers, (conventional B2 O3 and non-conventionally Bi2 O3 ) which are forming the base network of the glasses. 4. Conclusions Homogeneous glasses of the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] system were obtained within 0 x 50 mol%. EPR and FT-IR absorption spectra of these glasses have been analyzed in order to identify the contributions of each component on the structure and to point out the role of the manganese ions as a modifier of the glass network. The EPR absorption spectra with hfs at geff ≈ 4.3 revealed the presence of magnetically isolated Mn2+ ions in studied glasses, in distorted sites of octahedral symmetry. The geff ≈ 2.0 absorption line was attributed to isolated Mn2+ ions and those involved in dipole-dipole or/and superexchange interactions. The FT-IR measurements indicate the presence of the BiO3 , BiO6 , three- and tetraborate units in the glass structure and its dependence on the manganese content. References [1] D.L. Griscom, Glass Sci. Tech. 48 (1990) 151. [2] J. Wong, C.A. Angell, Glass Structure by Spectroscopy, Dekker, New York, 1976, pp. 410–496. [3] E.I. Kamitsos, M.A. Karakassides, Phys. Chem. Glasses 30 (1989) 19. [4] W.H. Dumbaugh, J.C. Lapp, J. Am. Ceram. Soc. 75 (1992) 2315. [5] R. Nassau, D.L. Chadwick, J. Am. Ceram. Soc. 66 (1983) 332. [6] H. Zheng, P. Lin, R. Xu, J. Mackenzie, J. Appl. Phys. 68 (1990) 894. [7] D.L. Grisscom, R.E. Griscom, J. Chem. Phys. 47 (1967) 2711. [8] P.C. Taylor, P.J. Bray, J. Chem. Phys. Solids 33 (1972) 43. [9] I. Ardelean, Gh. Ilonca, M. Peteanu, Solid State Commun. 52 (1984) 167. [10] D. Loveridge, S. Parke, Phys. Chem. Glasses 12 (1971) 19. [11] J.W.H. Schreurs, J. Chem. Phys. 69 (1978) 2151. [12] I. Ardelean, M. Peteanu, Gh. Ilonca, Phys. Status Solidi a 58 (1980) K33. [13] I. Ardelean, Gh. Ilonca, V. Simon, O. Cozar, V. Ioncu, S. Filip, Solid State Commun. 98 (1996) 651. [14] I. Ardelean, M. Peteanu, S. Filip, V. Simon, I. Todor, Solid State Commun. 105 (1998) 339. [15] R.C. Nicklin, C.P. Poole, H.A. Farach, J. Chem. Phys. 68 (1973) 2579. [16] V.N. Lazucin, V. Chepeleva, DAN SSSR 214 (1974) 787. [17] V. Cerny, B. Petrova, M. Frumar, J. Non-Cryst. Solids 125 (1990) 17. [18] B. Petrova, M. Frumar, E. Cernoskova, V. Cerny, J. Non-Cryst. Solids 161 (1993) 316. [19] J.G. Kliava, Phys. Status Solidi B 134 (1986) 431. [20] Gh. Ilonca, I. Ardelean, O. Cozar, J. Physique 49 (1988) 8. [21] I. Ardelean, M. Peteanu, S. Filip, D. Alexandru, J. Magn. Magn. Mater. 157 (1996) 239. [22] I. Ardelean, M. Peteanu, V. Simon, S. Simon, M. Flora, Phys. Chem. Glasses 41 (2000) 153. [23] I. Ardelean, M. Peteanu, I. Todor, Phys. Ghem. Glasses 43 (2002) 276. [24] E. Burzo, I. Ardelean, I. Ursu, J. Mater. Sci. 15 (1980) 581. [25] E. Burzo, I. Ursu, D. Ungur, I. Ardelean, Mater. Res. Bull. 15 (1980) 1273. [26] E. Burzo, I. Ardelean, Phys. Status Solidi B 87 (1978) K 137. [27] D.L. Griscom, J. Non-Cryst. Solids 40 (1980) 211. [28] P. Tarte, Spectrochim. Acta 18 (1962) 467. [29] P. Tarte, in: I.A. Prins (Ed.), Physics of Non Crystalline Solids, Elsevier, Amsterdam, 1964, p. 549. [30] R.A. Condrate, in: L.D. Pye, H.I. Stevens, W.C. Lacourse (Eds.), Introduction to Glass Science, Plenum Press, New York, 1972, p. 101.
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[31] R.A. Condrate, J. Non-Cryst. Solids 84 (1986) 26. [32] F. Bentley, L.D. Smithson, A.L. Rozek, Infrared-Spectra and Characteristic Frequencies 700–300 cm−1 , Interscience, New York, 1986, p. 103. [33] G. Fuxi, Optical and Spectroscopic Properties of Glass, Springer-Verlag, Berlin, 1991, pp. 32–40.
[34] Y.D. Yiannopoulos, G.D. Chryssikos, E.I. Kamitsos, Phys. Chem. Glasses 42 (3) (2001) 164. [35] V. Dimitrov, Y. Dimitriev, A. Montenero, J. Non-Cryst. Solids 180 (1994) 51. [36] R. Betsch, W. White, Spectrochim. Acta 34A (1977) 5051.
EPR and FT-IR spectroscopic studies of B2O3–Bi2O3 –MnO glasses I. Ardelean ∗ , Simona Cora, Raluca Ciceo Lucacel, Octavia Hulpus Faculty of Physics, Babes-Bolyai University, 400084, Cluj-Napoca, Romania Received 27 April 2004; received in revised form 8 August 2005; accepted 8 August 2005 Available online 20 October 2005
Abstract EPR and FT-IR absorption measurements performed on xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses with 0 x 50 mol% are reported. The EPR spectra of all investigated samples exhibit resonance signals that are characteristic for the Mn2+ ions. For x 20 mol% the spectra consists of two resonance lines centered at geff ∼ = 4.3 and geff ∼ = 2.0, their relative intensity depending on the manganese content of the sample. For x 3 mol%, ∼ the line from geff = 4.3 has a resolved hyperfine structure characteristic for isolated Mn2+ ions disposed in distorted sites of an octahedral symmetry. The resonance line centered at geff ∼ = 2.0 has not hyperfine structure and is attributed to coupled Mn2+ ions by dipolar (x 5 mol%) or/and superexchange interactions (x > 5 mol%). The FT-IR data indicate the presence in the glasses of the BO3 , BO4 , BiO6 and BiO3 units and its dependence on the MnO content. 2005 Elsevier SAS. All rights reserved. Keywords: Structure; EPR; FT-IR absorption; B2 O3 ·Bi2 O3 glass matrix; Manganese ions
1. Introduction Structural properties of the vitreous systems were frequently studied by means of the EPR and the FT-IR spectroscopy [1]. The borate glasses are very often investigated by a lot of methods because they are relatively easy to obtain and moreover because in their structure appears a large variety of structural units over a wide range of modifier concentration [2, 3]. Glasses that contain nonconventional network formers like Bi2 O3 , so-called heavy metal oxide glasses, are intensively studied because of their special properties such as high refractive index, high density, high nonlinear optical susceptibility and excellent infrared transmission [4,5]. Recently, interest in bismuthate glasses has increased because their suitability to synthesize high-temperature ceramic superconductors [6]. Manganese ions have been frequently used as paramagnetic probes for exploring the structure and properties of vitreous systems. Many oxide glasses such as borate [7–9], silicate [10,11], phosphate [11], tellurite [12], bismuthate [13, 14] and also chalcogenide [15,16] or halide [17,18] glasses doped with MnO ions have been investigated by means of EPR. * Corresponding author.
E-mail address: [email protected] (I. Ardelean). 1293-2558/$ – see front matter 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2005.08.017
A special effort was made to elaborate the theoretical support for explained the resonance lines at geff ∼ = 4.3 and geff ∼ = 2.0 2+ values for Mn ions absorption spectra [7–11,17–19]. Information concerning the structural details of the vitreous matrix revealed by the Mn2+ distribution on different structural units building the network, their coordination, etc., was obtained. This paper aim is to present our results concerning the structural details of the B2 O3 ·Bi2 O3 vitreous matrix containing manganese ions over a large concentration range. Investigations were made by EPR and FT-IR spectroscopy. 2. Experimental details Glasses of the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] system were prepared using pure reagent grade chemicals, i.e., H3 BO3 , MnCO3 and Bi(NO3 )3 ·5H2 O in suitable proportions. The mixtures were mechanically homogenized and melted in sintered corundum crucibles in an electric furnace. The mixtures were introduced directly at 1250 ◦ C in the pre-heated furnace. After 5 minutes the molten materials were quenched to room temperature by pouring on the stainless-steel plates. The structure of samples was analyzed by means of X-ray diffraction. The patterns obtained did not reveal any crystalline phases up to
I. Ardelean et al. / Solid State Sciences 7 (2005) 1438–1442
x = 50 mol%. The obtained glasses are transparent and become darker when the MnO content increase. EPR measurements were performed at room temperature using an ADANI Portable EPR PS 8400-type spectrometer, in the X frequency band (9.4 GHz) and a field modulation of 100 KHz. The microwave power used was 5 mW. To avoid the alteration of the glass structure due to the ambient condition, samples of equal quantities were enclosed immediately after preparation in the tubular holders of the same caliber. The FT-IR absorption spectra of studied glasses, in the 400–1500 cm−1 wave-number range, were obtained with on Equinox 55Bruker spectrometer using the KBr pellet technique. In order to obtain good quality spectra the samples were crushed in an agate mortar to obtain articles of micrometer size. This procedure was applied every time to fragments of bulk glass to avoid structural modifications due to ambient moisture. 3. Results and discussion 3.1. EPR data Recorded EPR spectra show resonance lines due to Mn2+ (3d5 , 6 S5/2 ) paramagnetic ions for all investigated concentrations. As can be observed in Fig. 1 the structure of the spectra
1439
strongly depends on the MnO content of the samples. The spectra consist mainly of resonance lines centered at geff ∼ = 4.3 and geff ∼ = 2.0 values, their relative intensity depending on the manganese content of the samples. For 0.3 x 3 mol%, the absorption line at geff ∼ = 4.3 is prevalent in the spectrum and shows the hyperfine structure (hfs) characteristic to the 55 Mn (I = 5/2) isotope. The resolution depends on the Mn2+ ion concentration as may be seen in Fig. 1(a) and is loosing with the increasing of the concentration due to the ligand field fluctuation in the Mn2+ ion surrounding. Superimposed on this absorption line, the narrow line corresponding to accidental impurities of Fe3+ (3d5 , 6 S5/2 ) ions was also detected (Fig. 1(a)). For 5 x 20 mol% the EPR resonance line centered at geff ≈ 4.3, had not hfs (Figs. 1(a) and (b)). The hfs sextet superimposes on a large absorption line, the envelope of all contributions at this absorption having geff ≈ 4.3. The concentration dependence of the peak-to-peak line width, B, and intensity, J , obtained as an integral of the area under the corresponding EPR signal, are presented in Fig. 2 for the absorption near geff ≈ 4.3. At lower values of manganese content (x 1 mol%) these parameters have been obtained approximately, taking account by the presence of a
(a) (a)
(b)
(b)
Fig. 1. The EPR spectra of Mn2+ in xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses for 0.3 x 5 mol% (a) and 10 x 50 mol% (b).
Fig. 2. Concentration dependence of the line intensity (a) and line-width (b) of the geff ≈ 4.3 EPR absorption.
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small Fe3+ ions quantity in the glasses. Up to 3 mol% MnO the intensity of the geff ≈ 4.3 lines increases (Fig. 2(a)) and for higher concentrations it decreases. Similar evolution was observed for B4.3 (Fig. 2(b)). According to the previous experimental and theoretic studies concerning the 3d5 paramagnetic ions in vitreous systems [1,17,18] the geff ≈ 4.3 resonance lines are due to magnetically isolated Mn2+ ions, in distorted sites of octahedral symmetry. The features of these resonance lines and their evolution when Mn2+ ions accumulates in the studied matrix, pointed out a great similarity in structure and symmetry of the local units involving manganese. The structural stability of the glass matrix with the progressive accumulation of manganese in its composition, through a wide range of concentration, reveals itself a distinct characteristic of the investigated glass system. The absorption line at geff ≈ 2.0 is prevalent in the spectrum for x 10 mol% and for this line no hfs was detected. This EPR line also depends on the MnO content of the samples. The concentration dependence of intensity and line-width of this resonance are presented in Fig. 3. Contrary to the evolution of geff ≈ 4.3-line intensity, the intensity of the resonance line centered at geff ≈ 2.0 increases very slowly in the x 5 mol% concentration ranges. The increasing character is more pronounced after 20 mol% MnO and appreciable for x > 35 mol% as may
be seen in Fig. 3(a). The evolution of the line-width vs. MnO content (Fig. 3(b)) is increasing almost linear until 5 mol%, which suggests that the Mn2+ ions are involved in dipolar interaction responsible for the EPR line broadening. At higher MnO content, the line-width vs. MnO content graphics reduced its slope. Therefore, the dipolar broadening is balanced, for higher concentrations, by narrowing mechanisms due to superexchange type interactions between the manganese ions. But, for x > 10 mol% the narrowing of the EPR signal centered at geff ≈ 2.0, can be balanced by the broadening effects due the interaction between manganese ions with mixed valance states or the progressive disordering of the vitreous structure. So that, at high MnO content, besides the Mn2+ ions species, the only ones giving rise to EPR absorption in our experiment, superior valence state of manganese ions may occur in the samples. In vitreous oxide matrices, Mn3+ ions have been frequently reported as progressively involved when increasing the MnO content [20–23] but the proportion of these ions depend on both glass matrix composition [24] and preparation conditions [25]. The geff ≈ 2.0 absorption line was generally attributed to isolated Mn2+ ions in octahedral symmetric sites slightly tetragonally distorted, to the Mn2+ ions participating at the dipolar interactions or/and to superexchange coupled pairs of these ions [26,27]. The vitreous structure of our glasses show an evolution with the MnO content from structural units involving Mn2+ ions in well-defined vicinities having certain symmetry, to structural units containing clustered magnetic ions. The change in the geff ≈ 4.3 and geff ≈ 2.0 absorption lines when increasing the MnO content revealed this evolution. 3.2. Infrared data The experimental FT-IR spectra for the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] with 0 x 50 mol% are presented in Fig. 4.
(a)
(b) Fig. 3. Concentration dependence of the line intensity (a) and line-width (b) of the geff ≈ 2.0 EPR absorption.
Fig. 4. FT-IR spectra of the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses.
I. Ardelean et al. / Solid State Sciences 7 (2005) 1438–1442
Table 1 Frequencies and their assignments for FT-IR spectra of xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] glasses Wavenumber (cm−1 ) ∼ 490 ∼ 610 ∼ 713 ∼ 875 ∼ 1012 ∼ 1174 ∼ 1400
Assignment Bi–O bending vibrations in BiO6 units Specific vibrations of Mn–O bonds Bi-O− stretching vibrations (of non-bridging oxygen) in BiO6 units Specific vibrations of Mn–O bonds B–O–B symmetrical bending vibrations Bi–O stretching vibrations in BiO3 units B–O stretching vibrations in BO4 units from tri-, tetra- and pentaborate groups B–O− stretching vibrations in BO3 units from pyro- and ortoborate groups B–O− stretching vibrations in BO3 units from varied types of borate rings
The FT-IR spectral bands of the glasses investigated in this paper and their assignments are summarized in Table 1. These data have been discussed on the basis of the method given by Tarte [28,29] and Condrate [30,31] by comparing the experimental data of glasses with those of related crystalline compounds. In our study we made use of the characteristic absorption lines for the crystalline MnO2 and Mn3 O4 [32] and the vitreous B2 O3 [3,32–34] and Bi2 O3 [33,35,36]. The FT-IR absorption band obtained for our glasses are centered at ∼ 490, ∼ 610, ∼ 713, ∼ 875, ∼ 1012, ∼ 1174 and ∼ 1400 cm−1 . The band at ∼ 490 cm−1 is assigned to the Bi–O bending vibrations in BiO6 units [33,35,36]. For x > 0, at this band may also contribute specific vibration of Mn–O bonds [32]. The band at ∼ 610 cm−1 is ascribed to the stretching vibrations of Bi–O− bonds (of non-bridging oxygen) in BiO6 pyramidal units [35,36] and has approximately the same amplitude for all the compositional range. For x > 0 at this band may also contribute specific vibration of Mn–O bonds [32]. At the ∼ 713 cm−1 the FT-IR spectra present a relatively strong absorption band assigned to the B–O–B bending vibrations [33,34]. This band is increasing for x 0.3 mol% up to x = 10 mol% and then remains the same. The absorption band situated at ∼ 875 cm−1 is ascribed to the symmetrical stretching vibrations in the BiO3 pyramidal units and has approximately the same intensity for all the compositional range. At the ∼ 1012 cm−1 a weak absorption band assigned to the B–O stretching vibrations in BO4 units from tri-, tetra- and pentaborate groups [3,33,34], which remain the same as intensity in all study concentration range. Absorption at ∼ 1174 cm−1 can be attributed to the B–O asymmetric stretching vibrations in BO3 units from pyroborate and ortoborate groups [3, 34]. The intensity of this band is maximum for the samples with x = 10 mol%. For higher concentration of manganese ions, the intensity of this band remains the same. The band at ∼1400 cm−1 is assigned to B–O− stretching vibrations in BO3 units in varied borate rings [3,34]. The intensity of this band remains approximately the same in all concentration range studied. The presence of BiO3 and BiO6 units in the glass all over the compositional range and the preponderance of the three co-
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ordinated boron atoms all over the compositional range is probably due to the reciprocal influence of these two glass formers, (conventional B2 O3 and non-conventionally Bi2 O3 ) which are forming the base network of the glasses. 4. Conclusions Homogeneous glasses of the xMnO·(100 − x)[B2 O3 ·Bi2 O3 ] system were obtained within 0 x 50 mol%. EPR and FT-IR absorption spectra of these glasses have been analyzed in order to identify the contributions of each component on the structure and to point out the role of the manganese ions as a modifier of the glass network. The EPR absorption spectra with hfs at geff ≈ 4.3 revealed the presence of magnetically isolated Mn2+ ions in studied glasses, in distorted sites of octahedral symmetry. The geff ≈ 2.0 absorption line was attributed to isolated Mn2+ ions and those involved in dipole-dipole or/and superexchange interactions. The FT-IR measurements indicate the presence of the BiO3 , BiO6 , three- and tetraborate units in the glass structure and its dependence on the manganese content. References [1] D.L. Griscom, Glass Sci. Tech. 48 (1990) 151. [2] J. Wong, C.A. Angell, Glass Structure by Spectroscopy, Dekker, New York, 1976, pp. 410–496. [3] E.I. Kamitsos, M.A. Karakassides, Phys. Chem. Glasses 30 (1989) 19. [4] W.H. Dumbaugh, J.C. Lapp, J. Am. Ceram. Soc. 75 (1992) 2315. [5] R. Nassau, D.L. Chadwick, J. Am. Ceram. Soc. 66 (1983) 332. [6] H. Zheng, P. Lin, R. Xu, J. Mackenzie, J. Appl. Phys. 68 (1990) 894. [7] D.L. Grisscom, R.E. Griscom, J. Chem. Phys. 47 (1967) 2711. [8] P.C. Taylor, P.J. Bray, J. Chem. Phys. Solids 33 (1972) 43. [9] I. Ardelean, Gh. Ilonca, M. Peteanu, Solid State Commun. 52 (1984) 167. [10] D. Loveridge, S. Parke, Phys. Chem. Glasses 12 (1971) 19. [11] J.W.H. Schreurs, J. Chem. Phys. 69 (1978) 2151. [12] I. Ardelean, M. Peteanu, Gh. Ilonca, Phys. Status Solidi a 58 (1980) K33. [13] I. Ardelean, Gh. Ilonca, V. Simon, O. Cozar, V. Ioncu, S. Filip, Solid State Commun. 98 (1996) 651. [14] I. Ardelean, M. Peteanu, S. Filip, V. Simon, I. Todor, Solid State Commun. 105 (1998) 339. [15] R.C. Nicklin, C.P. Poole, H.A. Farach, J. Chem. Phys. 68 (1973) 2579. [16] V.N. Lazucin, V. Chepeleva, DAN SSSR 214 (1974) 787. [17] V. Cerny, B. Petrova, M. Frumar, J. Non-Cryst. Solids 125 (1990) 17. [18] B. Petrova, M. Frumar, E. Cernoskova, V. Cerny, J. Non-Cryst. Solids 161 (1993) 316. [19] J.G. Kliava, Phys. Status Solidi B 134 (1986) 431. [20] Gh. Ilonca, I. Ardelean, O. Cozar, J. Physique 49 (1988) 8. [21] I. Ardelean, M. Peteanu, S. Filip, D. Alexandru, J. Magn. Magn. Mater. 157 (1996) 239. [22] I. Ardelean, M. Peteanu, V. Simon, S. Simon, M. Flora, Phys. Chem. Glasses 41 (2000) 153. [23] I. Ardelean, M. Peteanu, I. Todor, Phys. Ghem. Glasses 43 (2002) 276. [24] E. Burzo, I. Ardelean, I. Ursu, J. Mater. Sci. 15 (1980) 581. [25] E. Burzo, I. Ursu, D. Ungur, I. Ardelean, Mater. Res. Bull. 15 (1980) 1273. [26] E. Burzo, I. Ardelean, Phys. Status Solidi B 87 (1978) K 137. [27] D.L. Griscom, J. Non-Cryst. Solids 40 (1980) 211. [28] P. Tarte, Spectrochim. Acta 18 (1962) 467. [29] P. Tarte, in: I.A. Prins (Ed.), Physics of Non Crystalline Solids, Elsevier, Amsterdam, 1964, p. 549. [30] R.A. Condrate, in: L.D. Pye, H.I. Stevens, W.C. Lacourse (Eds.), Introduction to Glass Science, Plenum Press, New York, 1972, p. 101.
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