HAL Id: jpa-00222494
https://hal.archives-ouvertes.fr/jpa-00222494
Submitted on 1 Jan 1982
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
RAMAN STUDIES OF B2O3 GLASS STUCTURE : 10B→11B ISOTOPIC SUBSTITUTION
F. Galeener, A. Geissberger
To cite this version:
F. Galeener, A. Geissberger. RAMAN STUDIES OF B2O3 GLASS STUCTURE : 10B→11B ISOTOPIC SUBSTITUTION. Journal de Physique Colloques, 1982, 43 (C9), pp.C9-343-C9-346.
�10.1051/jphyscol:1982965�. �jpa-00222494�
Colloque C9, supplement au n°12, Tome 43, decemhre 1982 page C9-343
RAMAN STUDIES OF B ^ GLASS STRUCTURE :1 0B +l : LB ISOTOPIC SUBSTITUTION
F.L. G a l e e n e r and A.E. G e i s s b e r g e r
Xerox Palo Alto Research Centers, Palo Alto, CA 94304, U.S.A.
Résumé. - Nous présentons le déplacement des spectres Raman de B203 vitreux obtenus en remplaçant l'isotope 10B par l'isotope 11B, et nous interprétons les raies non déplacées (450 et 808 cm1) en terme de modes étendus et localisés (respectivement) d'un réseau d'anneaux de 'boroxol'.
Abstract. - We report the 10B-»11B isotope shifts of the Raman spectra of vitreous B203, and interpret the unshifted lines (450 and 808 cm'1) in terms of extended and localized modes (respectively) of a network of boroxol rings.
1. Introduction. - Vitreous ( v ) B203 is a colorless glass that has received much attention in recent times [1], partly because of controversy concerning the structural model based on boroxol rings [2]. These planar hexagonal (B303) rings do not occur in crystalline forms of B203 but do occur in many borate crystals [1]. Recently, Galeener [3] has proposed that similar planar rings exist in substantial concentration in numerous glasses, and that their presence may be revealed by Raman spectroscopy. It is therefore of particular interest to the authors to further test the boroxol ring hypothesis in v-B203, and to understand the Raman signature of such rings.
Galeener and Mikkelsen [4] have reported Raman scattering in 180-substituted v-Si02 and found that the single dominant (highly polarized) Raman line shifts as if there were no Si motion involved, confirming the prediction of a continuous random network (CRN) model based on central forces only [5]. More recently, Galeener and Thorpe [6]
have developed a central forces calculation for a CRN of planar boroxol rings, and this calculation predicts two highly polarized Raman lines which involve little or no B motion.
It is in this context that we report the effects of 10B->11B isotopic substitution on the Raman spectra of v-B203. For recent Raman and infrared studies of unsubstituted material, see Refs. 7 and 8.
2. Samples. - All samples were prepared from powdered orthoboric acid (H3B03) which was heated in a Pt crucible at ~380°C for 2 hours until all (H20) vapor was expelled, leaving a clear mass. The furnace was raised to 800°C for ~'/z hour to assure outgassing, and then to 1450°C for 2 hours. The melt was then poured into a carbon mold on a hotplate at 250°C, to produce a parallelepiped approximately 20 mm x 10 mm x 5 mm.
This was annealed at 270°C in a furnace for 12 hours, then furnace cooled. After very light polishing, the samples appeared strain-free under crossed polarizers. The 10B samples came from orthoboric acid enriched to 87.5 atomic percent 1 0B, kindly provided by Prof. A. C. Wright of Reading University, U. K. The 11B starting material was natural abundance H3B03 (from Alpha Ventron) and therefore contained 80.2 atomic percent 1 1B.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982965
C9-344 JOURNAL DE PHYSIQUE
These percentages are sufficiently high that we label the results 'OB and "B, respectively.
Special care was taken to assure that the samples had indentical thermal histories, since effects of thermal history on some Raman lines in other glasses (such as v-Si02) have been reported [9].
3. Experimental Results. - Representative Raman spectra obtained from these two materials are shown in Fig. 1. Spectroscopic equipment and parameters were as reported in Ref. 7. The only qualitative difference between the 'OB and "B spectra is the conversion of the shoulder at -750 cm-I in the HH spectrum of Fig. 1 (a) into a well defined peak at 737 cm-' in the HH spectrum of Fig. 1 (b). All the samples exhibited some luminescence which was minimized by obtaining the data at 457.9 nm. This luminescence accounts for the elevated level of background seen in the "gap" region 850-1200 cm-', relative to that reported in Ref. 7.
A precise measure of the peak positions was obtained from expanded presentations, and the values are recorded in Table 1, along with the resultant isotopic shifts A and their uncertainties.
4. Discussion. - As will be shown in detail elsewhere [6], most of these shifts compare well with predictions of the CRN of boroxol rings. The largest discrepancies are for the spectral lines entered in rows (4) and (5) of Table 1; these and other smaller discrepancies are probably due to omission of non-central forces [5] from the theory. The
1 1 1 1 ~ 1 1 1 1 ~ 1 I I I ~ I
10 - RAMAN SPECTRA HH PEAK
h, = 457 g nm AT 90 UNITS la)
- AND 808 em-' VITREOUS -
"'B2 o3 -
500 1000 1500
WAVE NUMBER. W icm-')
I 1 1 l j l l l I / 1 , , 1 1 1 RAMAN SPECTRA HH PEAK
hL = 457.9 nm AT 80 UNlTS lbl
AND 809 cm-' VITREOUS
500 1000 1500
WAVE NUMBER, W lcm-')
Fig. 1 - The polarized room
temperature Raman spectra of boric oxide glass, obtained for high concentrations of two different boron isotopes, atomic weight 10 in (a) and 11 in (b).
10 I l l l l l l l l i , l , l ,
- HH RAMAN SPECTRUM SS VITREOUS -
- - h , = 457 9 nm 808 cm-' 4 % -
>
-450 cm '
-1AVE NUMBER, W lcm-'1
Fig. 2 - The HH room temperature Raman spectrum of natural abundance boric oxide glass. The two highly polarized lines (450 and 808 cm-') are ascribed respectively to the relatively extended and localized modes shown. These modes involve little or no B motion and are therefore consistent with the observed absence of B isotope shifts in groups (1) and (6) of Table 1.
shifts A for boric oxide glass. The horizontal lines delineate a mode seen in both HH and HV polarization, for which the average shift is given in column (d).
The uncertainty in (e) is based on difficulty in reading the peak positions. Note that the shifts in groups (1) and (6) are essentially zero.
OBSERVA TlONS ISOTOPIC SHIFT DATA
(a) (b) (c) (dl (el
Average Uncertainty Group ' O B ~ O ~ 11B203 A = (a)-(b) A in A
(10) HH 1510 1467 4 3 -43 (*a
(11) HV 1555 1510 -45 -45 (*8>
shifts for the highest frequency modes are predicted quite accurately. The most highly polarized lines, rows (1) and (6) of Table 1, are predicted to have very small shifts, namely A(1)= 0 cm-I and A(6) -- -3 cm-l, and these compare well with the observations, tending to confirm the model and the nearly complete absence of B motion in the theoret~cal modes.
We interpret these two essentially unshifted lines as shown in Fig. 2. The broad highly polarized Raman line at -450 cm-I [see also Fig. I(b)] is analogous to the dominant Raman line in v-Si02 [5,4] in that it represents i;~-phase motion of the bridging 0 atoms with little or no cation motion. It is broad because of the spread in B-0-B angles [5]
bridging between rings and is extended because of the in-phase character [5,10]. The somewhat less polarized line at 808 cm.l has no analogue in v-Si02 since it represents a breathing mode of the structurally regular boroxol ring, and is therefore quite sharp. The
C9-346 JOURNAL DE PHYSIQUE
CRN model [6] shows that this mode is highly degenerate. We conclude that the mode at 808 cm-' represents motion similar to that shown in Fig. 2, centered on each ring and localized in its immediate neighborhood. Minimal cation motion accounts in both cases for the very small isotopic shifts.
The high polarization, sharpness, dominance over other features and absence of cation motion in the 808 cm-' line supports the assignment elsewhere [3] of the 606 cm-'
"defect" line in v-Si02 to planar 3-fold rings.
5. Acknowledgments. - The authors are grateful to the U.S. Office of Naval Research (G.B.Wright) for support of this work under contract N00014-80-(3-0713.
References
1. See, e.g., PYE, L. D., FRECHETTE, V. D., and KREIDL, N. J., Eds., Borate Glasses (Plenum, New York, 1978).
2. For a recent dissenting opinion, see ELLIOTT, S. R., Philos. Mag. (1978) 435.
3. GALEENER, F. L., J. Non-Crystall. Solids 49 (1982) 53.
4. GALEENER, F. L. and MIKKELSEN, J. C., Jr., Phys. Rev. B 23 (1981) 5527.
5. GALEENER, F. L., Phys. Rev. 8 19 (1979) 4292.
6. GALEENER, F. L. and THORPE, M. F., to be submitted to Phys. Rev. B.
7. GALEENER, F. L., LUCOVSKY, G. and MIKKELSEN, J. C., Jr., Phys. Rev. B (1980)
3983.
8. WALRAFEN, G. E., SAMANTA, S. R. and KRISHNAN, P. N., J. Chem. Phys. 2 (1980) 113.
9. GALEENER, F. L., MIKKELSEN, J. C., Jr., and JOHNSON, N. M., in The Physics of SiO:, and its Interfaces, PANTELIDES, S.T., Ed. (Pergamon, New York, 1978) p. 284;
also MIKKELSEN, J. C., Jr., and GALEENER, F. L., J. Non-Crystall. Solids 37 (1980) 71.
10. GALEENER, F. L.. J. Physique 42-C6 (1981) 24.
