224 Journal of Non-Crystalhne Solids 126 (1990) 224-230 North-Holland Raman study of lead borate glasses B.N. Meera, A.K. Sood, N. Chandrabhas and J. Ramakrishna 1 Department of Physws, In&an Insutute of Scwnce, Bangalore- 560 012, Indta Received 9 November 1989 Revised manuscript received 18 July 1990 Glasses in the system xPbO:(100- x)B203 (22 _<x < 85 mol%) have been studied by Raman spectroscopy with a view to understand the effect of PbO on the borate network. The conversion of three-fold to four-fold coordinated boron takes place primanly by incorporation of BO4 into boroxol rings in the form of pentaborate and diborate umts. For high lead content, back conversmn of four to three coordinatmn of borons occurs and the network consists primardy of pyroborate, orthoborate and metaborate groups. 1. Introduction Raman spectroscopy has proved to be a useful tool in the study of amorphous materials. Raman spectra of crystalline and vitreous borates have been used as a basis for the qualitative identifica- tion of glass forming structural units in these glasses [1-3]. Due to structural disorder a com- plete vibrational analysis in glasses is not possible from an ab-initio point of view and an analysis is done primarily by comparing the spectra of these glasses with those of crystalline borates for which the structures are known. Pure B203 and alkali borate glasses, R20-B203 (R = Li, Na, K, Cs and Rb), have been studied extensively by Raman scattering [4-16]. Pure vitreous B203 is known to be made up of a ran- dom network of boroxol rings in which borons are three coordinated [17]. The addition of alkali oxide results in the formation of four coordinated borons, and the fraction of these four coordinated units can be estimated by NMR [18-22]. By com- bining the Raman scattering studies and NMR investigations with the available crystallographic data, structural groups present in these glasses i Author to whom correspondence should be addressed. have been clearly identified. Figure 1 shows the several structural groups present in various borate compounds. Lead borate, xPbO : (100 - x)B203, is an inter- esting system because the glass phase can be formed over a wide concentration of lead oxide [23,24]. Moreover, PbO can enter the glass net- work both as a network modifier and also as a network former. Hence the structure of these glasses is expected to be different from that of alkali borate glasses. Bray and co-workers [25,26] have carried out NMR investigations of lead borate glasses and compounds and their study indicates that N 4 (the fraction of the four coordi- nated boron atoms in the glass) increases with the PbO content up to 50 mol% PbO. Further increase of PbO decreases the value of N 4. Not much Raman spectroscopic work has been carried out on lead borate glasses with the exception of the preliminary work of Konijnendijk and Verweij [27], in which the spectra of xPbO : (100 - x)B203 for x = 25, 33.3, 50 and 70 mol% are presented. The peak assignment and the identification of the structural groups have not been completely made. Therefore, the present work consists of a sys- tematic study of the xPbO :(100- x)B20 3 glass system covering a wide range of concentration with x varying between 22 and 85 mol%. 0022-3093/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)