Glass formation and structure of glasses in B 2 O 3 ―Bi 2 O 3 ―MoO 3 system R. Iordanova a , L. Aleksandrov a , A. Bachvarova-Nedelcheva a, ⁎, M. AtaaLa b , Y. Dimitriev b a Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, “Acad. G. Bonchev”, Bld. 11, 1113 Sofia, Bulgaria b University of Chemical Technology and Metallurgy, 8 Kl. Ohridski blvd., 1756 Sofia, Bulgaria abstract article info Article history: Received 15 September 2010 Received in revised form 9 November 2010 Accepted 9 December 2010 Available online 9 February 2011 Keywords: Non-traditional glasses; Amorphous network; Structure The purpose of this paper is to study the glass formation tendency in the ternary system B 2 O 3 ―Bi 2 O 3 ―MoO 3 and to define the main structural units building the amorphous network. A wide glass formation area was determined which is situated near the Bi 2 O 3 ―B 2 O 3 side. A liquid phase separation region was observed near the MoO 3 ―B 2 O 3 side for compositions containing below 25 mol% Bi 2 O 3 and their microheterogeneous structure was observed by SEM. The phase formation was characterized by X-ray diffraction (XRD). By DTA was established the glass transition temperature (T g ) in the range of 380–420 °C and crystallization temperature (T x ) vary between 420 and 540 °C. The main building units forming the amorphous network are BO 3 (1270 and 1200 cm -1 ), BO 4 (930–880, 1050–1040 cm -1 ), MoO 4 (840–760 cm -1 ) and BiO 6 (470 cm -1 ). It was proved that Bi 2 O 3 favors the BO 3 →BO 4 transformations while MoO 3 preserves BO 3 units in the amorphous network. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In our previous studies we examined the tendency of glass formation and immiscibility in the three component boromolybdate systems containing transition metal oxides [1,2] and rare earth oxides [3–5]. Most of the results obtained by us and other authors were summarized in a paper published recently [6]. Despite, the existing problem of homogeneity of the super cooled boro-molybdate melts it was found that MoO 3 could be a suitable component for decreasing the melting temperature and modifying the properties of high temperature rare-earth borate glasses [6]. From a practical point of view two striking examples could be pointed out. The Komatsu's group developed a technique for laser induced crystallization in Ln 2 O 3 ―MoO 3 ―B 2 O 3 (Ln = lanthanide) glasses with the formation of Ln 2 (MoO 4 ) 3 phase [7,8]. In multi-component nuclear waste glasses the MoO 3 content is of great importance in order to improve its solubility [9,10]. From a structural point of view, it is a challenge to study the glass formation in systems containing a typical glass former (B 2 O 3 ) and conditional network formers (Bi 2 O 3 , MoO 3 ,V 2 O 5 , WO 3 , etc.), because they are characterized by a different local structure and different connectivity between the polyhedra in the amorphous structure. The object of the present study is the MoO 3 ―Bi 2 O 3 ―B 2 O 3 system. Every one of the components forms independently a separate family of amorphous materials known as bismuthate, molybdate and borate glasses [11–14]. According to Zarzycki [15] due to the competitive action in the network formation of the components it is not possible to establish in advance if mixed chains form or there are micro-domains richer in one of the components. That is why we consider the investigation of such type of model systems as actual from a different point of view. In the binary system Bi 2 O 3 -MoO 3 , glasses were obtained only at a high cooling rate toward MoO 3 oxide and it was proved that it is the stronger network former. Most of the earlier investigations on the glass formation in the Bi 2 O 3 ―B 2 O 3 system were summarized by Ref. [16]. It was demonstrated that the transparent glasses could be obtained between 20 and 85 mol% Bi 2 O 3 . By X-ray diffraction, IR spectroscopy, Neutron diffraction and NMR it was proved that in the binary bismuth–borate glasses, BO 4 groups are formed in a wide concentration range [17–21]. Later, this problem was discussed again in a set of three component bismuth–borate glasses and was proved also the specific role of Bi 2 O 3 [22–31]. The collected data on several outstanding properties like high density, refractive index and very high coefficient for nonlinear phenomena (second and third harmonic generation) made these systems very attractive from a practical point of view [22–32]. The aim of the present work is to determine the glass formation range, to analyze the structural transformation depending on compo- sition. The IR spectroscopy was used as a simple and versatile structural method in this paper. The obtained preliminary results will be useful for the development of more realistic structural models. 2. Experimental procedure All compositions (10 g) were prepared using reagent grade oxides MoO 3 (Merck, p.a.), Bi 2 O 3 (Merck, p.a.) and H 3 BO 3 (Reachim, chem. pure) as starting materials. The homogenized batches were melted for 15 min in air atmosphere in alumina crucibles. The melting temper- ature was limited to 1200 °C in order to decrease the volatility of the Journal of Non-Crystalline Solids 357 (2011) 2663–2668 ⁎ Corresponding author. Tel.: + 359 2 979 63 17. E-mail address: albenadb@svr.igic.bas.bg (A. Bachvarova-Nedelcheva). 0022-3093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.12.056 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol