Journal of Physics and Chemistry of Solids 67 (2006) 2478–2488 Nickel ion—A structural probe in BaO–Al 2 O 3 –P 2 O 5 glass system by means of dielectric, spectroscopic and magnetic studies S.V.G.V.A. Prasad, M. Srinivasa Reddy, N. Veeraiah à Department of Physics, Acharya Nagarjuna University P.G. Centre, Nuzvid-521 201, AP, India Received 14 May 2006; received in revised form 4 July 2006; accepted 6 July 2006 Abstract BaO–Al 2 O 3 –P 2 O 5 glasses containing different concentrations of NiO (ranging from 0 to 1.0 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption spectra), magnetic susceptibility and dielectric properties (constant e 0 , loss tan d, AC conductivity s AC over a range of frequency and temperature) of these glasses have been carried out. The studies on chemical durability indicate that there is a significant increase in the corrosion resistance of the glasses; where as the results of differential thermal analysis suggests that there is a substantial improvement in the glass forming ability, with increase in the concentration of NiO up to 0.6 mol% in the glass matrix. The optical absorption, magnetic susceptibility and IR spectral studies point out nickel ions occupy both tetrahedral and octahedral positions in the glass network; the later positions seems to be dominant when the concentration of NiO is beyond 0.6 mol% in the glass matrix. The studies of dielectric properties reveal that the presence of nickel oxide in the glass network causes a considerable improvement in the insulating strength of the se glasses when the concentration of NiOp0.6 mol%. r 2006 Elsevier Ltd. All rights reserved. Keywords: A. Glasses; D. Electrical properties 1. Introduction Phosphate glasses are known due their superior physical properties such as high thermal expansion coefficients, low melting and softening temperatures and high ultra-violet and far infrared transmission [1–5]. However, the poor chemical durability, high hygroscopic and volatile nature of phosphate glasses restricted them from replacing the conventional glasses by and large in technological applica- tions. In view of these, a variety of metal oxides like CaO, MgO, ZnO, SnO, NiO, Al 2 O 3 , Ga 2 O 3 , Fe 2 O 3 , TiO 2 , MoO 3 , MnO, etc., have been added and were found to be good stabilizers of phosphate glasses [6–12]. The modifier oxide, BaO, when entered in to the glass matrix, a polyhedron is formed while it is surrounded by two Q 2 and several Q 3 , PO 4 tetrahedrons [13]. Among various other metal oxides, the introduction of Al 2 O 3 in to phosphate glass network is expected to enhance the chemical durability of these glasses, since Al 2 O 3 enters into the glass network with AlO 4 structural units. Incidentally, the vibrational frequency of Al–O stretching in AlO 4 structural units is found to be around 700 cm 1 [14] in this region, the band due to P–O–P stretching vibrations of PO 4 groups is also present [15,16]. As a consequence, it is quite likely that tetrahedral Al ions to cross-link with the neighbouring phosphor chains by the formation of AlPO 4 species that strengthen the glass network. The presence of such linkages improves the aqueous durability, increases the glass transition tempera- ture and reduces the thermal expansion coefficient of these glasses. The divalent nickel ion is an interesting paramagnetic ion to probe in the glass systems. Nickel ions are reported to occupy both tetrahedral and octahedral positions in the glass matrices [17–22]. Attempts were also made to investigate the lasing action of these ions in certain crystal and glass systems since these ions possess several strong absorption bands in the visible and NIR regions where the pumping sources are easily available [23]. The octahedrally ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2006.07.002 à Corresponding author. Tel.:+91 8656 235551; fax:+91 8656 235200. E-mail address: nvr8@redifmail.com (N. Veeraiah).