Materials Chemistry and Physics 85 (2004) 215–221 Effect of Bi 2 O 3 on electron paramagnetic resonance, optical transmission and conductivity in vanadyl-doped Bi 2 O 3 ·K 2 O·B 2 O 3 glasses A. Agarwal a,∗ , V.P. Seth b , P.S. Gahlot b , S. Khasa c , P. Chand d a Department of Applied Physics, G.J. University, Hisar 125001, India b Department of Physics, M.D. University, Rohtak 124001, India c Department of Physics, Government College, Bahadurgarh 124507, India d Department of Physics, Indian Institute of Technology, Kanpur, India Received 11 June 2003; received in revised form 18 January 2004; accepted 22 January 2004 Abstract Glasses with composition xBi 2 O 3 ·(30 - x)K 2 O·70B 2 O 3 doped with 2 mol% of V 2 O 5 have been prepared over the range 0 ≤ x ≤ 15 (in mol%). The electron paramagnetic resonance spectra of VO 2+ in these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature. The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that, with increase in Bi 2 O 3 :K 2 O ratio, tetragonal distortion of the V 4+ O 6 complex increases and there is an expansion of the 3d xy orbit of unpaired electron in the vanadium ion. The values of theoretical optical basicity have also been reported. The molecular orbital coefficients have been calculated by recording the optical transmission spectra in the wavelength range 500–850 nm. The direct-current electrical conductivity, σ , has been measured in the temperature range 443–523 K. σ decreases with increase in Bi 2 O 3 :K 2 O ratio because of the decrease in the mobility and number of mobile K + ions and there is no electronic contribution to the conductivity by Bi 2 O 3 . © 2004 Elsevier B.V. All rights reserved. Keywords: Electron paramagnetic resonance; Oxide glasses; Electrical conductivity; Vanadyl ion 1. Introduction Electron paramagnetic resonance (EPR) spectroscopy is an experimental technique to obtain detailed information on some of the structural and dynamic phenomena of a mate- rial and to identify site symmetry around transition metal ions in glasses [1,2]. The transition metal ions can be used to probe the glass structure, because their outer d electron orbital functions have rather broad radial distributions and their responses to surroundings cations are very sensitive [3]. The glasses doped with transition metal ions have at- tracted a great deal of attention because of their potential applications in the development of new tunable solid-state lasers, solar-energy converters, and fiber-optic communica- tion devices [4]. In the present study, the vanadyl ion (VO 2+ ) has been used as a spectroscopic probe for characterization of glasses because their EPR spectra are rich in hyperfine structure due ∗ Corresponding author. Tel.: +91-1662-277081; fax: +91-1662-276240. E-mail address: aagju@yahoo.com (A. Agarwal). to the 51 V nucleus (nuclear spin I = 7 2 ) and is easily observ- able at room temperature [5–11]. It has been well established that alkali borate glasses can be used as solid electrolytes [12–14]. These glassy electrolytes are of significance be- cause of their inherent advantages such as isotropic conduc- tivity, ease of preparation, better thermal stability and the large available composition ranges. It has been shown that the addition of Bi 2 O 3 leads to an improvement in the chemi- cal durability and thermal stability of oxide glasses [15]. The aim of the present work is to investigate the effect of Bi 2 O 3 on the EPR, optical transmission and direct-current (DC) conductivity in vanadyl-doped potassium borate glasses. 2. Experimental The analytical grade reagents of K 2 CO 3 ,H 3 BO 3 , Bi 2 O 3 and V 2 O 5 were used as starting materials. The glass compo- sitions in mol% are shown in Table 1. Each batch was melted at 1273 K in a porcelain crucible for 0.5 h in an electric muffle furnace. The melt was poured onto one carbon plate and pressed with another very quickly. The first-derivative 0254-0584/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2004.01.017