ISSN 1087-6596, Glass Physics and Chemistry, 2016, Vol. 42, No. 2, pp. 141–148. © Pleiades Publishing, Ltd., 2016. 141 1 INTRODUCTION Nonlinear variation in properties (density, viscos- ity, glass-transition temperature, and conductivity) was observed when one alkali component in a multi component glass is systematically replaced by another alkali. This phenomenon is referred as mixed-alkali effect (MAE). Besides glasses containing only alkali ions, such nonlinear behavior was exhibited by certain mixed alkali-alkaline earth oxide glasses [1]. Many articles were reported on the MAE in phosphate, borate, tellurite, bismuthate, and silicate glasses [2– 4]. Most technical glasses contain a variety of different cations, but almost all studies on the MAE are focused on glasses with only two kinds of alkali ions. There- fore, it is very important to study the ion dynamics of glasses with two or more types of mixed alkali-alkaline ions. Borate glasses with great variability in composi- tion, structure, and properties have a promising future in the fields of linear and nonlinear optics. Borate glasses can be used as thermal insulators and textile fiberglass. Bearing in mind the numerous applications of borate glasses, the authors made an attempt to study the MAE in borate glasses with two types of alkali ions. 1 The article is published in the original. Glasses doped with transition metal (TM) ions have attracted a great deal of attention because of their potential applications in the development of new tun- able solid-state lasers, solar energy converters. Copper is used in the preparation of some industrial colored glasses. In this paper, we report on the measurement of density, glass-transition temperature, EPR and optical absorption of copper doped binary mixed alkali-alka- line earth oxide borate glasses (25 – x)Li 2 O–xK 2 O– 12.5BaO–12.5MgO–49B 2 O 3 –1CuO (x = 0, 5, 10, 15 and 20 mol %). EXPERIMENTAL The oxide borate glasses (25 – x)Li 2 O–xK 2 O– 12.5BaO–12.5MgO–49B 2 O 3 –1CuO were prepared by the melt quenching technique. The starting materi- als were Merck (GR grades) boric acid H 3 BO 3 , lithium oxide (Li 2 O), potassium carbonate (K 2 CO 3 ), magne- sium oxide (MgO), barium oxide (BaO) and copper oxide (CuO). The calculated amounts by mol % of these compounds were thoroughly mixed and grind in agate mortar with pestle. The ingradients were taken into a porcelain crucible and melted in an electrically EPR and Optical Studies on Binary Mixed Alkali-Alkaline Earth Oxide Borate Glasses Doped with Cu 2+ Ions 1 G. Srinivas, J. Siva Kumar, Md. Shareefuddin, M. N. Chary, and R. Sayanna Department of Physics, Osmania University, Hyderabad, Telangana state, India e-mail: srinu123@gmail.com Received July 22, 2014 Abstract—Mixed alkali alkaline earth oxide borate glasses of the composition (25 – x)Li 2 O–xK 2 O– 12.5BaO–12.5MgO–49B 2 O 3 –1CuO (x = 0, 5, 10, 15 and 20 mol %) were prepared by the melt quenching technique. The X-ray diffractograms of all the glass samples were recorded at room temperature. Peak free X- ray spectra revealed the amorphous nature of all the prepared glasses. Modulated differential scanning calo- rimetry (MDSC) was used to determine the glass-transition temperature (T g ). The probable mixed alkali effect was investigated using experimental techniques like density, molar volume, MDSC, electron paramag- netic resonance (EPR), and optical absorption studies. From the EPR spectra the spin-Hamiltonian param- eters were evaluated. The spin-Hamiltonian parameter values indicated that the ground state of Cu 2+ is orbital ( 2 B 1g ) and the site symmetry around Cu 2+ is tetragonally distorted octahedral. The variation of g || and A || as a function of Li 2 O content was found to be nonlinear. A broad optical absorption band was observed in all the glasses containing Cu 2+ ions corresponding to 2 B 1g → 2 B 2g transition. From the optical absorption studies the values of the optical band gap (E opt ) for indirect, direct transitions and Urbarch energy (ΔE) have been evaluated. By co-relating the EPR and optical absorption data, bonding parameters α 2 , β 2 and were evaluated. Keywords: borate glasses, modulated differential scanning calorimetry, EPR and optical absorption DOI: 10.1134/S1087659616020152 - 2 2 x y d β 2 1