Physical, mechanical and structural properties of BaO–CaF 2 –P 2 O 5 glasses Manoj Kumar Narayanan ⁎, H.D. Shashikala Material Processing Laboratory, Department of Physics, National Institute of Technology Karnataka, Surathkal, Mangalore 575025, India abstract article info Article history: Received 18 August 2015 Received in revised form 30 September 2015 Accepted 2 October 2015 Keywords: Glasses; Mechanical properties; Fourier transform infrared (FTIR) spectroscopy; Raman spectroscopy Mechanical properties and structure of melt-quenched ternary barium phosphate glasses belonging to the com- position (50 - X)BaO–XCaF 2 –50P 2 O 5 (X = 0 to 10 mol%) were studied using Vickers indentation and vibrational spectroscopy. Elastic moduli of prepared samples were calculated using the Makishima and Mackenzie (M–M) model. Density of glasses was measured using the Archimedes method, while molar volume and atomic packing density were calculated from measured density to study structural changes in the glass matrix. Vickers hardness and brittleness increased and fracture toughness decreased with increase in CaF 2 content. This can be attributed to increase in the compactness of phosphate bonds and reduction in the molar volume of glasses with partial sub- stitution of Ba 2+ with Ca 2+ . Infrared and Raman spectroscopies revealed that the glass network mainly consisted of metaphosphate units arranged in chain and ring structures together with small amounts of ultraphosphate and pyrophosphate units. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Phosphate glasses have superior properties such as high refractive index, high ultraviolet (UV) transmission, high electrical conductivity, low melting temperature and low glass transition temperature, which make them suitable candidates for technological applications such as optical fibers for data transmission, host glasses for solid state lasers, luminescent solar energy concentrators, immobilization of nuclear wastes, solid state batteries and glass-to-metal sealing [1,2,3]. Poor ther- mal stability against crystallization, low chemical durability, volatile and hygroscopic nature of phosphate glasses limit their extensive practical applications. These properties can be improved by introducing different metal oxides into the glass matrix [4,5]. Barium phosphate glasses with higher concentration of barium oxide (≥ 50 mol%) show high solubility of active ions, low photoelastic constants and good water durability compared to other alkali earth phosphate glasses [6]. Barium and calci- um metaphosphate glasses are optically transparent dielectric matrices used for the preparation of noble metal nanoparticle embedded glasses due to their high metal solubility [7]. Addition of calcium fluoride (CaF 2 ) to the glass batch reduces the liquidus temperature to a substantial ex- tent and improves the durability of glasses by reducing the hydroxyl content [8,9]. Glasses with excellent mechanical and elastic properties are re- quired for many applications, which include glass components for tele- vision tubes, architectural use, optical fibers for data transmission, temporary implants for bone repair and reconstruction [10,11,12]. Therefore, an investigation of both mechanical and elastic properties is necessary for the selection of appropriate glasses for technological and biomedical applications. Properties of all glasses, including physical and mechanical properties depend on their local structure determined by the composition [13]. Structure determination in glasses is a difficult task compared to that of a crystal, because there is no particular method available for investigating the structure of an amorphous solid [14]. Some perception of the glass structure can be obtained by combining re- sults of different spectroscopic techniques such as infrared, Raman, NMR, neutron and X-ray diffraction. Raman and infrared spectroscopies are two powerful tools, which exhibit dependence of local structure on composition and help to understand the effect of composition on glass properties [15]. Hence both these techniques are used to study short and intermediate range orders in glass. Density of glasses, which is relat- ed to molar volume and atomic packing density, also plays an important role in the study of structure of glasses [16]. In the previous paper [8], we have reported that the addition of cal- cium fluoride (CaF 2 ) to barium metaphosphate glasses improves their thermal stability against crystallization and glass forming ability. These glasses with composition (50 - X)BaO–XCaF 2 –50P 2 O 5 (BaPF, X = 0 to 10 mol%) also show thermal stability parameter of 100 °C, hence they are suitable for fiber fabrication. In the present work less in- vestigated properties like brittleness, fracture toughness and hardness of these glasses are studied using Vickers indentation and Makishima and Mackenzie model (1973 and 1975) to check the improvement in mechanical properties with CaF 2 addition. Change in density, molar volume and atomic packing density with composition are also being investigated to get an insight into the structure of prepared glasses. In addition to this, infrared and Raman spectroscopies are used to probe the interaction of cations with their local environment and to determine Journal of Non-Crystalline Solids 430 (2015) 79–86 ⁎ Corresponding author. E-mail addresses: manukokkal01@gmail.com, mkn.ph11f03@nitk.edu.in (M.K. Narayanan). http://dx.doi.org/10.1016/j.jnoncrysol.2015.10.006 0022-3093/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol