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Item Optical and mechanical properties of calcium phosphate glasses(Maik Nauka Publishing / Springer SBM compmg@maik.ru, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.Binary calcium phosphate glasses in the system, xCaO-(100 - x) P 2O5 with x = 30, 35, 40, 45, and 50 mol % were prepared by conventional melt quenching technique. The density, molar volume and refractive index of the glasses were found to increase with the increase in CaO content. Structural investigation by FTIR spectroscopy revealed that the substitution of P2O5 by CaO depolymerizes the phosphate glass network by systematic conversion of Q3 structural units to Q2 structural units by breaking the P-O-P links. From the optical absorption studies, the optical band gap values were found to decrease with increasing CaO content which can be due to increase in the concentration of non-bridging oxygens in the glass network. Vickers hardness increased with the calcium oxide content due to densification. The fracture toughness decreases with the increase in CaO content due to the increase in the bond density between the modifying cations and the non-bridging oxygens in the glass network. It was observed that brittleness increases with the addition of CaO content which can be mainly attributed to the decrease in the molar volume. © 2014 Pleiades Publishing, Ltd.Item Structural, optical and mechanical properties of ternary CaO-CaF2-P2O5 glasses(Tsinghua University, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.The ternary phosphate glass series (50?x)CaO-xCaF2-50P2O5 (x = 0–20 mol%) were synthesized using melt quench technique. Structural, optical and mechanical properties were investigated with increase in CaF2 content. Using X-ray diffraction (XRD), synthesized glasses were confirmed to be amorphous in nature. Replacement of oxygen ions by fluorine ions increased the values of density. Decrease in refractive index due to the low polarizability of fluorine ions in the glass matrix was observed. In Fourier transform infrared (FTIR) spectra, the slight variation in ?as (PO2) band position and intensity could be attributed to replacement of fluorine ions for oxygen ions in phosphate glass structure. These data were well supported by Raman spectra. Optical band gap energy increased from 3.44 eV to 3.64 eV with increase in CaF2 content, and Urbach energy decreased suggesting that the fluorine ions reduced the tail energy states in the band gap compared to the oxygen ions. Mechanical parameters such as Vickers hardness, fracture toughness and brittleness were evaluated from the Vickers micro indentation measurements. Increase in Vickers hardness, decrease in fracture toughness and increase in brittleness were observed with increase in CaF2 content. © 2014, The Author(s).Item Optical, dielectric and mechanical properties of silver nanoparticle embedded calcium phosphate glass(Elsevier, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.Silver nanoparticles have been embedded in 50 mol% CaO-50 mol% P 2O5 glass using melt quenching technique. The quenched glasses were heat treated at 550 °C for different durations between 10 and 50 h. The growth of silver nanoparticles in glass matrix appeared to be time dependent. FTIR spectra revealed that silver nanocluster formation had not affected the position of vibration bands of basic phosphate tetrahedral network. The Ag nanoparticle embedded glass matrix showed the red shift and broadening of the surface plasmon resonance (SPR) peak in the visible region with the increase in the duration of the heat treatment. Results showed the increase in size of the nanoparticles in glass matrix with heat treatment which was further confirmed using transmission electron microscopy and XRD. X-ray diffraction studies indicated the presence of Ag crystalline peaks along with amorphous structure on heat treatment at 550 °C for 50 h. The dielectric constant of these glasses increased as the duration of the heat treatment increased. Increase in both Vickers hardness and fracture toughness, and decrease in brittleness were observed which can be attributed to the increase in size of the nanoparticles in glass matrix. © 2014 Elsevier B.V.