Browsing by Author "Asokan K"

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    CERAMIZATION OF ABO GLASSES UNDER THE INFLUENCE OF O7+ ION IRRADIATION (Article)
    (Elsevier Ltd, 2025-02) Karthika S; Asokan K; Marimuthu K; Meena, Ramcharan; Sundari, S Shanmuga
    Alkali borate (ABO) glasses of the composition 15A2O-85B2O3 where A = Li (lithium), Na (sodium) and K (potassium) are prepared using the thermal melt quenching technique. Pure analytical grades of boric acid (H3BO3), lithium carbonate (Li2CO3), sodium carbonate (Na2CO3) and potassium carbonate (K2CO3) are used for the preparation of LBO, NBO and KBO glasses respectively. The ABO glasses are irradiated with 100 MeV O7+ ion beam using 15 UD Pelletron tandem accelerators for fluences like 1 × 1011, 5 × 1011, 1 × 1012, 5 × 1012 and 1 × 1013 ions/cm2. The electronic energy loss is predominant and depth of propagation is calculated from SRIM and TRIM. The XRD and FE-SEM confirm the transformation of polycrystalline structure and growth of grains on the surface after the O7+ ion irradiation. LBO glasses at higher fluences revealed lithium tetrahydroxohexaoxopentaborate trihydrate with a monoclinic structure. The sharp and well-defined XRD peaks affirmed the transition from glass to glass ceramics after the irradiation. Formation of grains on the surface of the ABO glasses after the O7+ ion irradiation confirms the glass ceramics nature. KBO glasses possess enhanced stability even under ion irradiation. The optical bandgap decreased under ion irradiation. O7+ ion irradiation leads to a decrease in the tail of the Urbach energy, indicating reduced disorder in the ABO glasses. The transmission efficiency of both ABO glasses and glass ceramics is evaluated through reflection loss (Lr), transmission coefficient (T), and metallization criteria (M) and the suitability of the ABO glasses for nonlinear optical applications are discussed.
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    GAMMA IRRADIATION-INDUCED CHANGES IN THE STRUCTURAL, OPTICAL, ELECTRICAL AND RADIATION SHIELDING PROPERTIES OF LITHIUM BORATE GLASSES
    (Elsevier, 2023-01) Karthika S; Marimuthu K; Evangelin Teresa P; Meena R.C; Sulania I; Asokan K; Shanmuga Sundari S
    Lithium borate glass with the chemical composition 25Li2O–75B2O3 (LBO) was prepared using the melt quenching technique. The changes in their structural, optical and electrical parameters due to gamma irradiation were investigated and its radiation shielding ability was discussed. The as-prepared glasses were transparent, colourless and inclusion free. The glasses were irradiated for 20, 40, 60, 80 and 100 kGy using a60Co gamma source having a dose rate of 2.906 kGy/h. As the radiation dose increases colour centres were formed in the LBO glass, for higher dosages the glasses turned black. The theoretical structural parameters such as density, optical basicity, ionicity, boron-boron separation, bond density, molar volume and oxygen packing density were calculated. The structural changes were carried out using x-ray diffraction confirming the amorphous nature even after a high dose of gamma irradiation. Gamma irradiation induces the formation of BO4. The bandgap decreases from 3.72 to 3.64 eV with an increase in the dose of gamma irradiation. The dielectric spectroscopy and A.C. conductivity mechanism of the glasses were analyzed. The activation energy of the glasses was calculated before and after gamma irradiation using the Arrhenius plot. High doses of gamma irradiation resulted in an increase in activation energy of LBO glasses which increases from 0.12 eV to 0.42 eV at 100 kHz frequency. The radiation shielding ability of the prepared glass samples was estimated using theoretical simulations by Phy-X/PSD software.
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    STRUCTURAL AND OPTICAL PROPERTIES OF LITHIUM BORATE GLASSES UNDER EXTREME CONDITIONS OF ION IRRADIATION
    (IOP Science, 2023-07-05) Karthika S; Asokan K; Marimuthu K; Evangelin Teresa P; Ramcharan, Meena; Durairajan A; MA, Valente; Meena P; Shanmuga Sundari, Sankaran
    Lithium borate (LBO) glasses of the composition 10LiO2.90B2O3 were prepared by melt quenching technique and characterized for morphological, structural, and optical properties before and after the exposure to the extreme conditions of 100 MeV Ni ion irradiation. Both the morphological images and structural properties confirm the transformation of LBO glasses from amorphous to polycrystalline nature. This Ni irradiation provides thermal energy that causes the ceramization of glass. The beam interacts with the material where the top layer of the glass remelts, and ultrafast re-solidification occurs after the termination of the ion beams. The Rietveld refinement using the x-ray diffraction data shows that the irradiated LBO possesses a monoclinic crystal structure of lithium pentaborate pentahydrate (B5H10LiO13). The FTIR spectra of Ni ion irradiated glasses show the creation of non-bridging oxygens (NBO) by the formation of BO4 units at the expense of BO3 units. The direct band gap and the Urbach energy of the glasses are affected by the nickel ion irradiation and are in the range 2.73 to 2.55 eV and 0.59 to 0.42 eV. The refractive index also reveals a minor change (1.66 to 1.63). The molar electronic polarizability, metallization criteria, and transmission coefficient were estimated. The coexistence of crystalline and amorphous phases leads to a multiscale phase structure that has multilevel relaxation processes. This is a suitable condition for the improvement of the rheological properties of glass and glass ceramics. Future work involves optimization of the coexistence of these two phases during irradiation.