Spectroscopic studies of tantalum doped borate glasses

摘要

Glasses with formula 30Li _2O 60B _2O 3 xTa _2O _5 (10-x) Bi _2O _3 for x=0, 2, 4, 6 and 8 were prepared via normal melt quenching technique and characterized by refractive index and MDSC. Refractive index (μ) and glass transition temperature (T _g) are found to increase with increase in dopant concentration. Impedance spectra of the samples were recorded in the frequency range 100 Hz-5 MHz in the temperature range 175-275 °C. The plots are typical of those recorded for disordered systems. Conductivities and relaxation times are found to follow Arrhenius type of relation and activation energies are calculated. Optical absorption spectra were recorded in the wavelength range 200-900 nm range from which cutoff wavelength (λ _c) and optical band gap energy (E _g) are evaluated. λ _c is found to decrease while E _g to increase with increase in composition. FTIR spectra of the samples were recorded in the frequency range 400-1500 cm ~(-1) which exhibit characteristic bands corresponding to BO _3, BO _4 stretching vibrations and BO bending vibration. Tightening of the structure is indicated by increase in the vibration of BO _3 at the cost of BO _4 for 8 mol% of Ta _2O _5. This is in support of the highest value of T _g for this sample among the series. Raman spectra of the samples were recorded in the frequency range 200-1200 cm ~(-1). With successive addition of Ta _2O _5, increase in the vibration of Ta-O groups TaO _6 groups to be responsible for observed increase in μ and T _g. An attempt is made to prepare tantalum doped borate glasses and study them by spectroscopic techniques.