Interrelationship among dielectric constant, energy band parameters and ionicity in multi-component oxide glasses revealed by optical- and THz-band spectroscopy

The dielectric constant, energy band parameters and ionicity are key physical parameters for fully understanding the dielectric properties of glasses, but their mutual interrelationship and its applicability to a wide variety of multi-component glasses have not yet been confirmed. We have applied the optical and THz spectroscopic characterization to a set of multi-component silicate oxide glasses incorporating vastly different additive components. The key physical parameters evaluated in the optical region have been interpreted consistently by the single oscillator based dielectric model. The bandgap energy (E_g) and ionicity parameter (Wemple and DiDomenico's β parameter) estimated in the optical region have shown reasonable correspondence, respectively, with the homopolar energy (E_h) and the polarization ionicity (I_P) which are evaluated from the THz dielectric constant measurement. The comprehensive interrelation thus confirmed has provided simple rules between the physical parameters without limitation of glass compositions. For example, a tradeoff relation between the oscillator strength and characteristic resonance wavelength and a simple correlation between the dielectric constant and bandgap energy have been determined for the present set of multi-component glasses. The energy band parameters have been used for deriving the joint density of state diagrams, and characteristic physical/chemical nature has been identified to each glass.