The optical properties and a.c. conductivity of magnesium phosphate glasses

Magnesium phosphate [X MgO-(100−X) P2O5] glasses in the composition range [X=20, 25, 30, 40, 45, 50 mol %] have been made. The optical properties and a.c. conductivities were measured and their amorphous nature confirmed by X-ray diffraction technique. The variation of relative density with x was anomalous. In the ultraviolet/visible regions it was found that the fundamental absorption edge is a function of glass compositions and lower absorption coefficients, α(Ω) follow the so-called Urbach edge. At lower absorption levels (1 104 cm−1), the behaviour of α(Ω) suggests that there are two different transition energies for electrons in k-space, namely direct allowed transitions and non-direct transitions. In the infrared region at wavelengths λ=2.5–30 Μm, the transmission spectrum has four absorption bands. Using the Kramers-Kronig theory, the optical constants (refractive index n and extinction coefficient k) have been determined from the transmission spectrum. The a.c. conductivity, σ(Ω), real and imaginary dielectric constants, e1, e2, and loss factor, tan δ, have been determined at room temperature in the frequency region, Ω = 2×104−106 Hz. It has previously been established theoretically that σ(Ω)∼Ω s and s was found to be in the range 0.64–0.73, depending on glass composition.