THE OPTICAL-PROPERTIES AND AC CONDUCTIVITY OF MAGNESIUM PHOSPHATE-GLASSES

Magnesium phosphate [X MgO - (100 - X) P2O5] glasses in the com position 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, alpha(omega) follow the so-called Urbach edge. At lower absorption levels (1 < alpha < 10(4) cm(-1)), the width of the tail of localized states in the band gap, E(g), did not vary significantly with glass composition and lay in the range (0.26-0.343) eV. In the high absorption region (alpha(omega) > 10(4) cm(-1)), the behaviour of alpha(omega) 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 lambda = 2.5-30 mu m, 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, sigma(omega), real and imaginary dielectric constants, epsilon(1), epsilon(2), and loss factor, tan delta, have been determined at room temperature in the frequency reg ion, omega = 2 x 10(4)-10(6) Hz. It has previously been established theoretically that sigma(omega) similar to omega s and s was found to be in the range 0.64-0.73, depending on glass composition.