Dielectric properties of barium phosphate glasses doped with transition metal oxides

The effect of addition of small amounts of the transition metal (TM) ions of Co, Fe and Mn to the composition of barium phosphate glasses on the dielectric properties is studied by measurements of the dielectric constant ε′, insertion loss L and microwave absorption spectra of the glass system xTM · (1 − x)(0.6P2O5 · 0.4BaO), where 0 ⩽ x ⩽ 0.12 is the atom-gram fraction of the transition metal. The dielectric constant at 9.00 GHz, determined by the shorted-line method (SLM), has the minimum value of ε′ = 1.77 ± 0.02, at room temperature for x = 0, and increases with x following a different law for each of the TM. There is no similar behavior reported up to date and a further investigation is necessary in order to explain the nature of these transitions considered. A minimum of ε′ = 5.50 ± 0.05 at the frequency of 100 kHz was obtained using impedance analysis at the same conditions. For cobalt, it was observed a linear increase of ε′ in the temperature range of 25 ⩽ x ⩽ 250 °C, at the frequency of 9.00 GHz, with the slope dε′/dT = (12.2 ± 0.8) × 10−4 K−1 for x = 0 that decreases to (9.0 ± 0.8) × 10−4 K−1 for x = 0.12. The absorption coefficient α, measured at 9.00 GHz by insertion loss, increased from 0.15 to 1.03 cm−1 for Co content varying from 0.00 to 0.12 atom-gram, indicating the contribution of dispersive microwave scattering. Two peaks appeared at the approximate frequencies of 8.7 and 10.9 GHz, respectively, in the microwave absorption spectra, with maximum intensity at x = 0.04 followed by a further decrease with increasing Co content. Their nature is still a matter of further investigation.