Effect of H2O on dielectric properties of berlinite. II. Dielectric loss

For pt.I see ibid., vol.26, p.93 (1993). Audio frequency complex impedance measurements, have been carried out over the temperature range 5.5-380 K on samples of berlinite (aluminium phosphate) both parallel and perpendicular to the optic axis. The berlinite samples contain varying amounts of water. All of the berlinite samples exhibit a dielectric relaxation peak in the vicinity of 40 K and 1000 Hz. The data were best fit using an expression based on the stretched exponential (SE). The best fit SE parameter beta SE ranges from 0.68 to 0.85. In the direction perpendicular to the optic axis, the activation energy is approximately 0.053 eV and the relaxation is correlated with the aqueous solution inside inclusions. The relaxation parallel to the optic axis has an activation energy of about 0.049 eV and is attributed to hydroxyl ions at the surface of the inclusions. A dielectric relaxation peak is also observed near 240 K and 1000 Hz for the samples with a higher nominal water concentration. In addition, dielectrical loss, which is attributed to trace impurities or Maxwell-Wagner polarization of inclusions, is observed in the vicinity of room temperature.