Structural and electrical properties of the NH4DyHP3O10 compound

Low-frequency dielectric dispersion phenomena in NH4DyHP3O10 (ammonium dysp rosium hydrogen phosphate type) polycrystalline compounds have been analyze d by impedance spectroscopy. The thermal evolution of the dielectric consta nt shows a phase transition at 305 K which is ferroelectric-paraelectric ty pe. The ferroelectric phase is isotypic with KDyHP3O10 and exhibits the tri clinic symmetry P1 (at room temperature: a = 6.820 Angstrom, b = 7.583 Angs trom, c = 8.467 Angstrom, alpha = 104.396 degrees, beta = 103.545 degrees, gamma = 90.349 degrees, Z = 2). An empirical expression has been deduced fo r the complex permittivity epsilon*:(omega), epsilon*(omega) = epsilon(infinity) + epsilon(s)epsilon(i nfinity)/1 + (i omega/omega(1))(m) + sigma(0)/epsilon(0)omega[1 + (i omega/ omega(2))(n)]; where the (omega(1), m) and (omega(2), n) couples characterize the lattice and the charge carriers responses, respectively. This relation may be consi dered as a generalisation of the Cole-Cole dielectric expression. The influ ence of the charge carrier contribution on the dielectric permittivity at l ow frequency is significant, as shown when both lattice and carrier polariz ation mechanisms are simultaneously considered.