Phase transition in Pb(Mg_(1/4)Cd_(1/4)W_(1/2))O_3 ceramics

摘要

With the growing interest and suitability for device applications, a large number and variety of oxide materials, especially with perovskite type structure of a general formula ABO_3 (A=mono or divalent, B=tri, tetra, penta or hexavalent ions) have been prepared and examined in the search for new materials for device applications. It is interesting to note that complex/mixed perovskite compounds formed by substituting suitable single or multi-ions at A- and/or B-sites in the above general formula have yielded many interesting physical properties useful for devices such as computer memory and display, sensors, modulators etc. [1-4]. In the last decades lead-based perovskite compounds, viz. PbTiO_3, PbZrO_3, PbWO_3, PbMoO_3 etc., have been found very important either in pure or complex forms for devices [5-8]. Extensive literature survey on Pb-based complex perovskite shows that, except for a fw studies, not much work has been reported on complex PbWO_3 and PbMoO_3 because of their high electrical conductivity and dielectric loss at low frequency and at high temperature. Recently a diffuse phase transition has also been observed in many complex tungstates/molybdate ceramics modified with alkali, transition-metal and rare-earth ions [9-12]. In view of this, we have carried out systematic and extensive studies on the structural, dielectric and electric properties of Pb(Mg_(1/4)Cd_(1/4)W_(1/2)O_3 (hereafter PMCW) for a better understanding of its phase transition and dielectric behaviour.