Synthesis and dielectric characterization of manganese oxide doped pmn-pt ceramics

The aim of this work is to synthesize pure and manganese doped 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN-10PT) ceramics, also to investigate their microstructure, electrocaloric and dielectric properties. The electrocaloric (EC) effect, a reversible and adiabatic temperature change induced in a polar material by an external electric field, could be utilized in refrigeration as a substitute for conventionally employed vapour-compression cooling systems. PMN-10PT ceramic is one of the candidate EC materials due to its excellent dielectric properties, such as high dielectric permittivity, large change of polarization with temperature. It has been shown that Mn-doping of lead-based perovskites significantly reduces their dielectric losses. The PMN-10PT ceramic samples with addition of MnO2 (0.5 and 1.0 mol%) were prepared by the mechanochemical synthesis and sintering at 1473 K for 2 h. The samples were single-phase perovskites with a relative density above 95 % and grain sizes in the 3-5 micron range. The addition of Mn significantly decreases the dielectric permittivity and losses. Also EC temperature coefficient decrease when manganese is added. Furthermore, doped samples exhibit pinched polarization-electric field loops, indicating that Mn acts as an acceptor dopant. Obtained dielectric spectra were fitted using Col-Cole equation and relaxation times were found. Ceramics exhibit charge relaxation processes observed in different temperature and frequency ranges. All of them are well described by Vogel-Fulcher law. The value of activation energy for relaxation processes lies in the interval 0.07 eV – 0.39eV, activation energy grows as manganese is added. All the changes in electric properties is due to manganese induced pinning of domain walls, which limits domain walls movement

Implications of acceptor doping in the polarization and electrocaloric response of 0.9Pb(Mg1/3Nb2/3)O-3-0.1PbTiO(3) relaxor ferroelectric ceramics

In ferroelectrics, the effects of acceptor doping on electrical and electromechanical properties, often referred to as the "hardening" effects, are commonly related to domain-wall pinning mechanisms mediated by acceptor-oxygen-vacancy defect complexes. In contrast, the hardening effects in relaxor ferroelectric materials are complicated by the nano-polar nature of these materials, the associated dynamics of the polar nano-regions and their contribution to polarization, and the characteristic freezing transition between the ergodic and the non-ergodic phases. To shed light on this issue, in this study, we investigate the role of the acceptor (Mn) doping on the temperature-dependent broadband dielectric permittivity, high-field polarization-electric-field (P-E) hysteresis and electrocaloric (EC) response of 0.9Pb(Mg1/3Nb2/3)O-3-0.1PbTiO(3) (PMN-10PT) relaxor ferroelectric ceramics. The results suggest strong pinning effects, mediated by the acceptor-oxygen-vacancy defect complexes, which manifest similarly both in the ergodic and in the non-ergodic phases of PMN-10PT as revealed by the doping-induced suppression of the frequency dispersion of the permittivity maximum and pinched high-field hysteresis loops. In addition to these pinning effects, the Mn doping reduces the freezing temperature (T-f) by similar to 50 degrees C with respect to the undoped PMN-10PT. This is reflected in the EC response, which becomes less temperature dependent, making defect engineering a valuable approach for designing EC materials with an extended operational temperature range