Investigation of structural, dielectric and ferroelectric properties of Gd-doped lead magnesium niobate ceramics

The structural, microstructural, local ordering of B-site cations, dielectric and ferroelectric properties have been investigated for Pb1-xGdx(Mg1/3Nb2/3)(1-x/4)O-3; 0 <= x <= 0.1. Charge imbalance due to Gd3+ ion substitution at Pb2+ is compensated by creating B-site vacancies. The Gd-ion doping at Pb sites in PMN results in the formation of a secondary GdNbO4 phase, which is explained by considering the ionic radii of the Gd ion and its solubility limit at Pb-ion sites. A reaction mechanism for the formation of GdNbO4 has been proposed. Selected area electron diffraction along the < 110 > axis reveals enhancement in size of the non-stoichiometric chemical ordered regions leading to a decrease in the size of polar nano regions and their correlations, which manifests in a decrease of T-m, a more diffused epsilon(max) peak and enhancement of the dielectric relaxation strength calculated from fitting of the frequency and temperature dependence of the dielectric behavior. Linear dependence between polarization and electric field also signifies reduction in the correlation between the PNRs resulting in the decrease of the value of P-max (at similar to 30 kV cm(-1)).