Effect of A-site La, Ba, and Sr doping on the threshold field and characteristic temperatures of PbSc0.5Nb0.5O3 relaxor studied by acoustic emission

Abstract

The behavior of the temperature of the dielectric-permittivity maximum Tm, the intermediate temperature T*, and the Burns temperature Td in stoichiometric PbSc0.5Nb0.5O3 (PSN) as well as in PSN heavily doped on the A-site by La (PSN-La), Ba (PSN-Ba), and Sr (PSN-Sr) was studied by means of acoustic emission (AE) under an external dc electric field (E). For all compounds, Tm exhibits a non-trivial behavior when applying E, namely, it initially decreases with the increase of E, attain a minimum at a threshold field Eth, ranging from 0.55 kV/cm for PSN to 0.25 kV/cm for PSN-Sr, and then Tm starts to increase with further increase of E. The minimum of Tm is accompanied by a pronounced maximum of the AE count rate Ṅ, which at Eth varies from 10.0 s−1 to 3.0 s−1 for all the compounds, respectively. The similarities and difference between PSN, PSN-Ba, PSN-La, and PSN-Sr with respect to Eth, the Ṅ, and the normalized AE parameter η are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric fields due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of the substituting ion, and (iii) change in the tolerance factor and elastic fields related to the larger ionic radius of the substituting A-site ion. The characteristic temperatures T* and Td also exhibit a non-trivial behavior under E, which is better pronounced for pure PSN than for the A-site-substituted PSN compounds.