Site Redistribution, Partial Frozen-in Defect Chemistry, and Electrical Properties of Ba_1–x(Zr,Pr)O_3−δ

Abstract

Changes in nominal composition of the perovskite (ABO3) solid solution Ba1-x(Zr,Pr)O3-δ and adjusted firing conditions at very high temperatures were used to induce structural changes involving site redistribution and frozen-in point defects, as revealed by Raman and photoluminescence spectroscopies. Complementary magnetic measurements allowed quantification of the reduced content of Pr. Weak dependence of oxygen stoichiometry with temperature was obtained by coulometric titration at temperatures below 1000 °C, consistent with a somewhat complex partial frozen-in defect chemistry. Electrical conductivity measurements combined with transport number and Seebeck coefficient measurements showed prevailing electronic transport and also indicated trends expected for partial frozen-in conditions. Nominal Ba deficiency and controlled firing at very high temperatures allows adjustment of structure and partial frozen-in defect chemistry, opening the way to engineer relevant properties for high-temperature electrochemical applications.

Synthesis and Characterization of BaCe0.4Zr0.4Pr0.2O3−δ Mixed Conductor Perovskite

“…This E a is comparable to the values for proton transport mechanism, but also to activation energies reported for other MIEC compositions with Pr as Ba(Zr 0.7 Ce 0.2 ) 0.8 Pr 0.2 Y 0.1 O 3−δ [32] and Ba(Ce,Pr)O 3-δ [21,24]. Besides, the electrical conductivity values are too low as compared to these materials (~ 2 µS/cm at 200 ºC) [21,24,32], but they are comparable to the values obtained for BaZr 0.8 Pr 0.2 O 3−δ [43]. Then, all evidences con rm that BCZP presents mixed ionic and electronic conductivity.…”

“…However, TG and DCS con rmed the proton incorporation on BCZP. Electric charge transport of MIEC materials for PC-SOFC is given by hopping of interstitial protons between oxygen sites [7] and the electronic transport associated to small polaron conductivity [43]. High electronic and protonic conductivities are necessary in order to improve ORR and proton diffusion.…”

Structures, Phase Fields, and Mixed Protonic–Electronic Conductivity of Ba-Deficient, Pr-Substituted BaZr0.7Ce0.2Y0.1O3−δ

“…Praseodymium is an interesting dopant for perovskite cerates and zirconates as it can, in principle, occupy both A and B sites 9 , increase sinterability 10 and augment electronic conductivity 11,12 . Although compositions with low levels of Pr doping are reported to exhibit good stability 10 , Pr-rich perovskites are associated with poor stability in wet and reducing gases [12][13][14] .…”

“…Praseodymium is an interesting dopant for perovskite cerates and zirconates as it can, in principle, occupy both A- and B-sites, increase sinterability, and augment electronic conductivity. , Although compositions with low levels of Pr doping are reported to exhibit good stability, Pr-rich perovskites are associated with poor stability in wet and reducing gases. − We have recently studied the effects of Pr substitution in BZCY72, finding that substitution of Zr/Ce with Pr led to higher electronic conductivity and a number of symmetry changes dependent on Pr content and temperature . Of interest in this and other recent related studies of the Pr-substituted BaZrO 3 system , was the finding that Pr resides exclusively on the perovskite B-site in the IV oxidation state, despite the fact that ion site size requirements indicate that Pr 3+ is much more likely to occupy the A-site. Mixed Pr oxidation states were, therefore, discounted as the origin of the enhanced thermally activated electronic conductivity.…”

Site-selective symmetries of Eu3+-doped BaTiO3 ceramics: a structural elucidation by optical spectroscopy

“…Barium loss has been highly proved in the literature when doping perovskite-type structures with the general formula ABO 3 . [18][19][20][21][22][23][24][25][26][27] This process has been attributed not only to the firing conditions but also to the dopant concentration. Indeed, the decreasing thermodynamic stability of the perovskite with increasing the amount of dopant implies a higher BaO activity and a greater thermodynamic driving force for Ba vaporization.…”