Kacper Dzierzgowski

The modified DC Hebb–Wagner polarization method with an electron and oxygen-ion blocking electrode was for the first time applied to study partial protonic conductivity in triple-conducting oxides: BaZr_0.7Ce_0.2Y_0.1O_3−δ and BaGd_0.3La_0.7Co₂O_6−δ.

LaNb_0.8M_0.2O_4‐δ (where M=As, Sb, V, and Ta) oxides with pentavalent elements of different ionic sizes were synthesized by a solid‐state reaction method. The vibrational properties of these oxides have been investigated. These studies revealed that the substituent element influences both Debye temperature value as well as the Raman active vibrational modes. Additionally, the low‐temperature vibrational properties of LaNb_0.8Sb_0.2O_4‐δ have been determined to show the phase transition occurrence at 260 K which is lower than previously reported.

Oxides in which total electrical conductivity is determined by the partial conductivities of three types of charge carriers i.e. holes/electrons, oxygen ions, and protons are key components of well-functioning proton ceramic fuel cells. Apart from electrochemical properties also easily modified microstructure is an important feature of the electrodes. In the paper, a group of SrTi _1−x Fe _x O _{3− δ} (STF, x = 0.2–0.8) perovskites prepared by solid-state synthesis was studied. The microstructure of ceramics was studied using SEM, and the results showed a significant influence of Fe amount on the grain size and material’s porosity. The electrical transport results show a different conductivity in a dry and humidified atmosphere. The hydration kinetics related to the water incorporation are presented with the transition from single-fold to two-fold behaviour, related to the proton-electron hole interaction observed in measurements. The obtained results strictly show a triple-conductivity of SrTi _0.8 Fe _0.2 O _{3− δ} system at a lower temperature range, where the protonic defects are thermodynamically stable.

In this paper, the structural properties and the electrical conductivity of La_1−xPr_xNbO_4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) and PrNbO_4+δ are presented and discussed. All synthesized samples crystallized in a monoclinic structure with similar thermal expansion coefficients. The phase transition temperature between the monoclinic and tetragonal structure increases with increasing praseodymium content from 500 °C for undoped LaNbO_4+δ to 700 °C for PrNbO_4+δ. Thermogravimetry, along with X-ray photoelectron spectroscopy, confirmed a mixed 3⁺/4⁺ oxidation state of praseodymium. All studied materials, in humid air, exhibited mixed protonic, oxygen ionic and hole conductivity. The highest total conductivity was measured in dry air at 700 °C for PrNbO_4+δ, and its value was 1.4 × 10⁻³ S/cm.

Modified DC Hebb–Wagner polarization method was used to study oxygen ionic conductivity in BaCe_0.6Zr_0.2Y_0.2O₃. New measuring cell and calculation model proposed. Conduction mechanism of oxygen ions is influenced by protons in BaCe_0.6Zr_0.2Y_0.2O₃.

Ba _x Sr _1−x Ti _1−y Fe _y O _3−δ -based perovskite materials with different barium and iron contents are reported as triple conducting oxides (TCOs), which may conduct three charge carriers: oxygen ions, protons and electrons/holes.

Lanthanum orthoantimonate was synthesized using a solid‐state synthesis method. To enhance the possible protonic conductivity, samples with the addition of 1 mol % Ca in La‐site were also prepared. The structure was studied by the means of X‐ray diffraction, which showed that both specimens were single phase. The materials crystallized in the space group P2₁/n. Dilatometry revealed that the material expanded non‐linearly with the temperature. The nature of this deviation is unknown; however, the calculated linear fraction thermal expansion coefficient was 9.56×10⁻⁶ K⁻¹. Electrical properties studies showed that the material is a proton conductor in oxidizing conditions, which was confirmed both by temperature studies in wet in dry air, but also by the H/D isotope exchange experiment. The conductivity was rather modest, peaking at the order of 10⁻⁶ S cm⁻¹ at 800 °C, but this could be further improved by microstructure and doping optimization. This is the first time protonic conductivity in lanthanum orthoantimonates is reported.

X‐ray and neutron diffraction have been utilized to analyze the crystalline and electronic structure of lanthanum orthoniobate substituted by antimony. Using X‐ray absorption spectroscopy and photoelectron spectroscopy, changes in the electronic structure of the material upon substitution have been analyzed. The structural transition temperature between fergusonite and scheelite phases for 30 mol% antimony substitution was found to be 15°C. Based on the neutron data, the oxygen nonstoichiometry was found to be relatively low. Moreover no influence on the position of the valence band maximum was observed. The influence of the protonation on the electronic structure of constituent oxides has been studied. Absorption data show that the incorporation of protonic defects into the lanthanum orthoniobate structure leads to changes in lanthanum electronic structure and a decrease in the density of unoccupied electronic states.