Synthesis of a 12R-type hexagonal perovskite solid solution Sr3NdNb3-xTixO12-delta and the influence of acceptor doping on electrical properties

A solid solution forms for Sr3NdNb3−xTixO12−δ with approximate limits 0 ≤ x ≤ 0.06. The system crystallizes with a 12R-type hexagonal perovskite structure in the space group R[3 with combining macron], as determined by neutron diffraction and selected area electron diffraction. The electrical properties of the end members have been investigated by impedance spectroscopy in the temperature range 550–800 °C under various gas atmospheres and as a function of oxygen and water-vapour partial pressure. Proton transport dominates under wet oxidising conditions in the temperature range 550–700 °C, as confirmed by the H+/D+ isotope effect. Acceptor doping considerably enhances proton conductivity with a value of 3.3 × 10−6 S cm−1 for the bulk response of x = 0.06 at 700 °C in moistened air. The presence of a −¼ slope for both doped and undoped samples in the range 10−19 ≤ pO2 ≤ 10−8 atm at 900 °C indicates n-type transport under reducing conditions following the extrinsic model attributable to acceptor centres. The conductivity is essentially independent of pO2 at 600 °C under dry oxidising conditions, consistent with oxide-ion transport; a positive power-law dependence at higher temperature indicates extrinsic behaviour and a significant electron–hole contribution. The dielectric constant at RT of nominally stoichiometric Sr3NdNb3O12 is εr ∼ 37, with a moderately high quality factor of Q × f ∼ 16 400 GHz at fr ∼ 6.4 GHz. The temperature coefficient of resonant frequency of x = 0 is τf ∼ 12 ppm °C−1, which lowers to −3 ppm °C−1 for the Ti-doped phase x = 0.06

Enhancing microstructure homogeneity and electrical conductivity in flash-sintered 8YSZ: Impact of electric-current ramp control and thermal insulation

Our study aimed to comprehend how variations in flash sintering parameters affect the evolution of microstructure and electrical properties of yttria-stabilised zirconia. For this purpose, cylindrical samples were sintered via a classic flash method (voltage-current control), with controlled increase in the current ramp, employing thermal insulation, and combining current ramp control with thermal insulation. The results demonstrated that the combination of current ramp control and thermal insulation yielded higher densification compared to other variations. Microstructural analysis revealed finer grain sizes and lower grain-boundary tensions on employing current ramp control, particularly when combined with thermal insulation. For all flash-sintering methods, greater electrical conductivity of grain boundaries was observed compared to conventional sintering, suggesting an enhancement in ionic conduction. This study underscores the potential of customised FS techniques in optimising sintering processes and enhancing material properties. © 2024 Elsevier LtdThis work was supported by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (CAPES) - Finance Code 001, the Sao Paulo Research Foundation (FAPESP) [2015/07319-8 and 2019/14677-9] . We also acknowledge financial support from the project PID2021-123308OB-I00, funded by MCIN/AEI/10.13039/501100011033 and "ERDF A way of making Europe" by the European Union.Peer reviewe