Interface Tuned Structure And Property Of Low-dimensional Solid Oxide Electrolytes

Solid oxide electrolytes?SOEs?with fluorite structure have been widely used in various energy and environment applications such as solid oxide fuel cells,solid oxide electrolytic cells and gas sensors due to their excellent electrical and mechanical properties.The major challenges nowadays are to extend applications of SOEs-based devices in low and medium temperature range?400⁶00 o C?and to develop novel micro-devices.Therefore,it is of great importance to study low-dimensional SOEs with high oxygen ionic conductivity at low temperatures.In this work,we tuned microstructures and subsequently optimized the electrical and mechanical properties of ceria-based and zirconia-based electrolytes by designing the surface/interfaces?i.e.grain boundaries,surfaces and hetero-interfaces?of low-dimensional SOEs,and also explored their application in medium-temperature oxygen micro-sensors.The following aspects are included in this study.10 mol% scandia-stabilized zirconia?10Sc SZ?nanofibers electrolytes were prepared by electrospinning.The proportion of grain boundaries in the nanofibers was tuned,and its effect on phase structures and conductivities was investigated.It is found that the key to inhibit the transition from cubic phase?high conductivity?to rhombohedral phase?low conductivity?is to increase the proportion of grain boundaries.The grain boundaries provide high speed pathways for oxygen ions,and thus the oxygen ionic conductivity of 10 Sc SZ nanofibers is 900 times higher than that of the bulk 10 Sc SZ.Amorphous Al2O3?AO?coated 10 Sc SZ nanofibers were fabricated by coelectrospinning.It is found that the crystallite growth at high temperatures?700¹100 o C?is inhibited and the growth activation energy is doubled by surface-coating.The growth of crystallites in a fiber at high temperature is due to that crystallites with lower miller index on the fiber surface preferably grow along the fiber axis and foster the growth of inner crystallites.The growth of surface crystallites can be inhibited after coating.10Sc SZ/amorphous alumina thin film heterostructures were prepared by radio frequency magnetron sputtering.The crystallite orientations and oxygenionic conductivities were tuned by the heterophase interface.It was found that the amorphous alumina interlayer led to the change of orientation for 10 Sc SZ from?111?-preferred to?110?-preferred orientation.The?110?orientation is favorable for the transportation of oxygen ions.Multilayered thin film SOEs consisting of Ce0.8Sm0.2O₂-??SDC?and amorphous AO were preapred by RF magnetron sputtering.The effects of heterointerface on the crystallite orientation,distribution of grain boundary and structural defects and consequently electrical properties of the multilayer-heterostructured electrolytes were manifested.The non-textured SDC/AO shows rich structural defects in the interfacial regions which provide high speed pathways for migration of oxygen ions.Thus,the interfacial conductivity is increased by 1² orders of magnitude and the total conductivity increases with the increase of layer number.In contrast,the conductivity of?111?-prefer-oriented SDC/AO decreases with the increase of layer number.This is attributed to that the textured-multilayered structure introduces random grain orientations to the interfacial region which results in more pronounced grain boundary blocking effects.Ce0.8Sm0.1Nd0.1O₂-?/Al2O3?SNDC/AO?multilayer SOE with no preferred orientation was prepared by sputtering at room temperature,which showed a conductivity of 2 orders of magnitude higher than that of bulk YSZ measured at400 °C.Micro-oxygen-sensors were prepared based on SNDC/AO and bulk YSZ using microfabrication processes.It was found the operation temperature of sensors based on the former electrolyte is decreased by 200 °C relative to the latter one.SNDC/AO-based sensors showed high sensitivity?<1% vol.% O₂?,fast response?¹ s?,and high cyclic stability?>1000 cycles?.