ΔThe effect of co-doping on the yttrium local environment and ionic conductivity of yttria-stabilised zirconia

Abstract

The effect of co-doping yttria-stabilised zirconia with calcia and scandia has been investigated. Changes in the yttrium ion local environment have been monitored using solid-state magic angle sample spinning 89 Y nuclear magnetic resonance. The effect on the low-temperature (below 320°C) bulk ionic conductivity has been observed using AC impedance spectroscopy. It was found that the number of oxygen vacancies in the nearest-neighbour sites to yttrium ions decreased on co-doping with scandia, correlating with an increase in conductivity, but increased on co-doping with calcia, correlating with a decrease in conductivity. This behaviour can be explained by proposing the trapping of oxygen vacancies in the nearest-neighbour yttrium ion sites so that they no longer contribute to the conduction mechanism.

Method for making minor dopant additions to porous ceramics

“…An increased relative density has also been observed when using solution doping to add scandia to yttria stabilised zirconia. 7 The reduction in relative density with calcia content observed for solution doping here may be intrinsic and caused by the increasing amount of calcia.…”

“…Such a distribution 1 Schematic of solution doping process using calcium nitrate solution to achieve calcia doping of yttria stabilised zirconia pellet 2 Variation in lattice parameter measured by X-ray diffraction for solution doping yttria stabilised zirconia pellet with additional CaO, calcia contents given by EDX measurements was observed when penetrating a porous ceramic with a dye solution. 7 The surface of the sample became increasingly stained with dye as the dye solution was drawn from the body of the pellet for the solvent to evaporate from the surface. This resulted in the accumulation of dye on the surface of the ceramic.…”

Recent progress in solid-state NMR of spin-½ low-γ nuclei applied to inorganic materials

“…80 Small additions of CaO, Sc 2 O 3 and Y 2 O 3 to a base 8 mol% yttria-stabilised composition showed CaO created more oxygen vacancies around the yttrium site, whereas they were decreased when Sc 2 O 3 was added, which was explained as the larger Ca 2+ preferring to remain as CaO 8 whilst the smaller Sc 3+ ion prefers to be ScO 7 . 81 3.1.2 Pyrochlores. The general formula for pyrochlores is A 2 B 2 O 7 where the A cation is coordinated as a distorted AO 8 and the B cation as BO 6 .…”

Understanding the relationship between dopant and ionic transport in yttria-doped ceria-zirconia

“…The selection of these solid solution materials was based on two facts. Firstly, the ionic size of Y 3+ is higher than both Zr 4+ and Ce 4+ , however, the oxygen vacancies prefer to be located at the next-nearest neighboring position to Y 3+ in yttria stabilized zirconia (YSZ) 8 but are preferentially associated with Y 3+ at the first-nearest-neighbor position in yttria doped ceria (YDC). 9,10 This discrepancy between Y in zirconia and ceria perhaps opens a window of opportunity to discern the contribution on local structure from doping when both zirconium and cerium are present.…”