Direct interpretation of the X-ray and neutron three-dimensional difference pair distribution functions (3D-ΔPDFs) of yttria-stabilized zirconia

Abstract

Three-dimensional difference pair distribution functions (3D-ΔPDFs) from X-ray and neutron diffraction experiments are reported for yttria-stabilized zirconia (Zr0.82Y0.18O1.91). A quantitative analysis of the signatures in the three-dimensional difference pair distribution functions is used to establish that oxygen ions neighbouring a vacancy shift by 0.525 (5) Å along 〈1, 0, 0〉 towards the vacancy while metal ions neighbouring a vacancy shift by 0.465 (2) Å along 〈1, 1, 1〉 away from the vacancy. The neutron 3D-ΔPDF shows a tendency for vacancies to cluster along 〈½, ½, ½〉, which results in sixfold coordinated metal ions.

Quantitative three-dimensional local order analysis of nanomaterials through electron diffraction

“…The sample material that we use in the work presented here is yttria-stabilised zirconia (Zr 0.82 Y 0.18 O 1.91 , YSZ) – a well-known and technologically important material. YSZ shows pronounced diffuse scattering for which a consistent local order model has been established in the literature 23 , 37 – 40 . Pure ZrO 2 adopts the cubic fluorite structure at elevated temperatures but is monoclinic at ambient conditions 38 .…”

“…Metal sites are green and oxygen (and vacancy) sites are purple. The rightmost column ( q – t ) shows the signature generated from the calculated diffraction pattern of a simplified model 23 using the kinematic approximation. Black lines in the renderings are along the 〈100〉-directions and the crossing indicates the average interatomic vector.…”

“…This local order in YSZ leads to distinct signatures in the 3D-ΔPDFs measured using x-ray and neutron diffraction, which can be interpreted quantitatively in terms of a local order model 23 .…”

“…From a structural point of view, oxygen vacancies lead to local distortions 38 as illustrated in Fig. 1 : oxygen ions neighbouring a vacancy shift along the directions towards the vacancy, whereas metal ions neighbouring a vacancy shift along the directions away from the vacancy 23 , 38 , 40 . Furthermore, in YSZ there is a tendency to form 6-fold coordinated metal ions by vacancy pairs separated by vectors 23 , 38 , 40 .…”

“…1 : oxygen ions neighbouring a vacancy shift along the directions towards the vacancy, whereas metal ions neighbouring a vacancy shift along the directions away from the vacancy 23 , 38 , 40 . Furthermore, in YSZ there is a tendency to form 6-fold coordinated metal ions by vacancy pairs separated by vectors 23 , 38 , 40 . In YSZ the static displacements due to the introduction of the vacancies are the dominant reason for the diffuse scattering, while chemical short-range order seems to be less pronounced and hence only contributes to a minor degree to the observed diffuse scattering 38 .…”