On the influence of strain on ion transport: microstructure and ionic conductivity of nanoscale YSZ|Sc2O3 multilayers

Abstract

Multilayer samples of the type (YSZ|Sc2O3) × n with layer thicknesses between 8 nm (n=100) and 250 nm (n=5) were prepared on (0001) sapphire substrates by pulsed laser deposition (PLD). The samples were characterised using X-ray diffraction (XRD), scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM/HRTEM, SAED (selected-area electron diffraction) and quantitative EELS (electron energy-loss spectroscopy)). The polycrystalline layers show a columnar microstructure, which is typical for the used preparation technique. The layers are highly textured and only one axial orientation relation is found between yttria-stabilised zirconia (YSZ), scandium oxide and the substrate: (0001) Al2O3‖(111) Sc2O3‖(111) YSZ. A preferred orientation relationship also exists for the azimuthal rotation of the crystallites, which was demonstrated by SAED, XRD pole figure measurements and fast Fourier transformation (FFT) of HRTEM micrographs. The interfaces between YSZ, Sc2O3 and the substrate are sharp and do not contain diffuse transition regions. Dislocations appear not to be arranged in regular arrays. With increasing interface density (thinner individual layers in the multilayer), the conductivity of the multilayers decreases. We relate this to the negative nominal misfit present at the YSZ|Sc2O3 interfaces (compressive stress in YSZ at the phase boundaries). This observation agrees well with the previously investigated case of YSZ|Y2O3 (A. Peters et al., Phys. Chem. Chem. Phys., 2008, 10, 4623), where tensile misfit strain was present in YSZ at the phase boundaries, leading to a conductivity increase.

Tensile Lattice Distortion Does Not Affect Oxygen Transport in Yttria-Stabilized Zirconia–CeO2 Heterointerfaces

“…25 The analysis of several HR-TEM micrographs acquired for sample E showed an average total dislocation density of about 3x10 12 cm -2 . A very similar value of dislocation density, or even lower, was found for hetero-structures fabricated by coupling 9.5YSZ with Y, Lu and Sc oxides 13 and the interfaces were described as (quasi-)coherent.…”

“…7,10,[12][13][14][15][16] Polycrystalline 9.5YSZ-Y 2 O 3 multilayered films {(0001) Al 2 O 3 |Y 2 O 3 | (9.5YSZ|Y 2 O 3 ) x n} grown on sapphire substrates with (quasi-)coherent hetero-interfaces along each columnar grain showed that the conductivity slightly increased and the activation energy slightly decreased with increasing the number of interfaces 10 . According to the authors, the grain boundary conduction pathway played a negligible role in the charge transport.…”

First-principles study and modeling of strain-dependent ionic migration in ZrO2

“…Previous investigations [2][3][4][5][6][7][8][9][10][11] on the strain dependence already pointed out the increase in conductivity under expansion of the crystal lattice and a decrease under compression. Four groups [2][3][4]10,11 proposed sandwich-type epitaxially grown structures consisting of YSZ and an additional oxide with a larger lattice constant (e.g., Y 2 O 3 ), one group investigated a single layer YSZ of different thickness on a MgO substrate 9 and two other groups applied pressure directly to the electrolyte material.…”

“…Four groups [2][3][4]10,11 proposed sandwich-type epitaxially grown structures consisting of YSZ and an additional oxide with a larger lattice constant (e.g., Y 2 O 3 ), one group investigated a single layer YSZ of different thickness on a MgO substrate 9 and two other groups applied pressure directly to the electrolyte material. 5,8 In 1998 Suzuki et al 2 investigated the ionic motion of oxygen in YSZ/CeO 2 sandwich structures by molecular dynamics simulations.…”

Growth mechanisms of ceria- and zirconia-based epitaxial thin films and hetero-structures grown by pulsed laser deposition

“…A large increase in ionic conductivity was observed in case of incoherent interfaces due to the faster conduction pathways along dislocation lines [8,9]. More ordered oxygen-ion conducting hetero-interfaces have been also fabricated to investigate the effect on the conducting properties of the compressive or tensile strain occurring at quasi-coherent hetero-interfaces [10][11][12]. The fabrication of samples appropriately designed to allow isolating the effect of the interfacial strain field requires a careful control of the deposition process and a deep understanding of the growth mechanisms.…”