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Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering

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ABSTRACT

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO3 and SrTiO3 grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO2 and 8 mol% Y2O3 stabilized ZrO2 are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity.

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(a) TEM cross section micrograph of a CeO2/YSZ multilayer grown on STO-buffered MgO showing the columnar morphology originating at the STO buffer layer. HR-TEM image at high magnification of the same sample is shown in (b). The arrows show the grain boundary regions. The heterostructure is epitaxially oriented with the substrate but shows two different in-plane orientations 45° tilted one another, as evidenced in (c) and (d): RHEED patterns and intensity profiles acquired after the growth of the STO layer along the (01) crystallographic direction of the substrate (c) and along the (11) direction (d).
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Figure 1: (a) TEM cross section micrograph of a CeO2/YSZ multilayer grown on STO-buffered MgO showing the columnar morphology originating at the STO buffer layer. HR-TEM image at high magnification of the same sample is shown in (b). The arrows show the grain boundary regions. The heterostructure is epitaxially oriented with the substrate but shows two different in-plane orientations 45° tilted one another, as evidenced in (c) and (d): RHEED patterns and intensity profiles acquired after the growth of the STO layer along the (01) crystallographic direction of the substrate (c) and along the (11) direction (d).

Mentions: To directly measure the bulk conductivity of ionic conducting oxides, thin film with high crystalline quality grown on insulating substrates can be used. Good results have been achieved for thin films of doped ceria and for CeO2/YSZ multilayered heterostructures using STO-buffered MgO substrates [13, 24]. However, in our experience, this strategy has a limited reproducibility and tiny variation of the deposition conditions (difficult to control) and/or of the quality of the substrate surface, often result in a columnar morphology, epitaxially oriented with the substrate but with large grain boundary regions. As a consequence, the fabricated samples require an individual HR-TEM analysis to select those with no evidence of high angle grain boundary and columnar morphology. An example can be found in figure 1(a) that shows the cross section HR-TEM image of a multilayered heterostructure made of 15 CeO2/YSZ bilayers grown epitaxially oriented with the STO-buffered MgO substrate.


Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering
(a) TEM cross section micrograph of a CeO2/YSZ multilayer grown on STO-buffered MgO showing the columnar morphology originating at the STO buffer layer. HR-TEM image at high magnification of the same sample is shown in (b). The arrows show the grain boundary regions. The heterostructure is epitaxially oriented with the substrate but shows two different in-plane orientations 45° tilted one another, as evidenced in (c) and (d): RHEED patterns and intensity profiles acquired after the growth of the STO layer along the (01) crystallographic direction of the substrate (c) and along the (11) direction (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036489&req=5

Figure 1: (a) TEM cross section micrograph of a CeO2/YSZ multilayer grown on STO-buffered MgO showing the columnar morphology originating at the STO buffer layer. HR-TEM image at high magnification of the same sample is shown in (b). The arrows show the grain boundary regions. The heterostructure is epitaxially oriented with the substrate but shows two different in-plane orientations 45° tilted one another, as evidenced in (c) and (d): RHEED patterns and intensity profiles acquired after the growth of the STO layer along the (01) crystallographic direction of the substrate (c) and along the (11) direction (d).
Mentions: To directly measure the bulk conductivity of ionic conducting oxides, thin film with high crystalline quality grown on insulating substrates can be used. Good results have been achieved for thin films of doped ceria and for CeO2/YSZ multilayered heterostructures using STO-buffered MgO substrates [13, 24]. However, in our experience, this strategy has a limited reproducibility and tiny variation of the deposition conditions (difficult to control) and/or of the quality of the substrate surface, often result in a columnar morphology, epitaxially oriented with the substrate but with large grain boundary regions. As a consequence, the fabricated samples require an individual HR-TEM analysis to select those with no evidence of high angle grain boundary and columnar morphology. An example can be found in figure 1(a) that shows the cross section HR-TEM image of a multilayered heterostructure made of 15 CeO2/YSZ bilayers grown epitaxially oriented with the STO-buffered MgO substrate.

View Article: PubMed Central - PubMed

ABSTRACT

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO3 and SrTiO3 grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO2 and 8 mol% Y2O3 stabilized ZrO2 are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity.

No MeSH data available.


Related in: MedlinePlus