Nanoindentation of La-Cr-O Thin Films

Transcription

1 Nanoindentation of La-Cr-O Thin Films Anthony Coratolo1, Nina Orlovskaya1 Christopher Johnson2, Randall Gemmen2 1 Drexel University, Philadelphia, USA 2 National Energy Technology Laboratory, Morgantown, USA Acknowledgment The work at Drexel was supported by the National Energy Technology Laboratory, US Department of Energy under contract #

2 Objectives Develop a reliable method for the characterization of mechanical properties of La-Cr-O thin film Investigate the deformation behavior of the thin film during the contact loading by Berkovich indenter Measure Hardness and Modulus of films annealed in air over a range of temperatures

3 Background Interconnect Function- Electrically connect the cells in a stack, provide separation and flow control of gases, and provides mechanical stability. For Intermediate temperature SOFCs a Cr rich Stainless Steal can be used, but oxidation can be a problem. To improve oxidation resistance the stainless steal a thin layer of a conductive perovskite is applied to the surface.

4 Nano Indentation

5 Load, P Load, P Load, P Load vs. displacement Curves Pure Plastic (P max, h end ) Pure Elastic (P max, h end ) Displacement, h Displacement, h Plastic and Elastic H P max area S E r 2 A loading Unloading (P max, h end ) 1 E r 1 v E 2 1 E v i 2 i Displacement, h s

6 Oliver-Pharr Model of the Material Response h surface profile after load removal indenter h s h c h r P initial surface surface profile under load h s h h P max S c max h s A( h c ) 24.5h i 2 c i C h i c P = applied force h c = contact depth h = indenter displacement h r = plastic deformation after load removal C i = material property h s = surface displacement at the contact perimeter Oliver & Pharr, J. Mater. Res. 1992

7 Materials under study LaCrO 3 Target, 4% porous 5W power Picture of the thin film LaCrO 3 on the Stainless Steel Substrate Coatings done by Arshad Mumtaz of Thin Films, Inc., Schematic presentation of the experiment set up, Custom Sputter Down System Stainless steel substrate coated with LaCrO3 perovskite by magnetron RF sputtering

8 X-Ray Amorphous Nanoscrystalline X-Ray Amorphous Monoclinic LaCrO 4 Orthorhombic LaCrO C Beginning of oxygen absorption from air C Amorphous to monoclinic LaCrO4 structure phase transition C Monoclinic LaCrO4 to Orthorhombic LaCrO3 phase transition

9 Intensity, a.u. Intensity, a.u. Intensity, a.u. Intensity, a.u. Intensity, a.u. Intensity, a.u. Intensity, a.u. Intensity, a.u. Characterization of La-Cr-O Thin Film As received 1 5 C 1 7 C 1 8 C Nanoindentation Nanoindentation Nanoindentation Nanoindentation H=4.27GPa E=188.74GPa Unloading H=4.61GPa E=195.GPa Unloading H=5.29GPa E=185.65GPa Unloading H=3.61GPa E=179.2GPa Pop-in Unloading 5 Loading Loading Loading Loading as deposited Raman shift, cm Raman spectroscopy o C Raman spectroscopy Raman shift, cm Raman spectroscopy o C Raman shift, cm o C Raman spectroscopy Raman shift, cm X-ray analysis SS 2 X-ray analysis Short range order Clusters formation SS 6 X-ray analysis Monazite type 5 Monoclinic 4 phase X-ray analysis Orthorhombic Perovskite 1 3 SS?? SS 2 1?? Theta, o Theta, o Theta, o Theta, o

10 Hardness, GPa Modulus, GPa Hardness and Young s modulus of La-Cr-O thin film after annealing at different temperatures for one hour 12 1 as recieved 3 C 4 C 6 C 5 C 7 C 8 C 9 C as recieved 3 C 4 C 6 C 5 C 7 C 8 C 9 C The effect of stainless steel substrate on hardness and Young s modulus is clearly seen as a function of a penetration depth of the indenter. As an indenter penetrates into the film (8 nm thickness), the influence of substrate become more and more pronounced. As the indenter penetrates on the full depth of the film, the mechanical properties of the SS substrate material are measured.

11 LaCrO 3 orthorhombic to rhombohedra Transition Under pressures of 5.4 GPa at room temperature orthorhombic LaCrO 3 will transform in to a rhombohedral configuration. Rhombohedral structure is less dense than orthorhombic. Phase transition could be induced by pressure under berkovich tip

12 ACP, GPa Mechanical Response after annealing at 8 C for 1 hour Indentation total area unload elastic recovery plastic deformation 5nm nm pop in nm nm pop in nm nm pop in nm nm depth

13 ACP, GPa ACP, GPa 2 nm depth

14 ACP, GPa ACP, GPa 4 nm depth

15 ACP, GPa ACP, GPa 8 nm depth

16 Conclusions Mechanical behavior of La-Cr-O thin films was studied by nanoindentation. As deposited and annealed at 5, 6, and 8 o C films were used for mechanical and structural characterization. Hardness and Young s modulus of the as deposited amorphous and annealed La-Cr-O thin films were measured using Berkovich diamond indenter. Load-displacement curves were obtained in a displacement control mode. As a result of an annealing at different temperatures, different film structure was formed. After annealing at 5 o C for 1 hour the short order structure was formed; annealing at 6 o C lead to the formation of LaCrO 4 monoclinic structure; after annealing at 8 o C the orthorhombic LaCrO 3 perovskite structure was formed, as confirmed by XRD and micro-raman spectroscopy. Hardness and Young s modulus change from 1-12 GPa and 12 GPa to 3 GPa and 14 GPa respectively, as a result of the phase transition of the LaCrO3 phase transitions.