A technique we developed to identify ferroelectric and ferroelastic switching, published in Journal of Applied Physics

1. 800 nm x 800 nm

2. Polarization Difference Maps (PDMs) --- A technique to intuitively visualize ferroelastic and ferroelectric switching Focus on the CHANGE of polarization during switching: Decompose a polarization vector into components (Px, Py, Pz), measured by three dimensional (3D) Piezoresponse Force Microscopy (PFM) Distinguish 6 types of switching by different combinations of “switched” and “un-switched” states of Px, Py, Pz (given by LPFM1, LPFM2, VPFM) Each scanned pixel is assigned a color according to its switching type 11 (0o): None switch 12 (180o): All switch 13 (90o): Only VPFM switches 14 (90o): Both LPFM switches 15 (90o): One LPFM and VPFM switch 16 (90o): Only one LPFM switches

3. Three dimensional (3D) Piezoresponse Force Microscopy (PFM) VPFM LPFM 2 LPFM 1 Po Single crystal PZT film Vertical bend of the cantilever VPFM Lateral twist of the cantilever LPFM

4. Obtain a PDM |Pbefore- Pafter| = Pdifference LPFM1 LPFM2 VPFM Assign color 1 μm x 1 μm 11 (0o): None switch (All dark) 12 (180o): All switch 13 (90o): Only VPFM switches 14 (90o): Both LPFM switches 15 (90o): One LPFM and VPFM switch 16 (90o): Only one LPFM switches

5. Experiments: PDM to study ferroelectric/ferroelastic switching Without PDM, 6 PFM phase images are needed to identify the switching type for only 1 grain With PDM, the switching types for all grains can be shown simultaneously in 1 PDM

6. all 6 switching types appeared (IIIV) 2 6 4 5 1 3 (PDM of IIIV) 1 μm x 1 μm 11 (0o):(0)(0)(0) 12 (180o):(1)(1)(1) 13 (90o): (0)(0)(1) 14 (90o): (1)(1)(0) 15 (90o): (1)(0)(1) or (0)(1)(1) 16 (90o): (1)(0)(0) or (0)(1)(0) (0) for “un-switched”, (1) for “switched” 1 6 4 3 5 2

7. surprisingly large amount of 90o switching, and small amount of 180o switching (IIIV) PDM of II  IV Dark(0°),Green(90°), bright(180°) In our polycrystalline thin film: Less than 5% of grains switched 180o More than 50% of grains switched 90o In epitaxial thin films (of the same thickness and composition): 100% 180o switching 1 μm x 1 μm In addition: 90o switched grains are connected, potentially triggered by neighboring grains Nagarajan, V., et al., Dynamics of ferroelastic domains in ferroelectric thin films. Nat Mater, 2003. 2(1): p. 43-47.

8. 180o switching consisting of 2 successive 90o switching! PDM of II III PDM of I II PDM of I III I First direct observation Previously predicted by statistical XRD II III

9. Domain relaxation by lateral only 90o switching (III) 11, 4, 6 1 μm x 1 μm (PDM of III) Driven by neighboring grains, systematic study of the neighboring grain effects is ongoing 1 6 4 3 5 2

10. Vertical switching include both 180o and 90o switching (IIIV) 12, 3, 5 (PDM of IIIII) 1 μm x 1 μm A reversal of vertical applied E field leads to vertical (both 180o and 90o) switching 1 6 4 3 5 2