A technique has recently been proposed for determining the elastic constant ratio K22∕K11 in nematic liquid crystals [E. P. Raynes, C. V. Brown, and J. F. Strömer, Appl. Phys. Lett. 82, 13 (2003)]. This technique has been applied to five nematic materials that cover a range of K33∕K11 elastic constant ratio values. An unusually high value of K22∕K11 is found in one material. High values of the ratio K22∕K11 tended to occur in materials that also have high values of the ratio K33∕K11. The results are validated with independent measurements of K22 from cholesteric helix unwinding.
A technique has been developed for the measurement of the K22 twist elastic constant in nematic liquid crystal materials. This involves the measurement of the Freedericksz transition voltages in untwisted linear and π-twist regions in a wedge cell geometry. The method avoids the need for the accurate determination of the cell thickness and cholesteric pitch and is far more straightforward to implement than other methods in the literature. The validity of this method is demonstrated for the well-characterized material E7.
Scanning electron microscope imaging and electron backscatter diffraction are applied to 400 nm thick YBCO films grown on Ni-9at.%W and ABAD-YSZ tape. On Ni-9at.%W tape, the orientation of YBCO strongly varies from grain to grain, which is attributed to the different orientations of the underlying substrate grains with regard to the surface normal. On ABAD-YSZ, the structures causing the orientation variations are observed on a micrometer scale only, which is attributed to the granularity of the template. In contrast to Ni-9at.%W where no preferred misorientation axis is notable within single substrate grains, the misorientation of YBCO on the ABAD-YSZ tape is primarily caused by lattice rotations about the sample normal.
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