The ternary uranium compound UCu2Sn with a hexagonal ZrPt2Al-type structure shows a phase transition at 16 K. We reported previously that huge lattice-softening is accompanied by the phase transition, which originates from ferroquadrupolar ordering of the ground state non-Kramers doublet Γ5. A macroscopic strain, which is expected to emerge spontaneously, was not detected by powder X-ray diffraction in the temperature range between 4.2 and 300 K. To search the spontaneous strain, we have carried out thermal expansion measurements on a single-crystalline sample along the a, b and c axes using a capacitance technique with the resolution of 10−8. In the present experiment, we found the spontaneous exx−eyy strain which couples to the ground state doublet Γ5. The effect of uniaxial pressure along the a, b and c axes on the transition temperature is also discussed.
@article{arxiv.cond-mat/0306591,
title = {Spontaneous strain due to ferroquadrupolar ordering in UCu$_2$Sn},
author = {Isao Ishii and Haruhiro Higaki and Kenichi Katoh and Toshiro Takabatake and Hiroshi Goshima and Toshizo Fujita and Takashi Suzuki},
journal= {arXiv preprint arXiv:cond-mat/0306591},
year = {2009}
}