Phase transitions studied by ultra-low-temperature X-ray diffraction

Recently, we developed a low-temperature X-ray diffractometer with a dilution refrigerator. By using this measuring system, we investigated phase transitions of PrPtBi (T-C = 1.35 K) and Ce0.7La0.3B6 (T-C = 1.4 K). These phase transitions are expected to be electronic quadrupole ordering. But it has been unknown if these are ferro- or antiferro-quadrupole ordering. From the temperature dependence of the lattice constant and the full-width at half-maximum of the diffraction spectrum, it was found that the phase transition of PrPtBi seemed to be antiferro-quadrupole ordering and the phase IV in Ce(0.7)L(0.3)B-6 to be ferro-quadrupole ordered state. (C) 2003 Elsevier B.V. All rights reserved.