Antiferro-quadrupolar structures inUPd3 inferred from x-ray resonant Bragg diffraction

Abstract

A systematic analysis of resonant x-ray Bragg diffraction data forUPd3, with signalenhancement at the U MIV edge, including possible structural phase transitions leads to a newdetermination of the space groups of the material in the phases betweenT0 = 7.8 K andT+1 = 6.9 K, asP 2221, andbetween T−1 = 6.7 K and T2 = 4.4 K, as P 21. In addition, the quadrupolar order parameters,⟨Qab⟩, inferred from diffraction data for the phase betweenT−1 andT2, are⟨Qxz⟩ and⟨Qyz⟩ at the (103) Braggreflection and ⟨Qxy⟩ at the (104) reflection.