Quadrupolar ordering of Ce3Pd20Ge6

We present ultrasonic measurement of the ternary intermetallic compound Ce3 Pd20Ge6, where quadrupolar ordering at T-Q approximate to 1.2 K occurs at a higher temperature than the antiferromagnetic ordering at T-N = 0.75 K. Th e Curie term in the quadrupolar susceptibility for the crystal-held ground- state Gamma(8) gives rise to a softening of the transverse modes (C-11 - C- 12)/2 and C-44 above T-Q. The most pronounced softening of 50% is observed for (C-11 - C-12)/2 which suggests a ferroquadrupolar ordering of O-2(0) or of O-2(2) with Gamma(3) symmetry below T-Q. (C) 1999 Elsevier Science B.V. All rights reserved.