2003/10/23 by Yuichi Nemoto, Takashi Yamaguchi, Takenobu Horino +8 · 2 citations
Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Magnetic and transport properties of perovskites and related materials #Rare-earth and actinide compounds #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.68.184109
11 pages, 15 figures, to be published on Phys. Rev. B
arxiv created 2003/10/23 · openalex publication_date 2003/11/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
Lattice effects in a cerium based clathrate compound Ce3Pd20Ge6 with a cubic Cr23C6-type structure have been investigated by ultrasonic and thermal expansion measurements. Elastic softenings of (C11\ensuremath-C12)/2 and C44 proportional to the reciprocal temperature 1/T above TQ1=1.25 K are well described in terms of the quadrupole susceptibility for the ground state \ensuremathΓ8 quartet. A huge softening of 50% in (C11\ensuremath-C12)/2 and a spontaneous expansion \ensuremathΔL/L=1.9\ifmmode×\else\texttimes\fi10^\ensuremath-4 along the [001] direction in particular indicate the ferroquadrupole ordering of O20 below TQ1. The elastic anomalies associated with the antiferromagnetic ordering at TN2=0.75 K and the incommensurate antiferromagnetic ordering are also found. Notable frequency dependence of C44 around 10 K is accounted for by the Debye-type dispersion indicating a \ensuremathΓ5 rattling motion of an off-center Ce ion along the [111] direction with eight fractionally occupied positions around the 4a site in a cage. The thermally activated \ensuremathΓ5 rattling motion obeying a relaxation time \ensuremathτ=\ensuremathτ0exp(E/kBT) with an attempt time \ensuremathτ0=3.1\ifmmode×\else\texttimes\fi10^\ensuremath-11 sec and an activation energy E=70 K dies out with decreasing temperature, and then the off-center tunneling state of Ce ion in the 4a-site cage will appear at low temperatures.