Bulk properties of : A question of zero thermal expansion

¹ Department of Physics and Institute of Basic Science, Sungkyunkwan University Suwon 440-746, Korea
² Center for Strongly Correlated Materials Research, Seoul National University Seoul 151-742, Korea
³ Material Science Laboratory, Korea Basic Science Institute - Daejon 305-333, Korea
⁴ Institute of Solid State Physics, Vienna University of Technology A-1040 Wien, Austria

Corresponding authors: jgpark@skku.edu ernst.bauer@ifp.tuwien.ac.at

Received: 28 January 2004
Accepted: 26 October 2004

Abstract

Despite the recent report of zero thermal expansion in , our extensive studies of the physical properties of pure failed to find anomalous behavior of the thermal expansion of both X-ray and dilatometry measurements. Instead, the temperature dependence of the lattice constants can be simply explained in terms of the Debye model with the cutoff frequency of 226, which was estimated from heat capacity measurement. Additionally, susceptibility measurements have not revealed any sign of a change of the valency from 2 to 700, but magnetic correlations develop at low temperatures. Important findings of further interest are that has very strong low-lying optic phonons, 1.7 oscillator strength with an energy of 80, and shows strong increase of Grüneisen parameter below 20.