- Petr Doležal: Structural changes in (Ce,La)Pd2Al(1-x)Gax series
- 10. 5. 2017, 14:30
- lecture room F2, first floor Ke Karlovu 5
- more information
Abstract:
(Ce,La)Pd2Al(1-x)Gax belongs to the large and deeply studied family RT2X2 (R is a rare-earth element, T is a transition metal and X is a p-element) of intermetallic compounds. These compounds very frequently crystalize in two structural types: ThCr2Si2 (I4/mmm 139) and CaBe2Ge2 (P4/nmm 129). All parent compounds (Ce,La)Pd2(Al,Ga)2 undergo a structural phase transition at low temperature, which lowers their symmetry. In the case of the Al-rich end of the series the low temperature structure is orthorhombic Cmme (67) and corresponding transition temperatures are Tstr = 13.5 K for the CePd2Al2 and Tstr = 91.5 K for the LaPd2Al2 [1]. At the opposite Ga end the situation is different. CePd2Ga2 and LaPd2Ga2 have triclinic structure with transitions Tstr = 125 K and Tstr = 62 K [2] respectively. The enhanced electron-phonon interaction is suggested to be responsible for the lower structural transition temperature of CePd2Al2 compared to LaPd2Al2 compound [1]. Structural changes in CePd2Al2 and CePd2Al1.6Ga0.4 also influence significantly the crystal field excitations [3].
The present study is focused on the investigation of the structural phase transition in the full (Ce,La)Pd2Al(1-x)Gax series. In particular we study the temperature evolution of lattice parameters and the effect of substitution of Al by Ga and thereby generate a phase diagram for the structure of these materials. We also try to solve the puzzle why compounds with the same structure at room temperature have so different structure at low temperatures.
[1] L.C. Chapon, E.A. Goremychkin, et al., Physica B 378-380, 819 (2006).
[2] J. Kitagawa, M. Ishikawa, Journal of the Physical Society of Japan, 2380-2383, 68 (1999).
[3] M. Klicpera, et al., Physical Review B in press (2017)