|
|
| Type |
Poster Presentation |
| Area |
Material Chemistry |
| Room No. |
Event Hall |
| Time |
4월 20일 (금요일) 11:00~12:30 |
| Code |
MAT.P-320 |
| Subject |
Orbital ordering and thermoelectric properties in Cs2AgF4 ; Density functional approach |
| Authors |
Changhoon Lee*, Ji Hoon Shim
Department of Chemistry, Pohang University of Science and Technology, Korea
|
| Abstract |
Although a number of theoretical studies on the magnetic properties of Cs2AgF4 have been carried out [1,2] to show that the orbital order takes place in each AgF4 layer such that the magnetic orbitals of adjacent Ag2+ ions become orthogonal to each other, thereby leading to no overlap between them and hence a ferromagnetic spin exchange between nearest-neighbor Ag2+ ions, the study of Cs2AgF4 in terms of thermoelectric has not been tried yet as we know. Cs2AgF4, synthesized in 1971 by Odenthal [3], is an isoelectronic and isostructural analogue of La2CuO4, namely, Cs2AgF4 crystalizes in K2NiF4-type (I4/mmm) structure as shown in the Fig. 1. But, this system at 400K undergoes structural transition from tetragonal (I4/mmm) to orthorhombic (Bbcm) structure by 1st and 2nd order JT effects which is similar to the structure of K2CuF4.[4]
The main different between tetragonal and orthorhombic Cs2AgF4 is whether orbital ordering is allowed or not. Note that the orbital ordering would lead lowing electronic structure and then low dimensional electronic structure is responsible for the enhancement of Seebeck coefficients according to the Dresselhouse [5]. Thus, it is of interest and important to explore if the orbital ordering is closely connected with improving the thermoelectric properties. In this present work, we investigate relationship between orbital ordering and thermoelectric properties comparing electronic structure and thermal transport coefficients of orbital ordering allowed orthorhombic and orbital ordering not allowed tetragonal structure Cs2AgF4. Our result indicates that the Seebeck coefficients of orthorhombic Cs2AgF4 is substantially increased due to the lowering electronic structure induced by orbital ordering. Therefore, one speculates that the orbital ordering should be considered as a new useful way for enhancing PF.
References
[1] (a). D. Dai, M.-H. Whangbo, J. Köhler, C. Hoch, A. Villesuzanne, Chem. Mater. 2006, 18, 3281. (b). J. Tong, R. K. Kremer, J. Köhler, A. Simon, C. Lee, E. Kan, and M. –H. Whangbo, Z. Kristallogr. 2010, 225, 498–503
[2] (a) D. Kasinathan, K. Koepernik, U. Nitzsche, H. Rosner, Phys. Rev. Lett. 2007, 99, 247210. (d) E.-J. Kan, L.-F. Yuan, J. Yang, J. G. Hou, Phys. Rev. B, 2007, 76, 024417.
[3] R. –H. Von Odenthal, D. Paus, and R. Hoppe, Z. anorg. allg. Chem. 1974, 407, 144-150.
[4] S. E. Mclain, M. R. Dolgos, D. A. Tennant, J. F. C. Turner, T. Barnes, T. Proffen, B. C. Sales, and R. I. Bewley, Nat. Mater. 2006, 5, 560.
[5] L. D. Hicks, M. S. Dresselhaus, Phys. Rev. B 1993, 47, 16631-16634.
|
| E-mail |
chlee0887@postech.ac.kr |
|
121st General Meeting of the KCS