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KSUPS 2015: Abstracts / Extended abstracts / Synchrotron Radiation in Natural Science Vol. 14, No. 1-2 (2015)

59 P-23

Li0.95Mn2.05O4 under high pressure and at elevated temperature in DAC

P. Piszora1*, J. Darul1, C.Popescu2, F. Fauth2

1Department of Materials Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b,

61-614 Poznań, Poland

2CELLS-ALBA Synchrotron Light Source, 08290 Cerdanyola del Valles, Barcelona, Spain

Keywords: high pressure, high temperature, lithium-manganese spinel

*e-mail: pawel@amu.edu.pl

A displacive crystal distortion to lower symmetry that cooperatively removes a localized-electron orbital degeneracy so as to leave the atoms in the centre of symmetry of their distorted sites has been observed in many manganese oxides. Moreover, strong Jahn-Teller electron-phonon coupling has been proposed as the crucial component which localizes the eg electrons as polarons. High pressure and high temperature are a means to tune such an interplay between lattice and electronic degrees of freedom in the lithium manganese spinel [1,2].

The Li0.95Mn2.05O4 spinel sample was obtained from the appropriate amounts of thoroughly mixed powders of

-Mn2O3 and Li2CO3 (99.0% Merck) by thermal treatment in air at 1048 K. After heating, the specimen was quenched rapidly in solid CO2. Structural analyses showed the expected stoichiometry of the obtained powder and confirmed that no spurious phases were present.

The structural properties of Li0.95Mn2.05O4 under pressure and at elevated temperature were studied up to 13 GPa by X-ray powder diffraction at the MSPD-BL04 beamline [3] of the ALBA Synchrotron Light Source using monochromatic radiation ( = 0.4246 Å).

Diffraction patterns were recorded on image plates and then integrated [8] to yield intensity vs 2 diagrams.

For HP/HT experiments, sample was loaded in the 140-μm-diameter hole of an rhenium gasket inside a membrane-type diamond anvil cell (DAC) with a polydimethyl-siloxane oil of type ‘Rhodorsil 47V1000’

(VCR) as the pressure transmitting medium, which behaves hydrostatically up to 3 GPa (similar to the 4 : 1

methanol–ethanol mixture) and quasi-hydrostatically up to 10 GPa with a small maximum of nonhydrostaticity at 6 GPa [4]. Gold has been chosen as a pressure standard because of its moderate compressibility, chemical inertness, and large X-ray scattering power [5]. A small lump of gold with a purity of 999.9 (four nines fine) and an average particle size of 30 µm was put in the hole of a rhenium gasket.

Figure 1. Pressure-induced evolution of XRD pattern.

Li0.95Mn2.05O4 was studied by synchrotron X-ray diffraction isothermally at ambient temperature and at 107 °C under pressures up to 12 GPa. Usually the cooperative Jahn–Teller (JT) distortion is continuously reduced with increasing pressure. However, we obtained a strong indication that the JT effect and the concomitant orbital order are induced with pressure even if in the initial sample the cooperative Jahn–Teller distortion has been suppressed with temperature.

Acknowledgments: These experiments were performed at the MSPD-BL04 beamline at ALBA Synchrotron with the collaboration of ALBA staff.

___________________________________________________

[1] N. Ishizawa, K. Tateishi, S. Oishi, S. Kishimoto, Am.

Mineral. 99 (2014) 1528.

[2] J. Darul, C. Lathe, P. Piszora, R. Soc. Chem. Adv.

4 (2014) 65205.

[3] F. Fauth, I. Peral, C. Popescu, M. Knapp, Powder Diffr.

28 (2013) S360.

[4] S. Klotz, J. C. Chervin, P. Munsch, G. Le Marchand, J. Phys. D: Appl. Phys. 42 (2009) 075413.

[5] K. Takemura, A. Dewaele, Phys. Rev. B 78 (2008) 104119.

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