Jasmin Biehler

Goethe-Universität Frankfurt am Main, Frankfurt, Hesse, Germany

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Publications (4)5.93 Total impact

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    ABSTRACT: Powder X-ray diffraction experiments of sillenites Bi12M O20 (M=Si, Ge, Ti) were performed with synchrotron radiation at the ESRF, Grenoble, at pressures up to 39 GPa (M=Si), 50 GPa (M=Ge), and 37 GPa (M=Ti), respectively. These three sillenites were investigated for the first time over such a large pressure range and they show no phase transition up to the highest pressures achieved. Birch–Murnaghan equations of state of third order were fitted to the pressure dependence of the lattice parameters. The resulting bulk moduli B0 and their pressure derivatives B′B′ are B0=63(1)GPa with B′=6.6(3)B′=6.6(3) (M=Si), B0=63.0(5)GPa with B′=5.90(7)B′=5.90(7) (M=Ge), and B0=48(1)GPa with B′=9.4(5)B′=9.4(5) (M=Ti). In the case of Bi12SiO20 and Bi12TiO20 the equation of state fits were restricted to pressures below 15 GPa, because the experimental data were affected by non-hydrostatic stress at higher pressures. The equation of state of neon was redetermined (V0=11.7(6)cm3/molV0=11.7(6)cm3/mol, B0=5(1)GPa, B′=5.5(3)GPa) and its use as an internal pressure standard for diffraction experiments is discussed. A second cubic phase could be identified in our Bi12TiO20 sample. This was attributed to eulytite-type Bi4Ti3O12, which has B0=50.9(8)GPa and B′=6.9(3)B′=6.9(3).
    Journal of Solid State Chemistry 01/2013; 208:35–42. · 2.04 Impact Factor
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    ABSTRACT: The high-pressure behaviour of Bi2Fe4O9 was analysed by in situ powder and single-crystal x-ray diffraction and Raman spectroscopy. Pressures up to 34.3(8) GPa were generated using the diamond anvil cell technique. A reversible phase transition is observed at approximately 6.89(6) GPa and the high-pressure structure is stable up to 26.3(1) GPa. At higher pressures the onset of amorphization is observed. The crystal structures were refined from single-crystal data at ambient pressure and pressures of 4.49(2), 6.46(2), 7.26(2) and 9.4(1) GPa. The high-pressure structure is isotypic to the high-pressure structure of Bi2Ga4O9. The lower phase transition pressure of Bi2Fe4O9 with respect to that of Bi2Ga4O9 (16 GPa) confirms the previously proposed strong influence of cation substitution on the high-pressure stability and the misfit of Ga3+ and Fe3+ in tetrahedral coordination at high pressure. A fit of a second-order Birch–Murnaghan equation of state to the p–V data results in K0 = 74(3) GPa for the low-pressure phase and K0 = 79(2) GPa for the high-pressure phase. The mode Grüneisen parameters were obtained from Raman-spectroscopic measurements.
    Journal of Physics Condensed Matter 03/2012; 24(14):145401. · 2.22 Impact Factor
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    ABSTRACT: Tantalum nitrides were formed by reaction of the elements at pressures between 9(1) and 12.7(5) GPa and temperatures >1600–2000 K in the laser-heated diamond anvil cell. The incorporation of small amount of nitrogen in the tantalum structure was identified as the first reaction product on weak laser irradiation. Subsequent laser heating led to the formation of hexagonal -Ta2N and orthorhombic -Ta2N3, which was the stable phase at pressures up to 27 GPa and high temperatures. No evidence was found for the presence of -TaN, -TaN, -TaN, Ta3N5-I or Ta3N5-II, which was predicted to be the stable phase at P>17 GPa and T=2800 K, at the P,T-conditions of this experiment. The bulk modulus of -Ta2N3 was determined to be B0=319(6) GPa from a 2nd order Birch–Murnaghan equation of state fit to the experimental data, while quantum mechanical calculations using the density functional theory gave a bulk modulus of B0=348.0(9) GPa for a 2nd-order fit or B0=339(1) GPa and B′=4.67(9) for a 3rd-order fit. The values show the large incompressibility of this high-pressure phase. From the DFT data the structural compression mechanism could be determined.
    Journal of Alloys and Compounds. 01/2010;
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    ABSTRACT: In situ synchrotron X-ray diffraction was used to observe the reaction induced by laser heating of a mixture of tantalum and boron in a diamond anvil cell. Laser heating at pressures of 12 and 24 GPa resulted in the formation of TaB2. The bulk modulus of TaB2 (B0 = 341(7) GPa) was determined from a fit of a second-order Birch–Murnaghan equation of state to the p−V data. Density functional theory based calculations complemented the experimental observations and were used to obtain the full tensor of elastic stiffness coefficients. The choice of the most appropriate exchange-correlation functional for the description of elastic properties is discussed.
    Solid State Sciences 01/2010; 12(12):2059-2064. · 1.67 Impact Factor