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Roleder K.,University of Silesia | Bussmann-Holder A.,Max Planck Institute Fr Festkrperforschung | Gorny M.,University of Silesia | Szot K.,Forchungszentrum Jlich | Glazer A.M.,University of Oxford
Phase Transitions | Year: 2012

The structural instability of SrTiO3at T S=105K is reinvestigated experimentally and theoretically by birefringence measurements and within the self-consistent phonon approximation. Analogous to BaTiO 3 the phase transition shows precursor dynamics starting approximately 60K above the phase transition temperature. These rotational dynamic clusters compete with precursor effects stemming from the polar soft mode and appear on different length scales as compared to BaTiO3. © 2012 Taylor & Francis Group, LLC.

Santamara-Perez D.,Complutense University of Madrid | Vegas A.,CSIC - Institute of Physical Chemistry "Rocasolano" | Muehle C.,Max Planck Institute Fr Festkrperforschung | Jansen M.,Max Planck Institute Fr Festkrperforschung
Journal of Chemical Physics | Year: 2011

The high-pressure behaviour of cesium sulphide Cs2S has been studied up to 19 GPa at room temperature using angle-dispersive x-ray powder diffraction in a diamond-anvil cell. X-ray results show that the initial anticotunnite-type structure (S.G. Pnma) seems to undertake a continuous transformation to a distorted Ni2In-type structure (also with S.G. Pnma), starting below 1 GPa and being almost completed at 5 GPa. The profile of the x-ray diffraction patterns did not change noticeably from this pressure to 17 GPa. The observed structural changes in Cs2S are discussed in relation to the high-pressure behaviour of the rest of alkaline sulfides and their systematic trends are pointed out. Finally, we discuss the analogies between the structures of alkaline-metal chalcogenides and those of the cationic arrays of their corresponding oxides (sulfates, selenates, and tellurates) comparing the insertion of oxygen and the application of pressure. © 2011 American Institute of Physics.

Babizhetskyy V.,Max Planck Institute Fr Festkrperforschung | Simon A.,Max Planck Institute Fr Festkrperforschung | Mattausch H.,Max Planck Institute Fr Festkrperforschung | Hiebl K.,University of Vienna | Zheng C.,Northern Illinois University
Journal of Solid State Chemistry | Year: 2010

The ternary rare-earth boride carbides R15B4C 14 (R=Y, GdLu) were prepared from the elements by arc-melting followed by annealing in silica tubes at 1270 K for 1 month. The crystal structures of Tb15B4C14 and Er 15B4C14 were determined from single crystal X-ray diffraction data. They crystallize in a new structure type in space group P4/mnc (Tb15B4C14: a=8.1251(5) , c=15.861(1) , Z=2, R1=0.041 (wR2=0.088) for 1023 reflections with I o>2σ(Io); Er15B4C 14: a=7.932(1) , c=15.685(2) , Z=2, R1=0.037 (wR 2=0.094) for 1022 reflections with Io>2σ(I o)). The crystal structure contains discrete carbon atoms and bent CBC units in octahedra and distorted bicapped square antiprisms, respectively. In both structures the same type of disorder exists. One R atom position needs to be refined as split atom position with a ratio 9:1 indicative of a 10% substitution of the neighboring C4- by C24-. The actual composition has then to be described as R15B 4C14.2. The isoelectronic substitution does not change the electron partition of R15B4C14 which can be written as (R3)15(C4-)6(CBC 5-)4•e-. The electronic structure was studied with the extended Hckel method. The investigated compounds Tb 15B4C14, Dy15B4C 14 and Er15B4C14 are hard ferromagnets with Curie temperatures TC=145, 120 and 50 K, respectively. The coercive field BC=3.15 T for Dy15B 4C14 is quite remarkable. © 2010 Elsevier Inc. All rights reserved.

Smetana V.,Max Planck Institute Fr Festkrperforschung | Vajenine G.V.,Max Planck Institute Fr Festkrperforschung | Vajenine G.V.,University of Stuttgart | Kienle L.,University of Kiel | And 2 more authors.
Journal of Solid State Chemistry | Year: 2010

Three new intermetallic phases, BaLi2.1In1.9, BaLi1.12In0.98, and BaLi1.06In1.16 and two subnitrides Li35In45Ba39N9 and LiIn2Ba3N0.83 have been synthesized and their crystal structures have been determined. According to single crystal X-ray diffraction data BaLi2.1In1.9 and BaLi 1.12In0.98 crystallize with hexagonal symmetry (BaLi 2.1In1.9: P63/mmc, a=10.410(2), c=8.364(2) , Z=6, V=785.0(2) 3) and BaLi1.12In0.98: P6/mmm, a=17.469(1), c=10.6409(7) , Z=30, V=2813.5(8) 3), while BaLi 1.06In1.16 has a rhombohedral structure (R-3c, a=18.894(3), c=85.289(17) , Z=276, V=26368(8) 3). BaLi 2.1In1.9 is isostructural with the known phase BaLi 4. The phase BaLi1.12In0.98 is structurally related to Na8K23Cd12In48, while BaLi1.06In1.16 is isostructural with Li 33.3Ba13.1Ca3. A sample containing structurally similar BaLi1.12In0.98 and BaLi1.02In 1.16 was also investigated by transmission electron microscopy. Li35In45Ba39N9 and LiIn 2Ba3N0.83 crystallize with tetragonal (I-42m, a=15.299(2), c=30.682(6) , Z=2, V=7182(2) 3) and cubic (Fd-3m, a=14.913(2) , Z=8, V=3316.7(7) 3) symmetry, respectively. While the first-mentioned subnitride belongs to the Li80Ba39N 9 structure type, the second extends the structural family of Ba 6In4.78N2.72. The structural features of the new compounds are discussed in comparison to the known phases and the results of total energy calculations. © 2010 Elsevier Inc. All rights reserved.

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