Browsing by Author "Yakovlev, S"

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    High-pressure behavior and equations of state of the cobaltates YBaCo4O7, YBaCo4O7+δ, YBaCoZn3O7 and BaCoO3−x
    (Elsevier, 2012-12-01) Juarez-Arellano, EA; Avdeev, M; Yakovlev, S; Lopez-de-la-Torre, L; Bayarjargal, L; Winkler, B; Friedrich, A; Kharton, VV
    The compressibilities of the cobaltates YBaCo4O7, YBaCo4O7+δ, YBaCoZn3O7 and BaCoO3−x were investigated by in situ powder X-ray diffraction experiments up to 30GPa using diamond anvil cells. Pressure-induced phase transitions and amorphization were observed in all the samples. The onset of the pressure-induced phase transition and the onset of the amorphization were observed at ∼11.7 and 12.2GPa (YBaCo4O7), at ∼14.2 and 16.1GPa (YBaCo4O7+δ), and at ∼16.7 and 18.7GPa (YBaCoZn3O7), respectively. An attempt to laser anneal at high-pressure failed as it led to a decomposition of the YBaCo4O7 phase into a mixture of phases. Fits of second- and third-order Birch–Murnaghan equations-of-state to the p–V data result in B0=109(3)GPa for YBaCo4O7; B0=186(4)GPa and B′=1.5 for YBaCo4O7+δ; and B0=117(1)GPa for YBaCoZn3O7. The high-pressure behavior of the studied compounds was compared with isostructural compounds and it is shown that the oxygen-content has a very large effect on the high-pressure behavior of this class of materials. © 2012 Elsevier Inc.
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    Observation of a ferroelastic phase transition in the YBaCo4-xZnxO7+δ system
    (DFG, 2009) Juarez-Arellano, EA; Avdeev, M; Lopez-de-la-Torre, L; Yakovlev, S; Bayarjargal, L; Winkler, B; Friedrich, A
    No abstract available
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    Pressure-induced amorphization of La(1/3)NbO3
    (Elsevier, 2011-09-15) Noked, O; Yakovlev, S; Greenberg, Y; Garbarino, G; Shuker, R; Avdeev, M; Sterer, E
    La(1/3)NbO(3), an A-site cation deficient double perovskite, has been studied under pressure by synchrotron X-ray powder diffraction and Raman spectroscopy. In contrast to other highly distorted perovskites, transforming to post-perovskite on compression, La(1/3)NbO(3) undergoes irreversible pressure induced amorphization at similar to 14.5 GPa. Over a wide range of pressure before that transition it presents an almost linear volume decrease versus pressure, accompanied by convergence form orthorhombic to a cubic unit cell. The Raman spectroscopy also shows an amorphization at the same pressure. However, where upon full decompression the X-ray diffraction pattern remains amorphous, new Raman peaks become active. (C) 2011 Elsevier B.V.
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    Transitions between P21, P63 (√ 3A), and P6322 modifications of SrAl2O4 by in situ high-temperature x-ray and neutron diffraction
    (Elsevier, 2007-12-01) Avdeev, M; Yakovlev, S; Yaremchenko, AA; Kharton, VV
    The results of in situ high-temperature X-ray and neutron powder diffraction experiments reconcile inconsistencies in previous reports on the symmetry of high-temperature phases of SrAl2O4. The material undergoes two reversible phase transitions P21↔P63(3A) and P63(3A)↔P6322 at ∼680 and ∼860°C, respectively, and the latter one is experimentally observed and characterized for the first time. The higher symmetry above the P63(3A)↔P6322 transition is gained by disordering off-center split site of oxygen atoms around trigonal axis rather than by unbending Al–O–Al angle to the ideal value 180°. The analysis of the literature suggests that it is a common feature of the P6322 phases of stuffed tridymites.© 2007 Elsevier Inc.