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Benoit Roberge Serge Jandl Agung A. Nugroho Thomas T. M. Palstra Le D. Tung Geetha Balakrishnan 《Journal of Raman spectroscopy : JRS》2015,46(11):1157-1160
The coexistence at low temperature in YVO3 and LaVO3 of two competing phases with defined orbital and spin orientations is studied by Raman spectroscopy. The temperature evolution of the phonons indicates that phase coexistence, due to strain in YVO3 and fluctuations in LaVO3, is not restricted to small R ionic radius in RVO3 compounds. Also, a typical temperature at 50 K is inferred from the temperature dependence of the intensities in LaVO3. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Vollmer A Jurchescu OD Arfaoui I Salzmann I Palstra TT Rudolf P Niemax J Pflaum J Rabe JP Koch N 《The European physical journal. E, Soft matter》2005,17(3):339-343
We use ultraviolet photoelectron spectroscopy to investigate the effect of oxygen and air exposure on the electronic structure of pentacene single crystals and thin films. It is found that O2 and water do not react noticeably with pentacene, whereas singlet oxygen/ozone readily oxidize the organic compound. Also, we obtain no evidence for considerable p-type doping of pentacene by O2 at low pressure. However, oxygen exposure lowers the hole injection barrier at the interface between Au and pentacene by 0.25 eV, presumably due to a modification of the Au surface properties. 相似文献
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The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton. 相似文献
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B. Roberge S. Jandl A. A. Nugroho T. T. M. Palstra 《Journal of Raman spectroscopy : JRS》2012,43(1):127-130
First‐order and multiphonon Raman active excitations are studied in YbVO3 as a function of temperature in the orthorhombic and monoclinic phases. Below T ≃ 170 K, a G‐type orbital ordering with a concomitant monoclinic transition occurs. They enhance the phonon polarizabilities, allowing the resolution of room‐temperature bands, and activate new excitations around 700 cm−1. Below T ∼ 65 K, the 700 cm−1 excitations disappear, indicating a C‐type orbital ordering and a return to the orthorhombic structure. The observed phonon combinations around 1400 cm−1 with a dominant Jahn‐Teller vibration at ∼690 cm−1 reflect a possible orbiton‐phonon coupling. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Christine C. Mattheus Anne B. Dros Jacob Baas Auke Meetsma Jan L. de Boer Thomas T. M. Palstra 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):939-941
Pentacene, C22H14, crystallizes in different morphologies characterized by their d(001)‐spacings of 14.1, 14.5, 15.0 and 15.4 Å. We have studied the crystal structure of the 14.1 and 14.5 Åd‐spacing morphologies grown by vapour transport and from solution. We find a close correspondence between the 14.1 Å structure reported by Holmes, Kumaraswamy, Matzeger & Vollhardt [Chem. Eur. J. (1999), 5 , 3399–3412] and the 14.5 Å structure reported by Campbell, Monteath Robertson & Trotter [Acta Cryst. (1961), 14 , 705–711]. Single crystals commonly adopt the 14.1 Åd‐spacing morphology with an inversion centre on both molecules in the unit cell. Thin films grown on SiO2 substrates above 350 K preferentially adopt the 14.5 Åd‐spacing morphology, with a slightly smaller unit‐cell volume. 相似文献
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Bas B. van Aken Auke Meetsma Thomas T. M. Palstra 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(3):230-232
The crystal structure of hexagonal yttrium trioxomanganate has been determined at room temperature and at 180 K. It is isomorphous with LuMnO3. The Mn displacement vector has a frustrated component in the ab plane and a ferroelectric part along the c axis. The net ferroelectricity is zero due to inversion twinning, with 1:1 twin fractions. 相似文献
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We report evidence for phase coexistence of orbital orderings of different symmetry in SmVO3 by high resolution x-ray powder diffraction. The phase coexistence is triggered by an antiferromagnetic ordering of the vanadium spins near 130 K, below an initial orbital ordering near 200 K. The phase coexistence is the result of the intermediate ionic size of samarium coupled to exchange striction at the vanadium spin ordering. 相似文献