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A sequence of structural transitions occurring in the quasi-one-dimensional (1D) 3d1 system BaVS3 at low temperature was investigated by high resolution synchrotron X-ray diffraction. The orthorhombic Cmc21 structure of the intermediate-temperature (70K<T<240K) phase was confirmed. A model for the low-T (T<70K) k=(1 0 1/2)O superstructure (with Im...
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Citations
... Materials that bear the ABX 3 structure are continuously studied due to their novel properties, which have potential applications, for example MOSFET (metal-oxide-semiconductor field-effect transistor) device fabrication [1]. One member of this family is barium vanadium sulfide (BaVS 3 ), which has unique electronic properties such as metal-insulator transition [2][3][4][5][6], "bad metal" behavior [7], magnetic field induced structural transition [8], charge density waves (CDW) [5] and paramagnetic-antiferromagnetic phase transition [9]. It is experimentally [2][3][4][5][6] and theoretically [10,11] verified that the barium vanadium sulfide (BaVS 3 ) has an orthorhombic to monoclinic structural transition during the metal-insulator (MI) phase transition at a temperature of approximately T MI = 69 K. ...
... One member of this family is barium vanadium sulfide (BaVS 3 ), which has unique electronic properties such as metal-insulator transition [2][3][4][5][6], "bad metal" behavior [7], magnetic field induced structural transition [8], charge density waves (CDW) [5] and paramagnetic-antiferromagnetic phase transition [9]. It is experimentally [2][3][4][5][6] and theoretically [10,11] verified that the barium vanadium sulfide (BaVS 3 ) has an orthorhombic to monoclinic structural transition during the metal-insulator (MI) phase transition at a temperature of approximately T MI = 69 K. The given structural transition relates to an extensive regime of one-dimensional lattice fluctuations. ...
The present study deals with the anomalous heat capacity peak and thermal conductivity of BaVS 3 near the metal-insulator transition present at 69 K. The transition is related to a structural transition from an orthorhombic to monoclinic phase. Heat capacity measurements at this temperature exhibit a significant and relatively broad peak, which is also sample dependent. The present study calculates the entropy increase during the structural transition and we show that the additional entropy is caused by enhanced electron scattering as a result of the structural reorientation of the nuclei. Within the model it is possible to explain quantitatively the observed peak alike structure in the heat capacity and in heat conductivity.
The metal-insulator transition (MIT) of BaVS3 is suppressed under pressure, and above the critical pressure of pcr≈2 GPa the metallic phase is stabilized. We present the results of detailed magnetoresistivity measurements carried out at pressures near the critical value in magnetic fields up to B=12 T. We found that slightly below the critical pressure the structural tetramerization—which drives the MIT—is combined with the onset of magnetic correlations. If the zero-field transition temperature is suppressed to a sufficiently low value (TMI≤15 K), the system can be driven into the metallic state by application of magnetic field. The main effect is not the reduction of TMI with increasing B, but rather the broadening of the transition due to the applied magnetic field. We tentatively ascribe this phenomenon to the influence on the magnetic structure coupled to the bond order of the tetramers.
The charge response in the barium vanadium sulfide (BaVS3) single crystals is characterized by dc resistivity and low frequency dielectric spectroscopy. A broad relaxation mode in MHz range with huge dielectric constant ~= 10^6 emerges at the metal-to-insulator phase transition TMI ~= 67 K, weakens with lowering temperature and eventually levels off below the magnetic transition Tchi ~= 30 K. The mean relaxation time is thermally activated in a manner similar to the dc resistivity. These features are interpreted as signatures of the collective charge excitations characteristic for the orbital ordering that gradually develops below TMI and stabilizes at long-range scale below Tchi. Comment: 6 pages, 3 figures, submitted to PRB
The origin of the anomalous electronic phase transition (T X ≈ 30 K) caused by a single-electron-occupied t 2g orbital in quasi-one-dimensional BaVS 3 is studied by means of resonant soft x-ray diffraction taken at the V L 2,3 absorption edges. The energy and azimuthal angle dependence of the observed (0 k l) reflection can be explained by the presence of at least two electronically different V contributions. Moreover, analysis of the scattered x-ray polarization indicates that the observed reflection is purely magnetic in origin, which discourages models with orbital and charge modifications occurring at T X. The dependence of the reflection on left or right circular polarized incoming x rays indicates that the incommensurability of the reflection is connected to a helical component of the magnetic structure. These results, together with those from neutron scattering, are discussed in terms of the different models proposed for the electronic and magnetic ground state.
High-pressure crystal growth and synthesis of selected solid-state osmium oxides, many of which are perovskite-related types, are briefly reviewed, and their magnetic and electrical properties are introduced. Crystals of the osmium oxides, including NaOsO3, LiOsO3, and Na2OsO4, were successfully grown under high-pressure and high-temperature conditions at 6 GPa in the presence of an appropriate amount of flux in a belt-type apparatus. The unexpected discovery of a magnetic metal–insulator transition in NaOsO3, a ferroelectric-like transition in LiOsO3, and high-temperature ferrimagnetism driven by a local structural distortion in Ca2FeOsO6 may represent unique features of the osmium oxides. The high-pressure and high-temperature synthesis and crystal growth has played a central role in the development of solid-state osmium oxides and the elucidation of their magnetic and electronic properties toward possible use in multifunctional devices.
High oxygen pressures are a fruitful tool for the stabilization of the highest formal oxidation states of transition metals (M n+) leading to the strongest chemical bonds; the improvement of the M n+-O bond covalency induces different electronic phenomena. Among the physical characterizations applied to investigate such phenomena, 57Fe and 119Sn Mössbauer spectra are evaluated for studying unusual electronic configurations, orbital ordering, charge disproportionation and insulator-metal transitions in the perovskites series of 57Fe doped RENiO 3 nickelates (RE = rare earths, Y and Tl) and 119Sn doped AEFeO 3 ferrates (AE = Ca, Sr).
The development of new synthetic routes and instrumentation for characterisation have resulted in a number of outstanding publications in 2005. The increasing use of elevated pressure, combined with in situ diffraction techniques, has resulted in the identification of a new phase of elemental curium, the characterisation of a new polytype of silica, synthesis of a new superconductor GaTa4Se8, the first reports of the multiferroic compounds Bi2Ni1−xMnxO6 and a crystalline, mesoporous germanium oxide with the lowest framework density yet reported for an inorganic material. This review will provide an overview of these, and other publications, which have reported significant developments in the chemistry of extended, crystalline inorganic materials in 2005.
We use first-principles density functional theory (DFT) within the local
density approx- imation (LDA) to ascertain the ground state structure of real
and theoretical compounds with the formula ABS3 (A = K, Rb, Cs, Ca, Sr, Ba, Tl,
Sn, Pb, and Bi; and B = Sc, Y, Ti, Zr, V, and Nb) under the constraint that B
must have a d0 electronic configuration. Our findings indicate that none of
these AB combinations prefer a perovskite ground state with corner-sharing BS6
octahedra, but that they prefer phases with either edge- or face-sharing
motifs. Further, a simple two-dimensional structure field map created from A
and B ionic radii provides a neat demarcation between combinations preferring
face-sharing versus edge- sharing phases for most of these combinations. We
then show that by modifying the common Goldschmidt tolerance factor with a
multiplicative term based on the electronegativity dif- ference between A and
S, the demarcation between predicted edge-sharing and face-sharing ground state
phases is enhanced. We also demonstrate that, by calculating the free energy
contribution of phonons, some of these compounds may assume multiple phases as
synthesis temperatures are altered, or as ambient temperatures rise or fall.
Possible orbital orders below the metal-insulator transition temperature
in quasi-one-dimensional BaVS3 have been investigated in
relation to the monoclinic lattice distortion in the insulating phase
using a one-dimensional two-band Hubbard model. Orbital occupations in
the ground state and optical conductivity have been calculated by means
of exact diagonalization of finite size clusters. Depending on the size
of crystal field splitting of the t2g levels, two different
orbital orders in the t2g orbitals with the periodicity of
four V ion sites along the c-axis are found to be stabilized with the
lattice distortion. The on-site exchange interaction plays important
role in the formation of these orbital orders.
BaVS3 presents a metal-to-insulator (MI) transition at ambient pressure due to the stabilization of a 2kF commensurate charge density wave (CDW) Peierls ground state built on the dz2 V orbitals. The MI transition vanishes under pressure at a quantum critical point (QCP) where the electronic properties exhibit a non-Fermi liquid behavior. In this paper, we determine the CDW phase diagram under pressure and show that it combines both the vanishing of the second-order Peierls transition and a commensurate-incommensurate first-order delocking transition of the 2kF wave vector. We explain quantitatively the drop of the MI critical temperature by the decrease of the electron-hole pair lifetime of the CDW condensate due to an enhancement of the hybridization between the dz2 and e(t2g) levels of the V under pressure.
