Mixed valence and superconductivity

2007 ◽  
Vol 366 (1862) ◽  
pp. 47-54 ◽  
Author(s):  
Sven Larsson
Keyword(s):  
Potential Energy Surfaces ◽  
Inelastic Neutron Scattering ◽  
Mixed Valence ◽  
Inelastic Neutron ◽  
Intermediate Valence ◽  
Phonon Modes ◽  
X Ray ◽  
X Ray Scattering ◽  
Valence States ◽  
Energy Surfaces

Mixed-valence (MV) systems are referred to here as MV-2 and MV-3 depending on whether two or three consecutive valence states are involved. MV-3 systems range from systems with Hubbard U ≫0, corresponding to a single stable, intermediate valence state, and U ≪0, corresponding to stable alternating valences differing by two units. Experiments using inelastic neutron scattering or inelastic X-ray scattering show softening of breathing phonon modes in MV systems compared with related systems with a single valence. It is hypothesized that softening is due to coupling between potential energy surfaces, corresponding to differing localizations of the electron. As predicted, softening is larger in the delocalized case. A mechanism for superconductivity is suggested.

LATTICE DYNAMICS OF CALCIUM FLUORIDE: PART I. LYDDANE, SACHS, TELLER FORMULA, DIFFUSE X-RAY SCATTERING, AND SPECIFIC HEAT

1962 ◽  
Vol 40 (1) ◽  
pp. 74-90 ◽  
Author(s):  
S. Ganesan ◽  
R. Srinivasan
Keyword(s):  
Specific Heat ◽  
Calcium Fluoride ◽  
Inelastic Neutron Scattering ◽  
Interaction Force ◽  
Inelastic Neutron ◽  
Symmetry Operation ◽  
Absorption Frequency ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

The reported violation of the Lyddane, Sachs, Teller formula in calcium fluoride has been shown to arise from an error due to the non-application of a symmetry operation in the second neighbor fluorine–fluorine interaction in Cribier's work. By correct deduction of the force constants, the diffuse X-ray scattering measurements are shown to be in accord with the Lyddane, Sachs, Teller formula, but the specific heat calculation on this model is in disagreement with the experimental data.Reflection measurements in the infrared and dispersion of refractive index are shown to be consistent with the principal infrared absorption frequency near 40 μ and not near 51 μ as assumed in the previous model. The calculation of the specific heat using this new infrared frequency agreed with the measurements only at very low and very high temperatures.The two curves are brought into agreement by assuming that the non-Coulomb cross interaction force constant β1 between first neighbor calcium and fluorine decrease with the wave vector. The diffuse X-ray scattering was recalculated on the model, which explained the specific heat data, and was again found to be in agreement with the Lyddane, Sachs, Teller formula. It is suggested that detailed infrared and inelastic neutron scattering studies be made on this crystal.

scholarly journals Erratum: Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Simon Schreck ◽  
Annette Pietzsch ◽  
Brian Kennedy ◽  
Conny Såthe ◽  
Piter S. Miedema ◽  
...  
Keyword(s):  
Potential Energy ◽  
Ground State ◽  
Potential Energy Surfaces ◽  
X Ray ◽  
X Ray Scattering ◽  
State Potential ◽  
Energy Surfaces ◽  
Ray Scattering

scholarly journals Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Simon Schreck ◽  
Annette Pietzsch ◽  
Brian Kennedy ◽  
Conny Såthe ◽  
Piter S. Miedema ◽  
...  
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Ground State ◽  
Potential Energy Surfaces ◽  
Energy Surface ◽  
X Ray ◽  
X Ray Scattering ◽  
State Potential ◽  
Energy Surfaces ◽  
Ray Scattering

Abstract Thermally driven chemistry as well as materials’ functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.

scholarly journals Polycrystalline Time-of-Flight Inelastic Neutron Scattering beyond the Density of States

Proceedings ◽  
2019 ◽  
Vol 26 (1) ◽  
pp. 38
Author(s):  
Leitner
Keyword(s):  
Neutron Scattering ◽  
Density Of States ◽  
Inelastic Neutron Scattering ◽  
Time Of Flight ◽  
Inelastic Neutron ◽  
Single Crystalline ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

Conventionally, experimental phonon dispersions are determined by inelastic neutron scattering on triple-axis spectrometers or by inelastic X-ray scattering, in both cases requiring single crystalline samples. [...]

scholarly journals Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy

2019 ◽  
Vol 10 (22) ◽  
pp. 5749-5760 ◽  
Author(s):  
Kasper S. Kjær ◽  
Tim B. Van Driel ◽  
Tobias C. B. Harlang ◽  
Kristjan Kunnus ◽  
Elisa Biasin ◽  
...  
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Free Electron ◽  
Free Electron Laser ◽  
Potential Energy Surfaces ◽  
X Ray ◽  
X Ray Scattering ◽  
State Potential ◽  
Laser Techniques ◽  
Energy Surfaces

Combined X-ray free-electron laser techniques pinpoints loci of intersections between potential energy surfaces of a photo-excited 3d transition-metal centered molecule.

scholarly journals A novel and potentially scalable CVD-based route towards SnO2:Mo thin films as transparent conducting oxides

2021 ◽  
Author(s):  
Tianlei Ma ◽  
Marek Nikiel ◽  
Andrew G. Thomas ◽  
Mohamed Missous ◽  
David J. Lewis
Keyword(s):  
Thin Films ◽  
Photoelectron Spectroscopy ◽  
Mixed Valence ◽  
Chemical Vapour ◽  
X Ray Diffraction ◽  
X Ray ◽  
Conducting Oxides ◽  
Valence States ◽  
3 Omega ◽  
First Time

AbstractIn this report, we prepared transparent and conducting undoped and molybdenum-doped tin oxide (Mo–SnO2) thin films by aerosol-assisted chemical vapour deposition (AACVD). The relationship between the precursor concentration in the feed and in the resulting films was studied by energy-dispersive X-ray spectroscopy, suggesting that the efficiency of doping is quantitative and that this method could potentially impart exquisite control over dopant levels. All SnO2 films were in tetragonal structure as confirmed by powder X-ray diffraction measurements. X-ray photoelectron spectroscopy characterisation indicated for the first time that Mo ions were in mixed valence states of Mo(VI) and Mo(V) on the surface. Incorporation of Mo6+ resulted in the lowest resistivity of $$7.3 \times 10^{{ - 3}} \Omega \,{\text{cm}}$$ 7.3 × 10 - 3 Ω cm , compared to pure SnO2 films with resistivities of $$4.3\left( 0 \right) \times 10^{{ - 2}} \Omega \,{\text{cm}}$$ 4.3 0 × 10 - 2 Ω cm . Meanwhile, a high transmittance of 83% in the visible light range was also acquired. This work presents a comprehensive investigation into impact of Mo doping on SnO2 films synthesised by AACVD for the first time and establishes the potential for scalable deposition of SnO2:Mo thin films in TCO manufacturing. Graphical abstract

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