Temperature Dependence Of Debye-Waller Factor Research Articles

Suppressing Isomerization of Phosphine-Protected Au9 Cluster by Bond Stiffening Induced by a Single Pd Atom Substitution.

The fluxional nature of small gold clusters has been exemplified by reversible isomerization between [Au9(PPh3)8]3+ with a crown motif (Au9(C)) and that with a butterfly motif (Au9(B)) induced by association and dissociation with compact counteranions (NO3-, Cl-). However, structural isomerization was suppressed by substitution of the central Au atom of the Au9 core in [Au9(PPh3)8]3+ with a Pd atom: [PdAu8(PPh3)8]2+ with a crown motif (PdAu8(C)) did not isomerize to that with a butterfly motif (PdAu8(B)) upon association with the counteranions. Density functional theory calculation showed that the energy difference between PdAu8(C) and PdAu8(B) is comparable to that between Au9(C) and Au9(B), indicating that the relative stabilities of the isomers are not a direct cause for the suppression of isomerization. Temperature dependence of Debye-Waller factors obtained by X-ray absorption fine-structure analysis revealed that the intracluster bonds of PdAu8(C) were stiffer than the corresponding bonds in Au9(C). Natural bond orbital analysis suggested that the radial Pd-Au and lateral Au-Au bonds in PdAu8(C) are stiffened due to the increase in the ionic nature and decrease in electrostatic repulsion between the surface Au atoms, respectively. We conclude that the formation of stiffer metal-metal bonds by Pd atom doping inhibits the isomerization from PdAu8(C) to PdAu8(B).

Effects of local lattice disorder on the superconductivity studied by XAFS

The variation of local lattice displacements of the in-plane Cu-O bond upon Cu-site impurity doping in La2-xSrxCuO4 superconductor is investigated by Cu K-edge EXAFS studies. In Mn doping case, the analysis of the temperature dependence of Debye-Waller factor indicates that the local lattice displacements of the in-plane Cu-O bond exhibits similar behavior in all La1.875−1.5xSr0.125+1.5xCu1-xMnxO4 (0⩽x⩽0.15) samples. This may reflect that the doping of Mn does not alter the local lattice environments in the CuO2 plane and thus the Mn impurity does not destroy the superconducting transition in a similar way with other ionic doping cases. The local lattice displacements at room temperature upon ionic doping are compared, which indicates that Fe doping leads to largest local displacements while Ni doping is intermediate. The possible interplay between the local lattice displacements and the normal-state resistivity is compared. These results indicate that the local lattice displacements largely affect the superconducting properties in La2-xSrxCuO4 superconductor.

Lattice softening in superconducting compositions of Ba(K)BiO3.

Temperature dependent x-ray absorption spectra investigation were measured for Ba(1-x)K(x)BiO3 (Bi L3-edge) with x =0.0, 0.25, 0.4, 0.5 and for BaPbO3 (Pb L3-edge). It was found that at low temperatures the Debye-Waller factor of the square diagonal Bi-Bi bond has the maximum value near the insulator-metal phase transition for the compound with x = 0.25 and x = 0.4. Temperature dependence of the Debye-Waller factor of Bi-Bi bond strongly differs from the Einstein model curve that well describes the harmonic systems (for example BaPbO3). This behavior is consistent with the strong anharmonicity of the Bi-O shell due to the double-well vibration potential reported by us earlier. Presented results point to the essential lattice softening of the superconducting compositions, which is important for the understanding of superconductivity mechanism in perovskite type oxides.

Quantum Statistical Approach to Debye-Waller Factor in EXAFS, EELS and ARXPS. II. Application to One-Dimensional Models

Temperature dependence of Debye-Waller factor in EXAFS, EELS and ARXPS is calculated for one-dimensional models on the basis of first principle quantum statistical method developed in the previous paper I. In contrast to diffraction Debye-Waller factors for crystal we have no need to worry about the divergence for these thermal factors in one- and two-dimensional phonon systems. We consider anharmonic Morse potential as nearest neighbor interaction. We take up to quartic term into account and estimate up to fourth order cumulants for both monatomic and diatomic chains in wide temperature range from low temperature in which quantum effect is important, to high temperature in which classical approximation works. Characteristic features of the contributions from optical and acoustic modes are discussed in the diatomic model chain. The result obtained here give us clear physical insights of those thermal factors.

Temperature dependence of Debye-Waller factor in dye-doped polymers.

The temperature dependence of the Debye-Waller factor in dye-doped polymers has been investigated with femtosecond accumulated photon echo. The superiority of polyvinyl alcohol as the host polymer for the optical-memory material is ascribed to the higher phonon sideband frequency in this sample. It is pointed out that the temperature dependence of the Debye-Waller factor, in particular the phonon sideband frequency, is of fundamental importance to finding out the best polymer for high-temperature optical memory based on photochemical hole burning.

Low Energy Excitation Modes of Amorphous Polymers and Structural Relaxation at Low Temperatures Probed by PHB

Low energy excitation modes of amorphous linear and crosslinked polymers coupled with the photoreactive molecules and the temperature dependence of Debye-Waller factor for various chromophore/amorphous polymer matrix systems are estimated from PHB measurements. The requisites for high temperature hole formation are also discussed.

Note on Temperature Dependence of Debye-Waller Factor in a Unified Model of Ferroelectrics

Note on Temperature Dependence of Debye-Waller Factor in a Unified Model of Ferroelectrics

Temperature Dependence of Debye-Waller Factors in bcc Metals. I

The modified form of the non central force model which considers the electron-ion interaction term of Kreb's model to the Clark-Gazis-Wallis type angular forces is considered to calculate the Debye-Waller exponents at different temperatures for three bcc metals Sodium, α-iron and cromium and compared with the available X-ray measurements in terms of the temperature parameter Y of the Debye Waller factor, characteristic Debye temperature θ M and the mean square displacement u -2 of the atoms. The theoretical results are found to be in a reasonably satisfactory agreement with the experimental values.

Crystal Equilibrium and Lattice Dynamical Study of α-Iron and Chromium

Abstract Studies of the phonon dispersion, the temperature dependence of Debye-Waller factor, the Debye temperature, and the mean square displacement of α-iron and chromium have been made by means of a lattice dynamical model proposed by the authors. The model considers short range pairwise forces effective up to the second neighbours and electron-ion interactions on the lines of Bhatia using an appropriate value of the screening parameter. The volume force is aver­ aged over the whole Wigner-Seitz sphere. The ionic lattice is in equilibrium in a medium of electrons. The computed results compare well with experimental data.

Measurement of the temperature dependence of Debye–Waller factors by energy-dispersive methods: application to NbC0.98

A new method is reported for evaluating the temperature dependence of Debye-Waller factors, or equivalently the mean-square atomic displacements (MSD), from X-ray spectroscopic data. By irradiating a properly oriented single crystal with polychromatic radiation, several orders of a given Bragg reflection can be simultaneously excited at a fixed scattering angle. These multi-order peaks can then be recorded in a single measurement with an energy dispersive detector. For experiments requiring only relative intensity data, this method offers a number of improvements over conventional techniques, e.g., (i) a substantial reduction in data acquisition time, (ii) a possible reduction in angular flexibility requirements and (iii) access to regions of reciprocal space which might otherwise be inaccessible. This procedure has been employed to determine the temperature dependence of the mean-square displacements of NbC0.98 over the temperature range from 296 to 600 K. These results are compared with published values computed from a double-shell lattice-dynamical force model; the agreement is found to be satisfactory. The data have also been used to evaluate the thermal expansivity of NbC0.98 over the temperature range of measurement; excellent agreement is found upon comparison with published thermal expansion data.

Temperature dependence of Debye-Waller factors at a cooperative high-spin (5T2) ⇌ low-spin (1A1) transition in dithiocyanatobis(2,2'-bipyridyl)iron(II)

Debye-Waller factors f were determined over the temperature range 4.2 to 298°K in Fe(bipy)2(NCS)2 from 57Fe Mössbauer spectra (bipy = 2,2'-bipyridyl). Whereas magnetic data and other physical properties show an abrupt change at the temperature of a cooperative 5T2 ⇌ 1A1 transition, Tc = 214°K, a continuous change of -ln f is found. The significance of this result is discussed.