Determination Of Debye Temperature Research Articles

Determination of Debye temperatures in SmFe1-xCoxAsO superconductors by Mӧssbauer spectroscopy and effect of cobalt doping

Debye temperatures of 1111-type high-TC superconductors ReFeAsO (Re: rare earth element) are rarely reported in the materials science community. Herein, 57Fe Mӧssbauer spectroscopy, a sensitive technique to hyperfine interaction of Fe nucleus with environment, is applied to study the lattice dynamics in SmFe1-xCoxAsO (0.10≤x ≤ 0.20) superconductors. Two Debye temperatures θDδ and θDA are obtained from the temperature dependences of central shift (δCS) and resonant absorption area (A), respectively. Room-temperature mean-square vibrational displacement u2 and recoilless fraction (f) are also evaluated. The influence of Co-doping content on the lattice vibration is studied. It is revealed that Co-doping only affects θDA and u2, i.e. only the acoustical lattice vibrations with low energy (up to 30 meV) in phonon spectrum are sensitive to the cobalt content in SmFe1-xCoxAsO.

Determination of Debye temperatures and Lamb–Mössbauer factors for LnFeO3 orthoferrite perovskites (Ln = La, Nd, Sm, Eu, Gd)

Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO3 (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through x-ray diffraction and x-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO3 compounds. 57Fe Mössbauer spectroscopy was performed over a temperature range of 10 K–293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θD) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental centre shift and theoretical isomer shift, by allowing the Debye temperature and isomer shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mössbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, Ag(3) and Ag(5) from La to GdFeO3 corresponding to octahedral rotations and tilts in the [0 1 0] and [1 0 1] planes respectively.

Determination of debye temperatures of supported ion particles by m�ssbauer spectroscopy

The Debye temperatures ϑ of alumina- and titania-supported iron particles were determined using Mossbauer spectroscopy between 5 and 280 K. The Debye temperatures were obtained from a nonlinear optimization algorithm using the temperature dependence of the second order Doppler shift (SOD) and the resonant absorption area (RAA). To test its reliability, the same method was used to determine ϑ of an α-iron-foil and pyrophoric iron.

A simple method of determining Debye temperatures

A simple undergraduate laboratory experiment on the determination of Debye temperatures of solids is described. A sample of the solid is immersed in liquid nitrogen; from the mass of nitrogen boiled off in cooling the solid, the change in its internal energy is determined. The quantum corrections to the classical law of Dulong and Petit are calculated and the Debye temperature is obtained using a simple graphical technique.

Determination of Debye temperature of α-iron by X-ray diffraction

Abstract The Debye temperature of α-iron at 298°K has been determined from Geiger-counter measurements of the Bragg intensities from a polycrystalline sample (using Mo Kα) and theoretical atomic scattering factors. The value obtained (⪹D = 398 ± 9°K) is somewhat less than the average value (418 ± 4°K) calculated from all the available diffraction results. The diffraction values are significantly lower than those (467°K) derived from elastic-constants. Intensity measurements from annealed and ground samples placed experimentally on the same scale showed that plastic deformation did not reduce the integrated intensities of the reflections. This result provides further evidence for the rejection of the ‘frozen-in thermal motion' picture of plastic deformation.