Titanium’s high-temperature elastic constants through the hcp–bcc phase transformation

Structural and thermoelectric properties of metallic and semiconducting Sb2Te3 are reported. X-Ray diffraction and Raman spectroscopy studies reveal that semiconducting sample has higher defect density. Nature and origin of possible defects are highlighted. Semiconducting Sb2Te3 hosts larger numbers of defects, which act as scattering center and give rise to the increased value of resistivity, thermopower, and power factor. Thermopower data indicate p-type nature of the synthesized samples. It is evidenced that the surface states are often mixed with the bulk state, giving rise to metallicity in Sb2Te3. Role of different scattering mechanism on the thermoelectric property of Sb2Te3 is discussed.

Defect induced structural and thermoelectric properties of Sb2Te3 alloy

Structural and thermoelectric properties of metallic and semiconducting Sb2Te3 are reported. X-Ray diffraction and Raman spectroscopy studies reveal that semiconducting sample have higher defect density. Nature and origin of possible defects are highlighted. Semiconducting Sb2Te3 hosts larger numbers of defects, which act as scattering center and give rise to the increased value of resistivity, thermopower and power factor. Thermopower data indicates p-type nature of the synthesized samples. It is evidenced that the surface states are often mixed with the bulk state, giving rise to metallicity in Sb2Te3. Role of different scattering mechanism on the thermoelectric property of Sb2Te3 is discussed.

Electron–phonon coupling processes determine electronic transport properties of materials and are responsible for the transfer of electronic excess energy to the lattice. With decreasing device dimensions an understanding of these processes in nanoscale materials is becoming increasingly important. Here we use time-resolved electron diffraction to directly study energy relaxation in thin bismuth films after optical excitation. Precise measurements of the transient Debye–Waller-effect for various film thicknesses and over an extended range of excitation fluences allow to separate different contributions to the incoherent lattice response. While phonon softening in the electronically excited state is responsible for an immediate increase of the r.m.s. atomic displacement within a few hundred fs, 'ordinary' electron–phonon coupling leads to subsequent heating of the material on a few ps time-scale. The data reveal distinct changes in the energy transfer dynamics which becomes faster for stronger excitation and smaller film thickness, respectively. The latter effect is attributed to a cross-interfacial coupling of excited electrons to phonons in the substrate.

https://iopscience.iop.org/article/10.1088/1367-2630/17/11/113047/pdf

Thickness-dependent electron?lattice equilibration in laser-excited thin bismuth films

The timescales for structural changes in a single crystal of bismuth after excitation with an intense near-infrared laser pulse are studied with femtosecond pump-probe X-ray diffraction. Changes in the intensity and reciprocal-lattice vector of several reflections give quantitative information on the structure factor and lattice strain as a function of time, with a resolution of 200 fs. The results indicate that the majority of excess carrier energy that remains near the surface is transferred to vibrational modes on a timescale of about 10 ps, and that the resultant increase in the variance of the atomic positions at these times is consistent with the overall magnitude of lattice strain that develops.

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Non-equilibrium phonon dynamics studied by grazing-incidence femtosecond X-ray crystallography.

Debye–Waller factors of five h.c.p. elements (Ti, Zr, Ru, Tm, Hf) have been determined from X-ray diffraction intensities. Within the limits of experimental errors, the Debye–Waller factors associated with the two principal directions are equal. The Debye temperatures (θM) have been evaluated. The energy of formation of vacancies (Ef) has been estimated from a semi-empirical relation between Ef and θ.

X-ray determination of Debye-Waller factors and Debye temperatures of h.c.p. elements Ti, Zr, Ru, Tm, Hf.

The mean square amplitudes of vibration, Debye–Waller factors and Debye temperatures of bismuth (Bi), antimony (Sb) and Bi1–x–Sbx alloys have been obtained from X-ray intensities. The intensities have been measured with Philips 3020 diffractometer fitted with a proportional counter using filtered CuKα radiation at room temperature and have been corrected for thermal diffuse scattering. The X-ray Debye temperatures obtained for Bi and Sb have been compared with corresponding values obtained from specific heats and elastic constants. The values of Debye temperature obtained for Bi1–x–Sbx alloys have been compared with the values calculated from Kopp–Neumann relation. Vacancy formation energies of Bi, Sb and Bi1–x–Sbx alloys have been estimated using a relation connecting it with the X-ray Debye temperature. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

M. Shankar Narayana

Papers

X-ray determination of Debye-Waller factors and Debye temperatures of h.c.p. elements Ti, Zr, Ru, Tm, Hf.

X‐ray study of Bi, Sb and Bi1–x–Sbx alloys