Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPhoto-Seebeck effect in tetragonal PbO single crystals
88
0
0.0
(
0
)
Added by
Partha Mondal Sarathi
Publication date
2013
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We report the observation of photo-Seebeck effect in tetragonal PbO crystals. The photo-induced carriers contribute to the transport phenomena, and consequently the electrical conductivity increases and the Seebeck coefficient decreases with increasing photon flux density. A parallel-circuit model is used to evaluate the actual contributions of photo-excited carriers from the measured transport data. The photo-induced carrier concentration estimated from the Seebeck coefficient increases almost linearly with increasing photon flux density, indicating a successful photo-doping effect on the thermoelectric property. The mobility decreases by illumination but the reduction rate strongly depends on the illuminated photon energy. Possible mechanisms of such photon-energy-dependent mobility are discussed.
rate research
Read More
We examine how the photo-induced carriers contribute the thermoelectric transport, i.e. the nature of the photo-Seebeck effect, in the wide-gap oxide semiconductor ZnO for the first time. We measure the electrical conductivity and the Seebeck coefficient with illuminating light. The light illumination considerably changes the Seebeck coefficient as well as the conductivity, which is sensitive to the photon energy of the illuminated light. By using a simple parallel-circuit model, we evaluate the contributions of the photo-induced carriers to the conductivity and the Seebeck coefficient, whose relationship shows a remarkable resemblance to that in doped semiconductors. Our results also demonstrate that the light illumination increases both the carrier concentration and the mobility, which can be compared with impurity-doping case for ZnO. Future prospects for thermoelectrics using light are discussed.
We present measurements of resistivity and thermopower of Fe1+xTe1-ySey single crystalline samples with y=0, 0.1, 0.2, 0.3 and 0.45 in zero field and in a magnetic field B=8T. We propose a qualitative analysis of the temperature behavior of S, where the samples are described as almost compensated semimetals: different electron and hole bands with similar carrier concentrations compete and their relative contribution to the thermoelectric transport depends on the respective filling, mobility and coupling with phonons. For y>=0.2, superconductivity occurs and the optimum Se-doping level for a maximum Tc of 13 K turns out to be y=0.3. At low temperatures, evidence of a contribution to S by an excitation-drag mechanism is found, while at high temperatures a strikingly flat behavior of S is explained within a narrow band Hubbard model. The support of a theoretical background which could provide band resolved parameters such as carrier density, mobility and electron-phonon coupling of each band would allow to extract from our data valuable quantitative information on the transport and superconducting mechanisms of these iron chalcogenides.
Temperature dependent measurements of 57Fe Mossbauer spectra on CaFe2As2 single crystals in the tetragonal and collapsed tetragonal phases are reported. Clear features in the temperature dependencies of the isomer shift, relative spectra area and quadrupole splitting are observed at the transition from the tetragonal to the collapsed tetragonal phase. From the temperature dependent isomer shift and spectral area data, an average stiffening of the phonon modes in the collapsed tetragonal phase is inferred. The quadrupole splitting increases by ~25% on cooling from room temperature to ~100 K in the tetragonal phase and is only weakly temperature dependent at low temperatures in the collapsed tetragonal phase, in agreement with the anisotropic thermal expansion in this material. In order to gain microscopic insight about these measurements we perform ab initio density functional theory calculations of the electric field gradient and the electron density of CaFe2As2 in both phases. By comparing the experimental data with the calculations we are able to fully characterize the crystal structure of the samples in the collapsed-tetragonal phase through determination of the As z-coordinate. Based on the obtained temperature dependent structural data we are able to propose charge saturation of the Fe - As bond region as the mechanism behind the stabilization of the collapsed-tetragonal phase at ambient pressure.
We investigate the inverse spin Hall voltage of a 10nm thin Pt strip deposited on the magnetic insulators Y3Fe5O12 (YIG) and NiFe2O4 (NFO) with a temperature gradient in the film plane. We observe characteristics typical of the spin Seebeck effect, although we do not observe a change of sign of the voltage at the Pt strip when it is moved from hot to cold side, which is believed to be the most striking feature of the transverse spin Seebeck effect. Therefore, we relate the observed voltages to the longitudinal spin Seebeck effect generated by a parasitic out-of-plane temperature gradient, which can be simulated by contact tips of different material and heat conductivities and by tip heating. This work gives new insights into the interpretation of transverse spin Seebeck effect experiments, which are still under discussion.
We study the Seebeck effect in the three-dimensional Dirac electron system based on the linear response theory with Luttingers gravitational potential. The Seebeck coefficient $S$ is defined by $S = L_{12} / L_{11} T$, where $T$ is the temperature, and $L_{11}$ and $L_{12}$ are the longitudinal response coefficients of the charge current to the electric field and to the temperature gradient, respectively; $L_{11}$ is the electric conductivity and $L_{12}$ is the thermo-electric conductivity. It is confirmed that $L_{11}$ and $L_{12}$ are related through Motts formula in low temperatures. The dependences of the Seebeck coefficient on the chemical potential $mu$ and the temperature $T$ when the chemical potential lies in the band gap ($|mu| < Delta$) are partially captured by $S propto (Delta - mu) / k_{mathrm{B}} T$ for $mu > 0$ as in semiconductors. The Seebeck coefficient takes the relatively large value $|S| simeq 1.7 ,mathrm{m V/K}$ at $T simeq 8.7,mathrm{K}$ for $Delta = 15 ,mathrm{m eV}$ by assuming doped bismuth.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
