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1.
Measurement of thermoelectric power Θ of pressed pellets of A-type Nd2O3 from 550 to 1180K and electrical conductivity (σ) at dc, 50 Hz, 1.542 kHz and 3 kHz at different temperatures is reported. It is concluded that electrical conduction at high
temperature (T>600K) in this solid is due to positive large polarons in O2− : 2p (valence) band and negative intermediate polarons in Nd3+ : 5d (conduction band). The energy band gap of the solid has been found to be 2.44 eV. At low temperatures, conduction by
hopping of charge carriers from one impurity centre to another has been predicted. 相似文献
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David Emin 《哲学杂志》2013,93(31):2931-2945
AbstractPlanar-large-bipolarons can form if the ratio of the surrounding mediums’ static to high-frequency dielectric constants is especially large, ε0/ε∞ >> 2. A large-bipolaron in p-doped La2CuO4 is modelled as two electrons being removed from the out-of-plane orbitals of four oxygen ions circumscribed by four copper ions of a CuO2 layer. These oxygen dianions relax inwardly as they donate electrons to the surrounding outwardly relaxing copper cations. This charge transfer generates the strong in-plane electron–lattice interaction needed to stabilise a large-bipolaron with respect to decomposing into polarons. The lowest-energy radial in-plane optic vibration of a large-bipolaron’s four core oxygen ions with their associated electronic charges has d-symmetry. Electronic relaxation in response to multiple large-bipolarons’ atomic vibrations lowers their frequencies to generate a phonon-mediated attraction among them which fosters their condensation into a liquid. This liquid features distinctive transport and optical properties. A large-bipolaron liquid’s superconductivity can result when it undergoes a Bose condensation yielding macroscopic occupation of its ground state. The synchronised vibrations of large-bipolarons’ core-oxygen ions with their electronic charges generate this Bose condensate’s dynamic global d-symmetry. 相似文献
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David Emin 《哲学杂志》2019,99(10):1225-1239
Near-room-temperature (narrow-band) polaron transport of an amorphous semiconductor with embedded annealing-induced semiconducting crystallites is treated within an effective-medium approach. Carrier mobilities in the crystallites are assumed much larger than those of the amorphous phase. Nonetheless, crystallites act as macroscopic traps when their carriers’ energies lie below those in the amorphous phase. Then the mixture’s dc conductivity falls below that of the amorphous phase at low enough carrier concentrations. However, with increasing carrier concentration the shifting chemical potential diminishes this trapping effect, enabling crystallites’ larger mobilities to drive the mixtures’ electrical conductivity above that of the amorphous phase. Meanwhile the Seebeck coefficient remains insensitive to the annealing-induced introduction and growth of embedded crystallites. These features are qualitatively similar to those reported for an amorphous organic polymer FET with annealing-induced embedded crystallites. 相似文献
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PbO–Bi2O3–B2O3 glasses containing small concentrations of Fe2O3 (0–1 mol%) were subject to dielectric studies (dielectric constant ε′; loss tan δ; and ac conductivity σ ac) over a wide range of frequency and temperature. From spectroscopic (infrared, optical absorption and ESR spectra) and magnetic susceptibility studies, variations in these properties with dopant ion concentration were analyzed in terms of different oxidation states and iron ion environment in the glass network. 相似文献
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Md. Abdur Razzaque Sarker Satoshi WatauchiMasanori Nagao Takashi WatanabeIsamu Shindo Isao Tanaka 《Physica C: Superconductivity and its Applications》2012,472(1):87-91
Large single crystals of La2−xSrxCuO4 (LSCO) high-Tc superconductors were grown by the infrared heating floating zone (IR-FZ) method using a tilting-mirror-type image furnace. The maximum diameter of the LSCO crystals increased to 10 mm in the tilting-mirror-type image furnace from 6 mm in the conventional image furnace. CuO rich feeds were required for the crystal growth using the tilting-mirror-type image furnace to compensate for the lack of CuO caused by the significant evaporation of CuO during the growth. The evaporation of CuO was affected by the tilting angle of the mirrors of the image furnace and by feed diameter. The optimized growth conditions were as follows: mirror tilting angle, 20°; feed diameter, 10 mm∅; and feed composition 50.7 mol% CuO. 相似文献
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The large bipolaron in two and three dimensions is investigated by combining the reasonable asymptotic relative wavefunctions and the Lee-Low-Pines-Huybrechts (LLP-H) variational method. The values of the critical coupling constant αC above which bipolarons may exist and the critical ratio of dielectric constants ηc below which bipolarons may exist are evaluated, which are very close to the recent results obtained within totally different variational approaches. It is also found that low-dimensional materials are more favorable for the formation of bipolarons. 相似文献
8.
F. Yndurain 《Europhysics letters》2011,94(3)
The coupling of Fe magnetic moments in LaFeAsO1−x Fx with the As A 1g phonon is calculated. We present first-principles calculations of the atomic and electronic structure of LaFeAsO1−x Fx as a function of electron doping. We perform calculations using the virtual crystal approximation as well as supercells with F substitutional impurity atoms. The results validate the virtual crystal approximation for the electronic structure near the Fermi level. The electronic density of states at the Fermi level is maximum for x = 0.125, enhancing the electron-phonon interaction. An additional increase of the electron-phonon parameter λ is obtained if the coupling between the A 1g phonon and the Fe magnetic moment is included. It is found that the electron-phonon interaction can be one order of magnitude larger than its value if no spin resolution is included in the calculation.https://doi.org/10.1209/0295-5075/94/37001 相似文献
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P. Bourges;L. P. Regnault;Y. Sidis;J. Bossy;P. Burlet;C. Vettier;J. Y. Henry;M. Couach 《Europhysics letters》1997,38(4):313-318
Inelastic neutron scattering has been used to determine the dynamic spin fluctuations in an underdoped high-temperature superconductor single crystal. The magnetic resonance, that occurs around 40 meV in overdoped samples, is shifted to a lower energy, . A constant ratio, , almost independent of the doping level, is found. According to numerous theoretical approaches, this finding supports the idea that the resonance energy is proportional (approximately twice) to the superconducting gap. https://doi.org/10.1209/epl/i1997-00244-6 相似文献
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Javed Ahmad Muhammad Ehsan MazharMuhammad Qadeer Awan Muhammad Naeem Ashiq 《Physica B: Condensed Matter》2011,406(18):3484-3488
Potassium substituted nanosized magnesium aluminates having a nominal composition Mg1−xKxAl2O4 where x=0.0, 0.25, 0.5, 0.75, 1.0 have been synthesized by the chemical co-precipitation method. The samples have been characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and dc electrical resistivity measurements. The XRD results reveal that the samples are spinel single phase cubic close packed crystalline materials. The calculated crystallite size ranges between 6 and 8 nm. The behaviour of the lattice constant seems to deviate from the Vegard's law. While X-ray density clearly increases, the bulk density and consequently, the percentage porosity do not exhibit a significant change on increasing the K+ content. The SEM micrographs suggest homogeneous distribution of the nanocrystallites in the samples. The dc electrical resistivity exhibits a typical semiconducting behaviour. Substitution of a Mg2+ ion by a K+ ion provides an extra hole to the system, which forms small polaron. Thermally activated hopping of these small polarons is believed to be the conduction mechanism in the Mg1−xKxAl2O4. The activation energy of hopping of small polarons has been calculated and found K+ ions content dependent. 相似文献
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Polycrystalline samples of F-substituted LnOBiS2 (Ln?=?La, Ce, Pr, Nd, Yb) compounds were synthesized by solid-state reaction. The samples were characterized by X-ray diffraction measurements and found to have the ZrCuSiAs crystal structure. Electrical resistivity and magnetic susceptibility measurements were performed on all of the samples and specific heat measurements were made on those with Ln?=?La, Ce, and Yb. All of these compounds exhibit superconductivity in the range 1.9?K–5.4?K, which has not previously been reported for the compounds based on Ce, Pr, and Yb. The YbO0.5F0.5BiS2 compound was also found to exhibit magnetic order at ～2.7?K that apparently coexists with superconductivity below 5.4?K. 相似文献
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V. B. Zabolotnyy;A. A. Kordyuk;D. S. Inosov;D. V. Evtushinsky;R. Schuster;B. Büchner;N. Wizent;G. Behr;S. Pyon;T. Takayama;H. Takagi;R. Follath;S. V. Borisenko 《Europhysics letters》2009,86(4)
We present a photoemission study of LaEu0.2Srx CuO4 with doping level x = 1/8, where the charge carriers are expected to order forming static stripes. Though the local probes in direct space seem to be consistent with this idea, there has been little evidence found for such ordering in quasiparticle dispersions. We show that the Fermi surface topology of the 1/8 compound develops notable deviations from that observed for LaSrx CuO4 in a way consistent with the FS reconstruction expected for the scattering on the antiphase stripe order.https://doi.org/10.1209/0295-5075/86/47005 相似文献
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《Europhysics letters》2011,96(1)
In this paper the effects of replacing Fe with Co in SmFe1-x Cox AsO(x =0 to 1) are reported. X-ray diffraction patterns indicate that all the samples have formed the ZrCuSiAs-type structure with a space group P 4/nmm and a full solid solution forms between SmFeAsO and SmCoAsO. It is found that the antiferromagnetic spin-density-wave (SDW) order in the parent compounds is rapidly suppressed by Co-doping, and superconductivity emerges as 0.05 ≤ x ≤ 0.175. A phase diagram is derived based on the resistivity measurements and a dome-like T c-vs.-x curve is established. Furthermore, it was shown that the metallic character increases with the addition of more Co. Meanwhile we found that the two magnetic phase transitions in SmCoAsO are suppressed as Co is replaced by Fe. Our work demonstrates that the solid solution has been established in the SmFeAsO-SmCoAsO system. The systemic study in the SmFe1-x Cox AsO system would add more ingredients to the underlying physics of this material.https://doi.org/10.1209/0295-5075/96/17007 相似文献
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热电材料研究中的基础物理问题 总被引：1，自引：0，他引：1
热电转换技术主要包括利用半导体材料的泽贝克（Seebeck）效应将热能直接转化成电能和利用佩尔捷（Peltier）效应直接将电能转化成热能.文章简单回顾了热电转换材料中的物理效应及相关研究进展,重点介绍了常规热电材料（即窄带半导体）中的一些基本物理问题,其中包括一个好的热电材料应该具有的特性,以及提高半导体材料的电导率和泽贝克系数,降低热导率的物理机制和方法.文章还介绍了近年来电子晶体-声子玻璃类材料以及低维热电材料等热点问题的研究进展.最后还简单讨论了非常规热电材料的研究现状与趋势. 相似文献
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In the strange metal phase of the high-Tc cuprates, it is challenging to explain the linear temperature dependence of the in-plane resistivity and the quadratic temperature dependence of the inverse Hall angle. In this paper, we investigate the temperature dependence of the in-plane resistivity and inverse Hall angle in the nonlinear electrodynamics holographic model developed in our recent work. Maxwell electrodynamics and Born-Infeld electrodynamics are considered. Both cases support a wide spectrum of temperature scalings in parameter space. For Maxwell electrodynamics, the T-linear in-plane resistivity generally dominates at low temperatures and survives into higher temperatures in a narrow strip-like manner. Meanwhile, the T-quadratic inverse Hall angle dominates at high temperatures and extends down to lower temperatures. The overlap between the T-linear in-plane resistivity and the T-quadratic inverse Hall angle, if occurs, would generally present in the intermediate temperate regime. The Born-Infeld case with a 0 is quite similar to the Maxwell case. For the Born-Infeld case with a 0, there can be a constraint on the charge density and magnetic field. Moreover, the overlap can occur for strong charge density. 相似文献
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J. P. Sun;M. Z. Shi;B. Lei;S. X. Xu;Y. Uwatoko;X. H. Chen;J.-G. Cheng 《Europhysics letters》2020,130(6)
Whether the pressure-induced second high- superconducting phase (SC-II) is a universal phenomenon among the intercalated FeSe-derived superconductors deserves further investigations. Here,we report a high-pressure ac magnetic susceptibility study on the newly synthesized organic-ion-intercalated (CTA)0.3 FeSe single crystal,which has a high at ambient pressure. We found that the superconducting transition is quickly suppressed to below 20 K upon increasing pressure to ,above which the SC-II phase emerges and its increases gradually to a maximum of ca. 40 K at 5 GPa. For ,both and the superconducting volume decline quickly,presumably due to the collapse of the hybrid structure against the higher pressure. Nevertheless,our results indeed evidenced the pressure-induced SC-II phase in (CTA)0.3 FeSe,in reminiscent of the situations observed in (Li,Fe)OHFeSe and Li0.36 (NH3)y Fe2Se2. These results thus demonstrate that pressure-induced SC-II phase should be a universal phenomenon in the electron-doped intercalated FeSe-based superconductors.https://doi.org/10.1209/0295-5075/130/67004 相似文献
20.
We theoretically investigate the quasiparticle interference (QPI) in the optimally electron-doped BiS2-layered superconductors with a two-orbital model. We show that possible pairing symmetries can be identified from their unique features in the density of states and QPI maps from magnetic or nonmagnetic impurities. Additionally, the inter-orbital nonmagnetic impurity scattering breaks the C4 symmetry and exhibits a clear C2 patterns in the QPI maps, in contrast to its negligible effect in the superconducting state of iron pnictides. The unambiguous features indicated in the QPI patterns can be used to probe the pairing symmetry as well as to uncover the impurity nature in BiS2-layered superconductors with the STM measurement.https://doi.org/10.1209/0295-5075/103/27004 相似文献