Search results for "Solid-state physics"
showing 10 items of 112 documents
Magnon and Phonon Excitations in Nanosized NiO
2019
Single-crystal, microcrystalline and nanocrystalline nickel oxides (NiO) have been studied by Raman spectroscopy. A new band at ~200 cm-1 and TO-LO splitting of the band at 350–650 cm-1 have been found in the spectra of single-crystals NiO(100), NiO(110) and NiO(111). The Raman spectra of microcrystalline (1500 nm) and nanocrystalline (13–100 nm) NiO resemble those of the single crystals. They all contain the two-magnon band at 1500 cm-1, indicating that the oxides remain at room temperature in the antiferromagnetic phase. Besides, a new sharp Raman band has been observed at 500 cm-1 in nanocrystalline NiO. Its temperature dependence suggests the magnetic origin of the band, possibly associ…
Optimum Carrier Concentration in n-Type PbTe Thermoelectrics
2014
Taking La- and I-doped PbTe as an example, the current work shows the effects of optimizing the thermoelectric figure of merit, zT, by controlling the doping level. The high doping effectiveness allows the carrier concentration to be precisely designed and prepared to control the Fermi level. In addition to the Fermi energy tuning, La-doping modifies the conduction band, leading to an increase in the density of states effective mass that is confirmed by transport, infrared reflectance and hard X-ray photoelectron spectroscopy measurements. Taking such a band structure modification effect into account, the electrical transport properties can then be well-described by a self-consistent single…
Dielectric spectra of electron-irradiated PSN ceramics
1997
The influence of electron-irradiation on the dielectric properties of transparent PSN ferroelectric ceramics is studied by low (LF) and infralow (ILF) frequency spectrum analysis. Redistribution of relaxation frequencies caused by electron-irradiation has been discovered and is related to pinning impacts of the radiation-induced defects.
Optimization of the carrier concentration in phase-separated half-Heusler compounds
2014
Inspired by the promising thermoelectric properties of phase-separated half-Heusler materials, we investigated the influence of electron doping in the n-type Ti_(0.3−x)Zr_(0.35)Hf_(0.35)NiSn compound. The addition of Nb to this compound led to a significant increase in its electrical conductivity, and shifted the maximum Seebeck coefficient to higher temperatures owing to the suppression of intrinsic carriers. This resulted in an enhancement of both the power factor α^2σ and figure of merit, zT. The applicability of an average effective mass model revealed the optimized electron properties for samples containing Nb. There is evidence in the literature that the average effective mass model i…
Photoluminescence study of excitons in homoepitaxial GaN
2001
High-resolution photoluminescence spectra have been measured in high-quality homoepitaxial GaN grown on a free-standing GaN substrate with lower residual strain than in previous work. Unusually strong and well-resolved excitonic lines were observed. Based on free- and bound exciton transitions some important GaN parameters are derived. The Arrhenius plot of the free A exciton recombination yields a binding energy of 24.7 meV. Based on this datum, an accurate value for the band-gap energy, EG(4.3 K) = 3.506 eV, can be given. From the donor bound excitons and their “two-electron” satellites, the exciton localization energy and donor ionization energy are deduced. Finally, estimates of the ele…
Photoluminescence Imaging and LBIC Characterization of Defects in mc-Si Solar Cells
2018
Today’s photovoltaic market is dominated by multicrystalline silicon (mc-Si) based solar cells with around 70% of worldwide production. In order to improve the quality of the Si material, a proper characterization of the electrical activity in mc-Si solar cells is essential. A full-wafer characterization technique such as photoluminescence imaging (PLi) provides a fast inspection of the wafer defects, though at the expense of the spatial resolution. On the other hand, a study of the defects at a microscopic scale can be achieved through the light-beam induced current technique. The combination of these macroscopic and microscopic resolution techniques allows a detailed study of the electric…
Impact of nitrogen doping on the band structure and the charge carrier scattering in monolayer graphene
2021
The addition of nitrogen as a dopant in monolayer graphene is a flexible approach to tune the electronic properties of graphene as required for applications. Here, we investigate the impact of the doping process that adds N dopants and defects on the key electronic properties, such as the mobility, the effective mass, the Berry phase, and the scattering times of the charge carriers. Measurements at low temperatures and magnetic fields up to 9 T show a decrease of the mobility with increasing defect density due to elastic, short-range scattering. At low magnetic fields weak localization indicates an inelastic contribution depending on both defects and dopants. Analysis of the effective mass …
First-principles study of bulk and surface oxygen vacancies in SrTiO3 crystal
2009
The structural and electronic properties of the neutral and positively charged oxygen vacancies (F and F + centres) in the bulk and on the (001) surfaces of SrTiO3 crystal are examined within the hybrid Hartree-Fock and density functional theory (HF-DFT) method based upon the linear combination of atomic orbital (LCAO) approach. A comparison of the formation energy for surface and bulk defects indicates a perceptible propensity for the segregation of neutral and charged vacancies to both SrO and TiO2 surface terminations with a preference in the latter case which is important for interpretation of space charge effects at ceramic interfaces. It is found that the vacancies reveal more shallow…
Aging, rejuvenation, and memory phenomena in a lead-based relaxor ferroelectric
2002
Isothermal aging and temperature cycle experiments were done on the relaxor ferroelectric lead magnesium niobate mixed with 10% lead titanate (PMN-10PT) around and below the diffuse maximum of the dielectric loss. With increasing aging time tw the isothermal evolution of the linear susceptibility follows a power law and does not show frequency scaling. The non-linear susceptibility, however, obeys nearly perfect ωt w-scaling. After aging the sample at a single temperature we observed both rejuvenation and memory effects in temperature cycle experiments. This observation indicates symmetric behavior in the sense that it shows up irrespective of whether cooling with subsequent re-heating or h…
<title>Vibrational spectra of tungsten oxides with different lattice topology</title>
1997
It is determined that vibrations of linear chains -O-W-O-W- in tungsten-oxygen network are rather independent. The value of vibrational frequency is determined by asymmetry of O equals W - O bonds.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.