Search results for "MT"
showing 10 items of 2759 documents
Long-term stability of phase-separated Half-Heusler compounds
2015
Half-Heusler (HH) compounds have shown high Figure of merits up to 1.5. The key to these high thermoelectric efficiencies is an intrinsic phase separation, which occurs in multicomponent Half-Heusler compounds and leads to an significantly reduction of the thermal conductivity. For commercial applications, compatible n- and p-type materials are essential and their thermal stability under operating conditions, e.g. for an automotive up to 873 K, needs to be guaranteed. For the first time, the long-term stability of n- and p-type HH materials is proved. We investigated HH materials based on the Ti0.3Zr0.35Hf0.35NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both compounds exhibit a …
Including atomic vibrations in XANES calculations: polarization-dependent damping of the fine structure at the Cu K edge of (creat)$_{2}$CuCl$_{4}$
2016
Atomic vibrations are usually not taken into account when analyzing x-ray absorption near edge structure (XANES) spectra. One of the reasons is that including the vibrations in a formally exact way is quite complicated while the effect of vibrations is supposed to be small in the XANES region. By analyzing polarized Cu K edge x-ray absorption spectra of creatinium tetrachlorocuprate [(creat)$_{2}$CuCl$_{4}$], we demonstrate that a technically simple method, consisting in calculating the XANES via the same formula as for static systems but with a modified free-electron propagator which accounts for fluctuations of interatomic distances, may substantially help in understanding XANES of some l…
Interplay between local structure and electronic properties on CuO under pressure
2020
The electronic and local structural properties of CuO under pressure have been investigated by means of X-ray absorption spectroscopy (XAS) at Cu K edge and ab-initio calculations, up to 17 GPa. The crystal structure of CuO consists of Cu motifs within CuO$_4$ square planar units and two elongated apical Cu-O bonds. The CuO$_4$ square planar units are stable in the studied pressure range, with Cu-O distances that are approximately constant up to 5 GPa, and then decrease slightly up to 17 GPa. In contrast, the elongated Cu-O apical distances decrease continuously with pressure in the studied range. An anomalous increase of the mean square relative displacement (EXAFS Debye Waller, \sigma$^2$…
The high-pressure high-temperature phase diagram of calcium fluoride from classical atomistic simulations
2013
We study the phase diagram of calcium fluoride (CaF2) under pressure using classical molecular dynamic simulations performed with a simple pairwise interatomic potential of the Born-Mayer-Huggings form. Our results obtained under conditions 0 < P < 20 GPa and 0 < T < 4000 K reveal a rich variety of multi-phase boundaries involving different crystal, superionic and liquid phases, for all which we provide an accurate parametrization. Interestingly, we predict the existence of three special triple points (i.e. solid-solid-superionic, solid-superionic-superionic and superionic-superionic-liquid coexisting states) within a narrow and experimentally accessible thermodynamic range of 6…
Fabrication and characterization of semiconducting half Heusler YPtSb thin films
2012
The semiconducting half Heusler compound YPtSb was predicted theoretically to be capable of changing into topological insulator under proper strain. In this work, p type semiconducting half-Heusler YPtSb thin films were prepared by magnetron co-sputtering method from a specially designed target for the first time. Textured structure with (111) plane paralleling with (001) of MgO substrate was observed when YPtSb thin films were grown on MgO (100) substrate at 600{\deg}C.Electrical measurements show that the resistivity of YPtSb films decreases with increasing temperature, indicating a semiconductor-like behavior. The carrier density is as high as 1.15 X 10^21 cm-3 at 300 K. The band gap of …
Effect of confinement and Coulomb interactions on the electronic structure of (111) LaAlO$_3$/SrTiO$_3$ interface
2023
A tight binding supercell approach is used for the calculation of the electronic structure of the (111) LaAlO$_3$/SrTiO$_3$ interface. The confinement potential at the interface is evaluated solving a discrete Poisson equation by means of an iterative method. In addition to the effect of the confinement, local Hubbard electron-electron terms are included at mean-field level within a fully self-consistent procedure. The calculation carefully describes how the two-dimensional electron gas arises from the quantum confinement of electrons near the interface due to band bending potential. The resulting electronic sub-bands and Fermi surfaces show full agreement with the electronic structure dete…
Topological transition in Pb1-xSnxSe using Meta-GGA
2023
We calculate the mirror Chern number (MCN) and the band gap for the alloy Pb1-xSnxSe as a function of the concentration x by using virtual crystalline approximation. We use the electronic structure from the relativistic density functional theory calculations in the Generalized-Gradient- Approximation (GGA) and meta-GGA approximation. Using the modified Becke-Johnson meta- GGA functional, our results are comparable with the available experimental data for the MCN as well as for the band gap. We advise to use modified Becke-Johnson approximation with the parameter c=1.10 to describe the transition from trivial to topological phase for this class of compounds.
Role of precursor composition in the polymorph transformations, morphology control and ferromagnetic properties of nanosized TiO$_2$
2021
Pure phase and mixed phase TiO$_2$ nanoparticles have been produced using a pyrolytic method from a non-aqueous carboxylate precursor. The precursor was prepared by a multiphase cation exchange using pentanoic acid (C$_4$H$_9$COOH). The thermal stability, polymorph content, morphology, size distribution and surface region of the produced nanoparticles were studied by TGA/DSC, XRD, FTIR and TEM. High quality monodisperse nanoparticles have been produced in the size range from 7 to 27 nm. The nanoparticles showed room temperature ferromagnetism revealed by VSM within bound polaron model. The carboxylate precursor is a good alternative to standard sol-gel to produce nanoparticles free from imp…
Ultrafast laser-induced spin-lattice dynamics in the van der Waals antiferromagnet CoPS3
2023
CoPS3 stands out in the family of the van der Waals antiferromagnets XPS3 (X=Mn, Ni, Fe, Co) due to the unquenched orbital momentum of the magnetic Co2+ ions which is known to facilitate the coupling of spins to both electromagnetic waves and lattice vibrations. Here, using a time-resolved magneto-optical pump-probe technique we experimentally study the ultrafast laser-induced dynamics of mutually correlated spins and lattice. It is shown that a femtosecond laser pulse acts as an ultrafast heater and thus results in the melting of the antiferromagnetic order. At the same time, the resonant pumping of the 4T1g - 4T2g electronic transition in Co2+ ions effectively changes their orbital moment…
Dielectric properties of PLZT-x/65/35 (2 \leqslant x \leqslant 13) under mechanical stress, electric field and temperature loading
2013
We investigated the effect of uniaxial pressure (0-1000 bars) applied parallely to the ac electric field on dielectric properties of PLZT-x/65/35 (2 \leqslant x \leqslant 13) ceramics. There was revealed a significant effect of the external stress on these properties. The application of uniaxial pressure leads to the change of the peak intensity of the electric permittivity (\varepsilon), of the frequency dispersion as well as of the dielectric hysteresis. The peak intensity $\varepsilon$ becomes diffused/sharpened and shifts to a higher/lower temperatures with increasing the pressure. It was concluded that the application of uniaxial pressure induces similar effects as increasing the Ti io…