Подготовка врачей-стажеров. Состояние проблемы и перспективы развития

ОБРАЗОВАНИЕ МЕДИЦИНСКОЕМЕДИЦИНСКИЕ УЧЕБНЫЕ ЗАВЕДЕНИЯВУЗЫВРАЧИПОДГОТОВКА ВРАЧЕЙВРАЧИ-СТАЖЕР

Theoretical study of the phase transitions and electronic structure of (Zr-0.5, Mg-0.5)N and (Hf-0.5, Mg-0.5)N

Rock-salt scandium nitride has gained interest due to its thermoelectric properties including a relatively high Seebeck coefficient. This motivates research for other semiconductor materials that exhibit similar electronic structure features as ScN. Using density functional theory calculations, we have studied disordered solid solutions of (Zr-0.5, Mg-0.5)N and (Hf-0.5, Mg-0.5)N using the special quasi-random structure model. The results show that within a mean-field approximation for the configurational entropy, the order-disorder phase transformation between the monoclinic LiUN(2)prototype structure and the rock-salt cubic random alloy of these mentioned solid solutions occur at 740 K and 1005 K for (Zr-0.5, Mg-0.5)N and (Hf-0.5, Mg-0.5)N, respectively. The density-of-states for the two ternary compounds is also calculated and predicts semiconducting behavior with band gaps of 0.75 eV for (Zr-0.5, Mg-0.5)N and 0.92 eV for (Hf-0.5, Mg-0.5)N. The thermoelectric properties of both compounds are also predicted. We find that in the range of a moderate change in the Fermi level, a high Seebeck coefficient value at room temperature can be achieved.Funding Agencies|Linkoping University</p

Theoretical study of phase stability, crystal and electronic structure of MeMgN2 (Me = Ti, Zr, Hf) compounds

Scandium nitride has recently gained interest as a prospective compound for thermoelectric applications due to its high Seebeck coefficient. However, ScN also has a relatively high thermal conductivity, which limits its thermoelectric efficiency and figure of merit (zT). These properties motivate a search for other semiconductor materials that share the electronic structure features of ScN, but which have a lower thermal conductivity. Thus, the focus of our study is to predict the existence and stability of such materials among inherently layered equivalent ternaries that incorporate heavier atoms for enhanced phonon scattering and to calculate their thermoelectric properties. Using density functional theory calculations, the phase stability of TiMgN2, ZrMgN2 and HfMgN2 compounds has been calculated. From the computationally predicted phase diagrams for these materials, we conclude that all three compounds are stable in these stoichiometries. The stable compounds may have one of two competing crystal structures: a monoclinic structure (LiUN2 prototype) or a trigonal superstructure (NaCrS2 prototype; RmH). The band structure for the two competing structures for each ternary is also calculated and predicts semiconducting behavior for all three compounds in the NaCrS2 crystal structure with an indirect band gap and semiconducting behavior for ZrMgN2 and HfMgN2 in the monoclinic crystal structure with a direct band gap. Seebeck coefficient and power factors are also predicted, showing that all three compounds in both the NaCrS2 and the LiUN2 structures have large Seebeck coefficients. The predicted stability of these compounds suggests that they can be synthesized by, e.g., physical vapor deposition.Funding Agencies|European Research Council under the European Communitys Seventh Framework Programme (FP)/ERC [335383]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Swedish Foundation for Strategic Research (SSF) through the Future Research Leaders 5 and 6 programs; Knut and Alice Wallenberg foundation through the Academy Fellow program; Swedish Research Council (VR) [621-2012-4430, 2016-03365]; Swedish Research Council (VR) through International Career Grant [330-2014-6336]; Marie Sklodowska Curie Actions, Cofund [INCA 600398]; VR Grant [2016-04810]; Swedish e-Science Research Centre (SeRC)</p

Phase Transformation and Superstructure Formation in (Ti-0.5, Mg-0.5)N Thin Films through High-Temperature Annealing

(Ti-0.5, Mg-0.5)N thin films were synthesized by reactive dc magnetron sputtering from elemental targets onto c-cut sapphire substrates. Characterization by theta-2 theta X-ray diffraction and pole figure measurements shows a rock-salt cubic structure with (111)-oriented growth and a twin-domain structure. The films exhibit an electrical resistivity of 150 m omega center dot cm, as measured by four-point-probe, and a Seebeck coefficient of -25 mu V/K. It is shown that high temperature (similar to 800 degrees C) annealing in a nitrogen atmosphere leads to the formation of a cubic LiTiO2-type superstructure as seen by high-resolution scanning transmission electron microscopy. The corresponding phase formation is possibly influenced by oxygen contamination present in the as-deposited films resulting in a cubic superstructure. Density functional theory calculations utilizing the generalized gradient approximation (GGA) functionals show that the LiTiO2-type TiMgN2 structure has a 0.07 eV direct bandgap.Funding Agencies|Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Knut and Alice Wallenberg foundationKnut &amp; Alice Wallenberg Foundation [KAW-2020.0196, KAW-2018.0194]; Swedish Research Council (VR)Swedish Research Council [2016-03365, 2019-05403]; Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research [FFL 15-0290]; Swedish Research CouncilSwedish Research Council [2018-05973]</p