Electronic structure of Zr-Ni-Sn systems: role of clustering and nanostructures in Half-Heusler and Heusler limits

Half-Heusler and Heusler compounds have been of great interest for several decades for thermoelectric, magnetic, half-metallic and many other interesting properties. Among these systems, Zr-Ni-Sn compounds are interesting thermoelectrics which can go from semiconducting half-Heusler (HH) limit, ZrNiSn, to metallic Heusler (FH) limit, ZrNi$_2$Sn. Recently Makogo et al. [J. Am. Chem. Soc. 133, 18843 (2011)] found that dramatic improvement in the thermoelectric power factor of HH can be achieved by putting excess Ni into the system. This was attributed to an energy filtering mechanism due to the formation of FH nanostructures in the HH matrix. Using density functional theory we have investigated clustering and nanostructure formation in HH$_{1-x}$FH$_x$ systems near the HH and FH ends and found that excess Ni atoms in HH tend to stay close to each other and form nanoclusters of FH. On the other hand, there is competing interaction between Ni-vacancies in FH which prevent them from forming HH nano clusters. Effects of nano inclusions on the electronic structure at both HH and FH ends will be discussed.Comment: Published in J. Phys.: Condens. Matte

Magnetic phase diagram of Fe1.1Te1-xSex: A comparative study with the stoichiometric superconducting FeTe1-xSex system

We report a comparative study of the series Fe1.1Te1-xSex and the stoichiometric FeTe1-xSex to bring out the difference in their magnetic, superconducting and electronic properties. The Fe1.1Te1-xSex series is found to be magnetic and its microscopic properties are elucidated through Moessbauer spectroscopy. The magnetic phase diagram of Fe1.1Te1-xSex is traced out and it shows the emergence of spin-glass state when the antiferromagnetic state is destabilized by the Se substitution. The isomer shift and quadrupolar splitting obtained from the Moessbauer spectroscopy clearly brings out the electronic differences in these two series.Comment: 6 pages, 9 figure

\delta-doped LaAlO3-SrTiO3 interface: Electrical transport and characterization of the interface potential

Here we investigate LaAlO_3-SrTiO_3 heterostructure with\delta-doping of the interface by LaMnO_3 at less than one monolayer. This doping strongly inhibits the formation of mobile electron layer at the interface. This results in giant increase of the resistance and the thermopower of the heterostructure. Several aspects of this phenomena are investigated. A model to calculate the carrier concentration is presented and effect of doping and detailed temperature dependence is analyzed in terms of model parameters and the weak-scattering theory. The large enhancement of thermopower is attributed to the increased spin and orbital entropy originating from the LaMnO_3 mono-layer

Chalcogen Height Dependence of Magnetism and Fermiology in FeTe_xSe_{1-x}

FeTexSe1-x (x=0, 0.25, 0.50, 0.75 and 1) system has been studied using density functional theory. Our results show that for FeSe, LDA seems better approximation in terms of magnitude of magnetic energy whereas GGA overestimates it largely. On the other hand for FeTe, GGA is better approximation that gives experimentally observed magnetic state. It has been shown that the height of chalcogen atoms above Fe layers has significant effect on band structure, electronic density of states (DOS) at Fermi level N(EF) and Fermi surfaces. For FeSe the value of N(EF) is small so as to satisfy Stoner criteria for ferromagnetism, (I\timesN(EF)\geq1) whereas for FeTe, since the value of N(EF) is large, the same is close to be satisfied. Force minimization done for FeTexSe1-x using supercell approach shows that in disordered system Se and Te do not share same site and have two distinct z coordinates. This has small effect on magnetic energy but no significant difference in band structure and DOS near EF when calculated using either relaxed or average value of z for chalcogen atoms. Thus substitution of Se at Te site decreases average value of chalcogen height above Fe layers which in turn affect the magnetism and Fermiology in the system. By using coherent-potential approximation for disordered system we found that height of chalcogen atoms above Fe layer rather than chalcogen species or disorder in the anion planes, affect magnetism and shape of Fermi surfaces (FS), thus significantly altering nesting conditions, which govern antiferromagnetic spin fluctuations in the system.Comment: 24 pages Text+Figs: comments/suggestions welcome ([email protected]

Effectiveness of technology-enhanced learning in Endodontic education: a systematic review and meta-analysis

Sections ePDFPDF PDF Tools Share Abstract The aim of the present systematic review was to evaluate the effectiveness of technology‐enhanced learning (TEL) in the field of Endodontics to improve educational outcomes compared to traditional learning methods. Randomized controlled studies published in English were identified from two electronic databases (PubMed and Scopus) up to May 2018. Two authors independently performed study selection, data extraction and assessed the risk of bias (ROB). Any teaching method using TEL was considered as the intervention, and this was compared to traditional methods. The outcome measuring the effectiveness of learning activities was evaluated by Kirkpatrick's four‐level training evaluation model. The four levels of training outcomes are as follows: Reaction, Learning, Behaviour and Results. A meta‐analysis was performed to estimate the standardized mean difference (SMD) by the random effects model. In total, 13 studies were included in the systematic review. Only three studies were assessed as ‘low’ ROB. A meta‐analysis could not be performed in the domains of Reaction and Behaviour. No significant difference was observed in knowledge gain (Learning domain) between TEL and traditional methods (SMD, 0.14 (95% CI −0.10 to 0.39) I2 = 62.7%). Similarly, no difference was observed in performance (Behaviour domain). A variable response was found in attitude (Reaction domain). From the available evidence, it can be concluded that TEL is equally as effective as traditional learning methods

PRIRATE 2020 guidelines for reporting randomized trials in endodontics: a consensus-based development

In evidence-based healthcare, randomized clinical trials provide the most accurate and reliable information on the effectiveness of an intervention. This project aimed to develop reporting guidelines, exclusively for randomized clinical trials in the dental specialty of Endodontology, using a well-documented, validated consensus-based methodology. The guidelines have been named: Preferred Reporting Items for RAndomized Trials in Endodontics (PRIRATE) 2020. A total of eight individuals (PD, VN, HD, LB, TK, JJ, EP, SP), including the project leaders (PD, VN) formed a steering committee. The committee developed a checklist based on the items in the Consolidated Standards for Reporting Trials (CONSORT) guidelines and Clinical and Laboratory Images in Publications (CLIP) principles. A PRIRATE Delphi Group (PDG) and PRIRATE Face-to-Face Meeting group (PFMG) were also formed. Thirty PDG members participated in the online Delphi process and achieved consensus on the checklist items and flowchart that make up the PRIRATE guidelines. The guidelines were discussed at a meeting of the PFMG at the 19th European Society of Endodontology (ESE) Biennial congress, held on 13th September 2019 in Vienna, Austria. A total of 21 individuals from across the globe and four steering committee members (PD, VN, HD, LB) attended the meeting. As a consequence of the discussions, the guidelines were modified and then piloted by several authors whilst writing a manuscript. The PRIRATE 2020 guidelines contain a checklist consisting of 11 sections and 58 individual items as well as a flowchart, considered essential for authors to include when writing manuscripts for randomized clinical trials in Endodontics

Study of ferromagnetic instability in tau-MnAl, using first-principles

The tau- phase of the binary Mn-Al system is a promising rare-earth free permanent magnet. However, the experimentally determined figure-of-merit (energy-factor) is significantly lower than the theoretical estimate. This is partly being associated with the low volume fraction of tau-MnAl during synthesis, chemical disorder driven inter-sublattice antiferromagnetism, and presence of multiple binary phases. In this work, with the help of first-principles linear response calculations, we show that the presumed long range ferromagnetic ordering in tau-MnAl is unstable. Calculation of Mn magnetic pair-exchange interaction for tau-MnAl show competing ferromagnetic and antiferromagnetic interactions. As a result, the study infers to a non-collinear magnetic ground state, which then partly explains the low magnetization as observed in experiments. Local probe experiments such as neutron diffraction, corroborating our prediction of the non-collinear state in tau-MnAl is therefore desired

Anisotropy and high thermopower of LaOBiS2

Transport properties of LaOBiS2 are studied using the Boltzmann theory in the constant scattering time approximation, the input to which are derived from the ab-initio calculations with spin-orbit interactions included. By virtue of the materials chemical bonding and band structure, strong anisotropy in the transport is observed, which also have non-symmetric behavior with respect to carrier type. With thermopower being in few hundreds mu V/K, and LaO layers being charge inactive, it could be well anticipated that the thermal conductivity would be significantly suppressed along the crystallographic c-axis. We argue LaOBiS2 as a potential oxide thermoelectric material for high temperature applications. Further optimization of the materials properties in terms of "p" and "n" type conduction could also be accomplished via Sr and F doping, respectively, following the discovery of its isoelectronic counterpart SrFBiS2

Energetics and electronic structure of La/Sr disorder at the interface of SrTiO3/LaTiO3 heterostructure

In the artificially tailored heterostructures of certain materials, a polar discontinuity across the interface introduces a large energy cost. The total energy of such systems may be reduced either by electronic reconstruction leading to the interface phases or by simple atomic reconstruction by inter-site cation mixing. While most of the experiments and theoretical calculations assume an abrupt interface, in this work, we consider the La/Sr inter-site disorder across the interface of SrTiO3/LaTiO3 heterostructures and study its energetics and electronic structure properties. The calculations find that inter-site mixing of La/Sr atoms across the interface also reduces the total energy. However, the extent of such disorder is found to be dramatically minimized by allowing the interfacial atoms to relax fully and that for such systems, the changes in the electronic structure are negligible