To study the anomalous thermoelastic behavior of bcc V, Nb, Ta as well as fcc Pd and Pt a density functional theory (DFT) based model is used, which allows for the calculation of the elastic constant [Formula: see text] and [Formula: see text] as a function of temperature. Available experimental [Formula: see text] trends are correctly reproduced indicating that the electronic structure mechanisms enabling anomalous behavior are captured by the model. A DFT based correlative investigation between V, Nb, Ta, Pd and Pt with anomalous thermoelastic properties and Mo and Cu with ordinary behavior reveals a high density of states (DOS) at the Fermi level to be a necessary but not sufficient condition for an anomalous thermoelastic behavior. In addition, anomalous metals in contrast to ordinary metals reallocate electronic states in the vicinity of the Fermi level upon lattice distortion, causing an increase in bond strength as identified by crystal orbital Hamilton population (COHP) analysis. Hence, we have identified the combination of high DOS and electronic reallocation upon lattice distortion to be the physical origin for anomalous thermoelastic behavior in metals. The absence of an anomaly for [Formula: see text]-type distortion in V, Nb, Ta, Pd and Pt is suggested to be due to the less pronounced reallocation of states compared to [Formula: see text]-type distortion.
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http://dx.doi.org/10.1088/1361-648X/ab099b | DOI Listing |
Materials (Basel)
November 2020
Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, 52074 Aachen, Germany.
The HfV-HfVO composite is proposed as a material with potentially temperature-independent thermophysical properties due to the combination of anomalously increasing thermoelastic constants of HfV with the negative thermal expansion of HfVO. Based on literature data, the coexistence of both a near-zero temperature coefficient of elasticity and a coefficient of thermal expansion is suggested for a composite with a phase fraction of approximately 30 vol.% HfV and 70 vol.
View Article and Find Full Text PDFJ Phys Condens Matter
June 2019
Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, D-52074 Aachen, Germany.
To study the anomalous thermoelastic behavior of bcc V, Nb, Ta as well as fcc Pd and Pt a density functional theory (DFT) based model is used, which allows for the calculation of the elastic constant [Formula: see text] and [Formula: see text] as a function of temperature. Available experimental [Formula: see text] trends are correctly reproduced indicating that the electronic structure mechanisms enabling anomalous behavior are captured by the model. A DFT based correlative investigation between V, Nb, Ta, Pd and Pt with anomalous thermoelastic properties and Mo and Cu with ordinary behavior reveals a high density of states (DOS) at the Fermi level to be a necessary but not sufficient condition for an anomalous thermoelastic behavior.
View Article and Find Full Text PDFPhys Rev Lett
May 2013
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA.
The discovery of a pressure induced iron-related spin crossover in Mg((1-x))Fe(x)O ferropericlase (Fp) and Mg-silicate perovskite, the major phases of Earth's lower mantle, has raised new questions about mantle properties which are of central importance to seismology. Despite extensive experimental work on the anomalous elasticity of Fp throughout the crossover, inconsistencies reported in the literature are still unexplained. Here we introduce a formulation for thermoelasticity of spin crossover systems, apply it to Fp by combining it with predictive first principles density-functional theory with on-site repulsion parameter U calculations, and contrast results with available data on samples with various iron concentrations.
View Article and Find Full Text PDFProc Natl Acad Sci U S A
May 2009
Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute, Minneapolis, MN 55455, USA.
The thermoelastic properties of ferropericlase Mg(1-x)Fe(x)O (x = 0.1875) throughout the iron high-to-low spin cross-over have been investigated by first principles at Earth's lower mantle conditions. This cross-over has important consequences for elasticity such as an anomalous bulk modulus (K(S)) reduction.
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