Complex role for thallium in PbTe:Tl from local probe studies

Keiber, Trevor; Bridges, F.; Sales, B. C.; Wang, Hsin

doi:10.1103/physrevb.87.144104

Cited by 40 publications

(53 citation statements)

References 21 publications

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“…Our calculation clearly shows that the center of mass of the distributions is exactly at the equilibrium pair distance. We conclude, in line with Keiber et al [69], that Pb is not off-center in PbSe, similarly to the case of PbTe. There is a strong asymmetry of the peak around the equilibrium position, indicative of strong anharmonicity, however the center of mass is positioned exactly at the zero and no off-centering observed.…”

Section: Atomic Pair Distributionsupporting

confidence: 78%

Intrinsic localized mode and low thermal conductivity of PbSe

2017

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Lead chalcogenides such as PbS, PbSe, and PbTe are of interest for their exceptional thermoelectric properties and strongly anharmonic lattice dynamics. Although PbTe has received the most attention, PbSe has a lower thermal conductivity and a nonlinear temperature dependence of thermal resistivity despite being stiffer, trends that prior first-principles calculations have not fully reproduced. Here, we use ab initio calculations that explicitly account for strong anharmonicity and a computationally efficient stochastic phase-space sampling scheme to identify the origin of this low thermal conductivity as an anomalously large anharmonic interaction, exceeding in strength that in PbTe, between the transverse optic and longitudinal acoustic branches. The strong anharmonicity is reflected in the striking observation of an intrinsic localized mode that forms in the acoustic frequencies. Our work shows the deep insights into thermal phonons that can be obtained from ab initio calculations that do not rely on perturbations from the ground-state phonon dispersion.

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Section: Atomic Pair Distributionsupporting

confidence: 78%

Intrinsic localized mode and low thermal conductivity of PbSe

2017

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“…Kastbjerg et al claim an even larger off-center displacement of Pb based on synchrotron powder x-ray diffraction [24]. However, x-ray absorption fine structure spectroscopy experiments have been interpreted as showing no such symmetry breaking [25]. Given that our method faithfully reproduces the temperature dependence of the spectra, we can clearly answer this question with the position probability distribution function P α (x, y, z), where α labels a given Pb or Te atom.…”

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confidence: 77%

First-Principles Approach to Nonlinear Lattice Dynamics: Anomalous Spectra in PbTe

Chen

Marianetti

2014

Phys. Rev. Lett.

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Here we introduce a new approach to compute the finite temperature lattice dynamics from first-principles via the newly developed slave mode expansion. We study PbTe where inelastic neutron scattering (INS) reveals strong signatures of nonlinearity as evidenced by anomalous features which emerge in the phonon spectra at finite temperature. Using our slave mode expansion in the classical limit, we compute the vibrational spectra and show remarkable agreement with temperature dependent INS measurements. Furthermore, we resolve experimental controversy by showing that there are no appreciable local nor global spontaneously broken symmetries at finite temperature and that the anomalous spectral features simply arise from two anharmonic interactions. Our approach should be broadly applicable across the periodic table.Inelastic neutron scattering (INS) is a fundamental probe of materials which has allowed a unique view into the most basic aspects of mechanical behavior [1]. With the advent of the Spallation Neutron Source, massive amounts of data can be accumulated at an unprecedented rate, allowing for an extremely detailed inspection of phenomena throughout reciprocal space. Despite the enormous success of this experimental method, theory has greatly lagged behind in the context of vibrations. At present, one cannot compute the temperature dependence of the phonon spectrum for materials with appreciable phonon interactions from first-principles. Moreover, this scenario cannot even be routinely handled in the classical limit for indirect reasons. This assertion is empirically well illustrated by the strongly interacting phonon material PbTe. INS measurements demonstrated signatures of strong interactions in the temperature dependence of the phonon spectra [2,3], attracting significant attention to this system, yet complementary theoretical predictions have not yet been made. In this paper, we circumvent previous theoretical limitations, and resolve the experimental anomalies in PbTe.In many materials, density functional theory (DFT) is expected to describe the structural energetics to a high degree of accuracy. Therefore, the interatomic potential generated via solving the DFT equations (assuming the Born-Oppenheimer approximation) should be reliable to perform both quantum and classical dynamics of the nuclei. However, the problem is that the scaling of DFT is sufficiently prohibitive to forbid this in many scenarios. Even at the level of classical mechanics (aka. ab initio molecular dynamics), one would need a very large unit cell along with many time steps. In most cases this prevents one from directly being able to compute even the classical vibrational spectrum at finite temperature, as evidenced by the sparse number of such publications in the literature. There are a variety of approaches that attempt to circumvent this problem. One approach is the use of an empirical potential in place of DFT. If an accurate empirical potential exists this is acceptable, but this is generally not the case. Another approach wou...

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“…Based on chemical and thermodynamic arguments, the authors proposed lattice expansion-induced lone pair stereochemical activity as the mechanism for this unusual phenomenon, and in the case of SnTe found qualitative differences between this emergent high temperature phase and the ferroic low temperature phase. Following these reports, a number of articles have appeared, seeking to clarify the lattice dynamics and local structure of these materials based on ab initio calculations, [18][19][20][21] extended X-ray absorption fine structure (EXAFS) spectroscopy, 22,23 neutron scattering, 19,24,25 X-ray diffraction, 26 and piezoresponse force microscopy. 21 Most agree that a high degree of anharmonicity of the cation potential well exists within the region accessible at relevant thermal energies.…”

Section: Introductionmentioning

confidence: 99%

Dynamic Stereochemical Activity of the Sn²⁺ Lone Pair in Perovskite CsSnBr₃

et al. 2016

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Stable s 2 lone pair electrons on heavy main-group elements in their lower oxidation states drive a range of important phenomena, such as the emergence of polar ground states in some ferroic materials. Here we study the perovskite halide CsSnBr 3 as an embodiment of the broader materials class. We show that lone pair stereochemical activity due to the Sn s 2 lone pair causes a crystallographically hidden, locally distorted state to appear upon warming, a phenomenon previously referred to as emphanisis.The synchrotron X-ray pair distribution function acquired between 300 K and 420 K reveals emerging asymmetry in the nearest-neighbor Sn-Br correlations, consistent with dynamic Sn 2+ off-centering, despite there being no evidence of any deviation from the average cubic structure. Computation based on density functional theory supports the finding of a lattice instability associated with dynamic off-centering of Sn 2+ in its coordination environment. Photoluminescence measurements reveal an unusual blueshift with increasing temperature, closely linked to the structural evolution. At low temperatures, the structures reflect the influence of octahedral rotation. A continuous transition from an orthorhombic structure (P nma, no. 62) to a tetragonal structure (P 4/mbm, no. 127) is found around 250 K, with a final, first-order transformation at 286 K to the cubic structure (P m3m, no. 221).2

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Complex role for thallium in PbTe:Tl from local probe studies

Cited by 40 publications

References 21 publications

Intrinsic localized mode and low thermal conductivity of PbSe

Intrinsic localized mode and low thermal conductivity of PbSe

First-Principles Approach to Nonlinear Lattice Dynamics: Anomalous Spectra in PbTe

Dynamic Stereochemical Activity of the Sn²⁺ Lone Pair in Perovskite CsSnBr₃

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Complex role for thallium in PbTe:Tl from local probe studies

Cited by 40 publications

References 21 publications

Intrinsic localized mode and low thermal conductivity of PbSe

Intrinsic localized mode and low thermal conductivity of PbSe

First-Principles Approach to Nonlinear Lattice Dynamics: Anomalous Spectra in PbTe

Dynamic Stereochemical Activity of the Sn2+ Lone Pair in Perovskite CsSnBr3

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Dynamic Stereochemical Activity of the Sn²⁺ Lone Pair in Perovskite CsSnBr₃