High-pressure phase diagram of hydrogen and deuterium sulfides from first principles: Structural and vibrational properties including quantum and anharmonic effects

Bianco, Raffaello; Errea, Ion; Calandra, Matteo; Mauri, Francesco

doi:10.1103/physrevb.97.214101

Cited by 50 publications

(63 citation statements)

References 40 publications

(61 reference statements)

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“…In highly anharmonic materials 25,27,42,44,45 , the spectral functions show broad peaks, shoulders and satellite peaks, strongly deviating from the Lorentzian picture. In Fig.…”

Section: The Phonon Collapse Predicted Here Should Be Experimentally mentioning

confidence: 96%

Phonon Collapse and Second-Order Phase Transition in Thermoelectric SnSe

et al. 2019

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Since 2014 the layered semiconductor SnSe in the high-temperature Cmcm phase is known to be the most efficient thermoelectric material. Making use of first-principles calculations we show that its vibrational and thermal transport properties are determined by huge non-perturbative anharmonic effects. We show that the transition from the Cmcm phase to the low-symmetry P nma is a second-order phase transition driven by the collapse of a zone border phonon, whose frequency vanishes at the transition temperature. Our calculations show that the spectral function of the in-plane vibrational modes are strongly anomalous with shoulders and double-peak structures. We calculate the lattice thermal conductivity obtaining good agreement with experiments only when non-perturbative anharmonic scattering is included. Our results suggest that the good thermoelectric efficiency of SnSe is strongly affected by the non-perturbative anharmonicity. We expect similar effects to occur in other thermoelectric materials.Thermoelectric materials can convert waste heat into useful electricity 1,2 . The thermoelectric efficiency of a material is measured by the dimensionless figure of merit ZT = S 2 σT /κ, where S is the Seebeck coefficient, σ the electrical conductivity, T the temperature, and κ = κ e + κ l the thermal conductivity, constituted by electronic κ e and lattice κ l contributions. The thermoelectric efficiency can be thus enhanced by decreasing the thermal conductivity while keeping a high power factor S 2 σ. Materials have been doped 3-5 or nanostructured 6,7 in order to get a high power factor combined with a low thermal conductivity, yielding, i.e., ZT 2.2 in PbTe 8 . In the proximity to a phase transition ZT may also soar, as in the case of Cu 2 Se 9 . Recently, however, Zhao et al. reported for SnSe 10 the highest thermoelectric figure of merit ever reached in a material without doping, material treatment or without being in the proximity to a phase transition: ZT 2.6 above 800 K.SnSe is a narrow gap semiconductor that crystallizes at room temperature in an orthorhombic P nma phase. At T 800 K 10-13 it transforms into a more symmetric base-centered orthorhombic Cmcm structure (see Fig. 1). The order of the transition is not clear: some works 10-12 claim it is a continuous second-order transition and others it has a first-order character 13 . A recent work 14 argues the transition occurs in two steps, where increasing temperature induces first a change in the lat-tice parameters that induces after a lattice instability. There is no inelastic scattering experiment so far for the high-temperature phase, which should show a prominent phonon collapse at the transition temperature if it belonged to the displacive second-order type 15-17 .The most interesting thermoelectric properties appear in the high-temperature Cmcm phase, where the reduction of the electronic band gap increases the number of carriers providing a higher power factor, while the thermal conductivity remains very low 10 . The value of the intrinsic κ l of SnSe r...

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“…In highly anharmonic materials 25,27,42,44,45 , the spectral functions show broad peaks, shoulders and satellite peaks, strongly deviating from the Lorentzian picture. In Fig.…”

Section: The Phonon Collapse Predicted Here Should Be Experimentally mentioning

confidence: 96%

Phonon Collapse and Second-Order Phase Transition in Thermoelectric SnSe

et al. 2019

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“…In strongly anharmonic materials 7,8,11,19,29,44 , the phonon spectral functions σ(q, ω) show broad peaks, shoulders, and satellite peaks that cannot be captured by the simple Lorentzian picture. In Figure 4 (b) and (c) we show the spectral function keeping the full frequency dependence on the self-energy (see Eq.…”

Section: Anharmonic Phononsmentioning

confidence: 99%

Strong anharmonicity and high thermoelectric efficiency in high-temperature SnS from first principles

et al. 2019

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SnS and SnSe are isoelectronic materials with a common phase diagram. Recently, SnSe was found to be the most efficient intrinsic thermoelectric material in its high-temperature Cmcm phase above 800 K. Making use of first-principles calculations, here we show that the electronic and vibrational properties of both materials are very similar in this phase and, consequently, SnS is also expected to have a high thermoelectric figure of merit at high temperature in its Cmcm phase. In fact, the electronic power factor and lattice thermal conductivity are comparable for both materials, which ensures a similar figure of merit. As in the case of SnSe, the vibrational properties of SnS in the Cmcm phase are far from trivial and are dominated by huge anharmonic effects. Its phonon spectra are strongly renormalized by anharmonicity and the spectral functions of some particular in-plane modes depict anomalous non-lorentzian profiles. Finally, we show that non-perturbative anharmonic effects in the third-order force-constants are crucial in the calculation of the lattice thermal conductivity. Our results motivate new experiments in the high temperature regime to measure the figure of merit of SnS.

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“…When studying physical systems at finite temperatures, it is desirable to calculate thermodynamic quantities such as the internal energy, entropy, and corresponding Helmholtz free energy. Recently, there has been progress by several groups [1][2][3][4][5] in developing first principles methods to include temperature dependent effects including structural phase transitions. The detailed study of temperature dependent properties of disordered materials at the first principles level, however, remains a challenge.…”

Section: Introductionmentioning

confidence: 99%

First-principles estimation of partition functions representing disordered lattices such as the cubic phases of Li2OHCl and Li2OHBr

Howard

Holzwarth

2019

Phys. Rev. B

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In order to develop computational methods that can simulate thermodynamic properties of disordered materials at a first principles level, we investigate the use of a random set of configurations to evaluate the canonical partition function of lattice-based disordered systems. Testing the sampling method on the one and two dimensional Ising models indicates that for the ordered system at low temperature, convergence is achieved when the number of samples S is comparable or larger than the number of configurations Ω, while for the partially disordered system at high temperature, convergence is achieved for smaller sample sizes as low as S ≈ Ω/100 or S ≈ Ω/1000. The sampling method is combined with first principles calculations to examine the ordered ↔ disordered phase transition for the Li ion electrolyte materials Li2OHCl and Li2OHBr. Static lattice internal energies and harmonic phonon free energies were incorporated into the evaluation of the partition function. The evaluation of the partition function depends on the value of Ω corresponding to the number of metastable states of the system. Accordingly, we developed a method of approximating Ω using the properties of the sampled configurations. The results of the calculations are consistent with the experimental observation that the transition temperature for the orthorhombic ↔ cubic phase transition is higher for Li2OHCl than for Li2OHBr. We expect the sampling method to be generally useful for investigating the thermodynamic properties of other disordered lattice systems. We also investigate a "disordered subspace function" which is shown to satisfy inequality relationships with respect to the Helmholtz free energy.

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High-pressure phase diagram of hydrogen and deuterium sulfides from first principles: Structural and vibrational properties including quantum and anharmonic effects

Cited by 50 publications

References 40 publications

Phonon Collapse and Second-Order Phase Transition in Thermoelectric SnSe

Phonon Collapse and Second-Order Phase Transition in Thermoelectric SnSe

Strong anharmonicity and high thermoelectric efficiency in high-temperature SnS from first principles

First-principles estimation of partition functions representing disordered lattices such as the cubic phases of Li2OHCl and Li2OHBr

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