Anharmonicity Explains Temperature Renormalization Effects of the Band Gap in SrTiO3
Yu‐Ning WuWissam A. SaidiJeffrey WuenschellTerumasa TadanoPaul R. OhodnickiBenjamin ChorpeningYuhua Duan
39
Citation
44
Reference
10
Related Paper
Citation Trend
Abstract:
Soft phonon modes in strongly anharmonic crystals are often neglected in calculations of phonon-related properties. Herein, we experimentally measure the temperature effects on the band gap of cubic SrTiO3, and compare with first-principles calculations by accounting for electron-phonon coupling using harmonic and anharmonic phonon modes. The harmonic phonon modes show an increase in the band gap with temperature using either Allen-Heine-Cardona theory or finite-displacement approach, and with semilocal or hybrid exchange-correlation functionals. This finding is in contrast with experimental results that show a decrease in the band gap with temperature. We show that the disagreement can be rectified by using anharmonic phonon modes that modify the contributions not only from the significantly corrected soft modes, but also from the modes that show little correction in frequencies. Our results confirm the importance of soft-phonon modes that are often neglected in the computation of phonon-related properties and particularly in electron-phonon coupling.Keywords:
Harmonic
Although the quasi-harmonic approximation (QHA) method applies to many materials, it is necessary to study the anharmonic interaction for extremely anharmonic materials. In this work, the unusual negative thermal expansion (NTE) property of CaTiF6 is studied by combing QHA and anharmonic interaction. The improved self-consistent phonon approximation (ISCPA), which treats anharmonic effects in solids nonperturbatively, is employed. The agreement of NTE behavior between the calculation and the experiment can be further promoted from qualitative consistency by QHA to quantitative consistency by the ISCPA. From mode Grüneisen parameters, it is found that the low-frequency phonons, especially acoustic phonons, contribute greatly to the NTE behavior of CaTiF6. The rigid unit modes (RUMs) of low-frequency optical phonons can be identified. The phonon lifetime of CaTiF6 is calculated from three-phonon interactions; thereby, the NTE mechanism can be further explored by phonon lifetimes of phonons with different frequencies on heating. The anomalous lattice thermal conductivity (LTC) is predicted using the Boltzmann transport equation within the relaxation time approximation. The glasslike LTC can occur in crystal CaTiF6.
Lattice (music)
Negative Thermal Expansion
Cite
Citations (8)
Abstract We report a computational study, using the “moments method” [Y. Gao and M. Daw, Modell. Simul. Mater. Sci. Eng. 23 045002 (2015)], of the anharmonicity of the vibrational modes of single‐walled carbon nanotubes. We find that modes with displacements largely within the wall are more anharmonic than modes with dominantly radial character, except for a set of modes that are related to the radial breathing mode that are the most anharmonic of all. We also find that periodicity of the calculation along the tube length does not strongly affect the anharmonicity of the modes but that the tubes with larger diameter show more anharmonicity. Comparison is made with available experiments and other calculations.
Cite
Citations (4)
The theoretical and experimental studies of anharmonic temperature factor in X-ray and neutron diffraction are reviewed since early works in 1963. These studies are in the framework of effective one body particle potential in which atoms are treated as independent oscillators.The experimental works are classified into two major groups : investigations of anti-centrosymmetric anharmonicity and centrosymmetric anharmonicity. It is pointed out that anti-centrosymmetric anharmonicity is well determined from the accurate Bragg intensity data at a certain temperature but centrosymmetric anharmonicity, because of the correlation of harmonic and anharmonic potential parameters, both of which are centrosymmetric. It is more reliable to determine the centrosymmetric anharmoni-city using the temperature dependence of integrated Bragg intensities unless extremely high Q data are collected.It is suggested that the degree of anharmonicity is much betterdescribed by a ratio of anharmonic term to harmonic term in one body particle potential than the magnitude of anharmonic potential parameter itself. The anharmonic effect is more significant for those substances which have smaller anharmonic potential coefficients.The relationships between anharmonicity of temperature factor and structural phase transition is discussed in the case of several perovskite substances.
Harmonic potential
Harmonic
Cite
Citations (0)
The anharmonicity of the Ruddlesden Popper metal-halide lattice, and its consequences on their electronic and optical properties, is paramount in their basic semiconductor physics. It is thus critical to identify specific anharmonic optical phonons that govern their photophysics . Here, we address the nature of phonon-phono scattering probabilities of the resonantly excited optical phonons that dress the electronic transitions in these materials by means of variable-temperature resonant impulsive stimulated Raman measurements. Based on the temperature dependence of the coherent phonon lifetimes, we isolate the dominant anharmonic phonon and quantify its phonon-phonon interaction strength. Intriguingly, we also observe that the anharmonicity is distinct for different phonons, with a few select modes exhibiting temperature-independent coherence lifetimes, indicating their predominantly harmonic nature. However, the population and dephasing dynamics of excitons are dominated by the anharmonic phonon.
Dephasing
Cite
Citations (0)
<sec>Anharmonic effect is often one of the physical root causes of some special material properties, such as soft mode phase transition, negative thermal expansion, multiferroicity, and ultra-low thermal conductivity. However, the existing methods of quantifying the anharmonicity of material do not give a clear and accurate anharmonicity descriptor. The calculation of the anharmonic effect requires extremely time-consuming molecular dynamics simulation, the calculation process is complex and costly. Therefore, a quantitative descriptor is urgently needed, which can be used to implement quick calculation so as to understand, evaluate, design, and screen functional materials with strong anharmonicity.</sec><sec>In this paper, we propose a method to quantify the anharmonicity of materials by only phonon spectrum and static self-consistent calculation through calculating and analyzing the material composed of germanium and its surrounding elements. In this method, the lattice anharmonicity is decomposed into the anharmonic contribution of independent phonon vibration modes, and the quantitative anharmonicity descriptor <inline-formula><tex-math id="M3">\begin{document}$ {\sigma }_{\boldsymbol{q},j}^{A} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M3.png"/></alternatives></inline-formula> of phonons is proposed. Combining it with the Bose-Einstein distribution, the quantitative descriptor <inline-formula><tex-math id="M4">\begin{document}$ {A}_{{\mathrm{p}}{\mathrm{h}}}\left(T\right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M4.png"/></alternatives></inline-formula> of temperature-dependent material anharmonicity is proposed. We calculate the bulk moduli and lattice thermal conductivities at 300 K of nine widely representative materials. There is a clear linear trend between them and our proposed quantitative descriptor <inline-formula><tex-math id="M5">\begin{document}$ {A}_{{\mathrm{p}}{\mathrm{h}}}\left(T\right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M5.png"/></alternatives></inline-formula>, which verifies the accuracy of our proposed descriptor. The results show that the descriptor has the following functions. i) It can systematically and quantitatively classify materials as the strength of anharmonicity; ii) it intuitively shows the distribution of the anharmonic effect of the material on the phonon spectrum, and realizes the separate analysis of the phonon anharmonicity that affects the specific properties of the material; iii) it is cost-effective in first-principles molecular dynamics calculations and lays a foundation for screening and designing materials based on anharmonicity.</sec><sec>This study provides an example for the high-throughput study of functional materials driven by anharmonic effect in the future, and opens up new possibilities for material design and application. In addition, for strongly anharmonic materials such as CsPbI<sub>3</sub>, the equilibrium position of the atoms is not fixed at high temperatures, resulting in a decrease in the accuracy of quantifying anharmonicity using our proposed descriptor. In order to get rid of this limitation, our future research will focus on the distribution of atomic equilibrium positions in strongly anharmonic materials at high temperatures, so as to propose a more accurate theoretical method to quantify the anharmonicity in strongly anharmonic materials.</sec>
Lattice (music)
Cite
Citations (0)
This chapter begins with a discussion of the general theory of transition possibilities. It then discusses anharmonic lattice forces, effects of selection rules, interaction with optical modes, four-phonon processes, elastic anharmonicity, thermal expansion, and the absorption of sound in solids.
Lattice (music)
Cite
Citations (0)
Abstract Group I niobates (KNbO 3 and NaNbO 3 ) are promising lead-free alternatives for high-performance energy storage applications. Despite their potential, their complex phase transitions arising from temperature-dependent phonon softening and anharmonic effects on dielectric properties remain poorly explored. In this study, we employ density-functional theory (DFT) and self-consistent phonon (SCP) calculations to investigate finite-temperature phonons in cubic niobate perovskites. To include explicit anharmonic vibrational effects, SCP frequencies are shifted by the bubble self-energy correction within the quasiparticle (QP) approximation, providing precise descriptions of phonon softening in these strongly anharmonic solids. We further calculate the static dielectric constant of KNbO 3 and NaNbO 3 as a function of temperature using the Lyddane-Sachs-Teller (LST) relation and QP-corrected phonon dispersions. Our theoretical results align with experimental data, offering reliable temperature-dependent phonon dispersions while considering anharmonic self-energies and thermal expansion effects, enhancing our understanding of the complex relations between lattice vibrations and phase transitions in these anharmonic oxides.
Lattice (music)
Cite
Citations (8)
Since last several years, the author has been studying the phonons on functional materials and has established structure-property correlations on flexible framework structure materials, lead free oxides, thin film perovskites, low dimensional 2D materials like graphene nanosheets, TiS3 nanofiber, VSe2 nanosheets, SnO2 quasi nanoparticles etc. In this book chapter, temperature dependent Raman spectroscopic studies on negative thermal expansion framework material H3[Co(CN)6] have been presented in the temperature range 80-300 K to elucidate the phonon anharmonicity of different phonons. No discontinuous or slope changes of phonon mode frequencies, linewidths and their band intensities were noticed suggesting that the compound was stable in the entire temperature range of investigation. Phonon anharmonicity models were used to analyse the temperature dependencies of mode frequencies and their linewidths. It was observed that the three-phonon decay process was dominant over the four-phonon process in this flexible compound. Concisely, the present study demonstrates the anharmonicity of the phonons and their correlation on thermal expansion of H3[Co(CN)6] framework material.
Atmospheric temperature range
Negative Thermal Expansion
Cite
Citations (0)
We report a computational study, using the "moments method" [Y. Gao and M. Daw, Modelling Simul. Mater. Sci. Eng. 23 045002 (2015)], of the anharmonicity of the vibrational modes of single-walled carbon nanotubes. We find that modes with displacements largely within the wall are more anharmonic than modes with dominantly radial character, except for a set of modes that are related to the radial breathing mode which are the most anharmonic of all. We also find that periodicity of the calculation along the tube length does not strongly affect the anharmonicity of the modes, but that the tubes with larger diameter show more anharmonicity. Comparison is made with available experiments and other calculations.
Mode (computer interface)
Cite
Citations (0)
The anharmonicity of the Ruddlesden Popper metal-halide lattice, and its consequences on their electronic and optical properties, is paramount in their basic semiconductor physics. It is thus critical to identify specific anharmonic optical phonons that govern their photophysics . Here, we address the nature of phonon-phono scattering probabilities of the resonantly excited optical phonons that dress the electronic transitions in these materials by means of variable-temperature resonant impulsive stimulated Raman measurements. Based on the temperature dependence of the coherent phonon lifetimes, we isolate the dominant anharmonic phonon and quantify its phonon-phonon interaction strength. Intriguingly, we also observe that the anharmonicity is distinct for different phonons, with a few select modes exhibiting temperature-independent coherence lifetimes, indicating their predominantly harmonic nature. However, the population and dephasing dynamics of excitons are dominated by the anharmonic phonon.
Dephasing
Cite
Citations (2)