Phonon Dispersion in Superionic Copper Selenide: Observation of Soft Phonon Modes in Superionic Phase Transition

Danilkin, Sergey; Yethiraj, M.; Kearley, Gordon J.

doi:10.1143/jpsjs.79sa.25

Cited by 12 publications

(11 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The presence of imaginary frequencies for the DFT calculations of type II structural model is very similar to that found in superionic phase of copper selenide with antifluorite crystal structure. [39][40][41] with type II structural model is a narrow gap semiconductor. From this point of view, the type II structural model seems correct and in much better agreement with the experimental transport measurements than the type I structure.…”

Section: Resultsmentioning

confidence: 99%

Elaborating the Crystal Structures of MgAgSb Thermoelectric Compound: Polymorphs and Atomic Disorders

Ying

Sist

et al. 2017

Chem. Mater.

View full text Add to dashboard Cite

Gaining insight into crystal structure is essential for understanding thermoelectric transport mechanisms and predicting thermoelectric properties. The main challenge in studying thermoelectric mechanisms is often imprecise or wrong models of the crystal structure. This work examines the structure modifications observed in MgAgSb thermoelectric materials by multi-temperature high-resolution synchrotron radiation powder X-ray diffraction (SR-PXRD). Rietveld refinement reveals large atomic displacement parameters (ADPs) of the Ag1 atoms at the 4a position indicating possible atomic disorder, which may contribute to the low thermal conductivity observed in α-MgAgSb. The temperature dependence of anisotropic structural parameters indicates a tendency of increasing structural symmetry in α-MgAgSb with increasing temperature, largely contributing to the temperature evolution of the thermoelectric properties. Two MgAgSb polymorphs (β-MgAgSb and γ-MgAgSb) coexist at 700 K, and only the γ-MgAgSb crystalline phase is found at high temperatures (800-1000 K). The content of γ-MgAgSb phase decreases with temperature due to the increase of liquid impurities, and the sample is only 43.8% crystalline at 1000 K. At 800 K, the high resolution powder data are fitted equally well using type I (with Mg, Ag, and Sb on the 4b, 4c, and 4a sites, respectively) and type II (with Mg, Ag, and Sb on the 4a, 4b, and 4c sites, respectively) half-Heusler crystal structure models. Nonetheless, Maximum Entropy Method (MEM) analysis carried out on the extracted factors shows that the type II structure gives a more physically sound MEM electron density. The disorder in γ-MgAgSb consists of mixed sites of Mg and Ag as well as vacancies, and the strong disorder of the cation sublattice contributes to the low thermal conductivity.

show abstract

Section: Resultsmentioning

confidence: 99%

Elaborating the Crystal Structures of MgAgSb Thermoelectric Compound: Polymorphs and Atomic Disorders

Ying

Sist

et al. 2017

Chem. Mater.

View full text Add to dashboard Cite

show abstract

“…Труд-ность при реализации этого подхода в данном случае состоит в том, что рассчитанный фононный спектр соответствует 0 K, а кубическая фаза при температуре ниже 413 K в Cu 2 Se отсутствует. В результате в рас-четном спектре возникают мнимые фононные моды [9]. Кроме того, большая подвижность ионов меди в данном материале должна приводить к интенсивному рассеянию фононов, методы учета которого не очевидны.…”

Section: расчет теплопроводности по методу молекулярной динамикиunclassified

“…На рис. 1 при-ведены фононные спектры, рассчитанные в программе Phonopy [8] с использованием полученного EAM-потен-циала, которые для акустических фононных мод, вно-сящих основной вклад в теплопроводность, неплохо согласуются с экспериментальными данными [9].…”

Section: расчет теплопроводности по методу молекулярной динамикиunclassified

See 1 more Smart Citation

Исследование теплопроводности Cu-=SUB=-2-=/SUB=-Se с учетом влияния подвижных ионов меди

Булат¹,

Иванов²,

Osvenskii³

et al. 2017

Физика Твердого Тела

View full text Add to dashboard Cite

Исследована температурная зависимость теплопроводности наноструктурированных образцов селенида меди, полученных методом механохимического синтеза из исходных чистых компонентов в планетарной шаровой мельнице с последующим искровым плазменным спеканием. Измерение теплопроводности наноструктурированных образцов проводилось в диапазоне температур 410-860 K. При 410-780 K теплопроводность решетки kappaph слабо изменяется в диапазоне 0.35-0.37 W/(m·K). При более высокой температуре T>780 K kappaph снижается до 0.19 W/(m·K). Для анализа влияния подвижных ионов меди на теплопроводность решетки проведены расчеты методом молекулярной динамики с использованием классического межатомного потенциала, полученного из ab initio расчетов для кубической модификации beta-Cu2Se. Результаты моделирования демонстрируют высокую подвижность ионов меди, а расчетная температурная зависимость решеточной теплопроводности согласуется с экспериментом до 780 K. При температуре выше 780 K наблюдается отклонение kappaph от результатов расчета, которое особенно сильно выражено в наноструктурированном материале. В результате при максимальной температуре измерения решеточная теплопроводность снижается до уровня ~ 0.19 W/(m·K), что согласуется с литературными данными для наноструктурированных образов Cu2Se, полученных различными методами. DOI: 10.21883/FTT.2017.10.44983.091

show abstract

“…The dispersion curves were measured in [100], [110] and [111] directions [16]. Due to a strong broadening of phonon peaks data are limited to low energy modes.…”

Section: First Experiments On Taipanmentioning

confidence: 99%

TAIPAN: First Results from the Thermal Triple-axis Spectrometer at OPAL Research Reactor

Danilkin

Yethiraj

Saerbeck

et al. 2012

J. Phys.: Conf. Ser.

View full text Add to dashboard Cite

Abstract. The thermal triple-axis spectrometer TAIPAN is the first instrument for inelastic neutron scattering at the new Australian research reactor OPAL. TAIPAN started operation in February 2009 and is in full user service since November 2010. Conceptually, it is similar to the triple-axis spectrometers IN8 (ILL) and PANDA (FRM-II) with variable incident and final energies and a secondary spectrometer with a single detector. The instrument can be operated either in a high flux mode with a double-focusing monochromator and analyser, or with Soller collimators -gaining resolution at the expense of intensity. Presently the PG (002) doublefocusing monochromator and analyser are in use. The incident energy range on the TAIPAN TAS is from ~5 meV up to ~100 meV with neutron flux at sample position of 2.4 10 7 n/cm /s at incident energy of 14.8 meV. First experiments were performed with superionic conductor Cu 2-δ Se. The measurements reveal the presence of a soft mode related to ordering of Cu atoms followed by α -β phase transition at a lower temperature. The evolution of the magnetic structure with temperature in a magnetically modulated FePt 3 thin film was investigated in the diffraction mode of TAIPAN. The results show that the film fabricated by modulation of the chemical order parameter consists of a magnetic FM/AFM superlattice in single-crystalline FePt 3 . The spin wave and phonon dispersion was recently investigated in TbVO 3 single crystal. The acoustic and optical magnon branches were observed in the same energy range. This indicates that the 'orbital Peiers state' also exists in TbVO 3 .

show abstract

Phonon Dispersion in Superionic Copper Selenide: Observation of Soft Phonon Modes in Superionic Phase Transition

Cited by 12 publications

References 12 publications

Elaborating the Crystal Structures of MgAgSb Thermoelectric Compound: Polymorphs and Atomic Disorders

Elaborating the Crystal Structures of MgAgSb Thermoelectric Compound: Polymorphs and Atomic Disorders

Исследование теплопроводности Cu-=SUB=-2-=/SUB=-Se с учетом влияния подвижных ионов меди

TAIPAN: First Results from the Thermal Triple-axis Spectrometer at OPAL Research Reactor

Contact Info

Product

Resources

About