42 research outputs found

    Anharmonic theory of superconductivity in the high-pressure materials

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    Electron-phonon superconductors at high pressures have displayed the highest values of critical superconducting temperature TcT_c on record, now rapidly approaching room temperature. Despite the importance of high-PP superconductivity in the quest for room-temperature superconductors, a mechanistic understanding of the effect of pressure and its complex interplay with phonon anharmonicity and superconductivity is missing, as numerical simulations can only bring system-specific details clouding out key players controlling the physics. Here we develop a minimal model of electron-phonon superconductivity under an applied pressure which takes into account the anharmonic decoherence of the optical phonons. We find that TcT_c behaves non-monotonically as a function of the ratio Ξ“/Ο‰0\Gamma/\omega_0, where Ξ“\Gamma is the optical phonon damping and Ο‰0\omega_0 the optical phonon energy at zero pressure and momentum. Optimal pairing occurs for a critical ratio Ξ“/Ο‰0\Gamma/\omega_0 when the phonons are on the verge of decoherence ("diffuson-like" limit). Our framework gives insights into recent experimental observations of TcT_c as a function of pressure in the complex BCS material TlInTe2_2

    A Unified Understanding of minimum lattice thermal conductivity

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    We propose a first-principles model of minimum lattice thermal conductivity based on a unified theoretical treatment of thermal transport in crystals and glasses

    The Effect of Na Atom on TlInSe2 and TlInTe2 Compounds

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    Thermoelectric materials have widely used applications in technological areas such as electronic devices and data storage. TlInSe2 and TlInTe2 compounds are among these thermoelectric materials. In this study, while the structural, electronic, and optical properties of TlInSe2, TlInTe2, Tl0.75Na0.25InSe2 and Tl0.75Na0.25InTe2 compounds have been examined with the WIEN2k program based on DFT, their thermoelectric properties have been calculated with another program BoltzTrap. The electronic calculations show that, all compounds exhibit indirect band gap properties. In addition, the band gap energy of Tl0.75Na0.25InSe2 is shifted in the electromagnetic spectrum. The optical properties are found to change depending on the direction for all compounds. Finally, the thermoelectric parameters have been calculated depending on temperature. It is thought that especially the results for Na-doped compounds will be a leading reference for experimental studies

    Ab initio study of NaSrSb and NaBaSb as potential thermoelectric prospects

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    Zintl phases are excellent thermoelectric prospects to put the waste heat to good use. In the quest of the same, using first-principles methods combined with Boltzmann transport theory, we explored two recent phases NaSrSb and NaBaSb. We found low lattice thermal conductivity of 1.9 and 1.3 W mβˆ’1^{-1} Kβˆ’1^{-1} at 300~K for NaSrSb and NaBaSb, respectively, which are of the same order as other potential Zintl phases such as Sr3_3AlSb3_3 and BaCuSb. We account for such low values to short phonon lifetimes, small phonon group velocities, and lattice anharmonicity in the crystal structure. The calculated electrical transport parameters based on acoustic deformation potential, ionized impurity, and polar optical phonon scattering mechanisms reveal large Seebeck coefficients for both materials. Further, we obtain a high figure of merit of ZT∼\sim2.0 at 900~K for \textit{n}-type NaSrSb. On the other hand, the figure of merit of \textit{n}-type NaBaSb surpasses the unity. We are optimistic about our findings and believe our work would set a basis for future experimental investigations.Comment: 10 figures, 1 tabl

    Current-voltage characteristic of InGaTe?

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    ЦСль Ρ€Π°Π±ΠΎΡ‚Ρ‹: ΠŸΠΎΠ»ΡƒΡ‡Π΅Π½ΠΈΠ΅ ΠΈ исслСдованиС Π²ΠΎΠ»ΡŒΡ‚Π°ΠΌΠΏΠ΅Ρ€Π½ΠΎΠΉ характСристики монокристаллов ΠΈ Ρ‚ΠΎΠ½ΠΊΠΈΡ… ΠΏΠ»Π΅Π½ΠΎΠΊ соСдинСния InGaTe2 Π² статичСском ΠΈ динамичСском Ρ€Π΅ΠΆΠΈΠΌΠ°Ρ…, ΠΏΡ€ΠΈ Ρ€Π°Π·Π»ΠΈΡ‡Π½Ρ‹Ρ… Ρ‚Π΅ΠΌΠΏΠ΅Ρ€Π°Ρ‚ΡƒΡ€Π°Ρ… ΠΈ ΠΏΡ€ΠΈ Ρ€Π°Π·Π»ΠΈΡ‡Π½Ρ‹Ρ… площадях ΠΊΠΎΠ½Ρ‚Π°ΠΊΡ‚ΠΎΠ². ΠœΠ΅Ρ‚ΠΎΠ΄Ρ‹ исслСдования. ΠœΠΎΠ½ΠΎΠΊΡ€ΠΈΡΡ‚Π°Π»Π»Ρ‹ InGaTe? Π±Ρ‹Π»ΠΈ Π²Ρ‹Ρ€Π°Ρ‰Π΅Π½Ρ‹ ΠΌΠ΅Ρ‚ΠΎΠ΄Π°ΠΌΠΈ Π‘Ρ€ΠΈΠ΄ΠΆΠΌΠ΅Π½Π°-Π‘Ρ‚ΠΎΠΊΠ±Π°Ρ€Π³Π΅Ρ€Π°, Π° Ρ‚ΠΎΠ½ΠΊΠΈΠ΅ ΠΏΠ»Π΅Π½ΠΊΠΈ ΠΏΠΎΠ»ΡƒΡ‡Π΅Π½Ρ‹ с использованиСм ΠΌΠ΅Ρ‚ΠΎΠ΄Π° кондСнсации ΠΈΠ· ΠΏΠ°Ρ€ΠΎΠ²ΠΎΠΉ Ρ„Π°Π·Ρ‹. Π Π΅Π½Ρ‚Π³Π΅Π½ΠΎΠ³Ρ€Π°ΠΌΠΌΡ‹ InGaTe? ΠΏΠΎΠ»ΡƒΡ‡Π΅Π½Ρ‹ Π½Π° Π΄ΠΈΡ„Ρ€Π°ΠΊΡ‚ΠΎΠΌΠ΅Ρ‚Ρ€Π΅ Π”Π ΠžΠ-2 Π² CuKa ΠΈΠ·Π»ΡƒΡ‡Π΅Π½ΠΈΠΈ (l=1,54178C). ΠŸΠ°Ρ€Π°ΠΌΠ΅Ρ‚Ρ€Ρ‹ элСмСнтарной ячСйки ΠΎΠΏΡ€Π΅Π΄Π΅Π»ΠΈΠ»ΠΈ с Ρ‚ΠΎΡ‡Π½ΠΎΡΡ‚ΡŒΡŽ 0,005C. Π’ΠΎΠ»ΡŒΡ‚Π°ΠΌΠΏΠ΅Ρ€Π½Π°Ρ характСристика исслСдована Π½Π° ΠΎΠ±Ρ€Π°Π·Ρ†Π°Ρ… ΠΏΡ€ΡΠΌΠΎΡƒΠ³ΠΎΠ»ΡŒΠ½ΠΎΠΉ Ρ„ΠΎΡ€ΠΌΡ‹ Ρ€Π°Π·ΠΌΠ΅Ρ€Π°ΠΌΠΈ 7?1?1 ΠΌΠΌΡ– . ΠšΠΎΠ½Ρ‚Π°ΠΊΡ‚Π°ΠΌΠΈ слуТили I. n ΠΈ Cu. Π’ΠΎΠΊ, ΡΠ½Π°Π±ΠΆΠ°ΡŽΡ‰ΠΈΠΉ ΠΊΠΎΠ½Ρ†Ρ‹ ΠΏΡ€ΡΠΌΠΎΡƒΠ³ΠΎΠ»ΡŒΠ½Ρ‹Ρ… ΠΎΠ±Ρ€Π°Π·Ρ†ΠΎΠ², ΠΎΡ€ΠΈΠ΅Π½Ρ‚ΠΈΡ€ΠΎΠ²Π°Π½ Ρ‚Π°ΠΊ, Ρ‡Ρ‚ΠΎ Ρ‚ΠΎΠΊ Ρ‡Π΅Ρ€Π΅Π· ΠΎΠ±Ρ€Π°Π·Π΅Ρ† ΠΏΡ€ΠΎΡ‚Π΅ΠΊΠ°Π΅Ρ‚ вдоль ΠΏΠΎ оси c6 монокристалла InGaTe?. Π’ΠΎΠ»ΡŒΡ‚Π°ΠΌΠΏΠ΅Ρ€Π½Π°Ρ характСристика исслСдовалась Π½Π° постоянном Ρ‚ΠΎΠΊΠ΅ Π² статичСском ΠΈ динамичСском Ρ€Π΅ΠΆΠΈΠΌΠ°Ρ…. Π Π΅Π·ΡƒΠ»ΡŒΡ‚Π°Ρ‚Ρ‹: Π Π΅Π½Ρ‚Π³Π΅Π½ΠΎΡ„Π°Π·ΠΎΠ²Ρ‹ΠΌ Π°Π½Π°Π»ΠΈΠ·ΠΎΠΌ выявлСно, Ρ‡Ρ‚ΠΎ соСдинСниС InGaTe2 кристаллизуСтся Π² Ρ‚Π΅Ρ‚Ρ€Π°Π³ΠΎΠ½Π°Π»ΡŒΠ½ΠΎΠΉ сингонии с ΠΏΠ°Ρ€Π°ΠΌΠ΅Ρ‚Ρ€Π°ΠΌΠΈ Ρ€Π΅ΡˆΠ΅Ρ‚ΠΊΠΈ Π°=8,463C; с=6,981C. ИсслСдовались статичСская ΠΈ динамичСская Π²ΠΎΠ»ΡŒΡ‚Π°ΠΌΠΏΠ΅Ρ€Π½Ρ‹Π΅ характСристики InGaTe2 ΠΏΡ€ΠΈ Ρ€Π°Π·Π»ΠΈΡ‡Π½Ρ‹Ρ… Ρ‚Π΅ΠΌΠΏΠ΅Ρ€Π°Ρ‚ΡƒΡ€Π°Ρ…, ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ Ρ‚Π΅ΠΌΠΏΠ΅Ρ€Π°Ρ‚ΡƒΡ€Ρ‹ ΠΎΠ±Ρ€Π°Π·Ρ†ΠΎΠ² Π² области ΠΎΡ‚Ρ€ΠΈΡ†Π°Ρ‚Π΅Π»ΡŒΠ½ΠΎΠ³ΠΎ Π΄ΠΈΡ„Ρ„Π΅Ρ€Π΅Π½Ρ†ΠΈΠ°Π»ΡŒΠ½ΠΎΠ³ΠΎ сопротивлСния, Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡ‚ΡŒ ΠΏΠΎΡ€ΠΎΠ³ΠΎΠ²ΠΎΠ³ΠΎ напряТСния ΠΎΡ‚ Ρ‚Π΅ΠΌΠΏΠ΅Ρ€Π°Ρ‚ΡƒΡ€Ρ‹, Π²ΠΎΠ»ΡŒΡ‚Π°ΠΌΠΏΠ΅Ρ€Π½Π°Ρ характСристика Ρ‚ΠΎΠ½ΠΊΠΈΡ… ΠΏΠ»Π΅Π½ΠΎΠΊ InGaTe2 ΠΏΡ€ΠΈ Ρ€Π°Π·Π»ΠΈΡ‡Π½Ρ‹Ρ… площадях ΠΊΠΎΠ½Ρ‚Π°ΠΊΡ‚ΠΎΠ². ВыявлСно, Ρ‡Ρ‚ΠΎ данная Ρ„Π°Π·Π° ΠΎΠ±Π»Π°Π΄Π°Π΅Ρ‚ ΠΏΠ΅Ρ€Π΅ΠΊΠ»ΡŽΡ‡Π°ΡŽΡ‰ΠΈΠΌΠΈ свойствами с ΠΏΠ°ΠΌΡΡ‚ΡŒΡŽ ΠΈ с ΡƒΠΌΠ΅Π½ΡŒΡˆΠ΅Π½ΠΈΠ΅ΠΌ Ρ‚Π΅ΠΌΠΏΠ΅Ρ€Π°Ρ‚ΡƒΡ€Ρ‹ Π²Π΅Π»ΠΈΡ‡ΠΈΠ½Π° ΠΏΠΎΡ€ΠΎΠ³ΠΎΠ²ΠΎΠ³ΠΎ напряТСния увСличиваСтся, Π² Ρ€Π΅Π·ΡƒΠ»ΡŒΡ‚Π°Ρ‚Π΅ S-образная характСристика становится ярко Π²Ρ‹Ρ€Π°ΠΆΠ΅Π½Π½ΠΎΠΉ. ΠŸΡ€ΠΎΠ°Π½Π°Π»ΠΈΠ·ΠΈΡ€ΠΎΠ²Π°Π½ΠΎ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ ΠΏΠΎΡ€ΠΎΠ³ΠΎΠ²ΠΎΠ³ΠΎ напряТСния с ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ΠΌ Ρ‚Π΅ΠΌΠΏΠ΅Ρ€Π°Ρ‚ΡƒΡ€Ρ‹. ИсслСдовались ВАΠ₯ Ρ‚ΠΎΠ½ΠΊΠΈΡ… ΠΏΠ»Π΅Π½ΠΎΠΊ Π² зависимости ΠΎΡ‚ ΠΏΠ»ΠΎΡ‰Π°Π΄ΠΈ ΠΈ ΠΎΡ‚ Ρ€Π°Π·ΠΌΠ΅Ρ€Π° самой ΠΏΠ»Π΅Π½ΠΊΠΈ. ВыявлСно, Ρ‡Ρ‚ΠΎ ΠΏΠ»Π΅Π½ΠΊΠΈ Ρ‚Π°ΠΊΠΆΠ΅ ΠΎΠ±Π»Π°Π΄Π°ΡŽΡ‚ ΠΏΠ΅Ρ€Π΅ΠΊΠ»ΡŽΡ‡Π°ΡŽΡ‰ΠΈΠΌΠΈ свойствами ΠΈ с ΡƒΠΌΠ΅Π½ΡŒΡˆΠ΅Π½ΠΈΠ΅ΠΌ ΠΏΠ»ΠΎΡ‰Π°Π΄ΠΈ ΠΊΠΎΠ½Ρ‚Π°ΠΊΡ‚ΠΎΠ² Π²Π΅Π»ΠΈΡ‡ΠΈΠ½Π° ΠΏΠΎΡ€ΠΎΠ³ΠΎΠ²ΠΎΠ³ΠΎ напряТСния, ΠΏΡ€ΠΈ ΠΊΠΎΡ‚ΠΎΡ€ΠΎΠΌ происходит ΠΏΠ΅Ρ€Π΅ΠΊΠ»ΡŽΡ‡Π΅Π½ΠΈΠ΅, ΡƒΠΌΠ΅Π½ΡŒΡˆΠ°Π΅Ρ‚ΡΡ. А Ρ‚Π°ΠΊΠΆΠ΅ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ΠΌ Ρ‚Π΅ΠΌΠΏΠ΅Ρ€Π°Ρ‚ΡƒΡ€Ρ‹ ΠΈ ΠΏΠ»ΠΎΡ‰Π°Π΄ΠΈ ΠΊΠΎΠ½Ρ‚Π°ΠΊΡ‚ΠΎΠ² управляСтся Π²Π΅Π»ΠΈΡ‡ΠΈΠ½Π° ΠΏΠΎΡ€ΠΎΠ³ΠΎΠ²ΠΎΠ³ΠΎ напряТСния. А это ΠΎΠ·Π½Π°Ρ‡Π°Π΅Ρ‚, Ρ‡Ρ‚ΠΎ данная Ρ„Π°Π·Π° ΠΌΠΎΠΆΠ΅Ρ‚ ΡƒΡΠΏΠ΅ΡˆΠ½ΠΎ ΠΏΡ€ΠΈΠΌΠ΅Π½ΡΡ‚ΡŒΡΡ ΠΏΡ€ΠΈ создании Π±Ρ‹ΡΡ‚Ρ€ΠΎΠ΄Π΅ΠΉΡΡ‚Π²ΡƒΡŽΡ‰ΠΈΡ… ΠΈ Π²Ρ‹ΡΠΎΠΊΠΎΡ‡ΡƒΠ²ΡΡ‚Π²ΠΈΡ‚Π΅Π»ΡŒΠ½Ρ‹Ρ… ΠΏΡ€ΠΈΠ±ΠΎΡ€ΠΎΠ².The main aim of the research is to prepare and study the current-voltage characteristics of single crystals and thin films of InGaTe2 compound in static and dynamic modes at different temperatures and for different contact area. Methods: InGaTe? single crystals were grown by the Bridgman- Stockbarger, and thin films were prepared by the method of physical vapor deposition. InGaTe2 radiographs were obtained on a DRON-2 CuKa radiation (l=1,54178C). The unit cell parameters were determined with an accuracy 0,005C. The current-voltage characteristics was investigated on rectangular samples with dimensions 7?1?1 mmΡ– . In and Cu served as contacts. Current supplying the ends of rectangular samples is oriented in the way that current flows through the sample along a single crystal axis c6 of InGaTe?monocrystal. The current-voltage characteristics were examined for constant current in static and dynamic modes. Results. X-ray analysis revealed that InGaTe2 compound crystallizes in tetragonal syngony with lattice parameters a=8,463C; a=6,981C. The authors have investigated the static and dynamic current-voltage characteristics of InGaTe4 at different temperatures, change in the samples temperature in the region of negative differential resistance, dependence of the threshold voltage on the temperature, current-voltage characteristics of InGaTe2 thin films at different contact area. It was ascertained that this phase has switching properties with memory. The threshold voltage increases at temperature decreas. The S-pattern becomes clearly expressed. The authors analyzed the change in the threshold voltage at temperature change. The CVC of thin films were investigated depending on the area and the size of the film itself. It was revealed that the films also exhibit switching properties and decreasing contact area with the magnitude of the threshold voltage at which the switching is reduced. The threshold voltage value is controlled by the changes in temperature and contact area. This means that this phase can be successfully used in the design of fast and highly sensitive instrumentation

    Electronic Structure of a Chain-like Compound: TlSe

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    An ab-initio pseudopotential calculation using density functional theory within the local density approximation has been performed to investigate the electronic properties of TlSe which is of chain-like crystal geometry. The energy bands and effective masses along high symmetry directions, the density of states and valence charge density distributions cut through various planes are presented. The results have been discussed in terms of previously existing experimental and theoretical data, and comparisons with similar compounds have been made.Comment: 7 page

    Upgrade of the MARI spectrometer at ISIS

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    The MARI direct geometry time-of-flight neutron spectrometer at ISIS has been upgraded with an m=3m=3 supermirror guide and new detector electronics. This has resulted in a flux gain of β‰ˆ6Γ—{\approx}6{\times} at Ξ»=1.8\lambda=1.8 {\AA}, and improvements on discriminating electrical noise, allowing MARI to continue to deliver a high quality science program well into its fourth decade of life

    Upgrade of the MARI spectrometer at ISIS

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    The MARI direct geometry time-of-flight neutron spectrometer at ISIS has been upgraded with an m = 3 supermirror guide and new detector electronics. This has resulted in a flux gain of approximate to 6x at lambda = 1.8 angstrom, and improvements on discriminating electrical noise, allowing MARI to continue to deliver a high quality science program well into its fourth decade of life
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