Phonon Contribution Research Articles

Spectrum of Tunneling Transport through Phonon-Coupled Defect States in a Carbon-Doped Hexagonal Boron Nitride Barrier.

Defects in hexagonal boron nitride (h-BN) play important roles in tunneling transport through the h-BN barrier. Here, using carbon-doped h-BN (h-BN:C) as a tunnel barrier containing defects in a controlled manner, we investigated tunneling transport through defects in the h-BN:C/graphene heterostructures. Defect-assisted tunneling through a specific kind of carbon-related defect was observed in all measured devices, where the defect level was always located at ∼0.1 eV above the graphene's charge neutrality point. We revealed a phonon-assisted inelastic process in the defect-assisted tunneling, in which carriers tunnel through the defect with phonon emission. Furthermore, when the h-BN:C barrier was thick (12 layers, ∼4 nm), sequential tunneling through two defects became dominant, where the phonon-assisted inelastic process shows substantial effects between the two defects. This study reveals the contribution of phonons to defect-assisted tunneling transport, which is essential for the development of defect-related van der Waals (vdW) electronic techniques.

Impact of optical phonons on the thermal conductivity of monolayer WSe2 due to four-phonon scattering

There exists a large debate on the thermal conductivity(TC) of monolayer WSe2. The first-principles method is thus explored to investigate the TC of monolayer WSe2 with and without considering four-phonon scattering(FPS). It is observed that the TC of monolayer WSe2 is 52.49 W/m·K considering only three-phonon scattering(TPS) at 300 K. However, the TC is significantly reduced to 7.74 W/m·K, only 14.75 % of that of TPS considered, when the FPS is involved. Moreover, the optical phonons make negligible contributions to the total TC with TPS; however, their contribution increases to about 20 %, due to the inclusion of the FPS. Additionally, with temperature increasing, the thermal conductivity contribution from three- and four-phonon scattering tends to converge, indicating a diminishing contribution of the higher-order phonon scattering.

Broadband multiple resonant metasurface for mixture surface-enhanced infrared absorption based on polarization-sensitive folded nanoantennas

Multiple resonant metasurfaces for mixture component detection by surface-enhanced infrared absorption in a broadband spectrum region are still highly desirable. This paper presents a polarization-sensitive multi-resonant broadband metasurface in the mid-infrared (MIR) region based on an odd symmetric folded antenna array. Six major resonant modes are effectively excited in 6–15 μm covering the absorption peak of multiple gases and biomolecules. In addition, the calculation indicates the maximum electric field intensity enhancement reaches 3607 and the average electric enhancement factors are dominantly amplified to a maximum of 75.08. The excited multiple hotspots provide more spatial overlap with analytes and would be beneficial for label-free detection. Moreover, owing to the contributions of the intrinsic phonons and polaritons in the ENZ material, the spectroscopy features are relatively stable when changing the geometry parameters and the incident angles, allowing more fabrication tolerance and experiment flexibility. Furthermore, the multiple resonant metasurface is also effectively enabled under orthogonal circular polarizations. Finally, the sensing abilities of the designed metasurface for polyethylene terephthalate and isopropanol molecules have been computationally validated. These results indicate the potential for nanophotonic detection and mixture spectroscopy analysis.

A momentum-resolved view of polaron formation in materials

An ab-initio computational methodology for interrogating the phonon contribution to polaron formation in real materials is developed that can be directly compared to experiment. Using LiF as an example, we show that the recent ab-initio theory of Sio et al.1 makes predictions of the momentum- and branch dependent phonon amplitudes in polaron quasiparticles that are testable using ultrafast electron diffuse scattering (UEDS) and related techniques. The large electron polaron in LiF has UEDS signatures that are qualitatively similar to those expected from a simple isotropic strain field model, but the small hole polaron exhibits a profoundly anisotropic UEDS pattern that is in poor agreement with an isotropic strain field. We also show that these polaron diffuse scattering signatures are directly emblematic of the underlying polaron wavefunction. The combination of new time and momentum resolved experimental probes of nonequilibrium phonons with novel computational methods promises to complement the qualitative results obtained via model Hamiltonians with a first principles, material-specific quantitative understanding of polarons and their properties.

Preparation and characterization of conjugated PVA/PANi blend films doped with functionalized graphene for thermoelectric applications

Flexible nanocomposite thick films consisting of PVA0.7PANi0.3 polymer blend doped with different concentrations of nanoplatelets functionalized Graphene (NPFGx) (where x = 0, 5, 10, 15, 20, and 25 wt.%) were fabricated using the solution cast technique. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), energy dispersive spectroscopy analysis (EDX), and Fourier-transform infrared spectra (FT-IR) were used to study the structure of the samples. The results showed that the ordered structure, its orientation, the PANis' well dispersion, and the electrostatic forces play a significant role in enhancing the interfaces between the polymer blend and the NPFG. Thermogravimetric analyses (TGA) and Thermoelectrical analyses (TE) showed that the PVA-PANi conducts a promised conjugated blend for thermoelectric applications. The introduction of the NPFG contents into the blend increased the TE measurements as the DC electrical conductivity ≈ 0.0114 (S cm−1), power factor ≈ 3.93 × 10–3 (W m−1 K−2), and Z.T. ≈ 8.4 × 10–7, for the 25 wt.% NPFG nanocomposite film. The effect of the polymers’ phonon contribution in the thermal conductivity controlling and enhancing the thermal stability of the prepared nanocomposite films.

Electrical transport in nanostructured Ni3Al at low temperatures

The electrical resistivity in nanostructured Ni3Al has been discriminated to be dominated fully by the electron-magnon scattering with spin fluctuations and evolve in the form of T 5/3 and T 3/2 below and above its Curie temperature. In addition to doping into γ′-Ni3Al nanophases, excessive Ni atoms are demonstrated to aggregate at the cores of Ni3Al so that some γ-Ni nanophases are embedded in the γ′-Ni3Al ones for forming the core/shell nanostructure. The itinerant electrons from γ′-Ni3Al nanophases is further suggested to wander around the phonons in both γ-Ni and γ′-Ni3Al nanophases for screening the electron-phonon interactions. Consequently, the conduction electrons are scattered largely by spin fluctuations in γ′-Ni3Al shells to suppress the contribution of phonons to the electron transport in nanostructured Ni3Al.

Understanding thermal transport in magnesium solid solutions through first-principles approaches and machine learning feature screening

The solid solution phases have a large influence on the thermal conductivity of alloys, but the physics behind this effect is complicated. Existing works mainly utilize experimental methods to study the thermal conductivity of alloys. However, due to the coexistence of multi-phase and insufficient understanding of the microscopic property variations in different alloy systems, it remains unclear how different solute atoms can affect the thermal transport of solid solutions. In this work, we employ first-principles simulations based on the Korringa–Kohn–Rostoker coherent potential approximation method and the Boltzmann transport equation to calculate the thermal conductivity of 38 binary magnesium solid solutions with dilute solute atom concentration. Solute atoms can greatly reduce the thermal conductivity of magnesium. Phonon contribution is found to be less than 10 %. The machine learning feature screening methods are further applied to identify the key properties that influence their thermal conductivity the most. Different from the commonly used Linde's law, which states that the resistivity is proportional to the square of valence difference, the machine learning screening indicates that thermal conductivity is predominantly influenced by six features in total. Among them, the variance of the density of states of s + p, d + f orbitals at Fermi level is highly correlated to the electronic thermal conductivity of magnesium alloys. These correlations underscore the role of virtual bond states formed in magnesium alloys due to the presence of solute atoms. The developed method and uncovered physical mechanism can potentially be applied to other solid solution systems, which is an important step to achieve predictive design of high thermal conductivity metallic alloy.

Significant Enhancement of Negative Thermal Expansion Under Low Pressure in Cu2P2O7.

Much effort is made to achieve the negative thermal expansion (NTE) control, but rare methods reached the improvement of intrinsic NTE. In the present work, a significantly enhanced NTE is realized in Cu2P2O7 by applying low pressure. Especially, the volumetric coefficient of thermal expansion (CTE) of Cu2P2O7 reached to -50.0×10-6 K-1 (150-325K) under 0.25GPa, which is increased by 47.5% compared to its NTE in a similar temperature range under atmosphere pressure. This character enables a more effective manifestation of the thermal compensation role of Cu2P2O7 in composites. The enhanced NTE mechanisms are analyzed by high pressure synchrotron X-ray diffraction, neutron diffraction at variable temperature and pressure, as well as density functional theory (DFT) calculations. The results show that applied pressure accelerates the contraction of the distance between adjacent CuO layers and CuO columns. Meanwhile, the low-frequency phonon contribution to NTE in α-Cu2P2O7 is improved. This work is meaningful for the exploration of methods to enhance NTE and the practical application of NTE materials.

Influence of electron–phonon interaction on linear and nonlinear magneto-optical absorption properties in monolayer transition metal dichalcogenides

In this study, we investigate the linear and non-linear magneto-optical properties of TMDC monolayer semiconductors MX2 (M = Mo/W, X = S/Se) in a perpendicular magnetic field by evaluating the magneto-optical absorption coefficients (MOACs) and the refractive index changes (RICs) subject to the influence of electron–phonon interaction (EPI). Our results are achieved by considering the influence of electron couplings with acoustic (AC) and optical (OP) phonons via the absorption (AB) and emission (EM) mechanisms. When compared to the neglected EPI case, the intensity of the linear MOAC and RIC increases about 2.6–4 times and 5.3–10.5 times, respectively. The absorption peaks exhibit the blue-shifts, with the largest blue-shift observed for the OP-EM phonon scatterings, followed by the AC phonons and the smallest for the OP-AB phonon scatterings. Meanwhile, the greatest contribution to MOAC and RIC comes from the OP-AB phonons, which is followed by that of the AC phonons and the OP-EM phonons, respectively. The MoX2 group is more significantly affected by the scattering mechanism compared to the WX2 one. Although the OP-EM phonons contribution for the MoX2 group is much smaller than that of the other two interaction mechanisms, it nevertheless produces a very noticeable blue-shift. Meanwhile, for the WX2 group, all three mechanisms erect comparable results. The biggest (smallest) value of the linear MOAC and RIC are both founded in MoSe2 (MoS2). Notably, the absolute values of the non-linear MOAC and RIC terms increase by tens to hundreds of times, leading to the total MOAC terms being negative, contrary to when EPI is not taken into account, while the characteristics of the non-linear RIC curves also undergo considerable changes. Among the four TMDC materials, MoX2 is more significantly affected by the EPI effect than WX2.

Atomistic simulations of coherent thermoelectric transport in ultrathin pristine and decorated noble metals nanowires

Nanowires (NWs) are envisioned to be an important component of novel nanoscale electronic devices. Here, we perform atomistic simulations of coherent thermoelectric (TE) transport in free-standing ultrathin NWs of noble metals (viz. Au, Ag, Cu, Pt) cut along the [111] crystallographic direction using a non-equilibrium Greens function based first principles approach. Effect of decorating these NWs with Au or Pt atoms in an fcc environment, is also explored. Results of the calculated electronic structure show that all considered NWs, except the Pt and Pt-decorated NWs, are metallic and non-magnetic. Interestingly, Cu@Pt NW is found to be a magnetic semiconductor with an unequal band gap in ↑− and ↓−spin energy bands, while Pt NW and other Pt-decorated NWs (viz. Ag@Pt and Au@Pt) behave like a magnetic half-metal. To explore the TE potential of as-considered NWs, electrical conductance G, thermal conductance κT, and thermopower S are computed in the linear response regime. Notably, the metallic NWs exhibit a quantized G. Among these, pristine NWs show a quantized value 3G0 up to a temperature of 200 K, while Cu@Au NW preserves its quantized value 5G0 even at T exceeding 300 K. In thermal transport, valence electrons make a dominant contribution to the room-temperature κT of pristine NWs. The phononic contribution κph, however, goes up following decoration, with Pt-decorated NWs showing a pronounced increment (by a factor of ∼2). But, these NWs undergo a simultaneous reduction in the electronic contribution κel owing to half-metallic conduction, resulting in a net suppression of total thermal conductance κT. Moreover, Pt-decorated NWs show a manifold enhancement in zero-bias S, with Ag@Pt exhibiting the highest value ∼119μV/K. However, S can be augmented considerably by adjusting the chemical potential μ of electrodes, and an overall best S∼−890μV/K is found in Au NW for μ=0.575eV. In this way, TE figure of merit ZT is tunable in pristine NWs over the range 1−3.7. Correspondingly, the decorated NWs exhibit somewhat smaller S and ZT. Furthermore, spin-asymmetric electronic transport in Pt and Pt-decorated NWs results in net spin conductance Gs and spin thermopower Ss. It is found that the spin figure of merit ZsT, as high as 3.5, can be attained in Pt NW by controlling μ. Thus, noble metals NWs can be tailored for both thermoelectric and spin-thermoelectric applications. We have also investigated TE transport for the pristine NWs in the [110] direction, and found S and ZT to be comparatively much smaller. Such NWs may be useful as interconnects for low noise applications.

First-principles study of two-dimensional transition metal carbide M n+1 C n O2 (M = Nb,Ta)

In the present work, the three stable MXenes M n+1 C n O2 (M = Nb,Ta) are explored based on first-principles calculations. These materials are important derivatives of 2D materials and exhibit distinctive properties, holding vast potential in nanodevices. All these M n+1 C n O2 (M = Nb,Ta) materials exhibit outstanding superconducting performance, with corresponding superconducting transition temperatures of 23.00 K, 25.00 K, and 29.00 K. Analysis reveals that the high superconducting transition temperatures of MXenes M n+1 C n O2 (M = Nb,Ta) are closely associated with the high value of the logarithmic average of phonon frequencies, ωlog , and the strong electron–phonon coupling, attributed to the crucial contribution of low-frequency phonons. Additionally, we applied strain treatments of 2% and 4% to M n+1 C n O2 (M = Nb,Ta), resulting in varying changes in superconducting transition temperatures under different strains.

Contribution of individual phonon to the band gap renormalization in semiconductors

Understanding the origin of temperature-dependent bandgap in semiconductors is essential for their applications in photovoltaics, optoelectronic and space applications. In this regard the electron–phonon coupling is known to play a crucial role in the temperature dependence of the bandgap of semiconductors. Several models have also been proposed in this regard which are also found experimentally compatible; however, these models need to account for more information about the contribution of individual modes in band gap renormalization. The present report is an analytical attempt to do so by utilizing the Bose–Einstein oscillator model, thereby discussing a method for finding the individual renormalization term contributed by respective phonon modes to the overall bandgap. This study contributes to the fundamental understanding of the temperature variation of optical properties of semiconductors that correlates with the role of electron–phonon interaction.

Emergent facilitation and glassy dynamics in supercooled liquids

In supercooled liquids, dynamical facilitation refers to a phenomenon where microscopic motion begets further motion nearby, resulting in spatially heterogeneous dynamics. This is central to the glassy relaxation dynamics of such liquids, which show super-Arrhenius growth of relaxation timescales with decreasing temperature. Despite the importance of dynamical facilitation, there is no theoretical understanding of how facilitation emerges and impacts relaxation dynamics. Here, we present a theory that explains the microscopic origins of dynamical facilitation. We show that dynamics proceeds by localized bond-exchange events, also known as excitations, resulting in the accumulation of elastic stresses with which new excitations can interact. At low temperatures, these elastic interactions dominate and facilitate the creation of new excitations near prior excitations. Using the theory of linear elasticity and Markov processes, we simulate a model, which reproduces multiple aspects of glassy dynamics observed in experiments and molecular simulations, including the stretched exponential decay of relaxation functions, the super-Arrhenius behavior of relaxation timescales as well as their two-dimensional finite-size effects. The model also predicts the subdiffusive behavior of the mean squared displacement (MSD) on short, intermediate timescales. Furthermore, we derive the phonon contributions to diffusion and relaxation, which when combined with the excitation contributions produce the two-step relaxation processes, and the ballistic-subdiffusive-diffusive crossover MSD behaviors commonly found in supercooled liquids.

Thermophysical properties of equiatomic CrMnFeCoNi, CrFeCoNi, CrCoNi, and CrFeNi high- and medium-entropy alloys

High- and medium-entropy alloys have emerged as promising materials with significant potential for diverse technical applications. Notably, their use in the field of energy technology has attracted particular interest, where thermophysical properties play a pivotal role. In this context, this study aims to investigate the thermophysical properties, namely thermal expansion behavior, thermal diffusivity, specific heat capacity, thermal conductivity, and the electric resistivity of single-phase face-centered cubic alloys between 300 K and 773 K. In addition to thermal conductivity, the electric resistivity was measured. Based on the Wiedemann-Franz law, electronic and phononic contributions to the overall thermal conductivity were evaluated. Complementary insights into the electronic state of the investigated materials were obtained by electron spin resonance measurements, revealing the presence of short-range ordering in all alloys. The specific heat capacity is found to dominate the thermal conductivity. Furthermore, the study shows the decisive influence of chemical complexity on the thermophysical properties. Notably, the observed influences extend to the electronic thermal conductivity, pointing out the correlation between composition and heat transport properties. This comprehensive investigation provides a foundation for understanding and tailoring the thermophysical behavior of the studied alloys, offering valuable insights for their targeted deployment in advanced energy applications.

A new ferromagnetic semiconductor system of Eu[formula omitted]Sr[formula omitted]AgP [formula omitted] compounds: Crystallographic, magnetic, and magneto-resistive properties

Adjusting chemical pressure through doping is a highly effective method for customizing the chemical and physical properties of materials, along with their respective phase diagrams, thereby uncovering novel quantum phenomena. Here, we successfully synthesized Sr-doped Eu1−xSrxAgP (x=0.0−0.6) and conducted a comprehensive investigation involving crystallography, magnetization, heat capacity, and magnetoresistance. Utilizing X-ray diffraction and PPMS DynaCool measurements, we studied Eu1−xSrxAgP in detail. The hexagonal structure of parent EuAgP at room temperature, with the P63/mmc space group, remains unaltered, while the lattice constants expand. The magnetic phase transition from paramagnetism to weak ferromagnetism, as temperature decreases, is suppressed through the gradual introduction of strontium doping. Heat capacity measurements reveal a shift from magnon-dominated to predominantly phonon and electron contributions near the ferromagnetic phase with increasing doping levels. The resistivity–temperature relationship displays distinct characteristics, emphasizing the impact of Sr doping on modifying charge transport. Magnetoresistance measurements uncover novel phenomena, illustrating the adjustability of magnetoresistance through Sr doping. Notably, Sr doping results in both positive magnetoresistance (up to 20%) and negative magnetoresistance (approximately -60%). The resistivity and magnetic phase diagram were established for the first time, revealing the pronounced feasibility of Sr doping in modulating EuAgP’s resistivity. This study has provided valuable insights into the intricate interplay between structural modifications and diverse physical properties. The potential for technological advancements and the exploration of novel quantum states make Sr-doped Eu1−xSrxAgP a compelling subject for continued research in the field of applied physics.

Thermal and electrical properties of single‐phase high entropy carbide ceramics

AbstractThermal and electrical properties were investigated for five nominally phase‐pure high entropy carbide ceramics. The compositions (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C, (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Ta0.2Ti0.2W0.2Zr0.2)C, and (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C were synthesized by carbothermal reduction of oxides. The thermal diffusivity and heat capacity were measured from room temperature to 1800°C. The room temperature thermal conductivity ranged from 5.1 W/mK for (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C to 9.0 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C. The thermal conductivity increased over the temperature range with maximum conductivities of 19.6 W/mK measured for (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C to 29.7 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C at 1800°C. The electron contribution to thermal conductivity calculated from measured electrical resistivity varied from 41% to 52% of the total thermal conductivity. The tungsten and molybdenum containing compositions had higher phonon contributions while the niobium and chromium containing compositions had nearly equal electron and phonon contributions to thermal conductivity.

Mapping of Long-Wavelength Phonon Contribution in the Thermal Transport of Alloyed Semiconductor Superlattices.

The mapping of long-wavelength phonons is important to understand and manipulate the thermal transport in multilayered structures, but it remains a long-standing challenge due to the collective behaviors of phonons. In this study, an experimental demonstration of mapping the long-wavelength phonons in an alloyed Al0.1Ga0.9As/Al0.9Ga0.1As superlattice system is reported. Multiple strategies to filter out the short- to mid-wavelength phonons are used. The phonon mean-free-path-dependent thermal transport properties directly demonstrate both the suppression effect of the ErAs nanoislands and the contribution of long-wavelength phonons. The contribution from phonons with mean free path longer than 1 μm is clearly demonstrated. A model based on the Boltzmann transport equation is proposed to calculate and describe the thermal transport properties, which depicts a clear physical picture of the transport mechanisms. This method can be extended to map different wavelength phonons and become a universal strategy to explore their thermal transport in various application scenarios.

Temperature dependences of thermal conductivity of solid heterogeneous crystalline and amorphous materials: An empirical approach to the description in the high-temperature region

This paper presents a detailed analysis of the thermal conductivity behaviors exhibited by a diverse array of nanostructured materials, ranging from multilayer graphene nanocomposites to semiconductor-based nanostructures such as Bi0.5Sb1.5Te3 and In0.53Ga0.47As composites. The investigation extends to superlattices, nanowires, and hybrid nanostructures, encompassing materials like hexagonal boron nitride flakes, iron oxide nanoporous films, and organic-inorganic hybrid materials. The thermal conductivity of these materials is characterized by distinct trends, with some showcasing crystal-like behavior and others demonstrating glass-like characteristics. The analysis employs empirical expressions to discern the contributions of phonons and diffusons in crystal-like materials and incorporates Peierls contributions and Arrhenius-type terms for glass-like behavior. Noteworthy observations include deviations in fitting certain materials at lower temperatures and the identification of negative diffuson contributions in specific cases. These findings contribute to a nuanced understanding of thermal transport in nanostructured materials and have implications for applications in advanced thermal management systems and thermoelectric devices. The extracted parameters provide valuable insights for researchers exploring the thermal conductivity of diverse nanostructured materials.

Microstructural Examination and Thermodynamic Analysis of Sn-1.5Ag-0.5Cu-x mass% Ni Lead-Free Solder Alloys

The diminutive additions of nickel (Ni) element have been fused to Sn-1.5Ag-0.5 mass% Cu (SAC155) lead-free solder alloy. The study was examined experimentally and computationally (using JMatPro software program) the microstructural features, thermal behavior, density, thermal diffusivity, and conductivity as well as tensile stress strain of the Sn-1.5Ag-0.5Cu-x mass %Ni (x = 0.00, 0.05, 0.10, 0.20, and 0.50) solder alloys (SAC155-xNi). The fusing additions of Ni have a little impact on the melting point of SAC155 alloy which increasing from 502 to 504.2K\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$504.2 K$$\\end{document}. The microstructure of SAC155 solder alloy included coarse grains of β-Sn besides, large eutectic regions, and embedded IMCs of Ag3Sn and Cu6Sn5. The computed values of Gibbs free energy (G) during solidification of the β-Sn phase, Ag3Sn, and Sn3Sn4 IMCs show the stability at -130.7×103J.kg-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$- 130.7 \ imes 10^{3} {\ ext{J}}{\ ext{.kg}}^{ - 1}$$\\end{document}, -157.7×103J.kg-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$- 157.7 \ imes 10^{3} {\ ext{J}}{\ ext{.kg}}^{ - 1}$$\\end{document}, and -377.13×103J.kg-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$- 377.13 \ imes 10^{3} {\ ext{J}}{\ ext{.kg}}^{ - 1}$$\\end{document}, respectively. The SAC155-xNi alloys involved finer β-Sn grains, large fibrous eutectic regions, (Cu,Ni)6Sn5 and (Cu,Ni)3Sn4 IMCs. The G of Cu6Sn5 decreased from -233.1×103J.kg-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$- 233.1 \ imes 10^{3} {\ ext{J}}{\ ext{.kg}}^{ - 1}$$\\end{document} to -317.9×103J.kg-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$- 317.9 \ imes 10^{3} {\ ext{ J}}{\ ext{.kg}}^{ - 1}$$\\end{document} when Ni content increased up to 0.25 mass %, then stable and steady at -318.4×103J.kg-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$- 318.4 \ imes 10^{3} {\ ext{J}}{\ ext{.kg}}^{ - 1}$$\\end{document} with more addition of Ni element. The formation of the (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 IMCs is motivated by the lowest Gibbs free energy, especially when Ni mass% is added to a sufficient level. The measured and computed values of specific heat at constant pressure (Cp) of SAC155-xNi alloys show a good matching especially at lower temperatures and a little mismatch at high temperatures which decreases with increasing Ni content. The activation energy of atomic arrangement (Q) increased from 11.36 to 13.41kJ.mole-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$13.41 {\ ext{kJ}}{\ ext{.mole}}^{ - 1}$$\\end{document} with increasing Ni content in SAC155-xNi alloys. Thermal diffusivity (α) and conductivity (κ) of SAC155-xNi gradually decreased with increasing temperature in the range from 303 to 423 K and/or Ni content in alloys. The measured values of (κ) are slightly lower than the computed value at similar temperatures of the SAC155-xNi alloys. The decrease in (κ) may be assigned to scattering the electrons or reducing the phonon contributions due to the presence of various solute atoms and different IMCs. The results of stress-strain graphs reveal the enhancement of YS and UTS for all Ni-containing alloys. The improvement of the yield stress (YS) and ultimate tensile strength (UTS) of Ni-containing alloys is attributed to the uniform distribution of the IMCs, the reduction of β-Sn grain size, and the smoothed enlargement of the eutectic region.

Tuning charge density wave of kagome metal ScV6Sn6

Compounds with a kagome lattice exhibit intriguing properties and the charge density wave (CDW) adds an additional layer of interest to research on them. In this study, we investigate the temperature and magnetic field dependent electrical properties under a chemical substitution and hydrostatic pressure of ScV6Sn6, a non-magnetic CDW compound. Substituting 5% Cr at the V site or applying 1.5 GPa of pressure shifts the CDW from 92 K to ∼ 50 K. This shift is attributed to the movement of the imaginary phonon band, as revealed by the phonon dispersion relation. The longitudinal and Hall resistivities respond differently under these stimuli. The magnetoresistance (MR) retains its quasilinear behavior under pressure, but it becomes quadratic after Cr substitution. The anomalous Hall-like behavior of the parent compound persists up to the respective CDW transition under pressure, after which it decreases sharply. In contrast, the longitudinal and Hall resistivities of Cr substituted compounds follow a two-band model and originate from the multi carrier effect. These results clearly highlight the role of phonon contributions in the CDW transition and call for further investigation into the origin of the anomalous Hall-like behavior in the parent compound.