Lattice Conductivity Research Articles

Chemical short-range order increases the phonon heat conductivity in a refractory high-entropy alloy

We study the effects of the chemical short-range order (SRO) on the thermal conductivity of the refractory high-entropy alloy HfNbTaTiZr using atomistic simulation. Samples with different degrees of chemical SRO are prepared by a Monte Carlo scheme. With increasing SRO, a tendency of forming HfTi and TiZr clusters is found. The phonon density of states is determined from the velocity auto-correlation function and chemical SRO modifies the high-frequency part of the phonon density of states. Lattice heat conductivity is calculated by non-equilibrium molecular dynamics simulations. The heat conductivity of the random alloy is lower than that of the segregated binary alloys. Phonon scattering by SRO precipitates might be expected to reduce scattering times and, therefore, decrease thermal conductivity. We find that, in contrast, due to the increase of the conductivity alongside SRO cluster percolation pathways, SRO increases the lattice heat conductivity by around 12 %. This is expected to be a general result, extending to other HEAs.

Study of Mechanical, Optoelectronic, and thermoelectric aspects of lithium-based double perovskites Li2AgSbX6 (X=Cl, Br, I) for energy harvesting applications

Inorganic double perovskites appear to be incredible materials for renewable energy purposes, particularly in thermoelectric generators and solar cells. This article systematically examined the stability and various characteristics, including mechanical, thermodynamic, optical, and transport features of Li2AgSbX6 (X=Cl, Br, I), based on density functional theory (DFT) using Wien2k. The finding of formation energy is used to ensure thermodynamic strength and evaluate the tolerance factor for their structural integrity. Mechanical stability is verified by fulfilling the Born criteria involving elastic constants. The directional lattice conductivity and Debye temperature have been assessed using Navier’s velocities. The distinctive optoelectronic characteristics have been explored by adjusting the band gap from 1.40 to 0.49 eV through the varying halide ions (from Cl to I). We also examined various optical features such as absorption bands, refraction, light energy dispersion, and optical loss of the investigated materials. Key thermoelectric characteristics, including the Seebeck effect, conductivities, and performance, have been analyzed across temperatures ranging from 200 to 600 K. The high figure of merit and minimal lattice vibration at room temperature make Li2AgSbX6, double perovskites (DPs), promising for thermoelectric applications.

Thermoelectric properties of graphene through BN-ring doping: A theoretical investigation

Although graphene presents excellent transport properties, its potential for thermoelectric applications is still limited due to its low Seebeck coefficient and high thermal conductivity. Efforts to enhance its thermoelectric properties have involved the usage of carbon-based nanoribbons (Zheng et al., 2012; Hossain et al., 2016) [1,2], strain engineering (Nguyen et al., 2015), and heteroatom co-doping, particularly with nitrogen and/or boron atoms (Wang et al., 2018) [3]. In this work, multiscale simulation approaches combining density functional theory calculations and semi-empirical models are used to investigate the thermoelectric properties of graphene via borazine (B3N3)-ring doping. In particular, the bandgap engineering obtained by this doping technique (Caputo et al., 2022) can separate opposite electron and hole contributions and therefore results in a significant enhancement of the Seebeck effect and, accordingly, of the power factor. The results obtained are not only dependent on the concentration of B3N3 rings but are also notably influenced by their orientation configuration. Furthermore, the effects of distribution and rotational disorders are also considered, clarifying the thermoelectric properties of realistic systems. Lastly, the thermal lattice conductance is estimated revealing a substantial reduction of up to 40% compared to pristine graphene opening up the possibility of enhancing the thermoelectric efficiency of BNC materials. The present theoretical approach highlights how BN-ring doping can refine the thermoelectric properties of graphene, offering a pathway for enhancing its suitability in practical thermoelectric applications.

Thermal properties of In2O3 and α-Ga2S3 compounds

We investigate the thermal conductivity of In₂O₃ and α-Ga₂S₃ lattices using simulations based on the Boltzmann phonon transport equation (BTE) and first-principles calculations. The study employs a real-space finite displacement method to determine the second- and third-order interatomic force constants (IFCs), which are critical for solving the BTE iteratively. Our findings indicate that In₂O₃ and α-Ga₂S₃ exhibit relatively low thermal conductivities compared to other wide-bandgap semiconductors. At room temperature (300 K), the calculated isotropic thermal conductivity of cubic In₂O₃ is 16.2 Wm−1K⁻1. For monoclinic α-Ga₂S₃, the three principal components of thermal conductivity are 17.0, 20.7, and 15.2 W m⁻1 K⁻1, depending on the crystallographic direction. This low thermal conductivity is primarily attributed to significant phonon scattering via three-phonon processes. Furthermore, we estimate the phonon mean free path (MFP) to be approximately 56 nm for In₂O₃ and between 198 and 231 nm for α-Ga₂S₃, varying with crystal orientation. These findings offer valuable insights into the thermal transport properties of In₂O₃ and α-Ga₂S₃, highlighting their potential for thermoelectric applications while delineating the constraints these properties impose on their use in electronic devices.

Thermal transport and topological analyses of the heat-carrying modes and their relevant local structures in variously dense amorphous alumina

Engineering the thermal conductivities of amorphous materials is important for thermal management of various semiconducting devices. However, controlling the heat carriers—long-range propagating propagons and short-range hopping diffusons—in disordered lattices is difficult because the carriers are strongly correlated with lattice disorder. To clarify the relationship between lattice disorder and heat conduction, we must simultaneously investigate the important local structures hidden in a disordered system and the microscopic transport characteristics of propagons and diffusons. Here, we explore the variations in spectral thermal conductivity and the relevant local structures in amorphous alumina (a-Al2O3) at different densities by performing the spectral thermal transport and persistent homology analyses. As the density increases, the thermal conductivity of the high-frequency diffusons linearly increases but those of the propagons and low-frequency diffusons remain constant. The density increase enhances the local strain, thereby increasing the mean free paths of the high-frequency diffusons. The density of states competes with diffusivity, lowering the sensitivity of the density response to the thermal conductivity of low-frequency heat carriers. Furthermore, from the obtained topological features of the connections between the oxygen atoms, we inferred that the collapsed network of six-coordinated AlO6 octahedron clusters underlies the transport of high-frequency diffusons. Besides revealing the conductive pathways of heat-carrying modes in disordered lattices, topology-assisted spectral thermal transport analysis is useful for tailoring the thermal conductivities of amorphous materials.

Investigating the physical characteristics of inorganic cubic perovskite CsZnX3 (X = F, Cl, Br, and I): An extensive ab initio study towards potential applications in photovoltaic perovskite devices

CsZnX3 (X = F, Cl, Br, I) cubic perovskite compounds were investigated using Wien2K with PBE and mBJ energy exchange potentials to determine their structural, electronic, optical, thermoelectric, and thermodynamic properties. The results of Phonon vibrational frequency, formation energy, and cohesive energy show thatall compounds arestable. The electronic properties revealed that CsZnF3 has the highest indirect bandgap as an insulator, followed by CsZnCl3 and CsZnBr3, and CsZnI3 has the lowest indirect bandgap. CsZnX3 (X = Cl, Br, I) are classified as p-type semiconductors based on their electronic structure and the positive values of the Seebeck coefficient. High transparency was shown by low visible and infrared absorption. The investigated compounds exhibit high power factor and high figure of merit (ZT), which exceeds 0.7 over the temperature range 300–800 K. As the material’s temperature rises, its lattice heat conductivity decreases in accordance with thermodynamics. However, when the temperature exceeds the Debye temperature, the volume heat capacity matches the Dulong-Petit limits and the experimental results.

Divacancy and resonance level enables high thermoelectric performance in n-type SnSe polycrystals

N-type polycrystalline SnSe is considered as a highly promising candidates for thermoelectric applications due to facile processing, machinability, and scalability. However, existing efforts do not enable a peak ZT value exceeding 2.0 in n-type polycrystalline SnSe. Here, we realized a significant ZT enhancement by leveraging the synergistic effects of divacancy defect and introducing resonance level into the conduction band. The resonance level and increased density of states resulting from tungsten boost the Seebeck coefficient. The combination of the enhanced electrical conductivity (achieved by increasing carrier concentration through WCl6 doping and Se vacancies) and large Seebeck coefficient lead to a high power factor. Microstructural analyses reveal that the co-existence of divacancy defects (Se vacancies and Sn vacancies) and endotaxial W- and Cl-rich nanoprecipitates scatter phonons effectively, resulting in ultralow lattice conductivity. Ultimately, a record-high peak ZT of 2.2 at 773 K is achieved in n-type SnSe0.92 + 0.03WCl6.

A density functional theory study of the structural, mechanical, optoelectronics and thermoelectric properties of InGeX3 (X = F, Cl) perovskites

Structural, electronic, lattice dynamics, optical, elastic, and thermoelectric features of Indium based Perovskite InGeX3 (X = F, Cl) are studied by using WIEN2k code within density functional theory DFT. A level of the Boltzmann transport theory is used to derive electronic transport coefficients together with anticipated electronic relaxation times. These compounds exhibit stability and are cubic with the space group Pm-3m 221, according to the structural analysis. The band structure having the 2.15 eV and 1.29 eV band gap and density of state (DOS) are calculated for electronic characteristics, indicating that both compounds are semiconducting. For the analysis of elastic characteristics, elastic constants, bulk modulus (49.99, 22.69), Poisson’s ratio (0.343, 0.261), anisotropy factor (0.52, 0.59), and Pugh’s ratio (2.87, 1.75) are examined. The ductile nature of the compounds is described by Pugh’s ratio, and the ionic nature can be ascertained by evaluating the Cauchy pressure. In the energy range of 0–10 eV, optical features like reflectivity, optical conductivity, refractive index, extinction coefficient and absorption coefficient are computed. These compounds broad-range absorption in the UV spectrum suggests that they could be good optoelectronic device candidates. The transport feature like Seebeck coefficient, thermal and lattice conductivity, power factor, electrical conductivity, and figure of merit zT (0.99, 0.98) can be calculated against temperature. The chemical potential against an excellent thermoelectric property of InGeX3 (X = F, Cl) have high figure of merit due to high Seebeck and electrical conductivity. These predicted outcomes indicated that both compounds are suitable candidates for thermoelectric applications. Such compounds can replace with other renewable energy sources in thermoelectric devices because of their powerful thermoelectric response.

A layered perovskite La2Ni1-xSbxO4+δ-molten carbonate dual-phase membrane for CO2 separation

A new series of layered perovskite K2NiF4 structure La2Ni1-xSbxO4+δ (LNSx, x = 0, 0.025, 0.05) were used to prepare the LNSx-molten carbonate (MC) dual-phase membrane for CO2 separation. Sb doping at the Ni site is expected to enhance CO2 permeability and improve the resistance towards CO2/carbonate corrosion. In this work, the CO2 permeability of the LNSx- MC membrane was investigated for CO2-containing atmospheres with and without oxygen, and correlated with the lattice characteristics, microstructure, chemical bond, and conductivity of LNSx support. The result shows that the introduction of Sb improves the structure symmetry and increases the interstitial oxygen concentration, which is beneficial for oxygen ion transport. The superior CO2 permeability of Sb-doped sample is confirmed by the higher permeation fluxes with value of 0.15 mL min−1 cm−2 at 800 °C of LNS0.025-MC dual-phase membrane in 50% CO2 + 50% N2. In addition, the LNS0.025-MC dual-phase membrane achieves a great enhancement in chemical and structural stability compared to the LNS0. In the simulated flue gas 15% CO2 + 10% O2 + 75% N2, the LNS0.05-based dual phase membrane shows a high permeation flux of 1.07 mL min−1 cm−2 at 800 °C, which is 2 times higher than that of LNS0-based dual-phase membrane.

Footprints of scanning probe microscopy on halide perovskites.

Scanning probe microscopy (SPM) and advanced atomic force microscopy (AFM++) have become pivotal for nanoscale elucidation of the structural, optoelectronic and photovoltaic properties of halide perovskite single crystals and polycrystalline films, both under ex situ and in situ conditions. These techniques reveal detailed information about film topography, compositional mapping, charge distribution, near-field electrical behaviors, cation-lattice interactions, ion dynamics, piezoelectric characteristics, mechanical durability, thermal conductivity, and magnetic properties of doped perovskite lattices. This article outlines the advancements in SPM techniques that deepen our understanding of the optoelectronic and photovoltaic performances of halide perovskites.

Thermoelectric coupling effect in BNT-BZT-xGaN pyroelectric ceramics for low-grade temperature-driven energy harvesting

Pyroelectric energy harvesting has received increasing attention due to its ability to convert low-grade waste heat into electricity. However, the low output energy density driven by low-grade temperature limits its practical applications. Here, we show a high-performance hybrid BNT-BZT-xGaN thermal energy harvesting system with environmentally friendly lead-free BNT-BZT pyroelectric matrix and high thermal conductivity GaN as dopant. The theoretical analysis of BNT-BZT and BNT-BZT-xGaN with x = 0.1 wt% suggests that the introduction of GaN facilitates the resonance vibration between Ga and Ti, O atoms, which not only contributes to the enhancement of the lattice heat conduction, but also improves the vibration of TiO6 octahedra, resulting in simultaneous improvement of thermal conductivity and pyroelectric coefficient. Therefore, a thermoelectric coupling enhanced energy harvesting density of 80 μJ cm−3 has been achieved in BNT-BZT-xGaN ceramics with x = 0.1 wt% driven by a temperature variation of 2 oC, at the optical load resistance of 600 MΩ.

Structural, optical, and electrical characteristics of Ge18Bi4Se78 chalcogenide glass for optoelectronic applications

The melt quenching and thermal evaporation techniques were used to produce the chalcogenide glass Ge18Bi4Se78 powder and thin film samples, respectively. The as-deposited and annealed thin films at (180, 200, 300, 320 °C) are characterized by X-ray diffractometer and scanning electron microscopy. The Urbach tail energy Eu and the optical energy gap Eop are investigated. As well, the Swanepoel method revealed that the refractive index exhibited normal dispersion behavior. In addition, the single oscillator, dispersion energies, the lattice dielectric constant, εL, plasma frequency, ωp, and optical conductivity, σop were all examined. The electrical conductivity and the activation energies for as-deposited and annealed thin films were calculated. Whereas the J-E properties of the as-deposited and annealed films indicated varied ranges of negative differential conductance NDC depending on the annealing temperatures.

The magnetocaloric, magnetic, optical, and thermoelectric properties of EuB6 compound: DFT and Monte Carlo study

AbstractThe hexaboride EuB6 has been proven to have qualities that theoretically travel from being electronic to being magneto‐caloric. Under GGA‐PBE and GGA + SOC + U schemes, first‐principles calculations have been used to examine the electronic band structure and density of states. The magnetic moment and the interaction constant have each been calculated using DFT. Additionally, the thermoelectric properties are considered within the particular transport restrictions in order to determine the dimensionless figure of merit (ZT). The extremum of the ZT for EuB6 is determined by using the Seebeck, electrical, thermal, and lattice conductivity coefficients, which are computed. At 1800 K, a maximum ZT of 0.22 is discovered. The computed values of optical conductivity, electron energy loss, absorption coefficient, dielectric tensor, refractive index, and extinction coefficient throughout the range of 0–13 eV anticipate the optical considerations of such an alloy. The infrared spectrum is that where this chemical is active. The critical temperature (Tc) has been determined using the Metropolis algorithm and the Monte Carlo simulation. The material exhibits a ferromagnetic to paramagnetic phase transition, as indicated by temperature‐dependent magnetization. The magnetocaloric efficiency of this material can be measured using the magnetic entropy change (−ΔSm) and the relative cooling power.

Manipulation phonon energy for improved thermometric sensitivity of only-core nanoparticles

Luminescent nano thermometry using upconversion nanoparticles (UCNPs) has gained attention in recent years due to its potential advantages over conventional methods. One major challenge in practical applications of nanothermometers is achieving high sensitivity. While efforts have been made to improve the sensitivity of individual core nanoparticles, there are few reports on incorporating phonon energy and local crystal field distortions to improve the sensitivity of only-core upconversion nanoparticles. In this study, we propose a new approach to improve the sensitivity of only-core UCNPs thermometers through phonon tuning and self-photogenic heating. We use the ratio of the intensity of two bands (centered at 520 nm and 540 nm) based on dopant Er3+ as a referenced signal for optical sensing of temperature. We use a host material NaYF4 doped with K+ to produce local crystal field changes at the interface, modifying the phonon energy mode. As the temperature increases, the vibrational mode cannot propagate smoothly along the crystal axis throughout the crystal, disrupting the direction of lattice heat conduction and producing a significant local thermal effect on the nanoscale. This leads to a significant increase in sensitivity, and we achieve an enhanced thermal sensitivity more than twice that of conventional core-only nanoparticles.

Modeling Mesoporous 3D-Printed Lattice Electrodes for Energy Storage

3D printing could offer the versatility to design and manufacture energy storage devices on demand. The precision and material flexibility of 3D printing is ideal for integrating porous electrodes that can enhance electrochemical performance[1]. This work analyzes the electrical conductivity of 3D-printed mesoscale strut lattices at the 100 μm – 1 mm scale with 40 – 90 % volumetric porosity to develop optimal electrodes for energy storage devices. We use a graph-theory-based model[2] to compute the conductivity of multiple 3D lattice types with either solid conducting struts or struts coated with conductive material. These structures show 3 – 5X higher conductivity than random conductive foams that lack an internal periodic mesostructure[3]. Using microstereolithography, we 3D print samples with high-resolution struts (< 70 µm) that maintain their shape and achieve high conductivity after carbonization at 700 ˚C. By tuning the lattice architecture, we manipulate the tradeoff between conductivity, weight, and porosity, validating our simulations with experimental measurements. These results demonstrate that that body-centered cubic (BCC) strut lattices have optimal conductivity per weight compared with other lattice types. Implementing these 3D-printed conductive lattices as supercapacitor electrodes, we see that the lattice architecture impacts the gravimetric capacitance of the devices as well as the mechanical strength, with octet structures outperforming both cubic and BCC lattices. Electrochemical impedance spectroscopy (EIS) shows that 3D-printed electrodes with higher porosity exhibit higher gravimetric double layer capacitance and lower charge transfer resistance, making them ideal candidates for use in supercapacitor electrodes as free-standing 3D hosts for active materials. CV characterization of the electrodes also illustrates how our graph theory-based model for 3D lattices can predict the optimal structure for energy storage. This model can also serve to predict electrode performance and tailor design for integration of higher surface area nanoporous materials on these conductive 3D printed scaffolds. This allows us to guide the design of 3D printed electrodes to minimize charge transfer resistance and achieve an optimal balance between gravimetric and volumetric energy density for device applications.[1] J. Zhao, Y. Zhang, X. Zhao, R. Wang, J. Xie, C. Yang, J. Wang, Q. Zhang, L. Li, C. Lu, Y. Yao, Advanced Functional Materials 2019, 29, 1900809.[2] J. E. Huddy, M. S. Rahman, A. B. Hamlin, Y. Ye, W. J. Scheideler, Cell Reports Physical Science 2022, 3, 100786.[3] F. G. Cuevas, J. M. Montes, J. Cintas, P. Urban, J Porous Mater 2008, 16, 675. Figure showing (a) designed octet (blue), cubic (orange), and BCC (red) lattice types as well as (b) SEM images of their experimental 3D-printed counterparts and (c) measured electrical resistance. Figure 1

Optical conductivity of bilayer dice lattices

Optical conductivity of bilayer dice lattices

Porosity effect on the thermal and mechanical properties of U-50Zr alloy: A molecular dynamics study

The U-50Zr alloy is a promising candidate for helical cruciform fuel application, for the superior performance in neutronics and heat transfer properties. Under in-pile conditions, the formation and aggregation of fission gas products would introduce porosity effect, and further degrade the mechanical-thermal physical properties. However, no porosity model has been established for U-50Zr alloy. In this work, the Young's modulus and lattice conductivity for U-50Zr were predicted via molecular dynamics (MD) simulations with modified embedded atom method potential. The effective Young's modulus was obtained by multi-dimensional elongation tests and Voigt averaging scheme, and the phonon conductivity was computed with reverse non-equilibrium molecular dynamics method. The electron conductivity was estimated by Wiedemann-Franz Law with published resistivity data. To fulfill porosity effect modeling, void generation technique was utilized into the MD models, and effective medium theory was incorporated into the approximations of electron conductivity. Good agreements with experimental data were achieved to verify the research methodology. The semi-empirical models on porosity effects for U-50Zr were established, which could provide preliminary predictions of Young's modulus and thermal conductivity.

Graph Theory Design of 3D Printed Conductive Lattice Electrodes

Abstract3D printing has the promising capability to fabricate engineered lattice structures with broadly tunable surface area and optimal geometries for maximizing structural and functional properties. This study characterizes the electrical conductivity of 3D lattices of varying size, structure, and porosity to guide additively manufactured electrode design in energy storage devices. Graph theory‐based calculations and experiments comparing the conductivity of multiple strut lattice structures and illustrating the scaling laws governing architectures with either coated or solid conductive struts are presented. The lightweight lattices explored here show higher conductivity than random foams that lack a periodic mesostructure. It is experimentally demonstrated that the 3D lattice type influences the specific capacity when employed in supercapacitors, outperforming 2D supercapacitor counterparts, and other 3D printed electrodes while allowing for optimization of the design for different energy storage applications. Additionally, it is shown that tuning the physical structure of the lattices allows for precise control over the electrical response to mechanical loading, as confirmed through experimental measurements. The lattice structure programs the electrodes’ mechanical stiffness, with higher relative density samples showing higher Young's modulus. These results can serve to guide the design of 3D printed electrodes in a variety of electrochemical and electromechanical device applications.

Electronic and Thermoelectric Transport Properties of CaAgP from First Principles

Recent experimental and theoretical progress on semiconducting CaAgP prompted us to investigate in detail the electrical and thermal transport properties of this hexagonal pnictide, using first-principles calculations based on the density functional theory. In contrast to using a standard generalized gradient approximation, employing a hybrid Heyd–Scuseria–Ernzerhof functional yields its semiconducting nature, in agreement with the experimental observation with a bandgap of ∼0.15 eV. The narrow band gap semiconductor CaAgP, which under negative (chemical) pressure has been shown to turn into a nodal-line semimetal, is found to be dynamically stable, with a gapped electronic band structure when a hybrid functional is used. This is in an attractive range for applications in thermoelectric devices, and we have determined the lattice and electronic conductivity as a function of doping, which indeed predicts a promising thermoelectric performance, particularly for p-doped CaAgP.

Study of optoelectronic, thermoelectric, mechanical, and thermodynamic properties of Cs2NaTlX6 (X = Cl, Br, I) for energy harvesting

The inorganic double perovskites are remarkable materials for renewable energy which can be realized through solar cells and thermoelectric generators. Here, we have comprehensively elaborated the stability, mechanical, thermodynamic, optical and transport characteristics. The formation energy is computed to ensure thermodynamic validity and the tolerance factor is assessed for structural existence. The elastic constants satisfied the Born criteria and mechanical stability. Naviera's velocities have been used to study the Debye temperature and directional lattice conductivity. Modifying the band gap from 3.1 to 0.58 eV by halide ions (Cl to I) probes the distinct optoelectronic characteristics. Absorption bands, dispersion of light energy, refraction, and optical loss explain the optical characteristics. In addition, the above thermoelectric factors like conductivities, Seebeck effect, and performance are studied in the temperature range of 100–600 K. Large figure of merit and extremely low lattice vibration at room temperature indicate their significance for thermoelectric devices.