Reduction In Thermal Conductivity Research Articles

Enhanced Thermoelectric Properties of FeSe2 Alloys by Lattice Thermal Conductivity Reduction by Cl Doping

Enhanced Thermoelectric Properties of FeSe2 Alloys by Lattice Thermal Conductivity Reduction by Cl Doping

Evaluation into the effect of lignocellulosic biochar on the thermal properties of shape stable composite phase change materials

Biochar is suitable for preparing shape stable composite phase change materials (sscPCMs) due to the advantages of cost-effective, environmentally, and sustainability. However, the heat properties of biochar-based sscPCMs were not consistent. To investigate how different types of biochar influence the thermal properties of sscPCMs, three types of sscPCMs were successfully prepared using peanut shell biochar (PSC), poplar wood biochar (PWC), and corn straw biochar (CSC) as framework materials and combined with stearic acid (SA). A comprehensive analysis of the thermal properties of three sscPCMs was performed, taking into account thermal conductivity, phase change latent heat, encapsulation efficiency, crystallization rate, and energy storage efficiency. The study indicated that among the three types of sscPCMs, SA/PWC sscPCMs demonstrated excellent comprehensive performance. The phase change latent heat of SA/PWC reached 100.13 J/g, and the thermal conductivity was 0.38 W/mK. Compared to SA/PSC, the phase change latent heat of SA/PWC increased by 45.96 %, with only a 28.30 % reduction in thermal conductivity. In comparison to SA/CSC, the thermal conductivity of SA/PWC improved by 18.75 %, while the phase change latent heat decreased by only 14.02 %. In addition, the proportions of cellulose, hemicellulose, and lignin played a crucial role in determining the thermal properties of sscPCMs. This study clarified the mechanism by which biochar influences the thermal characteristic of sscPCMs, offering valuable insights for choosing biochar framework materials.

Synergistic Suppression of Bipolar Effect and Lattice Thermal Conductivity Leading to High Average Figure of Merit in Bi0.4Sb1.6Te3 Materials through Alloying with AgSbTe2.

Bismuth telluride-based materials have been widely used in commercial thermoelectric applications due to their excellent thermoelectric performance in the near-room-temperature range, yet further improvement of their thermoelectric properties is still necessary. Moreover, the narrow band gap of these materials results in a bipolar effect at elevated temperatures, which causes severe degradation of the thermoelectric performance. In this work, the commercial Bi0.4Sb1.6Te3 was alloyed with AgSbTe2 by using high-energy ball milling method combined with spark plasma sintering. It was found that ball milling can effectively reduce the lattice thermal conductivity of the samples. The alloying of AgSbTe2 leads to a gradual increase in hole carrier concentration, resulting in an enhanced electrical conductivity and optimized power factor. Additionally, the bipolar effect is also weakened due to the increased hole carrier concentration. Furthermore, the substitution of Ag in the Bi/Sb sublattice causes further reduction in the lattice thermal conductivity. Ultimately, the sample alloyed with 0.15 wt % AgSbTe2 demonstrates its best thermoelectric performance with a maximum zT of 1.35 at 393 K, showing a 20.5% improvement compared to the commercial sample. Besides, its average zT reaches a high value of 1.25 between 303 and 483 K, with a 27.6% improvement compared to that of the commercial sample.

Pressure-regulated rotational guests in nano-confined spaces suppress heat transport in methane hydrates

Materials with low lattice thermal conductivity are essential for various heat-related applications like thermoelectrics, and usual approaches for achieving this rely on specific crystalline structures. Here, we report a strategy for thermal conductivity reduction and regulation via guest rotational dynamics and their couplings with lattice vibrations. By applying pressure to manipulate rotational states, we find the intensified rotor-lattice couplings of compressed methane hydrate MH-III can trigger strong phonon scatterings and phonon localizations, enabling an almost three-fold suppression of thermal conductivity. Besides, the disorder in methane rotational dynamics results in anharmonic interactions and nonlinear pressure-dependent heat transport. The overall guest rotational dynamics and heat conduction changes can be flexibly regulated by the rotor-lattice coupling strength. We further underscore that this reduction mechanism can be extended to a wide range of systems with different structures. The results demonstrate a potentially universal method for reducing or controlling heat transport by developing a hybrid system with tailored molecular rotors.

Effects of sintering temperatures on the thermal conductivity and microstructural evolution of yttrium hydride monoliths by spark plasma sintering

In this study, YHx (where x represents the H/Y ratio) monoliths were fabricated using Spark Plasma Sintering (SPS), employing yttrium hydride powder as the raw material. The effects of different sintering temperatures (800 °C∼1200 °C) on the thermal conductivity and microstructural evolution of the YHx monoliths, including porosity, grain size, precipitated phases, and internal defects, were investigated. The results indicate that the sintering temperature exerts a significant influence on thermal conductivity and microstructural evolution. Notably, the thermal conductivity of these samples initially increases with rising sintering temperature, but subsequently decreases under identical testing conditions. This phenomenon is primarily attributed to the effects of porosity and precipitate phase. Furthermore, the presence of twin crystals also contributes to the reduction in thermal conductivity. The procedures provide an initial framework for understanding the relationship between thermal conductivity and the evolution of microstructure.

Investigation of Thermal Properties of Rare-Earth X2-Type Monosilicates through High-Entropy Design and Defect Engineering

Rare earth X2-type monosilicates with low thermal conductivity are crucial for material performance in extreme environments. Three high-entropy ceramics, (Er1/4Tm1/4Yb1/4Lu1/4)2SiO5, (Y1/4Er1/4Tm1/4Yb1/4)2SiO5, and (Gd1/4Dy1/4Er1/4Yb1/4)2SiO5, were synthesized in this study. Among these, the thermal conductivity of (Y1/4Er1/4Tm1/4Yb1/4)2SiO5 at 1200 °C is 1.03 W m–1 K–1. Concurrently, the stable existence of dislocation arrays was observed in the quaternary high-entropy monosilicate system of (Y1/4Er1/4Tm1/4Yb1/4)2SiO5. The scattering of medium-frequency phonons can be enhanced by the presence of dislocations, leading to a reduction in thermal conductivity. This provides direct experimental evidence supporting the feasibility of reducing material thermal conductivity through high-entropy design by introducing dislocations.

Reduced Thermal Conductivity of Constricted Graphene Nanoribbons for Thermoelectric Applications

Graphene nanoribbons (GNRs) hold promise as thermoelectric (TE) materials due to their advantageous electronic properties compared to conventional candidates. However, a key challenge to enhancing the TE performance of GNRs lies in reducing the thermal conductivity while maintaining the electronic transport properties. To address this challenge - this study proposes a GNR-based structure featuring nanoscale constrictions named graphene nano constrictions (GNCs). This work systematically analyzes the thermal transport properties of these GNCs and compares them to conventional GNRs. Non-Equilibrium Molecular Dynamics (NEMD) simulations were employed to evaluate the lattice thermal conductivity of the material, and a marked reduction of thermal conductivity exceeding 74% was observed in the proposed structures. Furthermore, it is revealed that the thermal conductivity of these structures can be further tailored by manipulating their physical geometry, focusing on the length and the constriction dimensions. Additionally, superlattice counterparts of the GNCs composed of graphene and h-BN are explored in this study. Subsequently, an 88% reduction of lattice thermal conductivity is observed in the superlattice counterparts of GNCs compared to GNRs. Overall, this study demonstrates the effectiveness of nanoscale constrictions in manipulating the thermal conductivity of GNR-based structures, creating a path for optimizing their TE performance and potential device applications.

Improved thermoelectric performance of α- and β- Cu2Se through suppression of hole density using extrinsic copper vacancies

Modulating Cu+ ion disorder in Cu2Se can enable control over the polymorphism and the carrier density leading to enhanced thermoelectric properties for both α- and β-Cu2Se. Here we report that the incorporation of Cr3+ into the Cu2Se crystal lattice facilitates the stabilization of α-Cu2Se at 300 K leading to a large (∼140%) reduction in the carrier density both below and above the phase transition. This is attributed to the reduction in the density of intrinsic copper interstitials (Cui∙) within the Cu(2-δ-λ)(CrCu..)λ(VCu′)δ(Cuix)δ-2λ(h∙)δ-2λSe crystal lattice. Such optimization of the carrier density led to a large (63%) increase in the thermopower and a drastic (46%) reduction in the total thermal conductivity for both α- and β-Cu2Se matrices. Consequently, a significant enhancement of the thermoelectric performance is observed in the entire temperature range from 300 K to 773 K. This results in high average ZT values for both α-Cu2Se (ZTave = 0.60) and β-Cu2Se (ZTave = 0.97), which paves the way for both near room temperature and high temperatures applications. This work provides a new approach to optimize the thermoelectric performance of Cu2Se-based materials by leveraging the interaction between mobile intrinsic Cui. and extrinsic VCu′ to suppress the hole density.

High Performance and Colorful Polymer Thermoelectrics with Imprinted Porous Film.

The rapid development of the Internet of Things and wearable electronics has generated growing interest in creating high-performance and visually striking polymer thermoelectric (TE) devices. However, existing polymer TE materials have yet to fully meet these diverse demands. In this study, imprinted porous polymer films are introduced that exhibit both high TE performance and a spectrum of structural colors. The porous architecture not only preserves excellent charge transport properties but also significantly enhances phonon-like scattering, resulting in a more than 50% reduction in thermal conductivity for the PDPPSe-12 film. This leads to a 170% increase in the figure of merit (ZT), achieving a peak value of 0.52 at 363K. Furthermore, the highly ordered porous structure imparts the PDPPSe-12 films with both a wide range of structural colors and remarkable stretchability, making them ideal for wearable TE generators. This approach is widely applicable to various polymeric systems, offering a novel strategy for advancing state-of-the-art plastic TE materials through microstructural engineering.

A Newly Bio-Based Material for the Construction Industry Using Gypsum Binder and Rice Straw Waste (Oryza sativa)

Construction is one of the economic sectors with the greatest influence on climate change. In addition to working procedures, the primary carbon footprint is attributed to the choice of materials and the energy required for their manufacturing. The underlying idea of this study is to minimize the effects and offer new solutions to emerging problems in the quest for materials that can be deemed as natural, such as gypsum (calcium sulphate dihydrate) and rice straw (Oryza sativa). The acquisition of these materials involves a lower carbon footprint compared to the conventional materials. It is well known since ancient times that gypsum and cereal straw can be used in construction, with numerous examples still available. Cereal straw is one of the oldest construction materials, traditionally combined with earth and occasionally with certain binders, with it continuing to be employed in construction in many countries to this day. This work showcases the feasibility of producing stable prefabricated elements from straw waste with construction gypsum, addressing a significant environmental concern posed by the alternative of having to burn such materials. In this study, for the proposed bio-based material, specific tests, such as thermal conductivity, flexural and compressive strength, and fire resistance, were carried out to evaluate the principal physical and mechanical characteristics for different compositions of water, gypsum, and straw fiber samples. The results highlighted the good performance of the proposed materials in order to spread their use in the green building industry. The addition of straw fibers improved, in different ways, some important physical characteristics of these components so as to diminish environmental pollution and to obtain better material performance. The tests highlighted the different behaviors of the proposed material with respect to the different cuts of the straw and as well as the water/gypsum ratio; this is not very well understood and probably depends on the micro structure of the straw fibers. The blocks with raw straw showed a significant improvement in the breaking mechanism (1775.42 N) compared to the blocks with cut straw (712.26 N) when subjected to bending tests, and their performance in compression tests was also acceptable. Additionally, a very interesting reduction in thermal conductivity was achieved by incorporating rice straw (0.233 W/mK), and high fire exposure times were obtained, with gypsum preventing the spread of ignition in any type of fiber.

Thermal transport and spin–phonon interaction in magnetic Janus Cr2X3S3 (X = Br, I) monolayers

Comprehending the relationship between spin and phonons is essential to regulate the lattice thermal conductivity in 2D magnetic materials. Lattice thermal conductivity is a relevant part to consider in magnetic data storage and the working of spin-based devices. In this article, we examined the origin and effect of spin–phonon coupling (SPC) on the lattice thermal conductivity of pristine CrI3 monolayer-based Janus monolayers Cr2X3S3 (X=Br,I). We find a high SPC in these Janus monolayers due to in-plane Cr–S atomic vibrations. We observe a reduction in the lattice thermal conductivity at Janus monolayer magnetic states (∼52.3% in Cr2Br3S3 and ∼63.9% in Cr2I3S3) compared to its paramagnetic states. The analysis is also conducted to determine which magnetic state has more anharmonicity using potential energy wells. A wide range of 2D magnetic materials can benefit from our results in the future development of spin-based thermal devices.

3DP for sustainable built environment – Synthesis and thermomechanical characterization of composite materials based on local soil and date palm fiber waste

There is an increasing demand for sustainable construction materials to address the challenges posed by the environmental impact of the built environment (BE), which is driven by climate change, population growth, and urbanization. Conventional construction materials like cement contribute significantly to carbon emissions during production, transport, use, and disposal phases, and their poor thermal conductivity hinders efforts to maintain comfortable indoor environments. To address these challenges, there is an urgent need for innovative, locally sourced thermal insulation materials specifically designed for regions with extreme climates and high energy demands to maintain building comfort. This research explores synthesizing novel, environmentally friendly building materials using locally sourced date palm fiber waste and clay. The study also investigates the developed material's 3D printing (3DP) capabilities and optimizes its printing parameters with lab-scale prototypes. Additionally, thermo-mechanical characterization is conducted to assess its suitability for built environment applications. Different concentrations, from 1 to 5 wt% of date palm fiber to clay ratio (Dpf/C), were studied regarding microstructural, thermal, and mechanical properties, dimensional accuracy, and feasibility for 3DP of BE structures. Results demonstrated a significant reduction in thermal conductivity by 73%, achieving 0.244 W/mK, and an increase in compressive strength by 106%, reaching 10.9 MPa at 5 wt% Dpf/C. The promising thermomechanical properties of these composites and their suitability for 3DP support their use in real-world applications in the future's sustainable built environment. This scalable methodology can be adapted to regions with similar sustainable local and waste resources, advancing the circular economy.

Phonon transmission and localization in disordered side branching graphene aperiodic lattice

Blocking phonon transport via localized resonance is a crucial method for controlling heat transfer and enhancing thermoelectric performance in nanostructures. However, the effects of disorder and asymmetrically distributed side branches on thermal transport and local resonant hybridization in two-dimensional materials remain insufficiently understood. In this work, we investigate the influence of symmetric and asymmetric disordered side branches on phonon transport in branching graphene superlattices. Our results demonstrate that aperiodic superlattices (ap-SL) can reduce thermal conductivity by up to 21% compared to periodic superlattices. The reduction in thermal conductivity in ap-SL is primarily due to phonon Anderson localization caused by disordered side branches. Interestingly, the localization lengths of symmetric and asymmetric ap-SLs are comparable, resulting in similar thermal conductivity in both cases. This finding suggests that the randomness in the upper and lower branches of asymmetric graphene superlattices does not significantly affect phonon transmission. Consequently, our work indicates that differences in symmetry between the upper and lower edge branches of graphene nanoribbons can be disregarded during experimental preparation without influencing their thermal conductivity.

Widening the frequency bandgap and reducing thermal conductivity in phononic crystals by tuning structural parameters using a novel computational simulation method

AbstractThis paper introduces and models a phononic structure based on single-crystal silicon, aiming to investigate the width of its frequency bandgap and the impact of key parameters on thermal conductivity. The modeled phononic crystal structure features a periodic arrangement of cylindrical holes in a silicon matrix. This research holds the potential to enhance thermal management performance of thermal metamaterials. Utilizing a 3D finite element method (FEM) model in COMSOL, we have computed phonon dispersion to estimate thermal conductivity. The study systematically has explored the influence of phononic crystal parameters—specifically, porosity, lattice constant, and thickness—along with their interactions on both thermal conductivity and frequency bandgap width.A comprehensive investigation of these parameters has been conducted for their optimization to achieve the maximum frequency bandgap width and minimum thermal conductivity using the response surface method model. Eigenfrequencies and wave vector parameters are extracted from the finite element model using a MATLAB script. Subsequently, thermal conductivity is calculated through the Callaway–Holland model, a simplification of the Boltzmann transport equation (BTE).Our results indicate that the frequency bandgap begins to form at approximately 43% porosity for a lattice constant and thickness of 100 nm each. Furthermore, adjusting the parameters led to a significant reduction in thermal conductivity, decreasing from 43.89 W m−1 K−1 to 0.39 W m−1 K−1. The novelty of our research lies in thermal conductivity control of phononic crystal metamaterials through their parameter variations, or a predictive method of thermal conductivity and its parameter sensitivity. This study advances the state of the art in phononic crystal metamaterial research, contributing to improved thermal management performance by enlarging frequency bandgaps.Overall, our findings deepen the understanding of how porosity, lattice constant, and thickness influence thermal conductivity and frequency bandgap width. They offer valuable insights into optimizing phononic crystal parameters, enhancing thermal management performance, and designing more efficient and effective phononic crystal structures.

Optimally Suppressed Phonon Tunneling in van der Waals Graphene-WS2 Heterostructure with Ultralow Thermal Conductivity.

Van der Waals heterostructures have great potential for realizing ultimately low thermal conductivity because defectless interfaces can be constructed at a length scale smaller than the phonon wavelength, allowing modulation of coherent phonon transport. In this Letter, we demonstrate the mechanism for thermal conductivity reduction at a mode-resolved level. The graphene-WS2 heterostructure with the lowest cross-plane thermal conductivity of 0.048 W/(m·K) is identified from 16,384 candidates by combining Bayesian optimization and molecular dynamics simulations. Then, the angle-resolved phonon transmission is calculated using the mode-resolved atomistic Green's function. The results reveal that the optimal heterostructure nearly completely terminates phonon transport with finite incident angles, owing to the reduced critical incident angle and suppression of phonon tunneling.

First-principles studies on the electronic and thermal transport properties of twin graphene and its analogues

The novel two-dimensional (2D) carbon allotropes with various carbon networks have provided an unprecedented platform to explore fascinating device applications beyond graphene. In this work, the electronic and thermal transport properties of the twin graphene and its structural analogues, i.e., γ-graphyne, twin T-graphene, and twin 4–8 graphene, have been systematically revealed through first-principles calculations. Our results confirm the energetic and dynamical stability of the twin graphene family, and the intrinsic semiconducting nature of these 2D carbon sheets superior to graphene. Based on the solution of the phonon Boltzmann transport equation, the evaluated thermal conductivity of the considered 2D carbon sheets indicates that the absence of acetylenic linkages in carbon networks leads to a relatively enhanced heat transfer capacity, i.e., a higher thermal conductivity in the twin graphene family than the γ-graphyne case. More interestingly, a way to effectively tune thermal transport properties in the twin graphene family has been proposed via the utilization of atom-embedded carbon nanocages. Our results indicate that a notable 63.8% reduction in thermal conductivity can be achieved for twin graphene through the embedding of Ti atoms into the nanocages, exhibiting great potential for robust thermal management in low-dimensional carbon networks.

Effect of magnetic entropy in the thermoelectric properties of Fe-doped Fe2VAl full-Heusler alloy

The effect of spin entropy on the transport of heat/charge carriers in the Fe-doped full-Heusler alloy Fe2+xVAl1-x with x = 0–0.1 has been studied through low-temperature magnetic and thermoelectric measurements. Magnetization (M) measurements confirm itinerant-electron weak-ferromagnetic behavior. A systematic increase of the magnetic transition temperature TC (from 40 K to 223 K) and of the saturation magnetization (from 0.13 to 0.41μB/Fe) with increasing Fe doping (from x = 0 to 0.1) is observed. Applying a magnetic field causes significant suppression of the Seebeck coefficient (S) and the entropy term (S/T) with a negative magnetoresistance near TC for all weak-ferromagnetic samples, demonstrating a clear effect of spin fluctuations. Analyzing M(T) and S(T), we rule out sizeable magnon drag contributions. A large spin fluctuations-induced enhancement in the thermoelectric power factor PF of about 18 % is achieved for x = 0.1 near TC when compared to measurements in a magnetic field of 7 T. The actual improvement in PF is even much higher, as the S shows a significant enhancement (about 34 %) compared to the estimated diffusion term of S(T) at TC. The number of point defects also increases with Fe doping, causing a significant reduction of the lattice thermal conductivity. This study demonstrates the role of spin fluctuations in enhancing the thermopower/thermoelectric performance of Fe-doped Fe2VAl and opens a vista for the strategy's applicability for various thermoelectric materials.

Optical and thermoelectric properties of layer structured Ba2XS4 (X = Zr, Hf) for energy harvesting applications

The main objective of this research is to provide a comprehensive insight into the optical and thermoelectric properties of layer structured Ba2XS4(X = Zr, Hf) for energy harvesting applications using Density Functional Theory (DFT) and semiclassical Boltzmann transport theory. There is a good match between the computed lattice parameters and the available experimental data. Both compounds are thermodynamically and mechanically stable and they are soft, ductile, machinable, and elastically anisotropic. The indirect band gaps are found to be 1.03 eV for Ba2ZrS4 and 1.48 eV for Ba2HfS4. Both compounds possess a mixture of ionic and covalent bonding confirmed by charge density distribution and Mulliken bond population analysis. The maximum absorption is in the ultraviolet regions (∼13.6eV) of light spectra. The total thermal conductivity increases with temperature due to increasing trend of electronic thermal conductivity. The total thermal conductivity at 700 K along c-axis is 4.6 (6.1 W/mK) for Ba2ZrS4 (Ba2HfS4). For p-type Ba2ZrS4 (Ba2HfS4), power factor (PF) is about 7 (5.7) mW/mK2, whereas for n-type it is about 4 (3.9) mW/mK2 at 700 K along c-axis. The power factors of the studied compounds are much higher than those of the reported GeTe and SnSe which would create great interest for further study. The predicted ZT values at 700 K for p-type Ba2ZrS4 and Ba2HfS4 are 0.7 and 0.6, respectively. These values may further be improved through reduction of thermal conductivity and tuning ductility employing known suitable strategies such as alloying and nano-structuring. Finally, Ba2ZrS4 and Ba2HfS4 can be considered new eco-friendly alternatives to previously studied toxic lead-based thermoelectric materials. Their unique advantages of high thermodynamic stability, non-toxic nature and high performance make them strong candidate for sustainable energy solutions.

Vat photopolymerization for thermal energy storage applications using encapsulated phase change material suspended in photocurable resin

A novel approach to additively manufacture latent heat thermal energy storage heat exchangers through the development of microencapsulated phase change material (MEPCM) suspensions in photocurable resin for vat photopolymerization (VPP) 3D printing is presented. Using MEPCM addresses the leakage risks that have typically been associated with PCMs and subsequently makes the particulates a suitable additive for VPP 3D printing. In the current study, VPP was employed to fabricate functional composites with varying MEPCM mass fractions for thermal, rheological, microstructure, and chemical characterization. Microstructure visualization was conducted to assess the overall distribution of MEPCM within the 3D printed samples and to confirm the structural integrity of the encapsulated particles after printing. The influence of the base resin viscosity was explored by investigating two photocurable resins with different viscosities—a high-tensile UV photopolymer and an ABS-like resin—during the printing process. Thermal properties, such as latent heat of fusion, phase-change temperature, thermal conductivity, and decomposition temperature of the 3D printed samples were determined. Rheology was used to observe the effect of varying shear rates on the MEPCM-resin mixtures to identify the optimal viscoelastic properties for VPP 3D printing. It was determined that the ABS-like resin was able to contain a larger amount of PCM (40 wt%) while maintaining printability due to the lower viscosity of the corresponding pure resin. The 40 wt% MEPCM composite exhibited an average viscosity of 18,817 cPs, a maximum latent heat of fusion of 54.12 kJ/kg, and a 12.4 % reduction in thermal conductivity compared to the pure polymer.

Evaluating the effect of Incorporating Chicken Feather Fibers on the Technological Properties of Eco-Friendly Compressed Earth Bricks

This paper investigates the feasibility of improving the performance of raw bricks by using chemically treated chicken feather fibers as a sustainable reinforcement material. Although numerous studies have already explored the use of chicken feathers in brick composites, this work is distinguished by the application of a novel chemical treatment involving formaldehyde and silane to enhance the fibers' compatibility with the clay matrix. The treated fibers were incorporated into raw brick samples at varying concentrations. The effects of fiber reinforcement on critical properties such as porosity, bulk density, compressive strength, and thermal conductivity were systematically analyzed. The results indicate that incorporating chemically treated chicken feather fibers reduces porosity and bulk density while increasing compressive strength within an optimal concentration range. Additionally, a significant reduction in thermal conductivity was observed, demonstrating the potential of these materials to improve thermal insulation in construction applications. This study highlights the promise of utilizing chicken feather waste, treated with formaldehyde and silane, as reinforcement in the production of eco-friendly bricks, with implications for sustainable construction practices.