Thermo-X (TX, Online ISSN 3106-8014) is a peer-reviewed, open-access journal published quarterly and owned by Science Exploration Press. The journal has a comprehensive scope, ranging from theoretical insights into the physics of heat, heat conduction, and quantum heat engines, to applied research on thermal energy storage, heat exchangers, thermal management, and sustainable heat-driven processes. Our mission is to provide a platform for scientists and researchers to share their experimental and theoretical advancements in a detailed, open-access format, thereby fostering innovation and collaboration in the thermal sciences.
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Thermo-X (TX, Online ISSN 3106-8014) is a peer-reviewed, open-access journal published quarterly and owned by Science Exploration Press. The journal has a comprehensive scope, ranging from theoretical insights into the physics of heat, heat conduction, and quantum heat engines, to applied research on thermal energy storage, heat exchangers, thermal management, and sustainable heat-driven processes. Our mission is to provide a platform for scientists and researchers to share their experimental and theoretical advancements in a detailed, open-access format, thereby fostering innovation and collaboration in the thermal sciences.
more >
Cu2SnSe3 exhibits exceptionally low lattice thermal conductivity (κL) and a nonclassical temperature dependence among ternary copper-based diamondoid compounds, yet the microscopic origins of these phonon ...
Cu2SnSe3 exhibits exceptionally low lattice thermal conductivity (κL) and a nonclassical temperature dependence among ternary copper-based diamondoid compounds, yet the microscopic origins of these phonon behaviors remain poorly understood. In this work, we theoretically investigate the intrinsic phonon transport in Cu2SnSe3 by employing a two-channel thermal transport model that separates particle-like (κp) and coherent contributions (κc), while fully incorporating both three-phonon (3ph) and four-phonon (4ph) scattering processes. Our calculations show that κc is negligible at 300 K but becomes progressively more significant at elevated temperatures, while κp remains the dominant contributor to κL over the entire temperature range. 4ph scattering is identified as the primary factor driving the deviation from the classical T-1 dependence, yielding a temperature scaling of T-1.1 that closely matches the experimental T-1.2 behavior. This strong 4ph scattering originates from flat optical phonon modes in the 1.2-2.2 THz range, which provide an exceptionally large scattering phase space. The low κL (e.g., ~ 0.8 W m-1 K-1 at 773 K) of Cu2SnSe3 relative to other ternary copper-based diamondoid compounds is attributed to the asymmetric potential energy of Cu atoms, which induces large atomic displacement parameters and pronounced anharmonicity in the Cu-related low-frequency optical branches. Furthermore, qualitative analyses of cation disorder and anion substitution show that disorder leads to significant phonon broadening, while replacing Se with S hardens the acoustic branches and markedly shifts the optical modes upward. Our findings not only clarify the origins of the nonclassical temperature dependence and low κL in Cu2SnSe3, but also provide a general guideline for designing diamondoid thermoelectrics with intrinsically suppressed κL.
Directional heat spreading enabled by intrinsic thermal conductivity (κ) anisotropy offers a promising route to address thermal bottlenecks in integrated circuits. Here, we demonstrate atomic-level engineering of anisotropic thermal transport in C24 ...
Directional heat spreading enabled by intrinsic thermal conductivity (κ) anisotropy offers a promising route to address thermal bottlenecks in integrated circuits. Here, we demonstrate atomic-level engineering of anisotropic thermal transport in C24 monolayers through atomic spatial arrangement. Based on the high-accuracy neuroevolution potentials (NEP) empowered multiscale simulations, we systematically investigate the lattice thermal transport properties of quasi-tetragonal (qTP) and quasi-hexagonal (qHP) C24 monolayers with distinct atomic arrangements. The results show that qTP C24 exhibits relatively higher and nearly isotropic κ. In contrast, the qHP C24 displays pronounced in-plane κ anisotropy, with a room-temperature anisotropy ratio of κy/κx ≈ 1.7. In-depth phonon transport analysis shows that direction-dependent acoustic transport and the substantial participation of low-frequency optical modes are responsible for the intrinsic κ anisotropy. Furthermore, orbital-projected electronic structures reveal a distinct px and py orbital splitting in qHP C24, indicating anisotropic orbital hybridization, which fundamentally underlies its intrinsic κ anisotropy. Device-level finite-element simulations further confirm that atomic-spatial-arrangement induced anisotropic thermal transport enables directional heat spreading and thermal crosstalk regulation. The findings in this study establish atomic-level design as an external-field-free strategy for engineering anisotropic thermal transport.
Layered chalcogenides X2PdY6 (X = Nb, Ta; Y = S, Se) offer tunable properties for energy conversion and electronic applications, yet their intrinsic lattice thermal transport remains poorly understood. ...
Layered chalcogenides X2PdY6 (X = Nb, Ta; Y = S, Se) offer tunable properties for energy conversion and electronic applications, yet their intrinsic lattice thermal transport remains poorly understood. Here, we develop neuroevolution potentials and use molecular dynamics to investigate phonon-mediated heat transport in ideal bulk and few-layer X2PdY6. At 300 K, the bulk crystals exhibit strong anisotropy, with the highest lattice thermal conductivity (LTC) along the in-plane [010] direction and the lowest along the cross-plane [102] direction. The corresponding anisotropy ratios are 10.4, 8.1, 14.3, and 9.0 for Nb2PdS6, Nb2PdSe6, Ta2PdS6, and Ta2PdSe6, respectively. Within each layer, LTC along [20] is lower than along [010] because the longer structural period and asymmetric X-Y bonding enhance anharmonicity. Variations in bond strength and atomic mass produce the composition-dependent ordering κNb2PdS6>κTa2PdS6>κNb2PdSe6>κTa2PdSe6. Exfoliation increases the in-plane LTC and reduces its anisotropy by preferentially enhancing low-frequency phonon transport along [20]. Below 2 THz, monolayer phonon mean free paths are 5-8 times longer than those in the corresponding bulk crystals. These results establish the intrinsic LTC trends and dimensional crossover in X2PdY6, providing a microscopic basis for controlling anisotropic phonon transport in layered chalcogenides.
Barocaloric materials have attracted considerable attention as promising thermal-management alternatives to conventional vapour-compression technologies; however, virtually all reported systems exhibit only a single type of barocaloric effect (BCE), ...
Barocaloric materials have attracted considerable attention as promising thermal-management alternatives to conventional vapour-compression technologies; however, virtually all reported systems exhibit only a single type of barocaloric effect (BCE), fundamentally constraining the functional versatility and accessible operating-temperature range of prospective devices. Here we report that two fluorinated alcohols, C9H6F14O2 (2OH) and C9H4F16O (1OH), harbour two mechanistically distinct phase transitions within a single material family: a solid-solid transition giving rise to a conventional normal BCE, and a solid-liquid transition yielding a rare inverse BCE. By systematically tuning the number of hydroxyl substituents (-OH), the transition temperatures of these two processes can be shifted by several tens of kelvin, enabling their natural alignment with distinct low- and high-temperature operating regimes. This intrinsic thermal property allows both heating and cooling functions to be realized within the same material system, solely through the exploitation of its barocaloric characteristics. Remarkably, 1OH exhibits exceptional pressure sensitivity during solid-liquid transition, reaching 0.34 K/MPa at 100 MPa. These findings establish fluorinated alcohols as a versatile and high-performance material platform, and open new avenues for the rational design of next-generation barocaloric energy conversion technologies.
Understanding the interplay between magnetic ordering and phonon thermal transport is crucial for the thermal management of two-dimensional magnetic devices. Here, using first-principles calculations combined with the phonon Boltzmann transport equation, ...
Understanding the interplay between magnetic ordering and phonon thermal transport is crucial for the thermal management of two-dimensional magnetic devices. Here, using first-principles calculations combined with the phonon Boltzmann transport equation, we systematically investigate the lattice thermal transport properties of four-layer CrSBr during its layer-by-layer magnetic switching process. As the magnetic configuration evolves from the antiferromagnetic (AFM) state to the ferromagnetic (FM) state through successive spin reversals, the lattice thermal conductivity exhibits a pronounced nonmonotonic variation. In particular, the intermediate first ferrimagnetic (FiM1) state shows a dramatic reduction in thermal conductivity of approximately 37.2% along x and 54.5% along y compared with the AFM state, whereas the second ferrimagnetic (FiM2) and FM states retain thermal conductivities close to the AFM configuration. Detailed analysis reveals that magnetic switching only weakly affects harmonic phonon properties, including phonon dispersions and group velocities. In contrast, the FiM1 state exhibits strongly enhanced anharmonic phonon scattering and reduced phonon participation ratios in the low-frequency region dominated by heat-carrying phonons. Further layer-resolved vibrational analysis identifies a mixed vibrational character in the FiM1 state, combining AFM-like layer-selective and FM-like layer-equivalent features, which is correlated with enhanced low-frequency anharmonic phonon scattering. Our results reveal a unique mechanism for magnetically tunable thermal transport in van der Waals magnets and provide microscopic insights into magnetic-order-dependent phonon thermal transport in layered magnetic materials.
The electrocaloric (EC) effect represents the changes of polarization entropy and/or temperature of dielectrics when an external electric field is applied and removed. An efficient EC effect relies on a highly reversible conversion between electrical energy ...
The electrocaloric (EC) effect represents the changes of polarization entropy and/or temperature of dielectrics when an external electric field is applied and removed. An efficient EC effect relies on a highly reversible conversion between electrical energy and thermal energy. Based on this effect, EC refrigeration has demonstrated advantages in terms of high energy efficiency, zero direct carbon emissions, and high specific volumetric cooling power densities. Consequently, EC refrigeration is recognized as one of the promising alternative technologies for next-generation refrigeration and heat pump. Over the past two decades, EC cooling devices have been extensively developed, driven by advances in EC materials and working bodies. In this review, we summarize recent progress in EC cooling devices, focusing on the mechanisms of solid-state refrigerants and thermodynamic cycles within these systems, and highlighting the characteristics of devices operating on different working principles.
With the continuous miniaturization of micro-devices and the rapid advancement of novel nanomaterials, thermal characterization techniques tailored for two-dimensional (2D) structures (films and coatings) and one-dimensional (1D) architectures (wires ...
With the continuous miniaturization of micro-devices and the rapid advancement of novel nanomaterials, thermal characterization techniques tailored for two-dimensional (2D) structures (films and coatings) and one-dimensional (1D) architectures (wires and fibers) have become essential for elucidating structure-property relationships and optimizing material performance. This review provides an in-depth analysis of the Transient Electro-Thermal (TET) technique, a recently developed method for measuring the thermal diffusivity and conductivity of 1D and 2D materials, including dielectric, metallic, and semiconductive films, coatings, and wires/fibers. We discuss the fundamental principles of TET operation, the associated physical and mathematical models for data reduction, and critical methodologies for data fitting, uncertainty analysis, and stray heat transfer mitigation to ensure high repeatability and accuracy. In addition, the latest developments and applications of TET are highlighted, including its extension to atomic-scale thickness, in-situ dynamic thermal property measurements during structural evolution, and the zero-temperature-rise limit method. The outstanding agreement (within ~0.6%) between the measured and reference thermal diffusivity of a Pt wire, validated through extensive experiments and zero-temperature-rise extrapolation, demonstrates the robustness and reliability of the TET technique. Owing to its simplicity in principles, experimental implementation, and data analysis, TET offers significant advantages in uncertainty control, measurement accuracy, and throughput.
The high integration density of modern energy and information devices often results in high power density and intense heat flux. Depending on the operating and optimal temperature range of the device, heat must be either effectively dissipated or retained. ...
The high integration density of modern energy and information devices often results in high power density and intense heat flux. Depending on the operating and optimal temperature range of the device, heat must be either effectively dissipated or retained. Precise regulation of heat flow is essential for the advancement of next-generation energy and information technologies. Dynamic heat flow control and nonlinear thermal transport open new avenues for developing smart battery thermal management systems, solid-state refrigeration devices, and thermal logic elements analogous to electronic circuits. Due to their unique capability to actively modulate heat transfer and exhibit thermal rectification behavior, thermal switches and thermal diodes have shown great potential in managing heat and/or maintaining thermal stability beyond the limits of conventional passive thermal materials and devices. Here, we review recent progress in the design principles, fundamental mechanisms, and applications of thermal switches and thermal diodes for energy and information technologies, and evaluate their potential for practical deployment. Furthermore, we discuss the emerging demands in these sectors and provide future perspectives to inspire applied research toward solving real engineering challenges.
Enhancing indoor visual comfort is crucial for the practical deployment of thermochromic smart windows. However, their application is often hindered by the low visible light transmittance (Tlum) in the activated state. In this study, we propose ...
Enhancing indoor visual comfort is crucial for the practical deployment of thermochromic smart windows. However, their application is often hindered by the low visible light transmittance (Tlum) in the activated state. In this study, we propose a thermally and optically dual-responsive smart window that improves both building energy efficiency and Tlum in the activated state. The design is based on a polyacrylamide (PAm)/poly(N-isopropylacrylamide) (PNIPAm)/indium tin oxide (ITO) composite film (PPI). Within this structure, PAm provides a hydrophilic matrix, PNIPAm microgels enable thermoresponsive optical modulation through reversible transmittance changes across the response temperature, and ITO particles act as light-to-heat transducers due to their photothermal and infrared reflective properties. Compared with the PNIPAm hydrogel film, the PPI composite film increases Tlum in the activated state from 9.7% to 50.0% and enhances infrared modulation capability from 39.2% to 50.4%. Under an illumination intensity of 95 mW·cm-2, the PPI composite film lowers the indoor temperature of simulated buildings by up to 7 °C. This dual-responsive thermochromic window provides improved indoor visual comfort along with effective temperature regulation, offering a promising strategy for advancing the practical use of smart windows.
Antiperovskites have attracted significant interest in the field of energy conversion in recent years. While extensive research has focused on the magnetism, ionic conductivity and superconductivity of antiperovskites, their thermal properties including ...
Antiperovskites have attracted significant interest in the field of energy conversion in recent years. While extensive research has focused on the magnetism, ionic conductivity and superconductivity of antiperovskites, their thermal properties including lattice anharmonicity and thermal transport remain less explored compared to their well-studied perovskite counterparts. Recently, nitrohalide double antiperovskites have been successfully synthesized. In this work, we investigate the thermal transport properties of nitrohalide double antiperovskites Li6NII2 and Li6NBrBr2 using first-principles machine-learning potentials. Our results reveal that within the perturbation theory framework, imaginary phonons appear throughout the entire Brillouin zone in both the harmonic regime and at elevated temperatures. Atomic vibrational analysis indicates that stochastic Li-ion movements confined within a single conventional unit cell are responsible for the presence of these imaginary phonons. Furthermore, homogeneous nonequilibrium molecular dynamics and equilibrium molecular dynamics simulations demonstrate that Li6NII2 and Li6NBrBr2 exhibit ultralow glass-like lattice thermal conductivities. Spectral thermal conductivity analysis shows that the dominant contributions arise from phonons with frequencies below 5 THz and around 11 THz. The substantial phonon contribution near 11 THz is attributed to the confined stochastic motions of Li ions. This work uncovers the unconventional microscopic cation dynamics and strong lattice anharmonicity in double antiperovskites Li6NII2 and Li6NBrBr2, thereby advancing the understanding of phonon transport in these materials.
With the continuous miniaturization of micro-devices and the rapid advancement of novel nanomaterials, thermal characterization techniques tailored for two-dimensional (2D) structures (films and coatings) and one-dimensional (1D) architectures (wires ...
With the continuous miniaturization of micro-devices and the rapid advancement of novel nanomaterials, thermal characterization techniques tailored for two-dimensional (2D) structures (films and coatings) and one-dimensional (1D) architectures (wires and fibers) have become essential for elucidating structure-property relationships and optimizing material performance. This review provides an in-depth analysis of the Transient Electro-Thermal (TET) technique, a recently developed method for measuring the thermal diffusivity and conductivity of 1D and 2D materials, including dielectric, metallic, and semiconductive films, coatings, and wires/fibers. We discuss the fundamental principles of TET operation, the associated physical and mathematical models for data reduction, and critical methodologies for data fitting, uncertainty analysis, and stray heat transfer mitigation to ensure high repeatability and accuracy. In addition, the latest developments and applications of TET are highlighted, including its extension to atomic-scale thickness, in-situ dynamic thermal property measurements during structural evolution, and the zero-temperature-rise limit method. The outstanding agreement (within ~0.6%) between the measured and reference thermal diffusivity of a Pt wire, validated through extensive experiments and zero-temperature-rise extrapolation, demonstrates the robustness and reliability of the TET technique. Owing to its simplicity in principles, experimental implementation, and data analysis, TET offers significant advantages in uncertainty control, measurement accuracy, and throughput.
The electrocaloric (EC) effect represents the changes of polarization entropy and/or temperature of dielectrics when an external electric field is applied and removed. An efficient EC effect relies on a highly reversible conversion between electrical energy ...
The electrocaloric (EC) effect represents the changes of polarization entropy and/or temperature of dielectrics when an external electric field is applied and removed. An efficient EC effect relies on a highly reversible conversion between electrical energy and thermal energy. Based on this effect, EC refrigeration has demonstrated advantages in terms of high energy efficiency, zero direct carbon emissions, and high specific volumetric cooling power densities. Consequently, EC refrigeration is recognized as one of the promising alternative technologies for next-generation refrigeration and heat pump. Over the past two decades, EC cooling devices have been extensively developed, driven by advances in EC materials and working bodies. In this review, we summarize recent progress in EC cooling devices, focusing on the mechanisms of solid-state refrigerants and thermodynamic cycles within these systems, and highlighting the characteristics of devices operating on different working principles.
The high integration density of modern energy and information devices often results in high power density and intense heat flux. Depending on the operating and optimal temperature range of the device, heat must be either effectively dissipated or retained. ...
The high integration density of modern energy and information devices often results in high power density and intense heat flux. Depending on the operating and optimal temperature range of the device, heat must be either effectively dissipated or retained. Precise regulation of heat flow is essential for the advancement of next-generation energy and information technologies. Dynamic heat flow control and nonlinear thermal transport open new avenues for developing smart battery thermal management systems, solid-state refrigeration devices, and thermal logic elements analogous to electronic circuits. Due to their unique capability to actively modulate heat transfer and exhibit thermal rectification behavior, thermal switches and thermal diodes have shown great potential in managing heat and/or maintaining thermal stability beyond the limits of conventional passive thermal materials and devices. Here, we review recent progress in the design principles, fundamental mechanisms, and applications of thermal switches and thermal diodes for energy and information technologies, and evaluate their potential for practical deployment. Furthermore, we discuss the emerging demands in these sectors and provide future perspectives to inspire applied research toward solving real engineering challenges.
Enhancing indoor visual comfort is crucial for the practical deployment of thermochromic smart windows. However, their application is often hindered by the low visible light transmittance (Tlum) in the activated state. In this study, we propose ...
Enhancing indoor visual comfort is crucial for the practical deployment of thermochromic smart windows. However, their application is often hindered by the low visible light transmittance (Tlum) in the activated state. In this study, we propose a thermally and optically dual-responsive smart window that improves both building energy efficiency and Tlum in the activated state. The design is based on a polyacrylamide (PAm)/poly(N-isopropylacrylamide) (PNIPAm)/indium tin oxide (ITO) composite film (PPI). Within this structure, PAm provides a hydrophilic matrix, PNIPAm microgels enable thermoresponsive optical modulation through reversible transmittance changes across the response temperature, and ITO particles act as light-to-heat transducers due to their photothermal and infrared reflective properties. Compared with the PNIPAm hydrogel film, the PPI composite film increases Tlum in the activated state from 9.7% to 50.0% and enhances infrared modulation capability from 39.2% to 50.4%. Under an illumination intensity of 95 mW·cm-2, the PPI composite film lowers the indoor temperature of simulated buildings by up to 7 °C. This dual-responsive thermochromic window provides improved indoor visual comfort along with effective temperature regulation, offering a promising strategy for advancing the practical use of smart windows.
Antiperovskites have attracted significant interest in the field of energy conversion in recent years. While extensive research has focused on the magnetism, ionic conductivity and superconductivity of antiperovskites, their thermal properties including ...
Antiperovskites have attracted significant interest in the field of energy conversion in recent years. While extensive research has focused on the magnetism, ionic conductivity and superconductivity of antiperovskites, their thermal properties including lattice anharmonicity and thermal transport remain less explored compared to their well-studied perovskite counterparts. Recently, nitrohalide double antiperovskites have been successfully synthesized. In this work, we investigate the thermal transport properties of nitrohalide double antiperovskites Li6NII2 and Li6NBrBr2 using first-principles machine-learning potentials. Our results reveal that within the perturbation theory framework, imaginary phonons appear throughout the entire Brillouin zone in both the harmonic regime and at elevated temperatures. Atomic vibrational analysis indicates that stochastic Li-ion movements confined within a single conventional unit cell are responsible for the presence of these imaginary phonons. Furthermore, homogeneous nonequilibrium molecular dynamics and equilibrium molecular dynamics simulations demonstrate that Li6NII2 and Li6NBrBr2 exhibit ultralow glass-like lattice thermal conductivities. Spectral thermal conductivity analysis shows that the dominant contributions arise from phonons with frequencies below 5 THz and around 11 THz. The substantial phonon contribution near 11 THz is attributed to the confined stochastic motions of Li ions. This work uncovers the unconventional microscopic cation dynamics and strong lattice anharmonicity in double antiperovskites Li6NII2 and Li6NBrBr2, thereby advancing the understanding of phonon transport in these materials.
