Ge-rich Ge-Sb-Te (GGST) alloys are of high interest for industrial production of complementary metal-oxide-semiconductor integrated phase change random access memories (PCRAM) of high performance. BEOL-integrated GGST-based PCRAM constitute a relevant solution for low-power on-chip non-volatile memory production and in-memory computing, addressing new challenges of automotive and artificial intelligence applications for example. During cycling, in the low-resistive SET state, the crystallized GGST alloy is mainly made of nano-grains of two phases: diamond Ge and a ternary rock-salt (RS) Ge-Sb-Te (GST) phase. The RS-GST phase is metastable and generally assumed to exhibit the stoichiometry Ge2Sb2Te5 corresponding to the stable hexagonal Ge2Sb2Te5 compound. However, recent works suggest that this metastable RS-GST phase is not stoichiometric and can accept higher Ge contents, meaning that the Ge content of RS-GST could vary depending on the Ge excess level in the GGST alloy compared to the Ge2Sb2Te5 reference stoichiometry. Consequently, the performance of GGST-based PCRAMs could vary with Ge composition of GGST alloy, suggesting the existence of an ideal GGST alloy composition showing a good compromise between crystallization temperature, programming current density, resistance, threshold voltage drift… In the present work, the structure and composition of crystallized GGST films elaborated through Ge, Sb, and Te co-sputtering were studied by X-ray diffraction, high resolution transmission electron microscopy, and atom probe tomography. The metastable RS-GST phase crystallized in GGST films exhibiting a Ge excess between 23% and 42% is found to be able to incorporate a large amount of Ge, of about 50 at% and sometimes beyond.

In recently published work in Advanced Materials, Zhao and colleagues proposed a “synergistic material-interface engineering” strategy that yielded a nearly Te-free PbSe-based thermoelectric module with high power generation and cooling efficiency across a broad temperature range. Their work offers valuable insights into developing sustainable thermoelectrics through integrated materials and device-level design.

ABSTRACT The bright promise of Mg 3 (Sb,Bi) 2 as a next‐generation near‐room‐temperature thermoelectric material is challenged both by the need for reliable and economical synthesis and by performance degradation from detrimental Mg‐vacancy defects at grain boundaries and within grains. Here, we reveal that Earth‐abundant oxides (Fe 2 O 3 , ZrO 2 and TiO 2 ) can unlock superior thermoelectric performance in Mg 3 (Sb,Bi) 2 via a simple metathesis strategy. Incorporation of the oxides (at only 1–3 mol%) in Mg‐excess Mg 3 (Sb,Bi) 2 powders during spark‐plasma sintering initiates “Mg‐oxide” reduction reactions; the subsequent “transition metal‐Mg 3 (Sb,Bi) 2 ” reactions release a source of additional Mg, whose global diffusion refills cationic vacancies in the bulk matrix, enabling markedly enhanced power factors and figures of merit. Our fabricated 8‐pair Mg 3 Sb 0.75 Bi 1.25 /MgAgSb device attained remarkable conversion efficiency and output power density of 11.7% and 1.0 W cm −2 at a temperature gradient (Δ T ) of 315 K. Notably, a Mg 3 Sb 0.5 Bi 1.5 /Bi 0.5 Sb 1.5 Te 3 module demonstrated maximum cooling Δ T s competitive with state‑of‑the‑art Bi 2 Te 3 coolers at 200–373 K. The proposed metathesis strategy not only offers an eco‐friendly and cost‐effective route to defect engineering, promoting applications of Mg 3 (Sb,Bi) 2 TEs, but also provides key insights into the structure‐property relationships and thermoelectric performance optimization of other Mg‐based TEs and Zintl phases.

This article explores the impact of grain boundary structures and compositions on the functional properties of various materials for photovoltaics, batteries, and other energy-related applications. Examples of correlative microscopy studies highlight the potential to discover structure–property relationships at grain boundaries, essential for the design of energy devices to achieve superior performance. A grain boundary transition that promotes grain growth and reduces the boundary resistance in solid electrolytes is given as an example. A key focus will be on transport phenomena at grain boundaries, including mass, thermal, electrical, and ionic transport mechanisms. These transport phenomena are directly correlated with the charge defects that lead to a buildup of electric charges and potential barriers at the grain boundaries. In addition, applied electric fields can also induce boundary transitions that can affect grain boundary transport and other properties. Finally, we demonstrate that these potential barrier heights can be tuned by modulating the chemical composition, structure, and carrier concentration of the grain boundaries.

Grain boundary (GB) scattering of charge carriers plays an important role in the electrical properties of materials. For thermoelectrics, this scattering can significantly reduce the carrier mobility and output power. Various GB engineering strategies, such as increasing the grain size and decreasing the GB potential barrier height, have been demonstrated in n-type Mg3Sb2-based thermoelectrics. Yet, similar effects in p-type Mg3Sb2 have been less reported, and effective methods to modify the GB potential are elusive. Here, we reveal that Cd can reduce the GB barrier height via segregation to the GB. The enrichment of Cd suppresses the formation of hole-killer defects (SbMg +) and thus reduces the GB resistance, leading to significant improvements in the electrical conductivity and power factor. A two-phase model shows a progressive decrease in the GB barrier height with increasing Cd content. Simultaneously, the GB Cd segregation and grain-interior Cd alloying strengthen the phonon scattering and reduce the sound velocity, substantially reducing the thermal conductivity. Consequently, a maximum ZT of 0.84 is achieved in Mg2.5Cd0.5Sb2-1 at% NaF at 773 K. These findings unravel the hidden role of Cd in tuning the GB characteristics and the transport properties of Mg3Sb2, revisiting the functionality of conventional dopants in materials design.

Tailoring chemical bonds offers an innovative way to design materials for a wide range of applications. Metavalent bonding is conducive to excellent thermoelectric performance in p‐bonded chalcogenides with octahedral coordination. However, the requirement to form a bond through only a single p‐electron between adjacent atoms (half of an electron pair), such as in PbTe and Bi 2 Te 3 , limits the number of possible materials. Here, it is shown that the essence of metavalent bonding is a half‐filled single‐electron σ‐bond, which can also be formed with a significant s‐orbital contribution. This is illustrated for AgBiSe 2 , which crystallizes in three different phases: hexagonal, rhombohedral, and cubic. Quantum chemical calculations and bond‐breaking behavior reveal that all three octahedrally coordinated AgBiSe 2 phases utilize metavalent bonding. In addition, PbTe alloying is used to tune the chemical bonding and Br doping to optimize the carrier concentration. With these modifications, a record‐high zT max value of 1.1 is achieved in n‐type cubic (AgBiSe 2 ) 0.75 (PbTe) 0.25 −0.01BiBr 3 at 798 K. The understanding and tailoring of chemical bonds achieved in AgBiSe 2 can be easily extended to other AgVVI 2 compounds.

The increasing global demand for clean energy and decarbonized industrial processes has accelerated interest in compact systems capable of producing both hydrogen and electricity with minimal carbon emissions. Among various approaches, methane reforming offers a promising route for hydrogen production, but conventional systems often suffer from low thermal efficiency and underutilized waste heat. To address these challenges, this study presents an innovative integration of a Swiss-roll reforming reactor with thermoelectric generators (TEGs) for simultaneous hydrogen generation and electricity recovery. The Swiss-roll design enables enhanced thermal recirculation, while strategically embedded TEGs convert waste heat from the reactor walls into electrical power. A computational fluid dynamics (CFD) model is developed to simulate fluid flow, chemical reactions, and heat transfer within the system, and to identify optimal TEG placement based on 3D temperature gradients. The results show that at an O/C ratio of 1.2, the reactor achieves 1.84 mol H-2.(mol CH4)(-1) with >96 % methane conversion. Five optimal TEG sites on the outer wall produce a combined output of 11.09 W using Bi2Te3 materials, with only a 0.6 % reduction in hydrogen yield. A life cycle assessment reveals a global warming potential as low as 13.25 kg CO2-eq.(kg H-2)(-1) at O/C = 1.2, and the electricity generated by TEG at location 30 can offset approximately 0.056 kg CO2-eq.(kg H-2)(-1). This integrated system demonstrates a compact, energy-efficient, and environmentally sustainable solution for decentralized hydrogen-electricity co-production.

The intrinsic trade-off between strength and plasticity is a major obstacle to improving the mechanical performance of materials, particularly brittle thermoelectric compounds. Developing intrinsically plastic thermoelectric materials with improved machinability and functionality has received increasing attention. Yet, the existing plastic thermoelectrics often show low strength and poor thermoelectric performance at elevated temperatures. Here, we introduce a microstructure-engineering strategy that integrates nanopore architectonics with heterointerface design to achieve a synergistic enhancement of strength, plasticity, and thermoelectric performance in Mg-3(Sb, Bi)(2). Dispersed nanopores improve both strength and plasticity by promoting dislocation-surface interactions. In parallel, TiB2 hetero-particles strengthen the material via pinning dislocations at phase interfaces while preserving plasticity via interfacial complexions that facilitate dislocation slip. These heteroparticles also enhance phonon scattering and provide charge compensation, thereby significantly improving the thermoelectric figure of merit (zT). As a consequence, polycrystalline Mg3.2Sb1.5Bi0.49Te0.01-0.03 TiB2 achieves an exceptional strength of similar to 730 MPa and a superior strain of similar to 45%, alongside zT above 1 across 400-723 K and a peak zT of similar to 1.55 at 723 K. This work demonstrates an effective strategy for simultaneously optimizing mechanical robustness and thermoelectric performance through microstructure manipulation, offering a pathway toward the design of next-generation high-performance plastic thermoelectrics.

The practical application of Mg3Sb2-based thermoelectrics has been largely retarded by their poor thermal stability, mainly due to the rapid loss of Mg at elevated temperatures. Here, we prove that grain boundaries are fast diffusion channels for Mg, and we block these channels by forming Ga-rich grain boundary complexions. This design suppresses the formation of Mg vacancies at grain boundaries and inhibits the outward diffusion of Mg and the inward growth of MgO-related phases. Consequently, the thermal stability of Mg3Sb2-based materials is significantly improved at a high temperature of 718 K for at least 80 h. The corresponding single-leg Mg3Sb2-based device can maintain a conversion efficiency of 12.5% ± 0.6% for 7 days at a temperature difference of 423 K during the cycle test. Our findings provide an atomic-scale grain boundary engineering approach to enhance the thermal stability of thermoelectric devices and other functional materials operating at elevated temperatures.

Low lattice thermal conductivity is a key physical parameter for realizing efficient thermal management and energy conversion. Halide perovskites have emerged as an ideal platform for exploring the physics of extreme thermal transport and for designing novel thermal management materials, owing to their rich structural tunability and intrinsically ultralow thermal conductivity. This review discusses the origins of ultralow thermal conductivity in halide perovskites, spanning from macroscopic thermal phenomena to microscopic phonon transport. Halide perovskites exhibit characteristic thermal signatures, including weak temperature dependence of thermal conductivity, a boson-like peak in heat capacity, and low sound velocities. These properties stem from a soft crystal lattice associated with metavalent bonding, as well as from strong anharmonic phonon scattering induced by lattice disorder and rattling modes. Such glass-like lattice dynamics lead to an anomalous accumulation of low-frequency phonons and intense phonon scattering, pushing phonons toward the Ioffe-Regel limit and causing a breakdown of the conventional phonon gas model. Therefore, the inclusion of coherent phonons is essential for properly describing the intrinsic "phonon glass" character of these materials.

The integration of porous metal-organic frameworks (MOFs) with thermoelectric materials offers an effective route toward the phonon-glass electron crystal paradigm. However, their application in high-temperature power generation remains severely limited by the intrinsic thermal instability of MOFs arising from weak coordination bonding. Here, we report a thermally robust heterostructure that is stable from 300 to 873 K, achieved by embedding sub-nanoporous Zn-[2-methylimidazolate] frameworks (ZIF-8) into Sn-rich SnTe nanomaterials synthesized by a base-amine-mediated solvothermal method. We reveal that the remarkably low solubility of Zn in SnTe inhibits Zn diffusion, thereby stabilizing the Zn nodes and preserving the Zn-N coordination network at elevated temperatures. The SnTe/ZIF-8 nanocomposite introduces an interface-induced energy filtering effect for electrical optimization. Simultaneously, the porosity-induced thermal radiation, the hierarchical defects, and the interfacial Kapitza resistance enable strong phonon scattering across a broad frequency spectrum. As a result, a maximum zT value of 1.3 at 873 K is achieved, among the highest values reported for heterostructure-enhanced SnTe thermoelectric materials without lattice doping. This work provides essential design principles for thermally stable MOF-based heterostructures and extends their applicability to high-temperature (>773 K) thermoelectric power generation.

ABSTRACT Grain boundary (GB) scattering of charge carriers plays an important role in the electrical properties of materials. For thermoelectrics, this scattering can significantly reduce the carrier mobility and output power. Various GB engineering strategies, such as increasing the grain size and decreasing the GB potential barrier height, have been demonstrated in n‐type Mg 3 Sb 2 ‐based thermoelectrics. Yet, similar effects in p‐type Mg 3 Sb 2 have been less reported, and effective methods to modify the GB potential are elusive. Here, we reveal that Cd can reduce the GB barrier height via segregation to the GB. The enrichment of Cd suppresses the formation of hole‐killer defects (Sb Mg + ) and thus reduces the GB resistance, leading to significant improvements in the electrical conductivity and power factor. A two‐phase model shows a progressive decrease in the GB barrier height with increasing Cd content. Simultaneously, the GB Cd segregation and grain‐interior Cd alloying strengthen the phonon scattering and reduce the sound velocity, substantially reducing the thermal conductivity. Consequently, a maximum ZT of 0.84 is achieved in Mg 2.5 Cd 0.5 Sb 2– 1 at% NaF at 773 K. These findings unravel the hidden role of Cd in tuning the GB characteristics and the transport properties of Mg 3 Sb 2 , revisiting the functionality of conventional dopants in materials design.

Hot cracking remains a critical challenge limiting the widespread adoption of superalloys in additive manufacturing. This defect primarily originates from stress-induced rupture of intergranular residual liquid films that persist during final solidification, typically comprising low-melting-point phases formed through solute-segregation. This understanding has guided conventional crack suppression strategies focused on eliminating such residual phases by strict compositional controls. Herein, an innovative approach is demonstrated that strategically engineers residual eutectic fractions (>= 2 vol.%) through trace element regulation to achieve an intrinsic capability for crack suppression. Hastelloy X is selected as the model system owing to its marked hot cracking susceptibility. Leveraging the ultra-low partition coefficient (k = 0.21) of carbon, a subtle increment in its content (<0.1 wt.%) significantly enhances the formation of ternary eutectic carbides through amplified segregation. The resulting adequate eutectic liquids successfully prevent crack initiation through stress-compensating backfilling while preserving structural cohesion via liquid buffering, revealing the context-dependent duality of eutectics-transitioning from crack initiators to healers. These crack-free samples exhibit superior strength-ductility synergy compared to carbon-restricted counterparts, benefiting from combined effects of carbide dispersion strengthening and multiple dynamic hardening mechanisms.

Thermoelectric materials, capable of realizing direct conversion between thermal and electrical energy, hold great promise for waste heat recovery and solid-state cooling. Their performance is quantified by the dimensionless figure of merit (zT). For decades, enhancement strategies have focused on macro-scale engineering, often treating materials as homogeneous media. However, the properties of polycrystalline thermoelectrics are governed by a complex landscape of microstructural features, particularly grain boundaries (GBs), which exhibit a dual nature in transport. They can scatter phonons to reduce lattice thermal conductivity but also impede charge carriers, degrading electrical conductivity. Recent advances in correlative characterization techniques, combining electron backscatter diffraction, focused ion beam milling, micro-fabrication, physical property measurement systems, and atom probe tomography (APT), enable a "one-to-one" structure-property relationship at the micro- and nanoscale. This review demonstrates how these methods reveal that the electrical transport across individual GBs is dictated by misorientation angle, chemical segregation, and, crucially, the local chemical bonding character. The collapse of metavalent bonding (MVB) at GBs, detected by a drop in the probability of multiple events in APT, drastically reduces dielectric screening and creates high potential barriers. Conversely, strategic dopant segregation can passivate GBs, and MVB-based precipitates in elemental Te can enhance bulk conductivity via favorable band alignment. By unifying insights from macro-scale performance with micro/nano-scale mechanisms and quantum-mechanical bonding maps, this work charts a path for the bottom-up design of next-generation, high-efficiency thermoelectric materials.

ABSTRACT Alloying is a well‐established strategy for reducing lattice thermal conductivity ( κ L ) and enhancing thermoelectric performance of materials, typically explained by the Klemens model, which describes the point‐defect phonon scattering via mass and size contrasts. Yet, in certain isovalent alloyed thermoelectrics, we observe an anomalously low κ L that falls below Klemens model predictions. Here, using YbMg 2 Sb 2 as a model system, we show that alloying Mg with isovalent Zn or Cd induces a substantial reduction in κ L beyond that attributable to mass and size effects of the dopants alone. Density‐functional‐theory calculations demonstrate that this stems from weakened local chemical bonds, which soften and slow both acoustic and optical phonons. Reduced interatomic force constants also lead to avoided crossing, further suppressing acoustic phonon propagation. Deformation electron density analyses reveal that the weak Zn‐Sb and Cd‐Sb bonds arise from delocalized electrons within Zn 2 Sb 2 and Cd 2 Sb 2 rhomboid rings. Benefiting from this pronounced κ L reduction and an enhanced density‐of‐states effective mass by band alignment, Cd‐alloyed YbMg 2 Sb 2 achieves a record‐high ZT of 1.4 at 873 K. These findings highlight the critical role of chemical bonds in reducing κ L and provide a design principle for enabling materials with ultralow thermal conductivity through local bond tailoring.

Long-term stability in materials is commonly associated with resistance to external perturbations. Yet metastable defect populations may relax spontaneously even in the absence of environmental stimuli, reshaping macroscopic properties over extended timescales. Here, we show the real-space visualization of intrinsic aging of n-type Mg_{3}(Sb,Bi)_{2} under inert and room-temperature conditions after two-year storage by atomic-scale characterizations. Density-functional-theory calculations and machine-learning molecular dynamics simulations prove that the aging originates from relaxation of a metastable Mg-rich state, in which low vacancy-formation energies and migration barriers enable thermodynamically favorable and kinetically accessible Mg redistribution. Multiscale characterizations further reveal that grain boundaries (GBs) act as fast-diffusion pathways and effective sinks, establishing a hierarchical Mg redistribution process from grain interiors to GBs and surfaces. These results identify intrinsic defect physics as one of the fundamental stability constraints in functional materials and underscore the importance of controlling defect thermodynamics and transport pathways for achieving practically durable materials.

The rapid development of wearable and portable electronics has intensified the demand for flexible thermoelectric devices that can convert human body heat into electricity. In practical use, however, such devices suffer from performance degradation caused by mechanical damage and thermal stress, which severely limit their service life and reliability. The recent introduction of self-healing materials offers a promising route to address these challenges. This review summarizes the fundamental principles, architectures, and performance requirements of thermoelectric devices, and surveys the current research progress of self-healing materials employed therein. Evidence to date demonstrates that the rational design and optimization of self-healing materials can markedly enhance the reliability and longevity of thermoelectric devices, providing strong support for the sustainable evolution of flexible electronics.

Thermal concealment is vital for minimizing the visibility of individuals and vehicles to contemporary infrared surveillance technologies. Traditional approaches, such as emissivity modulation, are effective only in scenarios where the ambient temperature is lower than that of the target and typically exhibit response times on the order of minutes. Other temperature regulation methods generally operate within a restricted temperature range. This work presents an active thermal concealment cloak based on thermoelectric devices, integrating functionalities of infrared camouflage, deception, and information display. By optimizing the circuit design and incorporating a low-reflectivity black porous Ethylene-Vinyl Acetate film, the cloak achieves a uniform temperature distribution, eliminating distinct cold or hot boundaries, and exhibits strong resistance to light interference. Enhanced by bottom-side heat dissipation, the device functions effectively across a wide temperature range from 5.77 °C to 109.16 °C and responds rapidly in just 2.03 seconds. Through the self-developed application, each panel pixel on the device can be independently temperature-controlled, allowing for pre-programmed alterations in the shape and color of the concealed target to enable infrared deception. Additionally, a kirigami structure is employed to enhance the device’s bendability, facilitating the implementation of curved camouflage and wearable IR information transmission.

High-performance thermoelectric (TE) devices offer great potential for power generation and solid-state cooling. However, their reliability and long-term stability are often constrained by the quality of interfaces between TE materials and electrodes. The substantial mismatch in physical, chemical, and mechanical properties among TE materials, TE interface materials (TEiMs), and electrodes presents major challenges in achieving stable, low-resistance electrical contacts. Thus, the rational design and selection of TEiMs are critical to advancing TE device technologies. This review provides a comprehensive overview of TEiMs from physical, chemical, and material perspectives. We trace the evolution of interface design strategies from the use of empirical metals borrowed from the semiconductor industry, to the identification of inert elements through high-throughput screening, the development of multi-element alloys to balance interfacial bonding and contact resistance, and the application of phase diagram-guided compound selection. Recent advances in TEiMs for key TE material systems, including Bi2Te3, MgAgSb, IV-VI compounds, Mg3(Sb,Bi)2, CoSb3, and half-Heusler alloys, are systematically summarized. Finally, we outline current challenges and future directions, aiming to guide the development of robust, efficient TE interfaces and accelerate the deployment of next-generation thermoelectrics.

Ternary CaAl2Si2-structure-type Zintl compounds are promising p-type counterparts to n-type Mg-3(Sb, Bi)(2) for thermoelectric energy conversion. However, many of these p-type Zintl compounds suffer from low carrier concentration and mobility, resulting in poor thermoelectric performance. Here, it is revealed that their ultralow mobility stems from strong polar optical phonon scattering, and demonstrate that their electrical transport properties can be dramatically boosted by employing a screening effect. By employing isovalent alloying with Cd and Yb, along with Li aliovalent acceptor doping in CaMg2Sb2 to increase carrier concentration and induce a strong screening effect, a significant improvement in carrier mobility and, consequently, the power factor is achieved. Moreover, isovalent alloying weakens chemical bonding, causing the softening and deceleration of both acoustic and optical phonons and, thus, a reduction in lattice thermal conductivity. As a result, a ZT of 1.1 is achieved in the Ca0.69Yb0.3Li0.01Mg1.5Cd0.5Sb2 sample at 773 K, representing a 30-fold increase compared to the pristine CaMg2Sb2 . It is also proposed that the polar coupling constant can serve as a criterion for identifying materials with low intrinsic carrier concentration and mobility but with potential for thermoelectric applications facilitating the development of other thermoelectric materials beyond CaAl2Si2-structure-type Zintl compounds.