Interstitial Cu: An Effective Strategy for High Carrier Mobility and High Thermoelectric Performance in GeTe

Dense point defects can strengthen phonon scattering to reduce the lattice thermal conductivity and induce outstanding thermoelectric performance in GeTe-based materials. However, extra point defects inevitably enlarge carrier scattering and deteriorate carrier mobility. Herein, it is found that the interstitial Cu in GeTe can result in synergistic effects, which include: 1) strengthened phonon scattering, leading to ultralow lattice thermal conductivity of 0.48 W m⁻¹ K⁻¹ at 623 K; 2) weakened carrier scattering, contributing to high carrier mobility of 80 cm² V⁻¹ s⁻¹ at 300 K; 3) optimized carrier concentration of 1.22 × 10²⁰ cm⁻³. Correspondingly, a high figure-of-merit of ≈2.3 at 623 K can be obtained in the Ge_0.93Ti_0.01Bi_0.06Te-0.01Cu, which corresponds to a maximum energy conversion efficiency of ≈10% at a temperature difference of 423 K. This study systematically investigates the doping behavior of the interstitial Cu in GeTe-based thermoelectric materials for the first time and demonstrates that the localized interstitial Cu is a new strategy to enhance the thermoelectric performance of GeTe-based thermoelectric materials.     

Low‐Dimensional Lead‐Free Inorganic Perovskites for Resistive Switching with Ultralow Bias

3D organic–inorganic and all‐inorganic lead halide perovskites have been intensively pursued for resistive switching memories in recent years. Unfortunately, instability and lead toxicity are two foremost challenges for their large‐scale commercial applications. Dimensional reduction and composition engineering are effective means to overcome these challenges. Herein, low‐dimensional inorganic lead‐free Cs₃Bi₂I₉ and CsBi₃I₁₀ perovskite‐like films are exploited for resistive switching memory applications. Both devices demonstrate stable switching with ultrahigh on/off ratios (≈10⁶), ultralow operation voltages (as low as 0.12 V), and self‐compliance characteristics. 0D Cs₃Bi₂I₉‐based device shows better retention time and larger reset voltage than the 2D CsBi₃I₁₀‐based device. Multilevel resistive switching behavior is also observed by modulating the current compliance, contributing to the device tunability. The resistive switching mechanism is hinged on the formation and rupture of conductive filaments of halide vacancies in the perovskite films, which is correlated with the formation of AgI_x layers at the electrode/perovskite interface. This study enriches the library of switching materials with all‐inorganic lead‐free halide perovskites and offers new insights on tuning the operation of solution‐processed memory devices.     

Strain-Mediated Lattice Rotation Design for Enhancing Thermoelectric Performance in Bi2S2Se

A unique strain-mediated lattice rotation strategy is introduced via nanocompositing to upsurge the optimized limits in the composition-to-structural pathway on rationally engineering the efficient thermoelectric material. In this study, a special lattice rotation via strain engineering is realized to optimize the desired electronic and chemical environment for enhancing thermoelectric properties in n-type Bi₂S₂Se. This approach results in a unique transport phenomenon to assist high-energy electrons in transferring through the optimized transport channels, and appropriate structure disparity to significantly localize phonons. As a result, Sb over Cl doping in Bi₂S₂Se gently reduces E_g and introduces defect states in bandgap with shifting down the Fermi level, thus causing increase in carrier concentration, which contributes to a higher power factor of ≈7.18 µW cm⁻¹ K⁻² (at T = 773 K). Besides, a lower thermal conductivity of ≈0.49 W m⁻¹ K⁻¹ is driven through lattice strain and defect engineering. Consequently, an ultra-high ZT_max = 1.13 (at T = 773 K) and a high ZT_ave = 0.54 (323 K-773 K) are realized. This study not only leads to an extraordinary thermoelectric performance but also reveals a unique paradigm for electron transportation and phonon localization via lattice strain engineering.     

High‐Performance N‐type Mg3Sb2 towards Thermoelectric Application near Room Temperature

Se‐doped Mg_3.2Sb_1.5Bi_0.5‐based thermoelectric materials are revisited in this study. An increased ZT value ≈ 1.4 at about 723 K is obtained in Mg_3.2Sb_1.5Bi_0.49Se_0.01 with optimized carrier concentration ≈ 1.9 × 10¹⁹ cm^?3. Based on this composition, Co and Mn are incorporated for the manipulation of the carrier scattering mechanism, which are beneficial to the dramatically enhanced electrical conductivity and power factor around room temperature range. Combined with the lowered lattice thermal conductivity due to the introduction of effective phonon scattering centers in Se&Mn‐codoped sample, a highest room temperature ZT value ≈ 0.63 and a peak ZT value ≈ 1.70 at 623 K are achieved for Mg_3.15Mn_0.05Sb_1.5Bi_0.49Se_0.01, leading to a high average ZT ≈ 1.33 from 323 to 673 K. In particular, a remarkable average ZT ≈ 1.18 between the temperature of 323 and 523 K is achieved, suggesting the competitive substitution for the commercialized n‐type Bi₂Te₃‐based thermoelectric materials.     

Discovering New Type of Lead-Free Cluster-Based Hybrid Double Perovskite Derivatives with Chiral Optical Activities and Low X-Ray Detection Limit

2D chiral hybrid perovskites have recently emerged as outstanding semiconductor materials. However, most of the reported 2D chiral perovskites have limited structural types and contain high levels of toxic lead, which severely hinders their further applications. Herein, by using a mixed-cation strategy, an unprecedented type of lead-free cluster-based 2D chiral hybrid double perovskite derivatives are successfully obtained, [(R/S-PPA)₄(IPA)₆Ag₂Bi₄I₂₄]·2H₂O ( 1-R and 1-S ), and [(R/S-PPA)₄(n-BA)₆Ag₂Bi₄I₂₄]·2H₂O ( 2-R and 2-S ) (R/S-PPA=R/S–1-phenylpropylamine; IPA=isopentylamine; n-BA=n-butylamine). Their inorganic skeletons are linked by binuclear {Bi₂I₁₀} and infinite chain {Ag₂Bi₂I₁₄}_∞, in which bismuth clusters and multiple coordination modes (e.g., tetrahedral AgI₄ and octahedral AgI₆) are introduced into the double perovskite system for the first time. This introduction induces distortion of the inorganic layer, which may facilitate the transfer of chirality from the chiral cations into achiral double perovskite skeletons. Further, circular dichroism measurements and circularly polarized light detection confirm their inherent chiral optical activities. In addition, 1-S exhibits an ultralow X-ray detection limit of 129.5 nGy s⁻¹, which is 42-fold lower than that of demands in regular medical diagnosis (5.5 µGy s⁻¹). This study provides a pathway to construct novel type of lead-free cluster-based double perovskite derivatives.     

Achieving Superior Thermoelectric Performance in Ge4Se3Te via Symmetry Manipulation with I–V–VI2 Alloying

Although orthorhombic GeSe is predicted to have an ultrahigh figure of merit, ZT ≈ 2.5, up to now, the highest experimental value is ≈0.2 due to the low carrier concentration (n_H ≈ 10¹⁸ cm⁻³). Improving symmetry is an effective approach for enhancing the ZT of GeSe-based materials. With Te-alloying, Ge₄Se₃Te displays the two-dimensional hexagonal structure and high n_H ≈ 1.23 × 10²¹ cm⁻³. Interestingly, Ge₄Se₃Te transformed from the hexagonal into the rhombohedral phase with only ≈2% I–V–VI₂-alloying (I = Li, Na, K, Cu, Ag; V = Sb, Bi; VI = Se, Te). According to the calculated results of Ge_0.82Ag_0.09Bi_0.09Se_0.614Te_0.386 single-crystal grown via AgBiTe₂-alloying, it exhibits a higher valley degeneracy than the hexagonal Ge₄Se₃Te. For instance, AgBiTe₂-alloying induces a strong band convergence and band inversion effect, resulting in a significantly enhanced Seebeck coefficient and power factor with a similar n_H from 17 µV K⁻¹ and 0.63 µW cm⁻¹ K⁻² for pristine Ge₄Se₃Te to 124 µV K⁻¹ and 5.97 µW cm⁻¹ K⁻² for 12%AgBiTe₂-alloyed sample, respectively. Moreover, the sharply reduced phonon velocity, nano-domain wall structure, and strong anharmonicity lead to low lattice thermal conductivity. As a result, a record-high average ZT ≈0.95 over 323–773 K with an excellent ZT ≈ 1.30 is achieved at 723 K.     

Silver Ions Assisted Inversion Temperature Crystallization of 2D Cs3Bi2Br9 Nanoflakes for Highly Sensitive X-Ray Detection

2D perovskites have attracted wide attention for optoelectronic applications because of their unique layer structure and tunable outstanding optical/electrical properties. In addition, 2D Cs₃Bi₂Br₉ nanoflakes possess large effective atomic number, high resistivity, high density as well as excellent stability, rendering it a promising material for X-ray detection. Nevertheless, it is full of challenges to synthesize 2D Cs₃Bi₂Br₉ nanoflakes by conventional inversion temperature crystallization (ITC) strategy due to the existence of Br^- vacancies in the Cs₃Bi₂Br₉ crystal nucleus. Herein, an Ag⁺ assisted ITC (SAITC) strategy to grow 2D Cs₃Bi₂Br₉ nanoflakes is proposed. The synthesis mechanism revealed by both experiments and theoretical calculations can be mainly ascribed to the passivated Br⁻ vacancies and enhanced structure stability by adding Ag⁺ which can effectively prevent the oxidation of 2D Cs₃Bi₂Br₉ nanoflakes from growth of hybrid crystals. The synthesized high-crystallinity 2D Cs₃Bi₂Br₉ nanoflakes possess direct bandgap characteristic, and the mobility lifetime can reach 9.8 × 10⁻⁴ cm² V⁻¹. Excitingly, the fabricated device based on 2D Cs₃Bi₂Br₉ nanoflakes demonstrates ultrahigh sensitivity of detecting X-ray (1.9 CGy_air⁻¹cm⁻²) at very low driven voltage (0.5 V) due to the photoconductive gain mechanism. The 2D Cs₃Bi₂Br₉ nanoflakes synthesized by SAITC method have great potential for developing highly sensitive optoelectronic devices.     

High Thermoelectric Performance in Sulfide‐Type Argyrodites Compound Ag8Sn(S1−xSex)6 Enabled by Ultralow Lattice Thermal Conductivity and Extended Cubic Phase Regime

Argyrodites with a general chemical formula of A₈BC₆ are known for complex phase transitions, ultralow lattice thermal conductivity, and mixed electronic and ionic conduction. The coexistence of ionic conduction and promising thermoelectric performance have recently been reported in selenide and telluride argyrodites, but scarcely in sulfide argyrodites. Here, the thermoelectric properties of Ag₈Sn(S_1?xSe_x)₆ are reported. Specifically, Ag₈SnS₆ exhibits intrinsically ultralow lattice thermal conductivities of 0.61–0.31 W m^?1 K^?1 over the whole temperature range from 32 to 773 K due to distorted local crystal structure, relatively weak chemical bonding, rattler‐like Ag atoms, low‐lying optical modes, and dynamic disorder of Ag ions at high temperatures. Se doping shifts the orthorhombic–cubic phase transition from 457 K at x = 0 to 430 K at x = 0.10, thereby expanding the temperature range of the thermoelectrically favored cubic phase. A figure of merit zT value ≈ 0.80 is achieved at 773 K in Ag₈Sn(S_1?xSe_x)₆ (x = 0.03), the highest zT value reported in sulfide argyrodites. These results fill a knowledge gap of the thermoelectric study of argyrodites and contribute to a comprehensive understanding of the chemical bonding, lattice dynamics, and thermal transport of argyrodites.     

High Thermoelectric Performance in the Wide Band‐Gap AgGa1‐xTe2 Compounds: Directional Negative Thermal Expansion and Intrinsically Low Thermal Conductivity

A deficiency of Ga in wide band‐gap AgGa_1‐xTe₂ semiconductors (1.2 eV) can be used to optimize the electrical transport properties and reduce the thermal conductivity to achieve ZT > 1 at 873 K. First‐principles density functional theory calculations and a Boson peak observed in the low temperature heat capacity data indicate the presence of strong coupling between optical phonons with low frequency and heat carrying acoustical phonons, resulting in a depressed maximum of Debye frequency in the first Brillouin zone and low phonon velocities. Moreover, the Ag? Te bond lengths and Te? Ag? Te bond angles increase with rising temperature, leading to a significant distortion of the [AgTe₄]^7? tetrahedra, but an almost unmodified [GaTe₄]^5? tetrahedra. This behavior results in lattice expansion in the ab‐plane and contraction along the c‐axis, corresponding to the positive and negative Gruneisen parameters in the phonon spectral calculations. This effect gives rise to the large anharmonic behavior of the lattice. These factors together with the low frequency vibrations of Ag and Te atoms in the structure lead to an ultralow thermal conductivity of 0.18 W m^?1 K^?1 at 873 K.     

Modulation Doping Leads to Optimized Thermoelectric Properties in n-Type Bi6Cu2Se4O6 due to Interface Effects

Heterogeneous composites consisting of Bi₆Cu₂Se_3.6Cl_0.4O₆ and Bi₂O₂Se are prepared according to the concept of modulation doping. With prominently increased carrier mobility and almost unchanged effective mass, the electrical transport properties are considerably optimized resulting in a peak power factor ≈1.8 µW cm⁻¹ K⁻² at 873 K, although the carrier concentration is slightly deteriorated. Meanwhile, the lattice thermal conductivity is lowered to ≈0.62 W m⁻¹ K⁻¹ due to the introduction of the second phase. The modified Self-consistent Effective Medium Theory is utilized to explain the deeper mechanism of modulation doping. The enhancement of apparent carrier mobility is derived from the highly active phase interfaces as fast carrier transport channels, while the reduced apparent thermal conductivity is ascribed to the existence of thermal resistance at the phase interfaces. Ultimately, an optimized ZT ≈0.23 is obtained at 873 K in Bi₆Cu₂Se_3.6Cl_0.4O₆ + 13% Bi₂O₂Se. This research demonstrates the effectiveness of modulation doping for optimizing thermoelectric properties once again, and provides the direct microstructure observation and consistent theoretical model calculation to emphasize the role of interface effects in modulation doping, which should be probably applicable to other thermoelectrics.     

Minimum Thermal Conductivity in Weak Topological Insulators with Bismuth‐Based Stack Structure

Contrary to the conventional belief that the consideration for topological insulators (TIs) as potential thermoelectrics is due to their excellent electrical properties benefiting from the topological surface states, this work shows that the 3D weak TIs, formed by alternating stacks of quantum spin Hall layers and normal insulator (NI) layers, can also be decent thermoelectrics because of their focus on minimum thermal conductivity. The minimum lattice thermal conductivity is experimentally confirmed in Bi₁₄Rh₃I₉ and theoretically predicted for Bi₂TeI at room temperature. It is revealed that the topologically “trivial” NI layers play a surprisingly critical role in hindering phonon propagation. The weak bonding in the NI layers gives rise to significantly low sound velocity, and the localized low‐frequency vibrations of the NI layers cause strong acoustic–optical interactions and lattice anharmonicity. All these features are favorable for the realization of exceptionally low lattice thermal conductivity, and therefore present remarkable opportunities for developing high‐performance thermoelectrics in weak TIs.     

Two-Dimensional Antimony-Based Perovskite-Inspired Materials for High-Performance Self-Powered Photodetectors

The ongoing Internet of Things revolution has led to strong demand for low-cost, ubiquitous light sensing based on easy-to-fabricate, self-powered photodetectors. While solution-processable lead-halide perovskites have raised significant hopes in this regard, toxicity concerns have prompted the search for safer, lead-free perovskite-inspired materials (PIMs) with similar optoelectronic potential. Antimony- and bismuth-based PIMs are found particularly promising; however, their self-powered photodetector performance to date has lagged behind the lead-based counterparts. Aiming to realize the full potential of antimony-based PIMs, this study examines, for the first time, the impact of their structural dimensionality on their self-powered photodetection capabilities, with a focus on 2D Cs₃Sb₂I_9−xCl_x and Rb₃Sb₂I₉ and 0D Cs₃Sb₂I₉. The 2D absorbers deliver cutting-edge self-powered photodetector performance, with a more-than-tenfold increase in external quantum efficiency (up to 55%), speed of response (>5 kHz), and linear dynamic range (>four orders of magnitude) compared to prior self-powered A₃M₂X₉ implementations (A⁺: monovalent cation; M³⁺: Sb³⁺/Bi³⁺; X⁻: halide anion). Detailed characterization reveals that such a performance boost originates from the superior carrier lifetimes and reduced exciton self-trapping enabled by the 2D structure. By delivering cutting-edge performance and mechanistic insight, this study represents an important step in lead-free perovskite-inspired optoelectronics toward self-powered, ubiquitous light sensing.     

Dual‐Phase All‐Inorganic Cesium Halide Perovskites for Conducting‐Bridge Memory‐Based Artificial Synapses

Neuromorphic computing, which mimics biological neural networks, can overcome the high‐power and large‐throughput problems of current von Neumann computing. Two‐terminal memristors are regarded as promising candidates for artificial synapses, which are the fundamental functional units of neuromorphic computing systems. All‐inorganic CsPbI₃ perovskite‐based memristors are feasible to use in resistive switching memory and artificial synapses due to their fast ion migration. However, the ideal perovskite phase α‐CsPbI₃ is structurally unstable at ambient temperature and rapidly degrades to a non‐perovskite δ‐CsPbI₃ phase. Here, dual‐phase (Cs₃Bi₂I₉)_0.4?(CsPbI₃)_0.6 is successfully fabricated to achieve improved air stability and surface morphology compared to each single phase. Notably, the Ag/polymethylmethacrylate/(Cs₃Bi₂I₉)_0.4?(CsPbI₃)_0.6/Pt device exhibits non‐volatile memory functions with an endurance of ≈10³ cycles and retention of ≈10⁴ s with low operation voltages. Moreover, the device successfully emulates synaptic behavior such as long‐term potentiation/depression and spike timing/width‐dependent plasticity. This study will contribute to improving the structural and mechanical stability of all‐inorganic halide perovskites (IHPs) via the formation of dual phase. In addition, it proves the great potential of IHPs for use in low‐power non‐volatile memory devices and electronic synapses.     

High Optical Gain of Solution-Processed Mixed-Cation CsPbBr3 Thin Films towards Enhanced Amplified Spontaneous Emission

A solution-processed thin film made of all-inorganic CsPbBr₃ perovskite is a promising candidate for low-cost and flexible green-color lasers. However, the amplified spontaneous emission (ASE) of solution-processed CsPbBr₃ films still experiences a high threshold owing to poor morphology and insufficient optical gain. Here, a multiple-cation doping strategy is demonstrated to develop compact, smooth thin films of Cs_0.87(FAMA)_0.13PbBr₃/(NMA)₂PbBr₄ (FA: formamidinium; MA: methylammonium; NMA: naphthylmethylammonium) with a record high net modal optical gain of ≈ 3030 cm⁻¹ and low propagation loss of 1.0 cm⁻¹. The FA and MA cations improve the crystallization kinetics to form continuous films, and the NMA cations reduce the grain dimension, increase film dispersibility/uniformity, and enhance spatial confinement to promote optical gain. Room-temperature ASE is demonstrated under a low threshold of ≈ 3.8  µ J cm⁻² without degradation after four months of storage in glove box or excitation by 3 × 10⁷ laser pulses. These findings provide insights into enhancing the optical gain and lowering the threshold of perovskite lasers in terms of molecular synthesis and microstructure engineering.     

Characterization of Bi2S3 nanorods prepared at room temperature

Bi₂S₃ is a direct band gap semiconductor with a band gap of 1.3 eV. It belongs to the family of metal chalcogenides of type A₂^VB₃^VI (A=As, Sb, and Bi; B=S, Se, and Te), whose importance in photovoltaic and thermoelectric applications is well recognized. Although nanostructures of Bi₂S₃ have been obtained using a number of techniques, reports on assemblies of Bi₂S₃ are sparse. In the present work, we prepared single crystalline bismuth sulfide (Bi₂S₃) nanorods at room temperature by reacting Bi(NO₃)₃, thioacetamide (TAA), hydrochloric acid and distilled water.Energy dispersive analysis of X-rays (EDAX) obtained from Bi₂S₃ nanorods indicated no incorporation of other foreign impurities in it. X-ray diffraction confirmed the single phase of Bi₂S₃ and different diffracting planes were indexed based on the orthorhombic structure and lattice parameters were determined. X-ray photoelectron spectroscopy (XPS) was used to evaluate its composition and purity. The synthesized nanorods with different images observed under transmission electron microscopy (TEM) are shown in the paper and the selected area electron diffraction (SAED) pattern obtained from these nanorods shows their single crystalline behavior. Raman measurement performed at room temperature using Ar⁺ laser (488 nm) confirms the presence of 238 cm⁻¹ and 972 cm⁻¹ phonon modes. The optical absorption spectra obtained by UV–vis spectrometer show blue shift in comparison to bulk Bi₂S₃ while its thermal stability was studied by thermogravimetric analysis.     

Lattice Instability Induced Concerted Structural Distortion in Charged and van der Waals Layered GdTe3

Structural mosaic of rare-earth tri-tellurides (RTe₃) inlaid with non-classical structural motifs like the 2D−polytelluride square nets has attracted immense attention owing to their enigmatic chemical bonding, unconventional structure, and harboring charge density wave (CDW) ground states. GdTe₃, an archetypal RTe₃, is a natural heterostructure of charged and van der Waals (vdW) layers, formed by intercalating vdW gap separated 2D square telluride nets [(Te₂)⁻]_n between the charged double corrugated slabs of n[GdTe]⁺. Here, we have investigated the evolution of structural distortions along with the electrical and thermal transport properties of GdTe₃ across its CDW transition through X-ray pair distribution function analysis, thermal conductivity measurements, Raman spectroscopy and first principles theoretical calculations. The results reveal that the unusual structure of GdTe₃ engenders a large anisotropic lattice thermal conductivity by concomitantly hampering the phonon propagation along parallel to the spark plasma sintering (SPS) pressing direction via chemical bonding hierarchy while facilitating phonon propagation along perpendicular to the SPS pressing direction through the metallic Te sheets and phason channel. The low lattice thermal conductivity is attributed to the strong vibrational anharmonicity caused by CDW-induced concerted local lattice distortions of both Gd–Te slab and Te square net, and the robust electron–phonon coupling.     

Enhanced On–Off Ratio Photodetectors Based on Lead‐Free Cs3Bi2I9 Single Crystal Thin Films

Hybrid organic–inorganic lead halide perovskite single crystal thin film (SCTF) recently has attracted enormous interest in the field of optoelectronic devices, since it efficiently resolves the trade‐off between thickness and carrier diffusion length. However, the toxicity of lead element and the instability induced by organic component still hinder its future developments. In this work, lead‐free all‐inorganic Cs₃Bi₂I₉ SCTF with a high orientation along (00h) has been in situ grown on indium tin oxide (ITO) glass via a space‐limited solvent evaporation crystallization method. The trap density of Cs₃Bi₂I₉ SCTF (5.7 × 10¹² cm^?3) is 263 folds lower than that of the polycrystalline thin film (PCTF) counterpart, together with a 5‐order‐of‐magnitude higher carrier mobility. These superior charge transfer properties enable a photoresponse on–off ratio as high as 11 000, which far surpasses that of the PCTF device by 460 folds, comparable to the lead halide perovskite. Furthermore, the Cs₃Bi₂I₉ SCTF photodetector exhibits outstanding stability even without any encapsulation, whose initial performance is well maintained after aging 1000 h in humid air of 50% RH or continuous on–off light illumination for 20 h. This work will pave the way to produce new families of high‐performance, stable, and nontoxic perovskite SCTF for future optoelectronic applications.     

Ultralow Loss and High Tunability in a Non-perovskite Relaxor Ferroelectric

Dielectric ceramics are fundamental for electronic systems, including energy storages, microwave applications, ultrasonics, and sensors. Relaxor ferroelectrics show superb performance among dielectrics due to their high efficiency and energy density by the nature of nanodomains. Here, a novel non-perovskite relaxor ferroelectric, Bi₆Ti₅WO₂₂, with ultralow loss, ≈10⁻³, highly tunable permittivity, ≈2200 at room temperature with 40% tunability and the superparaelectric region at room temperature is presented. The actual crystal structure and the nanodomains of Bi₆Ti₅WO₂₂ are demonstrat Various-temperature neutron powder diffraction and in situ high-resolution transmission-electron-microscopy illustrate the twinning effect, subtle structure change and micro-strain in the material influenced by temperature, manifesting the actual crystal structure of Bi₆Ti₅WO₂₂. Compared with dielectric loss of BaTiO₃-based dielectric tunable materials, the loss of Bi₆Ti₅WO₂₂ is more than an order of magnitude lower, which makes it exhibit a figure of merit (≈240), much higher than that of conventional dielectric tunable materials (< 100), endorse the material great potential for direct applications. The present research offers a strategy for discovering novel relaxor ferroelectrics and a highly desirable material for fabricating energy storage capacitors, microwave dielectrics, and ultrasonics.     

Highly Stable and Spectrally Tunable Gamma Phase RbxCs1–xPbI3 Gradient-Alloyed Quantum Dots in PMMA Matrix through A Sites Engineering

Perovskite quantum dots are emerging as new generation functional materials for display applications. The issue of perovskite “red wall” has been an obstacle for their use in display technology. In this study, the fabrication of γ-Rb_xCs_1–xPbI₃ gradient-alloyed quantum dots in polymeric matrix through a rational designed in situ fabrication process is reported. The formation of γ-Rb_xCs_1–xPbI₃ gradient-alloyed structure can be explained by considering the lattice mismatch and solubility difference between γ-CsPbI₃ and RbPbI₃. The photoluminescence emission of γ-Rb_xCs_1–xPbI₃ gradient-alloyed quantum dots can be tuned from 675 to 620 nm with full width at half maximum of 31 nm and maximum quantum yields up to 91%. Importantly, the packaged films retained about 95% of its original photoluminescence intensity after 1000 h aging at the test conditions of 60 °C, 90% RH and 40 °C, 90% RH with 3 mW cm⁻², 455 nm blue light irradiation, respectively. By integrating a red and green dual emissive film with blue Mini LEDs, a LCD backlight of a color space of ≈130% of NTSC 1931 standard is achieved with matching rate of 100%.     

Enhanced Thermoelectric Performance in GeTe by Synergy of Midgap state and Band Convergence

The good co-existence of midgap state and valence band degeneracy is realized in Bi-alloyed GeTe through the In-Cd codoping to play different but complementary roles in the valence band structure modification. In doping induces midgap state and results in a considerably improved Seebeck coefficient near room temperature, while Cd doping significantly increases the Seebeck coefficient in the mid-high temperature region by promoting the valence band convergence. The synergistic effects obviously increase the density of state effective mass from 1.39 to 2.65 m₀, and the corresponding carrier mobility still reaches 34.3 cm² V⁻¹ s⁻¹ at room temperature. Moreover, the Bi-In-Cd co-alloying introduces various phonon scattering centers including nanoprecipitates and strain field fluctuations and suppresses the lattice thermal conductivity to a rather low value of 0.56 W m⁻¹ K⁻¹ at 600 K. As a result, the Ge_0.89Bi_0.06In_0.01Cd_0.04Te sample obtains excellent thermoelectric properties of zT_max ≈2.12 at 650 K and zT_avg ≈1.43 between 300 and 773 K. This study illustrates that the thermoelectric performance of GeTe can be optimized in a wide temperature range through the synergy of midgap state and valence band convergence.