Temperature Self-Compensating Intelligent Wireless Measuring Contact Lens for Quantitative Intraocular Pressure Monitoring.

Flexible bioelectronic devices that can perform real-time and accurate intraocular pressure (IOP) monitoring in both clinical and home settings hold significant implications for the diagnosis and treatment of glaucoma, yet they face challenges due to the open physiological environment of the ocular. Herein, we develop an intelligent wireless measuring contact lens (WMCL) incorporating a dual inductor-capacitor-resistor (LCR) resonant system to achieve temperature self-compensation for quantitative IOP monitoring in different application environments. The WMCL utilizes a compact circuitry design, which enables the integration of low-frequency and high-frequency resonators within a single layer of a sensing circuit without causing visual impairment. Mechanically guided microscale 3D encapsulation strategy combined with flexible circuit printing techniques achieves the surface-adaptive fabrication of the WMCL. The specific design of frequency separation imparts distinct temperature response characteristics to the dual resonators, and the linear combination of the dual resonators can eliminate the impact of temperature variations on measurement accuracy. The WMCL demonstrates outstanding sensitivity and linearity in monitoring the IOP of porcine eyes in vitro while maintaining satisfactory measurement accuracy even with internal temperature variations exceeding 10 °C. Overcoming the impact of temperature variations on IOP monitoring from the system level, the WMCL showcases immense potential as the next generation of all-weather IOP monitoring devices.

Solution-processable mixed-anion cluster chalcohalide Rb6Re6S8I8 in a light-emitting diode.

Rhenium chalcohalide cluster compounds are a photoluminescent family of mixed-anion chalcohalide cluster materials. Here we report the new material Rb6Re6S8I8, which crystallizes in the cubic space group Fm[Formula: see text]m and contains isolated [Re6S8I6]4- clusters. Rb6Re6S8I8 has a band gap of 2.06(5) eV and an ionization energy of 5.51(3) eV, and exhibits broad photoluminescence (PL) ranging from 1.01 eV to 2.12 eV. The room-temperature PL exhibits a PL quantum yield of 42.7% and a PL lifetime of 77 µs (99 µs at 77 K). Rb6Re6S8I8 is found to be soluble in multiple polar solvents including N,N-dimethylformamide, which enables solution processing of the material into films with thickness under 150 nm. Light-emitting diodes based on films of Rb6Re6S8I8 were fabricated, demonstrating the potential for this family of materials in optoelectronic devices.

A unified understanding of minimum lattice thermal conductivity.

We propose a first-principles model of minimum lattice thermal conductivity ([Formula: see text]) based on a unified theoretical treatment of thermal transport in crystals and glasses. We apply this model to thousands of inorganic compounds and find a universal behavior of [Formula: see text] in crystals in the high-temperature limit: The isotropically averaged [Formula: see text] is independent of structural complexity and bounded within a range from ∼0.1 to ∼2.6 W/(m K), in striking contrast to the conventional phonon gas model which predicts no lower bound. We unveil the underlying physics by showing that for a given parent compound, [Formula: see text] is bounded from below by a value that is approximately insensitive to disorder, but the relative importance of different heat transport channels (phonon gas versus diffuson) depends strongly on the degree of disorder. Moreover, we propose that the diffuson-dominated [Formula: see text] in complex and disordered compounds might be effectively approximated by the phonon gas model for an ordered compound by averaging out disorder and applying phonon unfolding. With these insights, we further bridge the knowledge gap between our model and the well-known Cahill-Watson-Pohl (CWP) model, rationalizing the successes and limitations of the CWP model in the absence of heat transfer mediated by diffusons. Finally, we construct graph network and random forest machine learning models to extend our predictions to all compounds within the Inorganic Crystal Structure Database (ICSD), which were validated against thermoelectric materials possessing experimentally measured ultralow κL. Our work offers a unified understanding of [Formula: see text], which can guide the rational engineering of materials to achieve [Formula: see text].

Study on the CHZ-II Gravimeter and Its Calibrations along Forward and Reverse Overlapping Survey Lines.

The moving-base gravimeter is one of the key instruments used for Earth gravity survey. The accuracy of the survey data is closely related to the calibration precision of several key parameters, such as the damping delay time, the drift coefficient, the gravity scale factor, and the measurement accuracy. This paper will introduce the development of the CHZ-II gravimeter system in which a cylindrical sampling mass suspended vertically by a zero-length spring acts as a sensitive probe to measure specific force. Meanwhile, a GNSS (Global Navigation Satellite System) positioning system is employed to monitor the carrier motion and to remove the inertia acceleration. In order to achieve high-precision calibrations for the key parameters, a new calibration method performed along forward and reverse overlapping lines is proposed, which is used to calibrate the above parameters and to estimate the measurement accuracy of the instrument used for a normal gravity survey. The calibration principle and the shipboard calibration data processing method are introduced. The calibration was performed for three moving-base gravimeters and the corresponding results are determined, indicating that the method can significantly improve the accuracy of the parameters. For the CHZ-II gravimeter, the measurement accuracy of the survey is 0.471 mGal (1 mGal = 10-5 m/s2), which improved by 19.5% after applying the calibrated parameters. This method is also practical for use with aviation, marine and even vehicle-carried moving-base gravimeters.

2D Homologous Series SrFMnBiSn+2 (M = Pb, Ag0.5Bi0.5; n = 0, 1) and Commensurately Modulated Sr2F2Bi2/3S2.

We report three new mixed-anion two-dimensional (2D) compounds: SrFPbBiS3, SrFAg0.5Bi1.5S3, and Sr2F2Bi2/3S2. Their structures as well as the parent compound SrFBiS2 were refined using single-crystal X-ray diffraction data, with the sequence of SrFBiS2, SrFPbBiS3, and SrFAg0.5Bi1.5S3 defining the new homologous series SrFMnBiSn+2 (M = Pb, Ag0.5Bi0.5; n = 0, 1). Sr2F2Bi2/3S2 has a different structure, which is modulated with a q vector of 1/3b* and was refined in superspace group X2/m(0ß0)00 as well as in the 1 × 3 × 1 superstructure with space group C2/m (with similar results). Sr2F2Bi2/3S2 features hexagonal layers of alternating [Sr2F2]2+ and [Bi2/3S2]2-, and the modulated structure arises from the unique ordering pattern of Sr2+ cations. SrFPbBiS3, SrFAg0.5Bi1.5S3, and Sr2F2Bi2/3S2 are semiconductors with band gaps of 1.31, 1.21, and 1.85 eV, respectively. The latter compound exhibits room temperature red photoluminescence at ∼700 nm.

Nonmetallic Active Sites on Nickel Phosphide in Oxygen Evolution Reaction.

Efficient and durable catalysts are crucial for the oxygen evolution reaction (OER). The discovery of the high OER catalytic activity in Ni12P5 has attracted a great deal of attention recently. Herein, the microscopic mechanism of OER on the surface of Ni12P5 is studied using density functional theory calculations (DFT) and ab initio molecular dynamics simulation (AIMD). Our results demonstrate that the H2O molecule is preferentially adsorbed on the P atom instead of on the Ni atom, indicating that the nonmetallic P atom is the active site of the OER reaction. AIMD simulations show that the dissociation of H from the H2O molecule takes place in steps; the hydrogen bond changes from Oa-H⋯Ob to Oa⋯H-Ob, then the hydrogen bond breaks and an H+ is dissociated. In the OER reaction on nickel phosphides, the rate-determining step is the formation of the OOH group and the overpotential of Ni12P5 is the lowest, thus showing enhanced catalytic activity over other nickel phosphides. Moreover, we found that the charge of Ni and P sites has a linear relationship with the adsorption energy of OH and O, which can be utilized to optimize the OER catalyst.

Low Thermal Conductivity in Heteroanionic Materials with Layers of Homoleptic Polyhedra.

Although BiAgOSe, an analogue of a well-studied thermoelectric material BiCuOSe, is thermodynamically stable, its synthesis is complicated by the low driving force of formation from the stable binary and ternary intermediates. Here we have developed a "subtraction strategy" to suppress byproducts and produce pure phase BiAgOSe using hydrothermal methods. Electronic structure calculations and optical characterization show that BiAgOSe is an indirect bandgap semiconductor with a bandgap of 0.95 eV. The prepared sample exhibits lower lattice thermal conductivities (0.61 W·m-1·K-1 at room temperature and 0.35 W·m-1·K-1 at 650 K) than BiCuOSe. Lattice dynamical simulations and variable temperature diffraction measurements demonstrate that the low lattice thermal conductivity arises from both the low sound velocity and high phonon-phonon scattering rates in BiAgOSe. These in turn result primarily from the soft Ag-Se bonds in the edge-sharing AgSe4 tetrahedra and large sublattice mismatch between the quasi-two-dimensional [Bi2O2]2+ and [Ag2Se2]2- layers. These results highlight the advantages of manipulating the chemistry of homoleptic polyhedra in heteroanionic compounds for electronic structure and phonon transport control.

Ultralow Thermal Conductivity, Multiband Electronic Structure and High Thermoelectric Figure of Merit in TlCuSe.

The entanglement of lattice thermal conductivity, electrical conductivity, and Seebeck coefficient complicates the process of optimizing thermoelectric performance in most thermoelectric materials. Semiconductors with ultralow lattice thermal conductivities and high power factors at the same time are scarce but fundamentally interesting and practically important for energy conversion. Herein, an intrinsic p-type semiconductor TlCuSe that has an intrinsically ultralow thermal conductivity (0.25 W m-1 K-1 ), a high power factor (11.6 µW cm-1 K-2 ), and a high figure of merit, ZT (1.9) at 643 K is described. The weak chemical bonds, originating from the filled antibonding orbitals p-d* within the edge-sharing CuSe4 tetrahedra and long TlSe bonds in the PbClF-type structure, in conjunction with the large atomic mass of Tl lead to an ultralow sound velocity. Strong anharmonicity, coming from Tl+ lone-pair electrons, boosts phonon-phonon scattering rates and further suppresses lattice thermal conductivity. The multiband character of the valence band structure contributing to power factor enhancement benefits from the lone-pair electrons of Tl+ as well, which modify the orbital character of the valence bands, and pushes the valence band maximum off the Γ-point, increasing the band degeneracy. The results provide new insight on the rational design of thermoelectric materials.

Single-Metallic Thermoresponsive Coordination Network as a Dual-Parametric Luminescent Thermometer.

The single-metallic coordination networks (CNs), simultaneously exhibiting temperature-dependent lifetime (TDLT) and emission band shift (TDEBS), are desirable for application in luminescent thermometers with high accuracy and reliability in a large temperature range. Nonetheless, up to date, there are no reports on such kinds of materials due to the lack of in-depth understanding of the origin of TDLT and TDEBS at a molecule level, being critical for exploiting a universal approach to design a dual-parametric CN phosphorescent thermometer (CN-PT). Herein, we have constructed a thermoresponsive CN [Cu2(L1)Br2]∞ (IAM21-1, L1 = N1,N6-di(pyridin-3-yl)adipamide) via a flexible-ligand-implanted strategy. The TDLT and TDEBS properties of IAM21-1 enable it to be applied as a single-metallic dual-parametric CN-PT in 50-500 K, which is the widest temperature range reported so far. The combination of structure analysis and DFT calculations demonstrates that the redshift of the emission band upon the decreasing temperature originates from the reversible skeleton-shrinkage-triggered narrower band gap. This work has unveiled the origin of TDLT and TDEBS properties and proposed an efficient strategy for designing dual-parametric CN-PTs.

Pressure-induced ferroelectric-like transition creates a polar metal in defect antiperovskites Hg3Te2X2 (X = Cl, Br).

Ferroelectricity is typically suppressed under hydrostatic compression because the short-range repulsions, which favor the nonpolar phase, increase more rapidly than the long-range interactions, which prefer the ferroelectric phase. Here, based on single-crystal X-ray diffraction and density-functional theory, we provide evidence of a ferroelectric-like transition from phase I213 to R3 induced by pressure in two isostructural defect antiperovskites Hg3Te2Cl2 (15.5 GPa) and Hg3Te2Br2 (17.5 GPa). First-principles calculations show that this transition is attributed to pressure-induced softening of the infrared phonon mode Γ4, similar to the archetypal ferroelectric material BaTiO3 at ambient pressure. Additionally, we observe a gradual band-gap closing from ~2.5 eV to metallic-like state of Hg3Te2Br2 with an unexpectedly stable R3 phase even after semiconductor-to-metal transition. This study demonstrates the possibility of emergence of polar metal under pressure in this class of materials and establishes the possibility of pressure-induced ferroelectric-like transition in perovskite-related systems.

Zn3B7O13Cl: A New Deep-Ultraviolet Transparency Nonlinear Optical Crystal with Boracite Structure.

Nonlinear optical crystals play important roles in modern laser science and technology. However, the design and growth of new nonlinear optical (NLO) materials is still a challenging issue for researchers. Due to the excellent performance of Mg3B7O13Cl crystal, we paid attention to the optimization of its structure, in order to find new NLO materials with favorable properties. Here, Zn3B7O13Cl crystals were obtained by a high-temperature solution method. Its structure was determined to be the trigonal symmetry with a polar space group of R3c, which is more highly symmetric than that of Mg3B7O13Cl (Pca21). The experimental and theoretical investigations demonstrated that the title compound exhibits a short absorption cutoff (band gap ∼6.53 eV), moderate SHG responses (2.2 times that of KDP at 1064 nm), and the improved birefringence, which results from the large distortion and anisotropy of borate groups and zinc polyhedrons. Therefore, the structural modification of Mg3B7O13Cl by zinc cations achieves a balance between the deep-ultraviolet transparency, the nonlinear optical effect, and the moderate birefringence, which is very significant for the design of practical NLO materials.

Influence of γ-irradiation and oxygen conditions on the diffusion of I-125 in crushed Beishan granite.

The diffusion of iodine (labeled with 125I-) in compacted Beishan granite (BsG) was investigated using the in-diffusion capillary method at pH ~2.0 to ~11.0 under oxygen and irradiation conditions. With the advantages of simple and easy operation of the capillary diffusion devices, this work makes a preliminary investigation on the irradiation condition that cannot be performed by the traditional diffusion experiment. In this study, Da values of 125I as a tracer in the form of iodide were determined to investigate and assess the influence of irradiation and oxygen conditions, which must be considered in-situ environment of the geologic repository. The results indicate that capillary method is a simple and efficient method to study the diffusion behavior of radionuclides, which is a relatively feasible to quickly obtain the diffusion coefficient, especially for some special conditions, e.g., oxygen and irradiation conditions. The diffusion results showed that Da values of 125I- range from 1.4 × 10-10 to 1.5 × 10-9 m2∙s-1, which was much faster than other nuclides, such as 79Se (10-11 m2∙s-1). The batch adsorption experiments in this paper and related studies showed that the sorption could be neglected, i.e., 125I- is a weak adsorbent nuclide. Its diffusion and sorption process were hardly affected by pH、oxygen and irradiation conditions, which is very different from 79Se. Besides, ionic strength has a significant impact on the diffusion rate of 125I-, which is closely related to the double electric layer. Overall, this study indicates that natural BsG couldn't greatly attenuate the mobility of 125I- in the deep geologic repository and new retardation method or materials need to be explored.

CeTi2O6-A Promising Oxide for Solar Thermochemical Hydrogen Production.

A large entropy of reduction is crucial in achieving materials capable of high-efficiency solar thermochemical hydrogen (STCH) production through two-step thermochemical water splitting cycles. We have recently demonstrated that the onsite electronic entropy of reduction attains an extreme value of 4.26 kB at 1500 K in Ce4+ → Ce3+ redox reactions, which explains the high performance and uniqueness of CeO2 as an archetypal STCH material. However, ceria requires high temperatures (T > 1500 °C) to achieve a reasonable reduction extent because of its large reduction enthalpy, which is a major obstacle in practical applications. Therefore, new materials with a large entropy of reduction and lower reduction enthalpy are required. Here, we perform a systematic screening to search for Ce4+-based oxides which possess thermodynamics superior to CeO2 for STCH production. We first search the Inorganic Crystal Structure Database (ICSD) and literature for Ce4+-based oxides and subsequently use density functional theory to compute their reduction enthalpies (i.e., oxygen vacancy formation energies). We find that CeTi2O6 with the brannerite structure is the most promising candidate for STCH because it possesses three essential characteristics of an STCH material: (i) a smaller reduction enthalpy compared to ceria yet large enough to split water, (ii) a high thermal stability, as reported experimentally, and (iii) a large entropy of reduction associated with Ce4+ → Ce3+ redox. Our proposed design strategy suggests that further exploration of Ce4+ oxides for STCH production is warranted.

Particlelike Phonon Propagation Dominates Ultralow Lattice Thermal Conductivity in Crystalline Tl_{3}VSe_{4}.

We investigate the microscopic mechanisms of ultralow lattice thermal conductivity (κ_{l}) in Tl_{3}VSe_{4} by combining a first principles density functional theory based framework of anharmonic lattice dynamics with the Peierls-Boltzmann transport equation for phonons. We include contributions of the three- and four-phonon scattering processes to the phonon lifetimes as well as the temperature dependent anharmonic renormalization of phonon energies arising from an unusually strong quartic anharmonicity in Tl_{3}VSe_{4}. In contrast to a recent report by Mukhopadhyay et al. [Science 360, 1455 (2018)SCIEAS0036-807510.1126/science.aar8072] which suggested that a significant contribution to κ_{l} arises from random walks among uncorrelated oscillators, we show that particlelike propagation of phonon excitations can successfully explain the experimentally observed ultralow κ_{l}. Our findings are further supported by explicit calculations of the off-diagonal terms of the heat current operator, which are found to be small and indicate that wavelike tunneling of heat carrying vibrations is of minor importance. Our results (i) resolve the discrepancy between the theoretical and experimental κ_{l}, (ii) offer new insights into the minimum κ_{l} achievable in Tl_{3}VSe_{4}, and (iii) highlight the importance of high order anharmonicity in low-κ_{l} systems. The methodology demonstrated here may be used to resolve the discrepancies between the experimentally measured and the theoretically calculated κ_{l} in skutterides and perovskites, as well as to understand the glasslike κ_{l} in complex crystals with strong anharmonicity, leading towards the goal of rational design of new materials.

Ca2B5O9Cl and Sr2B5O9Cl: Nonlinear Optical Crystals with Deep-Ultraviolet Transparency Windows.

M2B5O9X is a prominent family with excellent nonlinear optical (NLO) responses, just as the Pb2B5O9I crystal with a large second harmonic generation (SHG) of 13.5 times that of KH2PO4. However, most of these compounds are limited to ultraviolet and visible regions because of their long absorption edge (small band gap). Here, we report two members of this family, which change the situation. Using a high-temperature solution method, we obtain Ca2B5O9Cl and Sr2B5O9Cl crystals, which exhibit a deep-ultraviolet (DUV) absorption edge of 170 nm (band gap ≈ 7.29 eV). It is an important breakthrough in the DUV transparency of the M2B5O9X family. Furthermore, Ca2B5O9Cl crystals display a phase-matching SHG response under a 1064 nm laser, which is further confirmed by the balance between the suitable birefringence and the small dispersion of refractive indexes in the wavelength range of 1064-532 nm. Therefore, they are promising DUV transparency windows and NLO candidates.

Mechanistic insight of KBiQ2 (Q = S, Se) using panoramic synthesis towards synthesis-by-design.

Solid-state synthesis has historically focused on reactants and end products; however, knowledge of reaction pathways, intermediate phases and their formation may provide mechanistic insight of solid-state reactions. With an increased understanding of reaction progressions, design principles can be deduced, affording more predictive power in materials synthesis. In pursuit of this goal, in situ powder X-ray diffraction is employed to observe crystalline phase evolution over the course of the reaction, thereby constructing a "panoramic" view of the reaction from beginning to end. We conducted in situ diffraction studies in the K-Bi-Q (Q = S, Se) system to understand the formation of phases occurring in this system in the course of their reactions. Powder mixtures of K2Q to Bi2Q3 in 1 : 1 and 1.5 : 1 ratios were heated to 800 °C or 650 °C, while simultaneously collecting diffraction data. Three new phases, K3BiS3, ß-KBiS2, and ß-KBiSe2, were discovered. Panoramic synthesis showed that K3BiQ3 serves an important mechanistic role as a structural intermediate in both chalcogen systems (Q = S, Se) in the path to form the KBiQ2 structure. Thermal analysis and calculations at the density functional theory (DFT) level show that the cation-ordered ß-KBiQ2 polymorphs are the thermodynamically stable phase in this compositional space, while Pair Distribution Function (PDF) analysis shows that all α-KBiQ2 structures have local disorder due to stereochemically active lone pair expression of the bismuth atoms. The formation of the ß-KBiQ2 structures, both of which crystallize in the α-NaFeO2 structure type, show a boundary where the structure can be disordered or ordered with regards to the alkali metal and bismuth. A cation radius tolerance for six-coordinate cation site sharing of ∼ 1.3 is proposed. The mechanistic insight the panoramic synthesis technique provides in the K-Bi-Q system is progress towards the overarching goal of synthesis-by-design.

[Automated hyphenation of in-tube boronate affinity solid-phase microextraction with high performance liquid chromatography for the determination of cis-diol compounds in tea beverages].

Automatic hyphenated analytical techniques hold great promise for reducing labour intensity, enhancing efficiency, and ensuring data reproducibility. In recent decade, Boronate affinity solid phase microextraction (BA-SPME) has emerged as a unique tool for the selective extraction of cis-diol-containing compounds. However, automatic hyphenation of SPME with high performance liquid chromatography (HPLC) has not yet been reported. Herein we report a new automated hyphenation of in-tube BA-SPME with HPLC for the determination of cis-diol compounds in tea beverages. The automated hyphenation was implemented through a flow-switch via the six-way valve of an autosampler. We prepared an in-tube SPME capillary, investigated the loading capacity of the coated column, characterized the morphology of the column, and investigated the factors influencing the separation. Finally, using the automatic hyphenated SPME-HPLC approach, we analyzed the cis-diol-containing compounds in three kinds of commercial tea beverages and investigated the effect of tea-making temperature on the content of the cis-diol-containing compounds in the prepared tea.

Antiferromagnetic Semiconductor BaFMn0.5Te with Unique Mn Ordering and Red Photoluminescence.

Semiconductors possessing both magnetic and optoelectronic properties are rare and promise applications in opto-spintronics. Here we report the mixed-anion semiconductor BaFMn0.5Te with a band gap of 1.76 eV and a work function of 5.08 eV, harboring both antiferromagnetism (AFM) and strong red photoluminescence (PL). The synthesis of BaFMn0.5Te in quantitative yield was accomplished using the "panoramic synthesis" technique and synchrotron radiation to obtain the full reaction map, from which we determined that the compound forms upon heating at 850 °C via an intermediate unknown phase. The structure refinement required the use of a (3+1)-dimensional superspace group Cmme(α01/2)0ss. The material crystallizes into a ZrCuSiAs-like structure with alternating [BaF]+ and [Mn0.5Te]- layers and has a commensurately modulated structure with the q-vector of 1/6a* + 1/6b* + 1/2c* at room temperature arising from the unique ordering pattern of Mn2+ cations. Long-range AFM order emerges below 90 K, with two-dimensional short-range AFM correlations above the transition temperature. First-principles calculations indicate that BaFMn0.5Te is an indirect band gap semiconductor with the gap opening between Te 5p and Mn 3d orbitals, and the magnetic interactions between nearest-neighbor Mn2+ atoms are antiferromagnetic. Steady-state PL spectra show a broad strong emission centered at ∼700 nm, which we believe originates from the energy manifolds of the modulated Mn2+ sublattice and its defects. Time-resolved PL measurements reveal an increase in excited-state lifetimes with longer probe wavelengths, from 93 ns (at 650 nm) to 345 ns (at 800 nm), and a delayed growth (6.5 ± 0.3 ns) in the kinetics at 800 nm with a concomitant decay (4.1 ± 0.1 ns) at 675 nm. Together, these observations suggest that there are multiple emissive states, with higher energy states populating lower energy states by energy transfer.

[Determination and classification of flammable liquids by headspace gas chromatography-mass spectrometry].

An effective method was established for the determination and classification of flammable liquids by headspace gas chromatography-mass spectrometry (HS-GC-MS). The volatile components, equilibrium temperature and equilibrium time of gravure ink were investigated. The volatile components of flammable liquids were identified by comparison with the standard mass spectrum databases, and quantified by the external standard method. The recoveries were in the range of 92.8%-103.1% with the relative standard deviations between 0.88% and 2.88%. The flash points of the samples were calculated by a prediction model and compared with the experimentally measured values. The results showed that the maximum deviation between the predicted and measured flash points was 3.2℃. This method provides a novel, efficient and convenient way for the classification of flammable liquids.

A Natural 2D Heterostructure [Pb3.1Sb0.9S4][Au xTe2- x] with Large Transverse Nonsaturating Negative Magnetoresistance and High Electron Mobility.

We report the two-dimensional (2D) natural heterostructure [Pb3.1Sb0.9S4][Au xTe2- x] ( x = 0.52-0.36) which shows anomalous, transverse nonsaturating negative magnetoresistance (MR). For x = 0.52, the material has a commensurately modulated structure with alternating [Pb3.1Sb0.9S4] rocksalt layers and atomically thin [Au xTe2- x] sheets, as determined by single-crystal X-ray diffraction using a (3 + 1)-dimensional space group; for other x compositions, the modulated structure is absent and the Au and Te atoms are disordered. The transport properties in this system at low temperature (<100 K) are dominated by an unusual 2D hopping mechanism, while at room temperature a high carrier mobility of ∼1352 cm2 V-1 s-1 is obtained ( x = 0.36). The confined electrons within the [Au xTe2- x] layers are also exposed to interlayer coupling with the insulating [Pb3.1Sb0.9S4] layers, and as a result, the properties of the heterostructures emerge not only from the constituent layers but also the interactions between them. Furthermore, the various Au and Te coordination patterns found in the [Au xTe2- x] sheets as a function of x further contribute to a unique electronic structure that leads to the anomalous nonsaturating negative MR with different field dependent behaviors. First-principles calculations indicate that the [Au xTe2- x] sheets are responsible for the unusual electrical transport properties in this 2D system.