Negative Thermal Expansion in ABC(MoO4)3 Compounds.

Negative thermal expansion (NTE) compounds provide a solution for the mismatch of coefficients of thermal expansion in highly integrated device design. However, the current NTE compounds are rare, and how to effectively design new NTE compounds is still challenging. Here, a new concept is proposed to design NTE compounds, that is, to increase the flexibility of framework structure by expanding the space in framework structure compounds. Taking the parent compound NaZr2(PO4)3 as a case, a new NTE system AIBIICIII(MoO4)3 (A = Li, Na, K, and Rb; B = Mg and Mn; C = Sc, In, and Lu) is designed. In these compounds, the large volume of MoO4 tetrahedron is used to replace the small volume of PO4 tetrahedron in NaZr2(PO4)3 to enhance structural space and NTE performance. Simultaneously, a joint study of temperature-dependent X-ray diffraction, Raman spectroscopy, and the first principles calculation reveals that the NTE in AIBIICIII(MoO4)3 series compounds arise from the coupled oscillation of polyhedral. Large-radius ions are conducive to enhancing the space and softening the framework structure to achieve the enhancement of NTE. The current strategy for designing NTE compounds is expected to be adopted in other compounds to obtain more NTE compounds.

Giant Negative Thermal Expansion in Ultralight NaB(CN)4.

Negative thermal expansion (NTE) is crucial for controlling the thermomechanical properties of functional materials, albeit being relatively rare. This study reports a giant NTE (αV ∼-9.2 ⋅ 10-5  K-1 , 100-200 K; αV ∼-3.7 ⋅ 10-5  K-1 , 200-650 K) observed in NaB(CN)4 , showcasing interesting ultralight properties. A comprehensive investigation involving synchrotron X-ray diffraction, Raman spectroscopy, and first-principles calculations has been conducted to explore the thermal expansion mechanism. The findings indicate that the low-frequency phonon modes play a primary role in NTE, and non-rigid vibration modes with most negative Grüneisen parameters are the key contributing factor to the giant NTE observed in NaB(CN)4 . This work presents a new material with giant NTE and ultralight mass density, providing insights for the understanding and design of novel NTE materials.

Squeezing-induced nonreciprocal photon blockade in an optomechanical microresonator.

We propose a scheme to generate nonreciprocal photon blockade in a stationary whispering gallery microresonator system based on two physical mechanisms. One of the two mechanisms is inspired by recent work [Phys. Rev. Lett.128, 083604 (2022)10.1103/PhysRevLett.128.083604], where the quantum squeezing caused by parametric interaction not only shifts the optical frequency of propagating mode but also enhances its optomechanical coupling, resulting in a nonreciprocal conventional photon blockade phenomenon. On the other hand, we also give another mechanism to generate stronger nonreciprocity of photon correlation according to the destructive quantum interference. Comparing these two strategies, the required nonlinear strength of parametric interaction in the second one is smaller, and the broadband squeezed vacuum field used to eliminate thermalization noise is no longer needed. All analyses and optimal parameter relations are further verified by numerically simulating the quantum master equation. Our proposed scheme opens a new avenue for achieving the nonreciprocal single photon source without stringent requirements, which may have critical applications in quantum communication, quantum information processing, and topological photonics.

Control of Thermal Expansion in TaVO5 by Double Chemical Substitution.

The control of thermal expansion is an important and challenging issue. Focusing attention on the class of AMO5 negative thermal expansion (NTE) materials, an approach to control their thermal expansion is still missing. In this work, the thermal expansion of TaVO5 has been controlled from strong negative to zero to positive by double chemical substitution, i.e., Ti and Mo replace Ta and V elements, respectively. A joint study of temperature-dependent X-ray diffraction, X-ray photoelectron spectroscopy, and first-principles calculations has been performed to investigate the thermal expansion mechanism. With the increasing substitution of Ti and Mo atoms, the valence state always remains balanced, and the volume decreases together with a lattice distortion, which leads to the suppression of the NTE. Lattice dynamics calculations confirm that the negative Grüneisen parameters of the low-frequency modes weaken and the thermal vibrations of the polyhedral units diminish after the substitution of Ti and Mo atoms. The present work successfully achieves a tailored thermal expansion in TaVO5 and draws a possible way to control the thermal expansion of other NTE materials.

The formation energy, phase transition, and negative thermal expansion of Fe2-xScxW3O12.

Tungstates with a molecular formula A2W3O12 exhibits a wider negative thermal expansion (NTE) temperature range than molybdates but are challenging to synthesize, especially when A = Fe or Cr with metastable structures. To enhance the structural stability of Fe2W3O12, Sc with lower electronegativity is adopted to substitute Fe according to Fe2-xScxW3O12, considering the thermodynamic stability of Sc2W3O12. It is shown that the solid solutions can be easily synthesized and the phase transition temperature (PTT) can be tuned to well below room temperature (RT). Theoretical calculations and experimental results show that the formation energy decreases and the W-O bond in Fe-O-W gradually strengthens as the substitution of Sc in Fe2-xScxW3O12 increases, indicating an increase in structural stability. NTE is enhanced after phase transition with an increase in the Sc content. The reduction in PTT and the enhancement in NTE properties of Fe2W3O12 could result in a decrease in the effective electronegativity of the Fe-site elements, resulting in a low formation energy and strengthened W-O bond in Fe-O-W, which corresponds to a more stable structure.

A Multiscale Instance Segmentation Method Based on Cleaning Rubber Ball Images.

The identification of wear rubber balls in the rubber ball cleaning system in heat exchange equipment directly affects the descaling efficiency. For the problem that the rubber ball image contains impurities and bubbles and the segmentation is low in real time, a multi-scale feature fusion real-time instance segmentation model based on the attention mechanism is proposed for the object segmentation of the rubber ball images. First, we introduce the Pyramid Vision Transformer instead of the convolution module in the backbone network and use the spatial-reduction attention layer of the transformer to improve the feature extraction ability across scales and spatial reduction to reduce computational cost; Second, we improve the feature fusion module to fuse image features across scales, combined with an attention mechanism to enhance the output feature representation; Third, the prediction head separates the mask branches separately. Combined with dynamic convolution, it improves the accuracy of the mask coefficients and increases the number of upsampling layers. It also connects the penultimate layer with the second layer feature map to achieve detection of smaller images with larger feature maps to improve the accuracy. Through the validation of the produced rubber ball dataset, the Dice score, Jaccard coefficient, and mAP of the actual segmented region of this network with the rubber ball dataset are improved by 4.5%, 4.7%, and 7.73%, respectively, and our model achieves 33.6 fps segmentation speed and 79.3% segmentation accuracy. Meanwhile, the average precision of Box and Mask can also meet the requirements under different IOU thresholds. We compared the DeepMask, Mask R-CNN, BlendMask, SOLOv1 and SOLOv2 instance segmentation networks with this model in terms of training accuracy and segmentation speed and obtained good results. The proposed modules can work together to better handle object details and achieve better segmentation performance.

Engineering Bimodal Oxygen Vacancies and Pt to Boost the Activity Toward Water Dissociation.

Water dissociation is the rate-limiting step of several energy-related reactions due to the high energy barrier required for breaking the oxygen-hydrogen bond. In this work, a bimodal oxygen vacancy (VO ) catalysis strategy is adopted to boost the efficient water dissociation on Pt nanoparticles. The single facet-exposed TiO2 surface and NiOx nanocluster possess two modes of VO different from each other. In ammonia borane hydrolysis, the highest catalytic activity among Pt-based materials is achieved with the turnover frequency of 618 min-1 under alkaline-free conditions at 298 K. Theoretical simulation and characterization analyses reveal that the bimodal VO significantly promotes the water dissociation in two ways. First, an ensemble-inducing effect of Pt and VO in TiO2 drives the activation of water molecules. Second, an electron promoter effect induced by the electron transfer from VO in NiOx to Pt further enhances the ability of Pt to dissociate water and ammonia borane. This insight into bimodal VO catalysis establishes a new avenue to rationally design heterogeneous catalytic materials in the energy chemistry field.

Atomic Interface-Exciting Catalysis on Cobalt Nitride-Oxide for Accelerating Hydrogen Generation.

The rational design of the interface structure between nitride and oxide using the same metallic element and correlating the interfacial active center with a determined catalytic mechanism remain challenging. Herein, a Co4 N-Co3 O4 interface structure is designed to determine the effect of interfacial active centers on hydrogen generation from ammonia borane. An unparalleled catalytic activity toward H2 production with a turnover frequency up to 79 min-1 is achieved on Co4 N-Co3 O4 @C catalyst for ten recycles. Experimental analyses and theoretical simulation suggest that the atomic interface-exciting effect (AieE) is responsible for the high catalytic activity. The Co4 N-Co3 O4 interface facilitates the targeted adsorption and activation of NH3 BH3 and H2 O molecules to generate H* and H2 . The two active centers of Co(N)* and Co(O)* at the Co4 N-Co3 O4 interface activate NH3 BH3 and H2 O, respectively. This proof-of-concept research on AieE provides important insights regarding the design of heterogeneous catalysts and promotes the development of the nature and regulation of energy chemical conversion.

Plasmon mode manipulation based on multi-layer hyperbolic metamaterials.

Metamaterial with hyperbolic dispersion properties can effectively manipulate plasmonic resonances. Here, we designed a hyperbolic metamaterial (HMM) substrate with a near-zero dielectric constant in the near-infrared region to manipulate the plasmon resonance of the nano-antenna (NA). For NA arrays, tuning the equivalent permittivity of HMM substrate by modifying the thickness of Au/diamond, the wavelength range of plasmon resonance can be manipulated. When the size of the NA changes within a certain range, the spectral position of the plasmon resonance will be fixed in a narrow band close to the epsilon-near-zero (ENZ) wavelength and produce a phenomenon similar to "pinning effect." In addition, since the volume plasmon polaritons (VPP) mode is excited, it will couple with the localized surface plasmon (LSP) mode to generate a spectrum splitting. Therefore, the plasmon resonance is significantly affected and can be precisely controlled by designing the HMM substrate.

Realizing PIT-like transparency via the coupling of plasmonic dipole and ENZ modes.

Plasmon induced transparency (PIT), known as the coupling of plasmon modes in metamaterials, has attracted intensive research interests in photonic applications. In this work, a PIT-like transparency is realized via the strong coupling of plasmonic dipole and epsilon-near-zero (ENZ) mode. Two types of metasurfaces, namely the gold nanoantenna and dolmen-like metasurface, are designed with an integrated ENZ material aluminum doped zinc oxide (AZO) film. Simulations with the finite element method (FEM) demonstrate that single and double transparent windows are achieved respectively. The adjustments of the peak position and transmittance of transparent windows via the structure parameters and the AZO film thickness are further investigated. This work provides an alternative coupling scheme of realizing PIT-like transparency with simple metasurface design, and offers great potential for future metamaterial applications.

Understanding Large Negative Thermal Expansion of NdFe(CN)6 through the Electronic Structure and Lattice Dynamics.

A large negative thermal expansion (NTE) (αv = -4.1 × 10-5 K-1, 100-525 K) has been discovered in NdFe(CN)6. Here, the synchrotron X-ray diffraction and lattice dynamics calculations using the density functional theory were conducted to understand the NTE in NdFe(CN)6. The information obtained on the bond nature of the Nd-N≡C-Fe linkage and on the atomic thermal vibrations suggests that the transverse vibrations of the -N≡C- group, in particular from N atoms, produced the NTE in NdFe(CN)6. This is corroborated by the calculated Grüneisen parameters, which confirm the relationship between NTE and CN atomic vibrations. The results provide a helpful contribution toward the realization of new materials with negative or controllable thermal expansion.

Insight into the Relationship between Negative Thermal Expansion and Structure Flexibility: The Case of Zn(CN)2-Type Compounds.

High structure flexibility can lead to large negative thermal expansion (NTE), but the reason is not clear. In this work, first-principles calculations have been carried out to investigate the relationship between NTE and structure flexibility in Zn(CN)2-type compounds. Smaller bulk modulus corresponds to larger compressibility, thus making the crystal structure more flexible and more suitable for NTE. It indicated that the ionic nature of the bond and the bond length jointly affect the structural flexibility and then act on the transverse vibration of C and N atoms. The results of lattice dynamic suggested that higher structural flexibility promotes a greater number of low-frequency optical modes with negative Grüneisen parameters, resulting in a larger NTE. This work also gives us new insight into the design of NTE materials.

Tailoring Thermal Expansion of (LiFe)0.5xCu2-xP2O7 via Codoping LiFe Diatoms in Cu2P2O7 Oxide.

Tailoring the thermal expansion coefficient of negative thermal expansion (NTE) materials to achieve near-zero thermal expansion has attracted great attention recently. Here, LiFe diatoms are adopted to substitute Cu in Cu2P2O7 oxide to design Li-O-P and Fe-O-P linkages, with the stronger bond strength of Li-O and Fe-O compared to Cu-O and hence lowering the bond strength of P-O. With increasing the diatomic LiFe in (LiFe)0.5xCu2-xP2O7, new Raman bands corresponding to LiFeP2O7 appear and the NTE coefficient decreases gradually to near-zero thermal expansion at x = 1 (αv = -0.90 × 10-6 °C-1, -100 to 55 °C). Comparing (LiFe)0.5CuP2O7 with Cu2P2O7 and LiFeP2O7, the average bond length of P-O increases while the bond angle of P-O-P decreases, and this is verified by some weakened vibrational energies of terminal PO3 and P-O-P, resulting in the obvious red shift of Raman bands. Ceramic (LiFe)0.5CuP2O7 presents a lower difference in grain size and a higher relative density than Cu2P2O7 and LiFeP2O7.

Excitation of ultraviolet range Dirac-type plasmon resonance with an ultra-high Q-factor in the topological insulator Bi1.5Sb0.5Te1.8Se1.2 nanoshell.

Excitation of ultraviolet (UV) range plasmon resonance with high quality (Q)-factor has been significantly challenging in plasmonics because of inherent limitations in metals like Au and Ag. Herein, we theoretically investigated UV-visible range plasmons in the topological insulator Bi1.5Sb0.5Te1.8Se1.2 (BSTS) nanosphere and nanoshell. In contrast to broad linewidth plasmon absorptions in the BSTS nanospheres, an ultra-sharp absorption peak with the Q-factor as high as 52 is excited at UV frequencies in the BSTS nanoshells. This peak is attributed to Dirac-type plasmon resonance originating from massless Dirac carriers in surface states of the BSTS. Furthermore, a tunable plasmon wavelength of the resonance is demonstrated by varying geometrical parameters of the BSTS nanoshells. This may find applications in surface enhanced Raman spectroscopies, nanolasers and biosensors in the UV regions.

Understanding Negative Thermal Expansion of Zn2GeO4 through Local Structure and Vibrational Dynamics.

Zn2GeO4 is a multifunctional material whose intrinsic thermal expansion properties below ambient temperature have not been explored until now. Herein, the thermal expansion of Zn2GeO4 is investigated by synchrotron X-ray diffraction, with the finding that Zn2GeO4 exhibits very low negative (αv = -2.02 × 10-6 K-1, 100-300 K) and positive (αv = +2.54 × 10-6 K-1, 300-475 K) thermal expansion below and above room temperature, respectively. A combined study of neutron powder diffraction and extended X-ray absorption fine structure spectroscopy shows that the negative thermal expansion (NTE) of Zn2GeO4 originates from the transverse vibrations of O atoms in the four- and six-membered rings with ZnO4-GeO4 tetrahedra. In addition, the results of temperature- and pressure-dependent Raman spectra identify the low-frequency phonon modes (50-150 cm-1) with negative Grüneisen parameters softening upon pressuring and stiffening upon heating during the lattice contraction, thus contributing to the NTE. This study not only reports the interesting thermal expansion behavior of Zn2GeO4 but also provides further insights into the NTE mechanism of novel structures.

Anomalous Thermal Expansion in Ta2WO8 Oxide Semiconductor over a Wide Temperature Range.

Expansion of material is one of the major impediments in the high precision instrument and engineering field. Low/zero thermal expansion compounds have drawn great attention because of their important scientific significance and enormous application value. However, the realization of low thermal expansion over a wide temperature range is still scarce. In this study, a low thermal expansion over a wide temperature range has been observed in the Ta2WO8 oxide semiconductor. It is a balance effect of the negative thermal expansion of the a axis and the positive thermal expansion of the b axis and the c axis to achieve low thermal expansion behavior. The results of the means of variable temperature X-ray diffraction and variable pressure Raman spectroscopy analysis indicated that the transverse vibration of bridging oxygen atoms is the driving force, which is corresponding to the low-frequency lattice modes with a negative Grüneisen parameter. The present study provides one wide band gap semiconductor Ta2WO8 with anomalous thermal expansion behavior.

Discovering Large Isotropic Negative Thermal Expansion in Framework Compound AgB(CN)4 via the Concept of Average Atomic Volume.

Exploring isotropic negative thermal expansion (NTE) compounds is interesting, but remains challenging. Here, a new concept of "average atomic volume" is proposed to find new NTE open-framework materials. According to this guidance, two NTE compounds, AgB(CN)4 and CuB(CN)4, have been discovered, of which AgB(CN)4 exhibits a large NTE over a wide temperature range (αv = -40 × 10-6 K-1, 100-600 K). The analysis by extended X-ray absorption fine structure spectroscopy and first-principles calculation indicate that (i) the NTE driving force comes from the transverse vibrations of bridge chain atoms of C and N, corresponding to the low-frequency phonon modes; and (ii) the same transverse vibration direction of C and N atoms is a key factor for the occurrence of strong NTE in AgB(CN)4. The present concept of "average atomic volume" can be a simple parameter to explore new NTE compounds especially in those open-framework materials.

Zero Thermal Expansion in Ta2Mo2O11 by Compensation Effects.

Although zero thermal expansion (ZTE) materials have broad application prospects for high precision engineering, they are rare. Here, a new ZTE material, Ta2Mo2O11 (αl = 0.37 × 10-6 K-1, 200-600 K), is reported. A joint study of high-resolution synchrotron X-ray diffraction, temperature- and pressure-dependent Raman spectroscopy, and first-principles calculations was performed to investigate the structure and dynamics of Ta2Mo2O11 with the aim of understanding its ZTE mechanism. Ta2Mo2O11 displays a layered structure, stacking along the [001] direction. Analysis of the phonon modes indicates that positive and negative contributions to thermal expansion are balanced, and a shrinkage occurs along the layers, while the interlayer distance expands with increasing temperature, thus giving rise to the ZTE behavior of Ta2Mo2O11. The present study provides a promising ZTE material and new insights into the mechanisms of thermal expansion.

Effect of H2O Molecules on Thermal Expansion of TiCo(CN)6.

Understanding the role of guest molecules in the lattice void of open-framework structures is vital for tailoring thermal expansion. Here, we take a new negative thermal expansion (NTE) compound, TiCo(CN)6, as a case study from the local structure perspective to investigate the effect of H2O molecules on thermal expansion. The in situ synchrotron X-ray diffraction results showed that the as-prepared TiCo(CN)6·2H2O has near-zero thermal expansion behavior (100-300 K), while TiCo(CN)6 without water in the lattice void exhibits a linear NTE (αl = -4.05 × 10-6 K-1, 100-475 K). Combined with the results of extended X-ray absorption fine structure, it was found that the intercalation of H2O molecules has the clear effect of inhibiting transverse thermal vibrations of Ti-N bonds, while the effect on the Co-C bonds is negligible. The present work displays the inhibition mechanism of H2O molecules on thermal expansion of TiCo(CN)6, which also provides insight into the thermal expansion control of other NTE compounds with open-framework structures.

Structure and Negative Thermal Expansion in Zr0.3Sc1.7Mo2.7V0.3O12.

A2M3O12-based materials have received considerable attention owing to their wide range of negative thermal expansion (NTE) and chemical flexibility toward novel materials design. However, the structure and NTE mechanism remain challenging. Here, Zr4+ and V5+ are used as a unit to compensatorily replace Sc3+ and Mo6+ in Sc2Mo3O12 to tune its thermal expansion. Its crystal structure, phase transition, NTE property, and corresponding mechanisms are studied by high-resolution synchrotron X-ray diffraction, powder X-ray diffraction, ultralow-frequency Raman spectroscopy, and density functional theory calculations. The results show that Zr0.3Sc1.7Mo2.7V0.3O12 adopts an orthorhombic (Pbcn) structure at room temperature, with V atoms occupying the position of Mo1 atoms and Zr atoms occupying the position of Sc atoms, and transforms to monoclinic (P21/a) structure at ∼133 K (45 K lower than that of Sc2Mo3O12). It exhibits excellent NTE in a broader range. Most of the phonon modes below 350 cm-1 have negative Grüneisen parameters, of which the lowest and next-lowest frequency (38.5 and 45.8 cm-1) optical phonon modes arising from the translational vibrations of the Sc/Zr and Mo/V atoms in the plane of the nonlinear linkage Sc/Zr-O-Mo/V have the largest and next-largest negative Grüneisen parameters and positive total anharmonicity, and contribute most to the NTE.