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Cr 2 Mo 3 O 12 ceramics show negative thermal expansion (NTE) in a narrow high-temperature range due to the phase transition around 385 °C. To widen its NTE temperature range, a series of (NaMg)3+ co-doped Cr 2 Mo 3 O 12 ceramics has been synthesized via a solid reaction process in this work. The effects of double cation (NaMg)3+ co-doping on the phase composition, morphology, phase transformation, and thermal expansion performance of Cr 2 Mo 3 O 12 ceramics were studied using XRD, Raman, XPS, SEM, and TMA. Results indicate that double cation (NaMg)3+ can partially substitute Cr3+ in Cr 2 Mo 3 O 12 , which causes a phase transition from monoclinic Cr 2 Mo 3 O 12 to hexagonal (NaMg) x Cr 2-x Mo 3 O 12. The single-phase (NaMg) x Cr 2-x Mo 3 O 12 ceramics with hexagonal structure is obtained when x = 0.5. (NaMg)3+ co-doping promotes the growth of grains and the density of hexagonal (NaMg) 0·5 Cr 1·5 Mo 3 O 12 ceramics. (NaMg)3+ co-doping also successfully eliminates the temperature-induced phase transition of Cr 2 Mo 3 O 12 at 385 °C. Hexagonal (NaMg) 0·5 Cr 1·5 Mo 3 O 12 ceramics presents a better NTE with a coefficient of thermal expansion (CTE) of −3.97 × 10−6 °C−1 over a larger temperature range from 30 °C to 700 °C. [ABSTRACT FROM AUTHOR]

A series of Lu 2(1- x) Tb 2 x (WO 4) 3 (x = 0.00–1.00) white powder materials were prepared by a high-temperature solid-phase method. The crystal structure, microscopic morphology, elemental composition, bandgap energy, photoluminescence properties, and thermal stability of luminescence of the prepared materials were analyzed and studied through room and high temperature X-ray diffraction patterns, field emission scanning electron microscopy images, energy energy-dispersive spectra and X-ray photoelectron spectra, diffuse reflectance spectra, room and high temperature photoluminescence spectra. Under 260 nm excitation, the green emitting Lu 2(1- x) Tb 2 x (WO 4) 3 samples exhibited an optimum Tb3+ doping concentration at x = 0.30. Calculated results illustrate that the concentration quenching was mainly caused by dipole-dipole interaction. Lu 1.98 Tb 0.02 (WO 4) 3 phosphor exhibited thermally enhanced luminescence at 120 °C, with a maximum luminescence intensity of 254 % of the initial room temperature intensity. Lu 1.4 Tb 0.6 (WO 4) 3 phosphor exhibited thermally enhanced luminescence at 150 °C, with a maximum luminescence intensity of 109 % of the initial room temperature intensity. The mechanism of the thermally enhanced luminescence phenomenon is further discussed to be the adsorbed crystal water and the negative thermal expansion of the material. Thermally enhanced luminescence is of great significance in overcoming luminescent thermal quenching phenomenon, improving the luminescence efficiency, optimizing the material design, and so forth. It has potential applications in high-temperature lighting, display technology, temperature sensing, and optical anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The negative thermal expansion (NTE) materials, which can act as thermal‐expansion compensators to counteract the positive thermal expansion, have great applications merit in precision engineering. However, the exploration of NTE behavior with a wide temperature range has reached its upper ceiling through traditional doping strategies due to composition limitations. In this paper, the unique sluggish characteristics and extended optimization space in empirically screened high‐entropy anti‐perovskite (HEAP) are utilized to broaden the NTE temperature range. Typically, the NTE temperature range in Mn3Cu0.2Zn0.2Ga0.2Ge0.2Mn0.2N is broadened to ΔT = 235 K (5 K ≤ T ≤ 240 K), which is two or three times wider than that of traditional low‐entropy doping systems. The neutron diffraction analysis reveals a unique sluggish characteristic in magnetic phase transition which survives in an ultra‐wide temperature range of 5 K ≤ T ≤ 350 K (ΔT = 345 K). The sluggish characteristic is further experimentally proved to come from disturbed phase transition dynamics due to distortion in atomic spacing and chemical environmental fluctuation observed by the spherical aberration‐corrected electron microscope. The demonstration provides a unique paradigm for broadening the temperature range of NTE materials through entropy engineering. [ABSTRACT FROM AUTHOR]

Incomplete bimaterial ring (a circular ring with a gap) capable of producing negative macroscopic thermal expansion is proposed and its behavior is analyzed. The ring exhibits negative thermal expansion (NTE) (in the plane of the ring) when the outer ring has higher thermal expansion coefficient than the inner one. When the thermal expansion coefficients are equal (monomaterial incomplete ring), the effective (macroscopic) planar thermal expansion becomes zero. (The complete thermal expansion will be positive but small.) It is the presence of the gap which is the basis of this thermal behavior. Similar effect can be achieved by spring or spiral structures where the role of the gap is played by the open ends. These structures will have higher stiffness than the incomplete bimaterial ring. The thermal expansion of the ring is characterized by the effective (macroscopic) coefficient of linear thermal expansion. The effective coefficient of linear thermal expansion depends on the temperature increase, making the thermal expansion nonlinear. Planar and 3D NTE structures are considered. [ABSTRACT FROM AUTHOR]

Achieving smart single‐phase materials with switchable thermal expansion is challenging, as most materials undergo volumetric thermal expansion upon heating. Here, it is reported that the porphyrin‐based metal‐organic frameworks (MOFs) can show switchable thermal expansion, ranging from negative to positive, by controlling the central metal ions. The pristine compound, along with those functionalized with Ni2+ or FePz2+ (Pz stands for pyrazine) show pronounced negative thermal expansion (NTE), while the FeCl2+ functionalized analogue shows moderate positive thermal expansion (PTE). Detailed molecular dynamic simulations shed light on that the NTE originates from the collective low‐frequency phonon modes, concerning the in‐plane/out‐of‐plane rotations and trampoline‐like vibrations of porphyrin groups. The introduction of FeCl2+ can disrupt the planarity of the porphyrin groups, stiffening the NTE related phonons, thus leading to the PTE. In contrast, the introduction of Ni2+ or FePz2+ groups can maintain the planar structure, thereby preserving the NTE. This study not only provides a molecular‐level understanding of thermal expansion but also opens a pathway for tailoring thermal expansion through post‐synthesis modification of molecular structures. [ABSTRACT FROM AUTHOR]

Zinc aluminosilicate (ZAS) glasses were synthesized along the peraluminous join (SiO 2 contents between 95 and 50 mol%) by melt-quenching or sol-gel spray-drying and subjected to controlled heat treatments to obtain ZAS quartz solid solutions (Zn-Qz-ss). The precipitation of Zn-Qz-ss is non-stoichiometric with respect to their parent glass and the crystals undergo a compositional evolution during annealing, even in absence of secondary crystalline phases. Near-hexagonal high-quartz-like crystals with negative thermal expansion (down to −3 × 10−6 K−1) can be obtained in the range 50–80 mol% SiO 2 , while SiO 2 -richer crystals exhibit positive thermal expansion at room temperature (up to 29 × 10−6 K−1). Zn2+ ions occupy two distinct positions within the structural channels of quartz, with a strong preference for 4-fold coordination. In analogy to lithium aluminosilicate quartz solid solutions (Li-Qz-ss), the low-to-high phase transition exhibits a linear correlation to the composition of the crystals. [ABSTRACT FROM AUTHOR]

In this study, robust silicon carbide (SiC)-niobium (Nb) joints were obtained using a composite filler consisting of a novel type of negative thermal expansion (Sr 0.2 Ba 0.8)TiO 3 particle–reinforced Cu composites (SBT-Cu) and an AgCuTi active filler. A systematic investigation was conducted to analyze the brazing temperatures and SBT-Cu thickness affect the microstructure and mechanical properties of brazed joints. The results indicated that the shear strength of SiC–Nb joints brazed with AgCuTi +80 μm SBT-Cu composite filler increased to 64 MPa at 900 °C for 15 min, which was an improvement of 146 % over the strength of joints brazed without SBT-Cu. The addition of the SBT-Cu interlayer relieved the coefficient of thermal expansion mismatch among SiC, AgCuTi and Nb. Meanwhile, the calculation results verified that the residual stresses in the joints were substantially reduced and that the coefficient of thermal expansion of the composite filler was reduced. [ABSTRACT FROM AUTHOR]

CaAl12O19, which can incorporate Ti as both Ti3+ and Ti4+ (charge coupled substitution with Mg2+), is one of the first minerals to condense from a gas of solar composition and is used as a ceramic. It is variously known as hibonite, calcium hexaluminate (CaO.6Al2O3), and CA6. The lattice parameters and unit cell volumes of Ti-substituted hibonite (P63/mmc) with the formulae CaAl11.8Ti3+0.2O19 and CaAl9.8Ti3+0.54Mg0.83Ti4+0.83O19 were determined as a function of temperature from ~ 10 to 275 K by neutron powder diffraction. The thermal expansion is highly anisotropic with the expansion in c a factor of ~ 5 greater than that in a. The change in a is approximately equal for the two compounds whereas the change in c is almost 50% larger for CaAl11.8Ti3+0.2O19. CaAl11.8Ti3+0.2O19 also exhibits negative thermal expansion between 10 and 70 K. The change in unit cell volume with temperature of both compositions is well described by a two term Einstein expression. The large change in c is consistent with substitution of Ti onto the M2 and M4 sites of the R-block structural unit. [ABSTRACT FROM AUTHOR]

The fluorescence intensity of lanthanide (Ln3+)-doped upconversion (UC) materials generally exhibits significant thermal quenching with increasing temperature, which is a critical challenge for their application. In this work, Yb2−xW3O12:xHo phosphors with thermally enhanced UC luminescence are fabricated by a facile solid-state sintering method. The x-ray diffraction (XRD) patterns reveal that the Yb2−xW3O12:xHo samples have a pure phase, which indicates that the Ho3+ ions are successfully doped into the crystal lattice of Yb2W3O12. In addition, the in situ XRD patterns show that when the temperature is increased, the diffraction peaks gradually shift to a higher angle, clearly illustrating the negative thermal expansion phenomenon of Yb2W3O12. The UC luminescence shows that Yb2−xW3O12:xHo phosphors have red and green emissions when excited by a 980 nm laser diode. By changing the doping amount of Ho, it has been found that the luminescence is strongest at 2 mol%. Further investigation of the temperature-dependent upconversion emission properties of Yb2−xW3O12:xHo samples shows that the red emission increases by several times from 323 K to 498 K. The temperature-sensing characteristics of Yb2−xW3O12:xHo are studied using fluorescence intensity ratio (FIR)-based technology. The maximum relative sensitivity and the maximum absolute sensitivity are calculated as 2.04%/K at 323 K and 0.066/K at 498 K, respectively. These results indicate that Yb2−xW3O12:xHo fluorescent powder can be used for optical temperature measurement. [ABSTRACT FROM AUTHOR]

CaAl12O19, which can incorporate Ti as both Ti3+ and Ti4+ (charge coupled substitution with Mg2+), is one of the first minerals to condense from a gas of solar composition and is used as a ceramic. It is variously known as hibonite, calcium hexaluminate (CaO.6Al2O3), and CA6. The lattice parameters and unit cell volumes of Ti-substituted hibonite (P63/mmc) with the formulae CaAl11.8Ti3+0.2O19 and CaAl9.8Ti3+0.54Mg0.83Ti4+0.83O19 were determined as a function of temperature from ~ 10 to 275 K by neutron powder diffraction. The thermal expansion is highly anisotropic with the expansion in c a factor of ~ 5 greater than that in a. The change in a is approximately equal for the two compounds whereas the change in c is almost 50% larger for CaAl11.8Ti3+0.2O19. CaAl11.8Ti3+0.2O19 also exhibits negative thermal expansion between 10 and 70 K. The change in unit cell volume with temperature of both compositions is well described by a two term Einstein expression. The large change in c is consistent with substitution of Ti onto the M2 and M4 sites of the R-block structural unit. [ABSTRACT FROM AUTHOR]

Due to the high structural flexibility and controllable thermal expansion, cubic double ReO3-type negative thermal expansion (NTE) fluorides provide a solution for solving the prominent phenomenon of thermal expansion mismatch between materials. However, the expensive raw materials and complex synthesis steps limit its practical application. In this work, we have designed a more advantageous method for the synthesis of NTE material CaZrF6, and it is expected to be generalized to the synthesis of other double ReO3-fluorides. Intriguingly, a new orthorhombic phase CaZrF6 has been synthesized via this method in a lower temperature. Unlike the strong isotropic NTE of the cubic phase CaZrF6, the orthorhombic phase shows the strong anisotropic positive thermal expansion (PTE). The combined analysis of temperature-dependent X-ray diffraction (XRD), Raman spectra, and first-principles calculations shows that the low frequency phonon vibration mode with negative Grüneisen parameter in cubic CaZrF6 are strongly correlated with the transverse thermal vibration of F atoms and dominates the NTE of the material. [ABSTRACT FROM AUTHOR]

The thermal expansion coefficient (TEC) mismatch between the cathode and electrolyte presents significant challenge to the thermo-mechanical stability of commercial solid oxide fuel cells (SOFCs). Here a thermal expansion offset composite cathode designated as Ba 0.5 Sr 0.5 FeO 3-δ (BSF)-xNdMnO 3-δ (NM) (x = 0–40 wt%) is developed to address this issue. For the first time, the phase boundary between heterogeneous oxides and the grain size of composite cathode are quantitatively studied with the electron backscatter diffraction (EBSD) technology. For x = 20 wt%, the TEC of cathode decreases by 41 % while the peeling strength of cathode/electrolyte interface increases by 87 %. The highest peak power density (PPD) is achieved for BSF-20NM cathode (1266 mW cm−2 at 650 °C), which is 81 % higher than that for BSF one. Meanwhile, markedly enhanced long-term and thermal cycling stability is obtained. The comprehensive results suggest that both the increased TPB length by enhanced cathode/electrolyte bonding and grain refinement of composite cathode should be responsible for the markedly improved performance and stability. [ABSTRACT FROM AUTHOR]

This study investigates the thermal behavior and structural transitions of silver vanadate microrods (AgVO 3) synthesized via coprecipitation. The samples were characterized at room temperature using scanning electron microscopy, Powder X-ray Diffraction, and Raman scattering. The AgVO 3 was obtained in the monoclinic phase (β-phase) with a Cm space group and rod-like morphology of micrometer-sized diameter. In situ temperature-dependent studies utilizing XRD and Raman spectroscopy revealed notable findings: at low temperatures (298–12 K), the β-AgVO 3 phase exhibited thermal stability alongside uniaxial negative thermal expansion (NTE) along the b lattice parameter of microcrystals. Conversely, experiments at high temperatures (298–673 K) demonstrated a reversible structural transition from the monoclinic phase to a triclinic phase at 473 K (β → β'), with NTE observed along the b direction in both high-temperature phases. These temperature-induced structural modifications and the observed uniaxial negative thermal expansion in β-AgVO 3 microrods constitute significant contributions to the field, providing valuable insights into their thermal behavior and potential applications. • Temperature-dependent behavior of silver vanadate (β-AgVO 3) microrods using in situ XRD and Raman scattering. • β-AgVO 3 microrods present reversible monoclinic to triclinic phase transitions at high temperatures. • The β-AgVO 3 microrods exhibit uniaxial negative thermal expansion along the b-axis at low and high temperatures. [ABSTRACT FROM AUTHOR]

Negative thermal expansion (NTE) defies the conventional wisdom of lattice dynamics and offers a novel way to control the expansion coefficient and address some challenges in modern science and technology. From an application standpoint, materials exhibiting NTE across a broad temperature range, including room temperature, are highly sought after. In this work, we propose the multi-doping strategy and prepared a series of rare-earth-based lithium oxides featuring negative thermal expansion, with the objective of adjusting their temperature range. The phase transition temperatures of these materials range from 202 K to 467 K, demonstrating a linear correlation with the average ionic radius of the rare-earth elements. By capitalizing on the synergistic effects of four rare-earth elements, we expand the full width at half maximum of the thermal expansion peak in Li(ErYHoDy)0.25O2 from 1.6 K to 14.5 K, a notable improvement of nearly tenfold is achieved. Additionally, we investigate the low-temperature magnetocaloric effects and inverse barocaloric effects within these rare-earth-based lithium oxides. Temperature- and pressure-dependent Raman scattering measurements indicate that the phase transitions and the barocaloric effects are associated with the stretching mode of the Li–O bond and the vibrational mode of the YO6 octahedron.

Orthorhombic In 0.5 Sc 1.5 Mo 3 O 12 thin films have been synthesized using the sol-gel spin coating. Influences of post-annealing temperatures on crystal structure, morphology, negative thermal expansion (NTE) and optical performances of the thin films were studied using XRD, SEM, XPS, high-temperature XRD and UV–Vis–NIR spectrophotometer. XRD and SEM results show that as-prepared thin film is in an amorphous state with a smooth and dense surface. Orthorhombic In 0.5 Sc 1.5 Mo 3 O 12 thin films were obtained after post-annealing in 550–750 °C. The higher the annealing temperature in 550–750 °C, the better the crystallinity of orthorhombic In 0.5 Sc 1.5 Mo 3 O 12 thin films. In addition, the grain size of the In 0.5 Sc 1.5 Mo 3 O 12 thin film also grows as the annealing temperature increases. The resulting orthorhombic In 0.5 Sc 1.5 Mo 3 O 12 thin films exhibit anisotropic NTE. Its volumetric coefficient of thermal expansion (CTE) is −3.44 × 10−6 °C−1, while the CTEs in a -, b - and c -axis directions are −4.70 × 10−6 °C−1, 5.37 × 10−6 °C−1, and -4.10 × 10−6 °C−1 in 25–700 °C, respectively. In addition, the transmittance of orthorhombic In 0.5 Sc 1.5 Mo 3 O 12 thin films post-annealed at 750 °C is around 87.75 %–95.03 %. [ABSTRACT FROM AUTHOR]

ZrW2O8 (ZrO2•2WO3) and HfW2O8 (HfO2•2WO3) have been the focus of thermal expansion studies due to their isotropic negative thermal expansion (NTE) measured previously at temperatures below 775°C. This work presents measurements of these materials at their thermodynamically stable temperature ranges of 1105 and 1257°C for ZrW2O8 and 1105–1276°C for HfW2O8, where they were characterized with in situ, powder X‐ray diffraction. The linear coefficients of thermal expansion were measured to be −5.52 × 10−6 and −4.87 × 10−6°C−1 for ZrW2O8 and HfW2O8, respectively. The mechanism leading to this NTE is discussed. Powder samples were synthesized by a solution‐based process called the organic–inorganic steric entrapment method. In situ characterization in air was carried out at the National Synchrotron Light Source II using a hexapole lamp, optical furnace and the Advanced Photon Source using a quadrupole lamp, optical furnace to achieve elevated temperatures. [ABSTRACT FROM AUTHOR]

(KMg)3+ co-doped Sc 2 W 3 O 12 ceramics have been prepared via co-precipitation method. Effects of (KMg)3+ co-doping amount and sintering temperature on the phase constitution, microstructure, morphology, and negative thermal expansion (NTE) performance of K x Mg x Sc 2- x W 3 O 12 (0 ≤ x ≤ 1.25) ceramics were studied. Results indicate that: Sc3+ cations can be substituted by (KMg)3+ dual-cations and a composition-induced structural phase transition was observed in K x Mg x Sc 2- x W 3 O 12. For x ≤ 0.25, orthorhombic Sc 2 W 3 O 12 gradually changed into hexagonal K x Mg x Sc 2- x W 3 O 12 and coexisted. Single phase K x Mg x Sc 2- x W 3 O 12 with hexagonal symmetry can be prepared for 0.25 < x ≤ 1. When x ≥ 1.25, (KMg)3+ substitution reaches its solid solution limit in Sc 2 W 3 O 12 , and impurity MgWO 4 formed in the samples. As co-doping amount x increased, the NTE performance of the K x Mg x Sc 2- x W 3 O 12 (0 ≤ x ≤ 1) ceramics gradually enhanced. The coefficient of thermal expansion (CTE) of K x Mg x Sc 2- x W 3 O 12 (0 ≤ x ≤ 1) ceramics enhanced from −2.14 × 10−6 °C−1 to −19.68 × 10−6 °C−1 in 30–700 °C. With the increase of sintering temperature from 800 to 1100 °C, the grains grew up and the density of the K 0.75 Mg 0.75 Sc 1.25 W 3 O 12 ceramics increased as well, and the NTE performance was also improved. The linear CTE of K 0.75 Mg 0.75 Sc 1.25 W 3 O 12 ceramics enhances from −2.15 × 10−6 °C−1 to −14.70 × 10−6 °C−1 in 30–700 °C. [ABSTRACT FROM AUTHOR]

(ZrCa)x Y2-2xW3 O12 (x = 0, 0. 1, 0. 2, 0. 3, 0. 4, 0. 5, 0. 6, 0. 7, 0. 8, 0. 9 and 1. 0) are developed with a simple solid state method, and characterized for crystal structure, hygroscopicity and thermal expansion by X-ray diffraction, Raman spectroscopy, thermal analysis and dilatometer. The results show that the hygrosopicity of solid solution decreases obviously, and the coefficient of thermal expansion (CTE) changes regularly after complete release of the crystal water with the increase of (ZrCa)6 + content. A near-zero thermal expansion (ZTE) is realized for (ZrCa)0. 6 Y0. 8 W3 O12 as x =0. 6, and the linear CTE (al) is measured to be 2. 79 ×10 -7 K-1 (453 ~1 000 K). [ABSTRACT FROM AUTHOR]

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The achievement of significant negative thermal expansion (NTE) over a wide temperature range (ΔTNTE) has posed a formidable challenge for NTE materials. In the present study, textured MnCo(Ge,Si)/epoxy composites were prepared by magnetic field-assisted dynamic self-assembly of multi-component Mn0.945Co1.055Ge1-xSix particles. The utilization of multi-component particles with tunable transition temperatures significantly amplifies the temperature range over which the NTE occurs, surpassing the limitations of conventional single-component composites. The textured microstructure enables the extension of lattice-level NTE to reach the macroscopic level, which is manifested by a remarkably large NTE coefficient of −328.7 × 10−6/K between 288.2 and 431.1 K.

Cubic ZrV 2 O 7 thin films have been synthesized by sol-gel spin-coating method. The influences of annealing temperatures on the phase composition and morphology of ZrV 2 O 7 thin films were investigated using XRD, SEM, and EDX. Negative thermal expansion (NTE) and optical performances of cubic ZrV 2 O 7 thin films were analyzed using variable temperature XRD and UV–Vis spectroscopy. Results indicate that as-deposited ZrV 2 O 7 thin films have an amorphous structure with smooth and dense surface. Cubic ZrV 2 O 7 thin films were prepared after heat treatment at 720 °C for 1 h. It was found that the thin films contained V 2 O 5 impurity with the Zr: V = 1:2 precursor solution. Pure cubic ZrV 2 O 7 thin films were fabricated with the Zr: V = 1.75:2 precursor solution. Cubic ZrV 2 O 7 thin films show isotropic NTE in the temperature range of 100–700 °C. The coefficients of thermal expansion (CTEs) of ZrV 2 O 7 films along the a , b , and c axes are −6.88 × 10−6 °C−1, and the volumetric and linear CTEs are −20.56 × 10−6 °C−1 and -6.85 × 10−6 °C−1, respectively. The transmittance of cubic ZrV 2 O 7 thin film is approximately 80 %. [ABSTRACT FROM AUTHOR]

The achievement of significant negative thermal expansion (NTE) over a wide temperature range (ΔTNTE) has posed a formidable challenge for NTE materials. In the present study, textured MnCo(Ge,Si)/epoxy composites were prepared by magnetic field-assisted dynamic self-assembly of multi-component Mn0.945Co1.055Ge1-xSix particles. The utilization of multi-component particles with tunable transition temperatures significantly amplifies the temperature range over which the NTE occurs, surpassing the limitations of conventional single-component composites. The textured microstructure enables the extension of lattice-level NTE to reach the macroscopic level, which is manifested by a remarkably large NTE coefficient of −328.7 × 10−6/K between 288.2 and 431.1 K. Colossal NTE with a coefficient αL of −328.7 × 10−6/K is achieved over a wide temperature range of 142.9 K between 288.2 and 431.1 K, representing the largest αL among all reported NTE materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Radical cation salts of π‐conjugated polycycles are rich in physical properties. Herein, two kinds of hetera‐buckybowls, ethoxy‐substituted trithiasumanene (3SEt) and triselenasumanene (3SeEt), are synthesized as electron donors. Galvanostatic oxidation of them affords radical cation salts (3SEt)5(TTFMPB)3, (3SeEt)5(TTFMPB)3, (3SEt)4PMA, and (3SeEt)4PMA, where PMA is Keggin‐type phosphomolybdate and TTFMPB is tetrakis[3,5‐bis(trifluoromethyl)‐phenyl]borate. In these salts, 3SEt/3SeEt are partially charged and show distinct conformation change with the site charge and counter anions. In TTFMPB salts, (TTFMPB)− forms hexagonal channels that accommodate the packing columns of 3SEt/3SeEt. In particular, (3SEt)5(TTFMPB)3 adopts the R3c space group and is a polar crystal with the columns of 3SEt all in the up‐bowl direction. The PMA salts of 3SEt/3SeEt are polar crystals (C2 space group) with 3SEt/3SeEt being planar and forming columnar stacks. (3SeEt)4PMA shows a structural modulation below 200 K, namely, negative thermal expansion (NTE) of the unit cell volume and enlargement of the intermolecular distances between neighboring 3SeEt molecules. The four salts are semiconductors with an activation energy of 0.18–0.38 eV. The conductivity of (3SeEt)4PMA shows a reversible transition upon cooling and heating, in accordance to the NTE structural modulation. This work paves the way toward conducting materials based on hetera‐buckybowls. [ABSTRACT FROM AUTHOR]

Thermal expansion, by which a material’s volume increases when heated, is a universal phenomenon deriving from the thermal vibration of the atoms that constitute solids. Since the discovery of low thermal expansion in Invar alloys at the end of the 19th century, the “abnormality” of thermal expansion has given birth to new sciences and technologies. This article describes studies of thermal expansion anomalies from low thermal expansion of Invar alloys to the giant negative thermal expansion (giant NTE) materials recently discovered. Moreover, prospects for future research are presented. One turning point is the large isotropic NTE of ZrW2O8 discovered in 1996. Starting with manganese nitride in 2005, various materials have been found to have negative linear expansion coefficients that are many times larger than those of conventional NTE materials, although some operating-temperature constraints exist. These achievements have overturned the conventional wisdom which holds that negative coefficients of linear expansion do not engender large values. Additionally, the achievements established the concept of “giant” or “colossal” NTE. This article emphasizes recent important findings of enhanced NTE caused by material microstructural effects that are peculiar to ceramic bodies, and “hybrid” NTE by which multiple mechanisms work simultaneously. Additionally, this article introduces an attempt to produce fine particles of NTE material and use them as a thermal expansion compensator, especially for thermal-expansion control of resin. [ABSTRACT FROM AUTHOR]

The rapid progress of modern technologies has accelerated the prominence of thermal expansion mismatch between materials, and tunable thermal expansion materials will be a powerful safeguard against this challenge. Here, isotropic MHfF6 (M = Ca, Mn, Fe, and Co) compounds with tunable thermal expansion have been produced via a low-cost synthetic method and investigated. By utilizing temperature dependent X-ray diffraction (XRD) and Raman spectroscopy, combined with first principles calculations, it was revealed that the transverse thermal vibrations of the F atoms are dominated by low-frequency phonons with negative Grüneisen parameters and are therefore the origin of the negative thermal expansion (NTE). Very interestingly, with the increase of the M atomic number, the metal⋯F atomic linkages become stiffer, reducing the number of vibrational modes with negative Grüneisen parameters, so that the strong NTE can be gradually adjusted to moderate NTE and to near zero thermal expansion. The present study achieves the tunable thermal expansion in a new compound family and shed light on the internal mechanism from the perspective of lattice vibrational dynamics. [ABSTRACT FROM AUTHOR]

The present study delves into the significant impact of secondary phases created during the formation process of Y 2 W 3 O 12. Thermomiotic ceramic materials exhibit negative thermal expansion (NTE). Among those ceramics, Y 2 W 3 O 12 is distinct for having phase stability over a high-temperature range as well as high volumetric NTE. These properties make Y 2 W 3 O 12 an unprecedented additive for thermal expansion coefficient (CTE) engineering for high-temperature composites. Synthesis of this material is continuously concluded with a higher thermal expansion than the theoretical. To fully take advantage of this material's unique properties, the origin of the mismatched NTE should be fully understood. In this study, the popular solid-state synthesis approach of Y 2 W 3 O 12 across all synthesis steps was examined in detail. Each secondary Y-W-O phase's contribution to the CTE was calculated, and the final value closely aligns with the measured NTE within 3.7 %, demonstrating the impact of secondary phases on the material's thermal behavior. [ABSTRACT FROM AUTHOR]

A novel negative thermal expansion (NTE) material NdMnO3 was synthesized by solid-state method at 1 523 K. The crystal structure, phase transition, pores effect and negative expansion properties of NdMnO3 were investigated by variable temperature X-ray diffraction (XRD), scanning electron microscope (SEM) and variable temperature Raman spectra. The compound exhibits NTE properties in the orderly O′ phase crystal structure. When the temperature is from 293 to 759 K, the ceramic NdMnO3 shows negative thermal expansion of −4.7×10−6/K. As temperature increases, the ceramic NdMnO3 presents NTE property range from 759 to 1 007 K. The average linear expansion coefficient is −18.88×10−6/K. The physical mechanism of NTE is discussed and clarified through experiments. [ABSTRACT FROM AUTHOR]

Additive manufacturing is proposed as a novel tool to produce complex scaffold constructs for use in cell cultured meat. The presence of scaffolds in the final cell cultured products raises the need to understand the thermal behavior of biopolymers through culturing and cooking as it relates to the final organoleptic properties. Therefore, the objective of this study was to understand how aqueous and high temperature environments influence plasticization and contraction of biopolymer scaffolds through the physio–chemical mechanisms of hydrolysis and negative thermal expansion. To achieve this objective, scaffolds were printed using a negative thermal expansion stretch–dominated design in both PLA and PLA-TPU material configurations. The samples were evaluated after a simulated cooking experiment (90 °C for 10 mins). The formation of crystals in the single material PLA during cooking led to bend–dominated contraction while the dual-material PLA-TPU experienced stretch–dominated contraction. Furthermore, exceeding the glass transition temperature of PLA during simulated cooking in an aqueous environment caused irreversible deformation to the scaffold structure that has the potential to influence organoleptic properties.

Zn2P2O7, a representative material in the A2P2O7 family, exhibits negative thermal expansion (NTE) and possesses a remarkable negative linear expansion coefficient. Here we employ variable temperature and high-pressure Raman spectroscopy to investigate the phonon anomalies arising from the α- to β-phase transition in Zn2P2O7. Combing with the refinement results of our X-ray diffraction (XRD) experiment, we have identified the specific variations of the bond lengths, bond angles and the polyhedral distortion indexes that result in the phonon anomalies. Some certain phonons, whose energy decreases with increasing pressure, have been demonstrated to give rise to negative Grüneisen parameters that can characterize phonon anharmonicity and lead to lower thermal expansion in the α-phase of Zn2P2O7 compared to the β-phase. These results provide new insight into the relationship between lattice deformation and phonon anomalies during the structural phase transition in the NTE material Zn2P2O7.

Negative thermal expansion (NTE) materials were utilized to alleviate the high residual stress of brazed joints by regulating the coefficient of thermal expansion (CTE) of metal composite filler. However, the confined addition amount of NTE materials restricted their ability to control the CTE of metal composite filler. In this study, the physical properties of the brazing seam were investigated by finite element analysis to understand their influence on the stress distribution of brazed joint. Based on theoretical analysis, a new method of preparation a high-content Sc2W3O12 dispersed interlayer by cold-pressing sintering method was proposed. This method increased the optimal addition amount of Sc2W3O12 materials from 10 vol.% to 40 vol.%. When the content of Sc2W3O12 materials was 40 vol.%, the CTE of Sc2W3O12 dispersed interlayer decreased from 16.5 (the CTE of AgCuTi) to 10.9 × 10−6 K−1, achieving a gradient transition of CTE from the Cf/SiC composite material/brazing seam/GH3536. The maximum shear strength of the Cf/SiC-GH3536 joint using Sc2W3O12 dispersed interlayer is 141 MPa, which was 5.9 times higher than that of AgCuTi filler. This study highlights the potential of proposed method for preparing brazed interlayer with high-content reinforcements, which may find practical applications in other metal composites.

A new functional ceramic material Y 2-x Zr x Mo 3-x P x O 12 was prepared by solid sintering method in the study. In order to further decrease the phase transition temperature of Y 2 Mo 3 O 12 and improve its water absorption, a new low-expansion material of Y 2-x Zr x Mo 3-x P x O 12 was prepared by replacing Y3+/Mo6+ ions in Y 2 Mo 3 O 12 with Zr4+/P5+ ions. The hygroscopicity and thermal expansion of the material were further analyzed. Y 2-x Zr x Mo 3-x P x O 12 (0.4 ≤ x ≤ 0.8) was an orthomorphic phase with space group Pbcn at room temperature and little crystal water existed in the lattice. With the increase in doped ions, the hygroscopicity of Y 2 Mo 3 O 12 was weakened significantly. When the substitution content reached x = 0.4, Y 1.6 Zr 0.4 Mo 2.6 P 0.4 O 12 realized the coefficient of thermal expansion (CTE) of 1.82 × 10−6 K−1 in the temperature range from 300 K to 700 K and showed the nearly non-hygroscopicity and low thermal expansion (LTE) at room temperature. [ABSTRACT FROM AUTHOR]

Refractory negative thermal expansion (NTE) materials can reduce stress when subjected to drastic temperature changes and therefore have potential applications in fire-fighting field. However, NTE ceramics are susceptible to impact damage due to their poor mechanical properties. We have found that treatment of a ceramic with hydrofluoric acid (HF) generated floral microstructures that enhanced the ceramic's impact resistance. Specifically, pellets of a refractory NTE ceramic, Zr 2 P 2 WO 12 (ZWP) ceramics, containing various doping ratios of MgO) are fabricated and then treated with hydrofluoric acid (HF) to induce the formation of flower-like microstructures. Structural analyses show that the concentration of MgO in the ZWP pellets affects the morphology of the microstructures. The crystal orientation of ZWP appears after HF acid corrosion, and the formation of floral particles corresponded to the content of MgO. This investigation demonstrates that HF treatment can alter the microstructure of a refractory NTE ceramic and may have wide application for enhancing such ceramics' mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Luminescence thermal quenching (TQ) is one of the most critical problems to be solved for further improvement of phosphors' applications in lighting and many other fields. Herein, a novel strategy is demonstrated to achieve outstanding anti‐TQ performance with a substantial enhancement of Eu3+ red emission at 613 nm from Sc2MO3O12:Tb3+,Eu3+ phosphor. Its anti‐TQ performance is endowed by dual energy transfer (ET) pathways and intensified by the negative thermal expansion (NTE) property of the Sc2MO3O12 host. Remarkably, the photoluminescence (PL) emission intensity of Eu3+ from Sc2MO3O12:20%Eu3+,2%Tb3+ phosphor at 648 K reaches 507.3% of the initial intensity taken at 298 K. The lifetime of Eu3+ emission at 613 nm elongates with increasing measurement temperature. The experimental data and density functional theory (DFT) calculations reveal that the host structure shrinkage via NTE leads to the thermally boosted Eu3+ red emission by intensifying the consecutive ET and confinement of the absorption light. The potential of this phosphor as a dual‐mode high temperature thermometer based on both emission lifetime and intensity ratio read‐out modes is realized. This work provides inspiration to combine multiple strategies to achieve broad and dramatic anti‐TQ phosphors with enhanced performance for various optical applications. [ABSTRACT FROM AUTHOR]

Negative thermal expansion (NTE) is an abnormal phenomenon that only exists in few materials but is of importance in tailoring the coefficients of thermal expansion (CTE) in some advanced devices and instruments. Herein, we find that a large volume shrinkage occurs in Co 2 P 2 O 7 crossing its structural transformation from α (P 2 1 /C) to β phase (C 2/ m) around 584 K which can be tuned even to below room temperature (RT) by the substitution of Mn2+ for Co2+. It is also found that the sintering temperature and the content of Mn2+ are crucial factors in controlling the proportions of α- and β- phases crystallized at RT and the rates of phase transition. A zero thermal expansion within a wide temperature window (173–573 K) is realized for Co 1.4 Mn 0.6 P 2 O 7 sintered at 1173 K. The NTE arises from the lattice volume difference between the low temperature α- phase and high temperature β- phase while a higher content of Mn2+ and lower sintering temperature favorites for the coexistence of both phases at RT and lowering the phase transition rate. This work not only adds new members for the NTE family but also presents a method for regulating the onset, width, and rate of NTE by the interplay of substitution content and sintering temperature. [ABSTRACT FROM AUTHOR]

In 2 Mo 3 O 12 is considered to be a positive thermal expansion (PTE) material at room temperature since its negative thermal expansion (NTE) response temperature range is above 343 °C. With the expectation of tuning the NTE performance of In 2 Mo 3 O 12 , a series of In 2 Mo 3-x W x O 12 solid solutions was synthesized via B-site replacement by W6+. The effects of W6+ substitution on the phase composition, morphology, phase transition temperature (T pt) and thermal expansion behavior of In 2 Mo 3-x W x O 12 were systematically investigated. Results indicate that the replacement of Mo6+ by W6+ does not induce a change in the crystal structure of parent phase In 2 Mo 3 O 12 and can form continuous solid solutions of In 2 Mo 3-x W x O 12. With increasing composition parameter x, the T pt of In 2 Mo 3-x W x O 12 decreases, the corresponding NTE response temperature range is widened and NTE performance is improved. The coefficient of thermal expansion (CTE) of In 2 Mo 3-x W x O 12 becomes more negative. As expected, the T pt of In 2 Mo 3-x W x O 12 is tunable by adjusting the composition parameter x, and the tuning mechanism of NTE performance is discussed from the prospect of crystal structure. [ABSTRACT FROM AUTHOR]

Lightweight materials with near-zero thermal expansion (NZTE) and high thermal conductivity have potential applications in precision instruments, aerospace industry and electronic packaging due to their high thermal stability. In this study, multiphase Mn 3 Zn 1-x Sn x N (MnZnSnN) with abnormal negative thermal expansion (NTE) were used to inhibit the positive thermal expansion of AlSi. The resulting composites multiphase-MnZnSnN/AlSi (mMnZnSnN/AlSi) achieved NZTE (0.40 × 10-6 °C-1) in a wide temperature range (-5–60 °C, ΔT = 65 °C). Compared with other NZTE materials, mMnZnSnN/AlSi exhibits high thermal conductivity of 60 W·m-1·K-1 and high bending strength of 211 MPa. The density of the composite is only 4.46 g/cm3, 45% lower than invar alloy. This work provides guidance for designing and fabrication of aluminum matrix materials with combined advantages of wide temperature range zero thermal expansion behavior, high thermal conductivity and high mechanical properties. [ABSTRACT FROM AUTHOR]

Zero thermal expansion (ZTE) materials show excellent dimensionally stability under temperature fluctuations, which are urgently demanded in high-precision devices. However, most ZTE materials display high density and narrow operating temperature. This study presents a lightweight ZrW 2 O 8 /Al–Si composite that not only exhibits ZTE of 0.79 × 10−6 K−1 between 113 and 423 K, but also possesses an excellent high thermal conductivity of ∼33 W/(mK), which is nearly two orders of magnitude higher than that of ZrW 2 O 8. Furthermore, the continuous aluminum in the ZTE composite contributes to its good electrical conducting property (3.0 × 104 (Ω cm)−1), surpassing that of titanium (2.3 × 104 (Ω cm)−1). Simulated and calculated results confirmed that the in-situ nanoparticles at the interface play a crucial role in dispersing thermal stress, resulting in minimal susceptibility to thermal cycling-induced changes in thermal expansion and strength. The present study opens a new frontier for the development of high-performance ZTE materials. [ABSTRACT FROM AUTHOR]

Transition-metal oxides show lots of interesting and useful properties. The wide variety of their crystal structures gives rise to various electronic structures, which lead to various chemical and physical properties. The author has been interested in such transition-metal oxides and is seeking new materials with novel functional properties. In this review article new functional properties found in A-site-ordered quadruple perovskite structure oxides with the unusually high-valence cations are highlighted. Negative thermal expansion was found in NdCu3Fe4O12 at the intersite-charge-transfer transition temperature near room temperature. The property is useful for developing materials to compensate the normal positive thermal expansion. Significant latent heat was also found to be provided by the intersite-charge-transfer transition in NdCu3Fe4O12. The large latent heat is considered to be related with unusual first-order magnetic entropy change induced by the charge transition. The large entropy change can be utilized for thermal control through a caloric effect, which can make effective energy systems for thermal energy storage and refrigeration. [ABSTRACT FROM AUTHOR]

The negative thermal expansion (NTE) phenomenon is of great significance in fabricating zero thermal expansion (ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of materials, e.g., metal cyanides, oxometallates, and metal-organic frameworks, but has not been reported in the family of metal hydrides. Herein, a colossal and continuous negative thermal expansion is firstly developed in the low-temperature phases of LT1- and LT2-Mg2NiH4 between 488 K and 733 K from in-situ transmission electron microscope (TEM) video, with the volume contraction reaching 18.7% and 11.3%, respectively. The mechanisms for volume contraction of LT1 and LT2 phases are elucidated from the viewpoints of phase transformation, magnetic transition, and dehydrogenation, which is different from common NTE materials containing flexible polyhedra units in the structure. The linear volume shrinkage of LT2 in the temperature of 488–553 K corresponds to the phase transition of LT2→HT with a thermal expansion coefficient of –799.7 × 10–6 K–1 revealed by in-situ synchrotron powder X-ray diffraction. The sudden volume contraction in LT1 between 488 and 493 K may be caused by the rapid dehydrogenation of LT1 to Mg2Ni. The revealed phenomenon in single composite material with different structures would be significant for preparing zero thermal expansion materials by tuning the fraction of LT1 and LT2 phases.

The authors reveal a thermal actuating bilayer that undergoes reversible deformation in response to low-energy thermal stimuli, for example, a few degrees of temperature increase. It is made of an aligned carbon nanotube (CNT) sheet covalently connected to a polymer layer in which dibenzocycloocta-1,5-diene (DBCOD) actuating units are oriented parallel to CNTs. Upon exposure to low-energy thermal stimulation, coordinated submolecular-level conformational changes of DBCODs result in macroscopic thermal contraction. This unique thermal contraction offers distinct advantages. It's inherently fast, repeatable, low-energy driven, and medium independent. The covalent interface and reversible nature of the conformational change bestow this bilayer with excellent repeatability, up to at least 70 000 cycles. Unlike conventional CNT bilayer systems, this system can achieve high precision actuation readily and can be scaled down to nanoscale. A new platform made of poly(vinylidene fluoride) (PVDF) in tandem with the bilayer can harvest low-grade thermal energy and convert it into electricity. The platform produces 86 times greater energy than PVDF alone upon exposure to 6 °C thermal fluctuations above room temperature. This platform provides a pathway to low-grade thermal energy harvesting. It also enables low-energy driven thermal artificial robotics, ultrasensitive thermal sensors, and remote controlled near infrared (NIR) driven actuators.