Giant negative thermal expansion in Zn2-xCuxP2O7 ceramics via microstructure effect

As a novel thermophysical behavior, negative thermal expansion (NTE) has been studied in many materials. However, rare materials have realized giant NTE, and the methods to improve NTE are lacking. Herein, a giant NTE has been achieved in Zn_2-xCu_xP₂O₇ ceramics via microstructure effect. In the Zn_1.96Cu_0.04P₂O₇ ceramic body, the linear contraction measured by dilatometry reaches to 0.9% (3ΔL/L = 2.7%) when heated from ?30 °C to 125 °C, while the intrinsic crystallographic volume contraction derived by X-ray diffraction is only 1.68%. The remarkable NTE enhancement in the ceramic sample is attributed to the microstructure effect. An apparent shrinkage of the voids has been observed by in-situ atomic force microscope (AFM). The voids with large size in the ceramic body is the key factor to enhance NTE. This is the first time to observe direct experimental evidence by AFM for microstructure effect. Microstructure effect is an effective method to produce giant NTE.     

Expanding negative thermal expansion range of ZrMnMo3O12 to cover room temperature by introducing V5+

Solid solutions of Zr_1+xMn_1-xMo_3-2xV_2xO₁₂ (0 ≤ x ≤ 0.5) are developed with reduced phase transition temperature (from 362 to 160 K) by introducing V⁵⁺ into ZrMnMo₃O₁₂. Zr_1+xMn_1-xMo_3-2xV_2xO₁₂ adopt monoclinic (P2₁/a) and orthorhombic (Pbcn) structure at room temperature (RT) for x ≤ 0.1 and x ≥ 0.2, respectively. The formation of bond V–O induces a larger average effective negative charge on oxygen to enhance the repulsive force between them and then strengthens the bond of Mo–O, which reduces the phase transition temperature due to the reduction in effective electronegativity and expands negative thermal expansion (NTE) range covering RT. NTE property in a wide temperature range (from 160 to 673 K) for Zr_1.5Mn_0.5Mo₂VO₁₂ is realized, implying great potential for applications. The NTE property of the materials is induced by low-frequency phonons.     

Negative thermal expansion and shift in phase transition temperature in Mo-substituted ZrW2O8 thin films prepared by pulsed laser deposition

Mo-substituted ZrW₂O₈ (ZrW_1.1Mo_0.9O₈) thin films have been deposited on quartz substrates by the pulsed laser deposition (PLD) method. The effects of oxygen pressure, substrate temperature and annealing temperature on the morphologies and phase compositions of the ZrW_1.1Mo_0.9O₈ thin films were systematically investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The negative thermal expansion and shift in phase transition temperature in cubic ZrW_1.1Mo_0.9O₈ thin films were characterized using high temperature X-ray diffraction. The results indicate that as-deposited ZrW_1.1Mo_0.9O₈ thin films show amorphous phases. Crystallized cubic ZrW_1.1Mo_0.9O₈ thin films were prepared by heating at 1050 °C for 7 min. The growth of the ZrW_1.1Mo_0.9O₈ thin films was strongly influenced by the substrate temperature and oxygen pressure. The ZrW_1.1Mo_0.9O₈ thin film deposited at 500 °C with an oxygen pressure of 10 Pa was smooth and compact, and its thickness was about 720 nm. The high temperature X-ray diffraction analyses demonstrated that the cubic ZrW_1.1Mo_0.9O₈ thin film exhibited strong negative thermal expansion and its thermal expansion coefficient was calculated to be −8.65×10⁻⁶ K⁻¹ from 100 °C to 600 °C. The substitution of Mo in ZrW₂O₈ thin film leads to a remarkable decrease in phase transition temperature, with the α to β structure phase transition occurring below 100 °C. However, with increased testing temperature, the substitution results in part of the cubic ZrW_1.1Mo_0.9O₈ thin film gradually changing into a trigonal phase.     

Negative thermal expansion of (Al1/3Fe1/3Cr1/3)2(Mo1/2W1/2)3O12 (AFCMW) and low thermal expansion of AFCMW-(Co1/2Ni1/2)(Mo1/2W1/2)O4 with high entropy

A₂Mo₃O₁₂ (A-Al, Fe, Cr) have large negative thermal expansion (NTE) coefficients and structural stability but high phase-transition temperatures (PTTs). Herein, we prepared (Al_1/3Fe_1/3Cr_1/3)₂(Mo_1/2W_1/2)₃O₁₂ (AFCMW), and found it to have a low NTE coefficient and a low PTT. Furthermore, combination of AFCMW with (Co_1/2Ni_1/2)(Mo_1/2W_1/2)O₄ (CNMW) afforded an AFCMW–CNMW composite with a low thermal expansion (LTE). We determined that the PTT reductions in A₂Mo₃O₁₂ are largely due to the high-entropy effect resulting from the introduction of different ions into its A and M sites. Moreover, we found that the low LTE of the AFCMW–CNMW composite is attributable to the opposite thermal expansion behaviours of AFCMW and CNMW. We suggest that the suppressed thermal expansion during the phase transition process of the AFCMW–CNMW composite could be derived from the high-entropy effect resulting from its increased diversity of polyhedra, the influence of Co²⁺ and Ni²⁺ dopants, and CNMW-induced lattice distortion.     

Correlation between crystallinity and thermal expansion in LiAlSiO4 ceramics prepared by spark plasma sintering

LiAlSiO₄ (LAS) ceramics are prepared by using the sol-gel method followed by spark plasma sintering. XRD patterns and SEM images verify that the ceramics contain amorphous and LAS phases and that microcracks appear in the sample prepared at 900 °C due to its larger grain size. Compared with applied pressure and soaking time, sintering temperature has a greater impact on the crystallinity and density of the ceramics during sintering. High-temperature XRD results reveal that the LAS phase exhibits its intrinsic negative thermal expansion independently in all samples regardless of crystallinity. The coefficients of thermal expansion (CTE) measured by the dilatometric method change from positive values in samples prepared at 600 and 650 °C to near zero in samples prepared at 700 and 800 °C and then to a negative value in the sample prepared at 900 °C. The combined effects of an amorphous phase with a positive CTE and the LAS phase with a negative CTE are responsible for the observed transformation of thermal expansion in the samples. The calculated total CTEs of the glass-ceramic bulks are in agreement with the results measured through the dilatometric method in samples prepared at 650–800 °C. Microcracks in the sample prepared at 900 °C cause a more negative bulk CTE than the calculated CTE.     

Solid state sintering of very low and negative thermal expansion ceramics by Spark Plasma Sintering

Lithium aluminosilicate powder precursors of compositions Li₂O:Al₂O₃:SiO₂ as 1:1:2; and 1:1:3.11 were synthesized and sintered by the Spark Plasma Sintering technique. The sintering conditions were adjusted to obtain dense ceramic materials in an attempt to avoid the presence of a glassy phase. XRD and SEM images were employed for composition and microstructure characterization. The coefficient of thermal expansion of the sintered samples was studied down to cryogenic conditions. Rietveld quantification was performed with the use of an external standard. Pure β-eucryptite of different compositions in dense ceramic bodies was obtained with a negative expansion coefficient.     

Negative thermal expansion properties of Cu1.5Mg0.5V2O7

Cu_1.5Mg_0.5V₂O₇ was prepared by a solid state method. Its phase, microstructure, thermal expansion property, and Raman spectra were analyzed in detail. Results show that Cu_1.5Mg_0.5V₂O₇ maintains a monoclinic crystal structure and exhibits an excellent linear negative thermal-expansion property with coefficient of thermal expansion of ?8.72?×?10^?6?K^?1 over a wide temperature range of 153–673?K. The mechanism underlying the negative thermal expansion of Cu_1.5Mg_0.5V₂O₇ involves the coupling effect of the tetrahedron caused by the lateral vibration of the bridge oxygen atom and the tensile effect of the tetrahedron, The partial collapse caused by the loss of the oxygen atoms also plays an important role in the mechanism.     

Effects of HCl concentration on the growth and negative thermal expansion property of the ZrW2O8 nanorods

A kind of negative thermal expansion ZrW₂O₈ nanorods were synthesized using a hydrothermal method, followed with a post-annealing at 570 °C for 2 h. Effects of HCl concentration on the microstructure, morphology and negative thermal expansion property in resulting ZrW₂O₈ powders were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). Results indicate that the formation of the precursor ZrW₂O₇(OH)₂(H₂O)₂ significantly depends on the HCl concentration, and the precursors ZrW₂O₇(OH)₂(H₂O)₂ can form in the 2-8 mol/L HCl solution. With increasing the concentration of the HCl solutions from 2 to 8 mol/L, the rod-like ZrW₂O₈ particles become more homogeneous, and the average dimension change from 10 μm × 0.5 μm to 700 nm × 50 nm. All the ZrW₂O₈ powders obtained in different conditions exhibit negative thermal expansion property, and the average negative thermal expansion coefficients from 15 °C to 600 °C decrease gradually with the increasing HCl concentration.     

复合氧化物材料的负热膨胀机理

介绍了相转变、桥氧原子的横向热振动、刚性多面体的旋转耦合、固体内压转变、相界面弯曲、阳离子迁移等六种模式的负热膨胀机理。并对其应用前景和发展趋势进行了预测     

Preparation of In0.5Sc1.5Mo3O12 nanofibers and its negative thermal expansion property

Orthorhombic In_0.5Sc_1.5Mo₃O₁₂ nanofibers were prepared by electrospinning followed by a heat treatment. The effects of post-annealing temperatures on the phase composition, microstructure and morphology were investigated by XRD, SEM, HRTEM and XPS. Negative thermal expansion (NTE) behaviors of the In_0.5Sc_1.5Mo₃O₁₂ nanofibers were analyzed by high-temperature XRD. Results indicate that the as-prepared In_0.5Sc_1.5Mo₃O₁₂ nanofibers show an amorphous structure with smooth and homogeneous shape. The average diameter of the as-prepared In_0.5Sc_1.5Mo₃O₁₂ nanofibers is around 515 nm. Well crystallized orthorhombic In_0.5Sc_1.5Mo₃O₁₂ nanofibers could be prepared after post-annealing at 550 °C for 2 h with an average diameter of about 192 nm. The crystallinity of In_0.5Sc_1.5Mo₃O₁₂ nanofibers gradually improved with the increase of annealing temperature. However, too high post-annealing temperature leads to a damage of sample's fiber structure. The high-temperature XRD results reveal that In_0.5Sc_1.5Mo₃O₁₂ nanofibers show an anisotropic NTE, and the coefficients of thermal expansion (CTEs) along a-axis and c-axis were −5.95 × 10⁻⁶ °C⁻¹ and -3.54 × 10⁻⁶ °C⁻¹, while the one along b-axis is 5.61 × 10⁻⁶ °C⁻¹. The volumetric CTE of In_0.5Sc_1.5Mo₃O₁₂ nanofibers is −3.90 × 10⁻⁶ °C⁻¹ and the linear one is 1.3 × 10⁻⁶ °C⁻¹ in 25–700 °C.     

High configurational entropy for low phase transition temperature and thermal expansion of A2M3O12 oxide ceramics

Transverse vibrations of bridging atoms in framework structure oxides contribute to negative thermal expansion (NTE), increasing the configurational entropy. Herein, the configurational entropy of NTE (Al_1/3Fe_1/3Cr_1/3)₂Mo₃O₁₂ (AFCM) is tuned by introducing ZrMg and W to AlFeCr and Mo sites to lower NTE. The NTE of ((Zr_1/2Mg_1/2)_x(Al_1/3Fe_1/3Cr_1/3)_(1-x))₂Mo₃O₁₂ (ZMAFCM) reduce obviously with increasing the content of ZrMg and also the phase transition temperatures (PTTs) (x = 0∼0.5). For ((Zr_1/2Mg_1/2)_x(Al_1/3Fe_1/3Cr_1/3)_(1-x))₂(Mo_1/2W_1/2)₃O₁₂ (ZMAFCMW), the NTE and PTTs reduce at a faster rate than that of ZMAFM. The configurational entropy increases with the content of ZrMg firstly (x = 0∼0.4) and then decreases. The possible mechanism of thermal expansion change is related to the enhanced lattice configuration, high entropy. The inconsistent transverse vibrations of bridging oxygen atoms could reduce their contribution to NTE, especially for high entropy. The PTT of high configurational entropy oxides is reduced obviously due to the influenced on the effective electronegativity. The investigation paves a high entropy way to lower thermal expansion and PTT of A₂M₃O₁₂ oxide ceramics and explores the further mechanism of NTE.     

负热膨胀填料钨酸锆对环氧封装材料性能影响

由于封装材料与电子元件线膨胀系数差异大,成型后造成开裂、空洞和离层等缺陷,采用化学固相分步法制备的高纯度负热膨胀材料钨酸锆(ZrW2O8)颗粒作为填料,制备ZrW2O8/E-51及SiO2/E-51电子封装材料,测试了不同种类和含量的填料下封装材料线膨胀系数、显微硬度、玻璃化转变温度及磨损性能。实验结果表明:随ZrW2O8含量的增加,ZrW2O8/E-51材料线膨胀系数不断下降,显微硬度不断提高。ZrW2O8/E-51材料的磨损性能优于SiO2/E-51材料,磨损机理主要是粘着磨损和疲劳剥落,后期发生了磨粒磨损。     

Anomalous thermal expansion behavior in Er1-xCaxMnO3

Perovskite Er_1-xCa_xMnO₃ (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5) was synthesized using a solid-state method. Thermal expansion behavior was tested using a thermal dilatometer and high-temperature X-ray diffraction (XRD). The experimental results indicated the doping contents of Ca (x) in the Er_1-xCa_xMnO₃ have a dramatic effect on their thermal expansion behavior. The samples of Er_1-xCa_xMnO₃ (x = 0.1,0.2 and 0.25) exhibit positive thermal expansion (PTE) characteristics while Er_0.7Ca_0.3MnO₃ (x = 0.3) exhibits a negative thermal expansion (NTE) property with a thermal expansion coefficient of −3.1 × 10⁻⁶ K⁻¹ in room temperature (RT) −750 K. In addition, Er_0.6Ca_0.4MnO₃ (x = 0.4) exhibits NTE properties only at RT–500 K, and Er_0.5Ca_0.5MnO₃ (x = 0.5) exhibits PTE properties at RT–750 K. The thermal shrinkage mechanism is the Jahn–Teller effect of the Mn³⁺ ions and the double exchange of Mn³⁺–O–Mn⁴⁺ in Er_0.7Ca_0.3MnO₃. This phenomenon causes Mn–O octahedral distortion and oxygen vacancy, causing Er_0.7Ca_0.3MnO₃ to become anisotropic. This feature results in the elastic deformation of Er_0.7Ca_0.3MnO₃ during heating, which consumes the void and displays NTE at macro level.     

Enhanced negative thermal expansion of (KMg)3+-substituted Fe2Mo3O12 ceramics

Herein, we report the solid-state synthesis of (KMg)_xFe_2-xMo₃O₁₂ (0 = x ≤ 1.5) ceramics. Phase composition, crystal structure, morphology, phase transition and thermal expansion behavior of the (KMg)_xFe_2-xMo₃O₁₂ ceramics were investigated by XRD, Raman, XPS, HRTEM, EDX, SEM, TMA and high-temperature XRD. Results indicate that (KMg)³⁺ dual-cations have successfully replaced Fe³⁺ in Fe₂Mo₃O₁₂ ceramics and single-phase monoclinic (KMg)_xFe_2-xMo₃O₁₂ ceramics were prepared for 0.25 = x ≤ 1. (KMg)³⁺ introduction can increase the density of (KMg)_xFe_2-xMo₃O₁₂ ceramics and effectively improve their negative thermal expansion (NTE) performance. In addition, the phase transition temperature (Tc) of Fe₂Mo₃O₁₂ was reduced from 508.1 °C to room temperature with the increase of (KMg)³⁺-substitution. Monoclinic KMgFeMo₃O₁₂ ceramics was observed to show stronger NTE in a wider temperature range of 30–700 °C for the first time. Its corresponding coefficient of thermal expansion (CTE) is as high as ?17.21 × 10^?6 °C^?1. The distortion of [FeO₆/MgO₆] polyhedra in (KMg)_xFe_2-xMo₃O₁₂ caused by (KMg)³⁺-substitution contributed to the stronger NTE.     

Synthesis and characterization of zirconia toughened alumina ceramics prepared by co-precipitation method

Undoped and 3 mol% yttrium doped ZrO₂–Al₂O₃ composite powders with partially stabilized ZrO₂ (PSZ) content varying from 0 to 30 wt% were prepared by a co-precipitation route using inorganic precursors Al(NO₃)₃, ZrOCl₂ and Y(NO₃)₃. The precipitates were characterized by DTA and subsequently calcined at 1200 °C for 4 h to achieve fine grained composite powders. The calcined powders were characterized by FTIR and XRD. In order to enhance the sinterability, the calcined powders were wet milled in a high energy ball mill. Powders were uniaxially pressed to form pellets and sintered at 1600 °C for 5 h to achieve greater than 96% relative density. Microstructural analysis of the sintered compacts revealed the uniform distribution of the zirconia particles among the alumina matrix. It was also observed that the faceted intergranular zirconia grains were present at the grain boundaries and junctions in the alumina matrix. Vickers indentation was carried out at 1 kgf load for hardness and 2 kgf load for estimating the critical stress concentration factor (K_c). Microscopic studies of the indented samples showed that cracks were propagating around the grain boundaries. Highest K_c ∼8.40 ± 0.4 MPa√m and hardness ∼16.31 ± 0.58 GPa was obtained for the 30 wt% PSZ-Al₂O₃ composite. The sintered density and critical stress intensity factor (K_c) achieved were compararble to that achieved earlier by hot press and SPS.     

Re-examination of the relationship between packing coefficient and thermal expansion coefficient for aromatic polyimides

The existence of a possible relationship between molecular packing coefficient and thermal expansion coefficient for various aromatic polyimides was investigated. Rod-like low-thermal-expansion polyimides without side groups were seen to have very high packing coefficients, pointing to free volume as a factor in lowering their thermal expansion coefficients. But the small packing coefficients for low-thermal-expansion polyimides with side groups indicated that this was not so. Also, even if the large packing coefficients tended to increase the Young's moduli for these polyimides without side groups, the rod-like polyimides with side groups have small packing coefficients and large Young's moduli. The polyimides with low packing coefficients were found to have very small diffusion coefficients for water vapour.     

Direct ink writing of cordierite ceramics with low thermal expansion coefficient

Since the application of cordierite ceramics is limited by the disadvantages of traditional preparation techniques, 3D printing technology provides the only choice for the rapid preparation of cordierite ceramics with highly complex structures. In this work, the fabrication of cordierite ceramics with complex structures was achieved by direct ink writing. The near-net-shape of cordierite ceramics was realized by the volume expansion caused by the phase transformation. A cordierite ceramic with an average shrinkage rate of 1.58 % was obtained at 1400 °C. The low shrinkage avoids design and manufacturing procedures carried out for dimensional and alignment errors. In addition, the coefficient of thermal expansion was as low as 1.69 × 10^?6 °C^?1. The effect of configuration on the thermal behavior of cordierite ceramics is understood by analyzing the phase composition and microstructure. The cordierites ink reported in this work offers additional possibilities for the production of novel complex structures.     

Negative in-plane CTE of benzimidazole-based polyimide film and its thermal expansion behavior

Non-stretched polyimide films based on 5,4′-diamino-2-phenyl benzimidazole (DAPBI) show curious thermal expansion properties: the in-plane CTE value of PI film is negative when cured at 350 °C (contract upon heating). However, the value of CTE turns positive when cured at 400 °C. In-plane and out-of-plane CTE of PI films annealed at various temperatures have been measured to study the annealing effect on thermal expansion feature. The in-plane CTE value increases from negative to positive as the raise of the annealing temperatures (T_anneal), while the out-of-plane CTE decreases as a function of T_anneal. Morphologies of PI films change from amorphous to semi-crystalline accompanied with the change of in-plane CTE from negative to positive. Mechanism of the thermal expansion behavior of DAPBI-based PI films is proposed: negative in-plane CTE is generated under the combination of the more preferential thermal expansion in the out-of-plane direction and the amorphous structure when the films are cured at lower temperatures; while thermal expansion in the in-plane and out-of-plane directions are both available for semi-crystallized PI films, affording positive in-plane CTE values.     

Electrospinning synthesis and negative thermal expansion of one-dimensional Sc2Mo3O12 nanofibers

Orthorhombic Sc₂(MoO₄)₃ nanofibers have been prepared by ethylene glycol assisted electrospinning method. The effects of annealing temperature, precursor concentration, spinning distance and solvent on the preparation of Sc₂(MoO₄)₃ nanofibers were characterized by XRD, SEM, HRTEM, EDX and high-temperature XRD. XRD analysis shows as-prepared nanofibers are amorphous. Orthorhombic Sc₂(MoO₄)₃ nanofibers can be fabricated after annealing at different temperatures in 500–800 °C for 2 h. The crystallinity of Sc₂(MoO₄)₃ nanofibers improves and the nanofiber diameter decreases gradually as the annealing temperature increases. However, the nanofiber structure was destroyed at the annealing temperature above 700 °C. Higher precursor concentration results in a slight increase of diameter and decrease in destroying temperature of Sc₂(MoO₄)₃ nanofibers. Spinning distance also affects the diameter of nanofibers, and the nanofiber diameter decreases as the distance increases. One-dimensional orthorhombic Sc₂(MoO₄)₃ nanofibers exhibit anisotropic negative thermal expansion. In 25–700 °C, the coefficients of thermal expansion (CTE) of α_a, α_b and α_c are ?5.81 × 10^?6 °C^?1, 4.80 × 10^?6 °C^?1 and -4.33 × 10^?6 °C^?1, and the α_l of Sc₂(MoO₄)₃ nanofibers is ?1.83 × 10^?6 °C^?1.     

Anodic lithium ion battery material with negative thermal expansion

Negative thermal expansion materials will effectively counteract possible severe expansion and contraction due to the insertion and extraction of Li ions in lithium ion batteries. Herein, negative thermal expansion ZrScMo₂VO₁₂ and its carbon-coating composites are prepared as electrode material in lithium ion batteries by a heating treatment route. The galvanostatic charge/discharge process, cyclic voltammetry measurement and electrochemical impedance spectroscopy are tested to relate their thermal expansion and electrochemical properties. The initial specific capacity reaching 1062 mA h g^-1 at the current density of 0.2 A g^-1 is obtained with ideal negative thermal expansion properties. The reversible specific capacity still remains stable at 310 mA h g^-1 for that material coated with carbon after 100 cycles. The corresponding theoretical simulations and in situ XRD patterns propose a Li ion storage mechanism based on Li ion insertion process in open framework structure. As a proof-of-concept research, this work paves a way to the promising application of negative thermal expansion materials in lithium ion batteries and other energy storage systems.