Thermal Expansion Behavior Research Articles

Thermal expansion, [formula omitted] phase diagram and polarization of (1-x)Na[formula omitted]Bi[formula omitted]TiO[formula omitted]-xBaTiO[formula omitted] solid solutions

The paper presents the results of detailed studies of thermal expansion of solid solutions (1-x)Na1/2Bi1/2TiO3-xBaTiO3 with x=0.04-0.97 in the temperature range from 100 to 900 K. A change in chemical pressure associated with the complex cationic substitution, (Na1/2Bi1/2)2+→ Ba2+, result in a very rapid decrease in the temperatures of the transformation P4mm→C2mm→R3m below 100 K which are characteristic of BaTiO3. Significant features in the behavior of thermal expansion were observed near two triple points in the T−x phase diagram where the phases Pm3̄m, P4mm, P4bm (x≈0.15-0.20) and P4bm, P4mm, R3c (x≈0,06) coexist, allow the studied solid solutions to be divided into three groups. The relationship between the effects of internal chemical pressure and external hydrostatic one is discussed. By analyzing the thermodynamic potential, the root-mean-square polarization Pd is determined, which increases by about 16% with a decrease in the BT content from 0.97 to 0.4.

Multifunctional design of lattice metamaterial with desired thermal expansion behaviors using topology optimization

Designing metamaterials with unprecedented coefficients of thermal expansion (CTEs) is an urgent demand for the majority engineering structures suffering from ambient temperature variation. Current studies on such artificial materials are mainly focused on achieving CTE tunnability through the purposeful design of material microstructure using an intuition based mechanism. In this study, the mechanical properties including maximum bulk modulus, specific stiffness and high thermal conductivity are combined with desired CTEs for designing multifunctional lattice metamaterials through the application of a non-intuitive topology optimization method. Toward this end, the continuous variable of member cross-sectional area is adopted to optimize lattice topology, section sizes of lattice members and material distributions, simultaneously. To meet the manufacturing requirements, an improved member intersection constraint that can cooperate with the present continuous design variable is introduced. A self-programmed routine that can be coupled with any commercial FEA software is developed to implement the present optimization method for the design of lattice metamaterials. Four typical optimization cases corresponding to different practical engineering issues are completed. Compared with the previously reported representative lattice metamaterials that are devised from the intuition or experience of designers, the optimization results obtained in this work demonstrate an obvious superiority in bulk modulus and specific stiffness. Additionally, a bimetallic specimen, fabricated using mechanical processing technology and composed of the metallic constituents Invar and Aluminum alloy, is presented to demonstrate the manufacturability of the optimized lattice microstructures.

Study on the Thermal Expansion Behavior of Mg-3RE Alloys and Mg-3Y/SiCp Composites

Study on the Thermal Expansion Behavior of Mg-3RE Alloys and Mg-3Y/SiCp Composites

Order-disorder structural transition and thermal expansion properties in Ce-substituted Y2Zr2O7 system

In the pursuit of advancing inert matrix fuel (IMF) applications, zirconate pyrochlores have emerged as promising candidates for the incorporation of minor actinides and plutonium. This study employs CeO2 as a nonradioactive surrogate for PuO2 and focuses on the synthesis of cerium-substituted Y2Zr2O7 samples (Y2-xCexZr2O7, 0.0 ≤ x ≤ 2.0) through a solid-state route under both reducing and oxidizing conditions to mimic plutonium incorporation. The impact of cerium content and its valence state, which in turn is influenced by synthesis conditions, on crystal structure and phase stability has been investigated through X-ray diffraction and Raman spectroscopic studies. Samples synthesized under reduced conditions undergo a defect fluorite to pyrochlore phase transition through a biphasic mixture consisting of these two phases upon increasing Ce-substitution. Conversely, the high temperature oxidizing synthesis conditions yield a defect fluorite phase field over a wide composition range (0.0 ≤ x ≤ 1.6) and a tetragonal phase at x = 2.0. Intriguingly, pyrochlore-type phases obtained under reducing conditions transform into the metastable kappa-phases upon mild oxidation at a relatively low temperature (1073 K), as confirmed by Raman spectroscopic studies. A combination of thermo-gravimetric and Raman spectroscopic investigations confirms the complete reduction of Ce4+ to Ce3+ under reducing conditions. The lattice thermal expansion behavior has also been investigated for the defect fluorite phases, synthesized under oxidizing conditions, by means of high temperature XRD spanning the temperature range 298–1273 K. Notably, the thermal expansion of compositions exhibits an increasing trend with increasing cerium content.

Classifying and Predicting the Thermal Expansion Properties of Metal-Organic Frameworks: A Data-Driven Approach.

Metal-organic frameworks (MOFs) are versatile materials for a wide variety of potential applications. Tunable thermal expansion properties promote the application of MOFs in thermally sensitive composite materials; however, they are currently available only in a handful of structures. Herein, we report the first data set for thermal expansion properties of 33,131 diverse MOFs generated from molecular simulations and subsequently develop machine learning (ML) models to (1) classify different thermal expansion behaviors and (2) predict volumetric thermal expansion coefficients (αV). The random forest model trained on hybrid descriptors combining geometric, chemical, and topological features exhibits the best performance among different ML models. Based on feature importance analysis, linker chemistry and topological arrangement are revealed to have a dominant impact on thermal expansion. Furthermore, we identify common building blocks in MOFs with exceptional thermal expansion properties. This data-driven study is the first of its kind, not only constructing a useful data set to facilitate future studies on this important topic but also providing design guidelines for advancing new MOFs with desired thermal expansion properties.

Influence of Si on the thermal expansion behavior and photo-electrochemical protection of Al-13 wt.% Si binary casting alloy

Influence of Si on the thermal expansion behavior and photo-electrochemical protection of Al-13 wt.% Si binary casting alloy

Friction stir additive manufactured AA 6061/TiC/GS composite: assessment of microstructural and mechanical properties

Friction stir additive manufacturing (FSAM) technique was used to fabricate the composite. Present investigation deals with the additive manufacturing of three AA 6061 sheets filled with TiC/GS particles in a groove with the variation reinforcement wt-%. Micro-structural investigation of the fabricated sample was conducted through optical microscopy, SEM and EDS. Optical and SEM results depict the uniform dispersal of the TiC and GS particles in the processed zone. Due to hard TiC and GS particles embedded in AA 6061, an improvement in hardness by 37.2% was observed for AA 6061/4 wt-%TiC/6 wt-%GS composite. Tensile and compressive strength was enhanced by 25.8% and 11% for the developed material. Corrosion test and thermal expansion behavior was investigated for the fabricated composite. 0.2 gm was the weight loss observed for the sample kept in NaCl solution for 72 h. Negligible amount of thermal expansion was noticed for the prepared material. TiC and GS particles, observed in the fractographic image shows the brittle fracture. EDS analysis confirmed the existence of elements like Al, Mg, Mn etc in the surface of the specimens. The present experimental results were also compared from the previous published work by the various academicians.

Growth of Size-Tunable Ag2O Polyhedra and Revelation of Their Bulk and Surface Lattices.

By primarily adjusting the reagent amounts, particularly the volume of AgNO3 solution introduced, Ag2O cubes with decreasing sizes from 440 to 79 nm, octahedra from 714 to 106 nm, and rhombic dodecahedra from 644 to 168 nm are synthesized. 733 nm cuboctahedra are also prepared for structural analysis. With in-house X-ray diffraction (XRD) peak calibration, shape-related peak shifts are recognizable. Synchrotron XRD measurements at 100 K reveal the presence of bulk and surface layer lattices. Bulk cell constants also deviate slightly. They show a negative thermal expansion behavior with shrinking cell constants at higher temperatures. The Ag2O crystals exhibit size- and facet-dependent optical properties. Bandgaps red-shift continuously with increasing particle sizes. Optical facet effect is also observable. Moreover, synchrotron XRD peaks of a mixture of Cu2O rhombicuboctahedra and edge- and corner-truncated cubes exposing all three crystal faces can be deconvoluted into three components with the bulk and the [111] microstrain phase as the major component. Interestingly, while the unheated Cu2O sample shows clear diffraction peak asymmetry, annealing the sample to 450 K yields nearly symmetric peaks even when returning the sample to room temperature, meaning even moderately high temperatures can permanently change the crystal lattice.

Fabrication of flexible (Mg0.2Al0.2Fe0.2Ni0.2Co0.2)2Ti2.8O8 ceramics via compositionally complex ceramics method

A novel compositionally-complex flexible (Mg0.2Al0.2Fe0.2Ni0.2Co0.2)2Ti2.8O8 (abbreviated as CCC) ceramic with pseudobrookite structure was synthesized by solid-state reaction method. As compared to the fabrication process of flexible aluminum titanate ceramic (C. Babelot, 2011), the sintering temperature was significantly reduced from 1600 °C to 1200 °C by co-doping. And, the combinations of displacement (0.11–0.25 mm) and bending strength (10–40 MPa) were achieved by controlling the sintering condition. Among these, the specimen sintered at 1200 °C for 2 h (abbreviated as CCC-1200-2) presents a single-phase crystal structure and uniform elemental distribution. After that, its near-zero thermal expansion coefficient of 0.47 × 10−6 K−1 at low temperature was obtained and the nonlinear thermal expansion behavior was observed. Lastly, the thermal stability of sample CCC-1200-2 was checked out by annealing the samples between 900 °C and 1600 °C for various times up to 100 h. As a result, this study successfully fabricated the flexible CCC ceramics with improved mechanical properties, high thermal stability, and low sintering requirements, providing a new technology strategy for pseudobrookite-type ceramics and compositionally-complex ceramics fabrication.

Isotropic negative thermal expansion in the multiple-phase La-Fe-Co-Si alloys with enhanced strength and ductility

The negative thermal expansion materials based on the magneto-volume transition are usually poor in mechanical properties, severely inhibiting their application. Here in this article, we present the enforcement of the compressive strength and ductility of La(Fe,Co,Si)13 by directly adding extra Cu element and forming natural multiple phases alloys. Our study demonstrates that the extra Cu will facilitate the formation of LaCu2 phase that is semi-coherent with the La(Fe,Co,Si)13 phase, and the LaCuSi phase that exhibits a high density of stacking faults, which facilitates the enforcement of the strength and ductility of the alloy. Consequently, the natural alloys present increased strength from 70 MPa to 645 MPa, and the deformation behavior transforms from brittle to plastic, the ductility is simultaneously increased from 0.5 % to 4.4 %. The introduced phases exhibit positive thermal expansion behavior and compensate for the negative thermal expansion of the La(Fe,Co,Si)13 phase, inducing a tunable isotropic negative to zero thermal expansion is achieved in the alloys. Moreover, the alloys have high mechanical and negative thermal expansion performance reliability after 104 times thermal cycles. This work denotes that Cu is a functional element to enforce the mechanical properties of the La(Fe,Co,Si)13 alloys, and also promotes a new possibility for obtaining low-cost and isotropic negative/zero thermal expansion materials with high application reliability.

Effects of (KMn)3+ co-doping on the negative thermal expansion property of In2W3O12

At room temperature, monoclinic In2W3O12 ceramics exhibits positive thermal expansion. However, it transforms into an orthorhombic phase above 253 ℃, and then stably exhibits negative thermal expansion (NTE). In this work, to improve the NTE performance and extend the NTE temperature range of In2W3O12, the KxMnxIn2-xW3O12(0≤x≤0.5) ceramics were synthesized via the solid-state reaction method. The effects of (KMn)3+ double cation co-doping on the composition, microstructure, and thermal expansion behaviors of In2W3O12 ceramics were studied using XRD, Raman, XPS, SEM, and TMA. The results show that (KMn)3+ cations can replace In3+ in In2W3O12 ceramics. As the (KMn)3+ doping amount increases, monoclinic In2W3O12 gradually changed into monoclinic KxMnxIn2-xW3O12. Meanwhile, the grains grow up and the density of KxMnxIn2-xW3O12 ceramics was increased. Pure monoclinic KxMnxIn2-xW3O12 ceramics were prepared when x rises to 0.25 and 0.4. Among them, the thermal expansion coefficient of K0.4Mn0.4In1.6W3O12 ceramics in 100–700 ℃ is as high as -17.83×10-6 ℃-1, which was significantly improved compared to In2W3O12 ceramics. In addition, the structural phase transition of In2W3O12 ceramics around 253 ℃ was gradually eliminated and the NTE temperature range was widened. Double cation (KMn)3+ co-doping effectively improves the NTE performance of In2W3O12.

Thermophysical properties of equiatomic CrMnFeCoNi, CrFeCoNi, CrCoNi, and CrFeNi high- and medium-entropy alloys

High- and medium-entropy alloys have emerged as promising materials with significant potential for diverse technical applications. Notably, their use in the field of energy technology has attracted particular interest, where thermophysical properties play a pivotal role. In this context, this study aims to investigate the thermophysical properties, namely thermal expansion behavior, thermal diffusivity, specific heat capacity, thermal conductivity, and the electric resistivity of single-phase face-centered cubic alloys between 300 K and 773 K. In addition to thermal conductivity, the electric resistivity was measured. Based on the Wiedemann-Franz law, electronic and phononic contributions to the overall thermal conductivity were evaluated. Complementary insights into the electronic state of the investigated materials were obtained by electron spin resonance measurements, revealing the presence of short-range ordering in all alloys. The specific heat capacity is found to dominate the thermal conductivity. Furthermore, the study shows the decisive influence of chemical complexity on the thermophysical properties. Notably, the observed influences extend to the electronic thermal conductivity, pointing out the correlation between composition and heat transport properties. This comprehensive investigation provides a foundation for understanding and tailoring the thermophysical behavior of the studied alloys, offering valuable insights for their targeted deployment in advanced energy applications.

Effect of Compressive Stress on Copper Bonding Quality and Bonding Mechanisms in Advanced Packaging.

The thermal expansion behavior of Cu plays a critical role in the bonding mechanism of Cu/SiO2 hybrid joints. In this study, artificial voids, which were observed to evolve using a focused ion beam, were introduced at the bonded interfaces to investigate the influence of compressive stress on bonding quality and mechanisms at elevated temperatures of 250 °C and 300 °C. The evolution of interfacial voids serves as a key indicator for assessing bonding quality. We quantified the bonding fraction and void fraction to characterize the bonding interface and found a notable increase in the bonding fraction and a corresponding decrease in the void fraction with increasing compressive stress levels. This is primarily attributed to the Cu film exhibiting greater creep/elastic deformation under higher compressive stress conditions. Furthermore, these experimental findings are supported by the surface diffusion creep model. Therefore, our study confirms that compressive stress affects the Cu-Cu bonding interface, emphasizing the need to consider the depth of Cu joints during process design.

Promoting nanoprecipitates via prefabricated defects to pin dislocations and grain boundaries for trading off high-strength and low-thermal-expansion of invar alloys

Invar alloys that combine high strength with a low coefficient of thermal expansion (CTE) are urgently required for industrial applications. Based on the lower coarsening rate during aging and the CTE values of carbonitrides, a novel strategy is proposed to prepare carbonitrides by reducing carbon and increasing nitrogen to design high-strength and low-thermal-expansion invar alloys. The V(C, N) nanoprecipitate was introduced into the invar alloy, and its effects on the microstructure, thermal expansion behavior, and mechanical properties were investigated. The direct-aged alloy exhibited an enhanced tensile strength of 525 MPa and a ductility of 47.6%. The cold-deformation aging alloy achieved an enhanced tensile strength of 815 MPa while retaining 7.4% ductility and a low CTE value of 1.23×10−6 /°C. The V(C, N) nanoprecipitates effectively immobilized dislocations and grain boundaries, leading to a high dislocation density and small grain size in the alloy. The contributions of each strengthening mechanism were calculated, and the precipitation and dislocation strengthening were found to be the main mechanisms of strength enhancement. These results provide a novel approach for preparing high-strength and low-CTE invar alloys.

Advancing Light Scattering Control Through the Exploration of Temperature‐Sensitive Optical Modifiers

AbstractLight scattering holds immense significance in various applications, including LED lighting, display enhancement, and solar cell optimization, emphasizing the critical role of understanding scattering mechanisms, especially light–matter interactions, achieving effective optical diffusion. Consequently, the influence of stimuli on material properties, including refractive indices and thermal expansion behavior, has emerged as a pivotal consideration, leading to the development of stimuli‐responsive light scattering modifier. Here, a temperature‐sensitive light scattering modifier composed of poly(methyl methacrylate‐co‐styrene) and poly(ethylene‐co‐vinyl acetate) is presented as scattering particles and matrix, respectively, using a melt‐blending process. Optical properties are evaluated across controlled temperatures 0–70 °C. These findings demonstrate an increasing trend in diffuse transmission and haze as temperatures increased across all light scattering modifiers. Significantly, the optimized light scattering modifier, integrating a dual particle system, showcased uniform reduction gaps in parallel transmission and adjustable haze characteristics across the visible spectrum under temperature control. This optical modifier achieved a total transmission of 92% and adjustable haze levels ranging from 35% to 90% under temperature control. Furthermore, this fabrication of three‐layer films incorporating the light scattering modifier exhibited identical characteristics to the developed light scattering modifier, emphasizing their potential for seamless integration across diverse technological domains.

Lithium oxides LiRO2 (R = rare earth elements) with negative thermal expansion behavior and inverse barocaloric effect

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.

High temperature structure and vibrational properties of ScXO4 (X= V5+ and P5+): A comparative study

ScVO4 and ScPO4 represent the zircon (xenotime) type structures with smallest trivalent cations, and that enable them to host both transition metal and rare-earth ions for applied optical materials. Thus, their crystal chemistry and thermophysical properties becomes relevance for their application in non-ambient conditions. In this report, high temperature crystal chemistry and vibrational properties of ScVO4 and ScPO4, as observed from in situ high temperature powder XRD and Raman spectroscopic studies, are reported. The comparative analyses of the results indicate that, though both are isostructural, they show drastically different thermal expansion behavior. In case of ScVO4, the c-axis shows significantly larger expansion compared to a-axis, while in ScPO4 the thermal expansion along and a and c-axes are more or less similar. At ambient condition, the thermal expansion anisotropy in ScPO4 and ScVO4 are 1.02 and 3.97, respectively. Additionally, ScPO4 shows relatively lower coefficient of volume thermal expansion compared to ScVO4, (αv = 23.64 × 10−6 K−1 for ScPO4 and 26.09 × 10−6 K−1 for ScVO4), and is contributed by the expansion of ScO8 units in their structures. The thermal expansion coefficients of ScO8 unit in ScPO4 and ScVO4 are 36.3 × 10−6 K−1 and 39.1 × 10−6 K−1, respectively. Temperature evolution of Raman modes indicates weakening of all the modes, except a symmetric stretching mode, with increasing temperature. The anharmonic analyses of the Raman modes indicate that implicit contributions in ScVO4 and ScPO4 are appreciably higher than the explicit contributions, and hence the changes in mode wavenumbers with volume play dominating role in governing their thermal expansion behaviors. Further, it is concluded that ScPO4 is characterized by more or less like rigid unit cell compared to ScVO4.

Stacking fault energy, thermal expansion behavior, and elastic coefficients of a single-crystalline CrFeNi medium-entropy alloy

The equiatomic CrFeNi alloy is considered to be a model single-phase face-centered cubic medium-entropy alloy. The Bridgman technique was employed to grow a single crystal of this alloy and its dilatation behavior and elastic properties were measured in the temperature range: 100 K–673 K. Based on transmission electron microscopy investigations, plastic deformation is initially caused by the glide of dissociated dislocations (Shockley pairs bounded by a stacking fault ribbon). From their dissociated widths, a stacking fault energy of 36 mJ∙m-2 was determined.

Relaxor ferroelectricity and elevated thermal expansion behaviour of (1−x)Bi0.5Na0.5TiO3-xBaSnO3 lead-free piezoelectric ceramics

The study on piezoelectric and ferroelectric properties of sodium bismuth titanate-based materials is essential for piezoelectric electronic components. In this study, a series of lead-free relaxor ferroelectric (1−x)Bi0.5Na0.5TiO3-xBaSnO3 (BNT-xBS) ceramics were prepared by a conventional solid-state reaction method. The phase performance, fracture morphologies, permittivity, ferroelectricity, piezoelectricity, and thermal expansion for various BS contents (x) were systematically studied. With an increase in x, the phase transition from R3c to P4bm, and the grain size marginally decreased from 1.79 to 1.51 μm. Meanwhile, the degree of dielectric relaxor and diffused phase transition improved, and the ferroelectricity and piezoelectricity initially increased and then decreased. The optimal electrical properties of Pr = 41.6 μC/cm2, d33 = 167.8 pC/N, and kp = 0.318 were observed at x = 0.06. The paper discusses how site disorder, long-range electric dipole ordering, and grain size influence various electrical properties. The mechanism of the thermal expansion behaviour was investigated based on Born-Lande theory. This study could serve as a landmark for studying multifunctional BNT-based piezoelectric materials for potential energy-harvesting devices.

Transition from isotropic positive to negative thermal expansion by local Zr6O8 node distortion in MOF-801

The chemical designability and diversity of metal-organic frameworks (MOFs) endow them with plenty of anomalous properties, such as negative thermal expansion (NTE). Herein, we investigated the thermal expansion behaviors of the well-known MOF-801, which has been widely used in water adsorption and gas separation. The analyses of variable temperature powder X-ray diffraction and Rietveld refinements revealed a fascinating transition from positive thermal expansion to NTE. Further in situ Raman spectra and pair distribution function investigations shed light on the transition being attributed to the local Zr6O8 node distortion rather than a long-range phase transition. Our findings will enhance the comprehension of NTE and contribute to the effective utilization of MOF-801 over a broad temperature range.