Phase stability,mechanical, and thermal properties of high-entropy transition and rare-earth metal diborides from first-principles calculations

The narrow composition design space of high-entropy transition metal diborides (HE TMB₂) limits their further development. In this study we designed six quaternary and quinary high-entropy transition metal and rare-earth diborides (HE TMREB₂) and investigated their phase stability using the energy distribution of the local mixing enthalpy of all possible configurations. The results show that both quaternary and quinary HE TMREB₂ have higher enthalpic driving forces, which facilitates the formation of single-phase AlB₂-type structures between TMB₂ and REB₂. Calculations of elastic constants show that the TMB₂ component has the greatest effect on the c₄₄ elastic constant and shear modulus G, while REB₂ significantly influences the bulk modulus B. Furthermore, LuB₂ and TmB₂ substantially affect the elastic modulus anisotropy of HE TMB₂. Rare-earth atoms in HE TMREB₂ can enhance the nonharmonic interactions between phonons, which results in a significant hindrance in the thermal transport of low-frequency phonons as well as an increase in the volume thermal expansion coefficients. Thus, the incorporation of REB₂ into HE TMB₂ has a significant impact on the phase stability and properties.     

Tuning stoichiometry of high-entropy oxides for tailorable thermal expansion coefficients and low thermal conductivity

Thermal barrier coating materials with proper thermal expansion coefficient (TEC), low thermal conductivity, and good high-temperature stability are of great significance for their applications in next-generation turbine engines. Herein, we report a new class of high-entropy (La_0.2Sm_0.2Er_0.2Yb_0.2Y_0.2)₂Ce_xO_3+2x with different Ce⁴⁺ contents synthesized by a solid-state reaction method. They exhibit different crystal structures at different Ce⁴⁺ content, including a bixbyite single phase without Ce⁴⁺ doping (x = 0), bixbyite-fluorite dual-phase in the RE₂O₃-rich region (0 < x < 2), and fluorite single phase in the stoichiometric (x = 2) and CeO₂-rich region (x > 2). The high-entropy (La_0.2Sm_0.2Er_0.2Yb_0.2Y_0.2)₂Ce_xO_3+2x exhibit tailorable TECs at a large range of 9.04 × 10^–6–13.12 × 10^–6 °C^–1 and engineered low thermal conductivity of 1.79–2.63 W·m^–1·K^–1. They also possess good sintering resistance and high-temperature phase stability. These results reveal that the high-entropy (La_0.2Sm_0.2Er_0.2Yb_0.2Y_0.2)₂Ce_xO_3+2x are promising candidates for thermal barrier coating materials as well as thermally insulating materials and refractories.     

New class of high-entropy rare-earth niobates with high thermal expansion and oxygen insulation

Tailoring the structure and properties of materials using the high-entropy (HE) effect is of significant interest in the fields of environmental and thermal barrier coatings (TBCs). In this work, a new class of dense HE rare-earth niobates was successfully prepared by a solid-phase reaction method, including (Sm_1/5Dy_1/5Ho_1/5Er_1/5Yb_1/5)NbO₄ (5HERN), (Sm_1/6Dy_1/6Ho_1/6Er_1/6Yb_1/6Lu_1/6)NbO₄ (6HERN), (Sm_1/7Dy_1/7Ho_1/7Er_1/7Yb_1/7Lu_1/7Gd_1/7)NbO₄ (7HERN), and (Sm_1/8Dy_1/8Ho_1/8Er_1/8Yb_1/8Lu_1/8Gd_1/8Tm_1/8)NbO₄ (8HERN), along with eight single rare-earth niobates (RENbO₄, RE = Sm, Dy, Ho, Er, Yb, Lu, Gd, and Tm). X-ray diffraction analysis showed that 5–8HERN are single-phase solid solutions with a monoclinic structure (space group C12/c1). The thermal expansion coefficients of 7HERN and 8HERN exceed 11 × 10⁻⁶ K⁻¹ at 1200°C and are much higher than those of the RENbO₄ compositions (10.13–10.74 × 10⁻⁶ K⁻¹) and other some HE rare-earth oxides (10.27–10.87 × 10⁻⁶ K⁻¹). Importantly, 5–8HERN have lower oxygen-ion conductivity and higher activation energy than yttrium-stabilized zirconia (YSZ) and the RENbO₄ compositions. The oxygen-ion conductivity of 5HERN (7.52 × 10⁻⁷ S cm⁻¹, 900°C) was 10⁵ times lower than that of YSZ (0.01 S cm⁻¹, 750°C). The hardness of 5–8HERN is ∼7.81–8.46 GPa and these compositions have low intrinsic lattice thermal conductivity at high temperature (1.28–1.69 W m⁻¹ K⁻¹ at 900°C). The mechanism by which the HE effect improved the material properties was elucidated. Young's modulus, hardness, thermal expansion coefficient, and intrinsic lattice thermal conductivity are linearly related to the mass, size, and distortion degree of samples. In contrast, the oxygen-ion conductivity depends on both the degrees of disorder and distortion and the oxygen-ion vacancy concentration. Based on their overall performance, especially their high thermal expansion coefficients and excellent oxygen-barrier performance, HE rare-earth niobates show potential for further development as TBC materials.     

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.     

Phase stability and tensorial thermal expansion properties of single to high-entropy rare-earth disilicates

Temperature limitations in nickel-base superalloys have resulted in the emergence of SiC-based ceramic matrix composites as a viable replacement for gas turbine components in aviation applications. Higher operating temperatures allow for reduced fuel consumption but present a materials design challenge related to environmental degradation. Rare-earth disilicates (RE₂Si₂O₇) have been identified as coatings that can function as environmental barriers and minimize hot component degradation. In this work, single- and multiple-component rare-earth disilicate powders were synthesized via a sol-gel method with compositions selected to exist in the monoclinic C 2/m phase (β phase). Phase stability in multiple cation compositions was shown to follow a rule of mixtures and the C 2/m phase could be realized for compositions that contained up to 25% dysprosium, which typically only exists in a triclinic, P $\overline{1}$, phase. All compositions exhibited phase stability from room temperature to 1200°C as assessed by X-ray diffraction. The thermal expansion tensors for each composition were determined from high-temperature synchrotron X-ray diffraction and accompanying Rietveld refinements. It was observed that ytterbium-containing compositions had larger changes in the α₃₁ shear component with increasing temperature that led to a rotation of the principal axes. Principal axes rotation of up to 47° were observed for ytterbium disilicate. The results suggest that microstructure design and crystallographic texture may be essential future avenues of investigation to ensure thermo-mechanical robustness of rare-earth disilicate environmental barrier coatings.     

Formation of high entropy metal diborides using arc-melting and combinatorial approach to study quinary and quaternary solid solutions

High entropy metal diborides (HEBs) represent a radically new approach to extend the chemical composition window of ultra-high temperature ceramics (UHTCs). In this work, arc-melting was used to produce dense HEBs starting from UHTC powders. In order to understand the influence of each individual diboride within the quinary system (HfB₂, ZrB₂, TiB₂, TaB₂ and CrB₂), we investigated five quaternary equimolar solid solutions e.g. Hf-Zr-Ti-Ta, Hf-Zr-Ti-Cr, Hf-Zr-Ta-Cr, Hf-Ti-Ta-Cr, Zr-Ti-Ta-Cr and the overall quinary equimolar combination. Arc-melting allowed a rapid screening of favorable and unfavorable combinations. The produced HEBs were free from undesired oxides and characterized by linear variation of lattice parameters typical of diborides and binary solid solutions. Because of evaporation during arc melting, CrB₂ was hardly found in the solid solution, suggesting that vapor pressure should be taken into account when designing HEB compositions especially for operating temperatures exceeding 2000 °C. Finally, Vickers microhardness ranged between the typical values of starting diborides.     

Sand corrosion,thermal expansion,and ablation of medium- and high-entropy compositionally complex fluorite oxides

Sand corrosion, thermal expansion, and ablation properties of a new class of medium- and high-entropy compositionally complex fluorite oxides (CCFOs) are examined as potential protective coating materials. Five binary oxides were mixed and sintered into dense, single-phase CCFOs of the general formula: [Hf_(1-2x)/3Zr_(1-2x)/3Ce_(1-2x)/3Y_xYb_x]O_2-δ (x = 0.2, 0.074, and 0.029). These CCFOs exhibit decreased molten sand infiltration and interaction at intermediate temperatures (1200-1300°C) in comparison with a cubic yttria-stabilized zirconia (YSZ) reference; however, at higher temperatures, the trend is reversed due to the increased chemical reactivity. The equimolar high-entropy (Hf_0.2Zr_0.2Ce_0.2Y_0.2Yb_0.2)O_2-δ exhibits no grain boundary penetration by molten sand at all examined temperatures (1200°C-1500°C), although reaction and precipitation are significant. Moreover, these CCFOs exhibit higher intrinsic thermal expansion coefficients (CTE) than the YSZ reference, thereby being more compatible with Ni-based superalloys. The 8YSZ-like (Hf_0.284Zr_0.284Ce_0.284Y_0.074Yb_0.074)O_2-δ exhibits the highest CTE in this series of CCFOs due to oxygen clustering effects. Finally, these CCFOs also exhibit lower emissivities and form unique faceted microstructures in ablative environments.     

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.     

Improving electrochemical properties of LiCoO2 by enhancing thermal decomposition of Cobalt and Lithium carbonates to synthesize ultrafine powders

Ultrafine LiCoO₂ powders were directly synthesized by enhancing thermal decomposition of Cobalt and Lithium carbonates through a mechanochemical activation treatment to intensify the solid state diffusion reaction. Effects of activation treatment time on particle size and structure of the LiCoO₂ compound were investigated. In the present study, the optimum mechano-chemical activation time was found to be 10 h. In this study, the ultrafine LiCoO₂ powders (particle size in the range from 200 nm to 400 nm) show good structural stability and higher structural integrity. X-ray photoelectron spectroscopy (XPS) results indicate that most of Co cations exist as Co³⁺, which contributes to the improvement of the electrochemical performance. Cyclic voltammetry (CV) curves of different cycles display almost a complete overlap, which can be regarded as another evidence of the excellent cycle performance. The LiCoO₂ powders exhibit a high initial discharge specific capacity of 175.2 mAh/g at 0.1 C (274 mA/g at 1 C) and a remarkable cycle stability from 167.5 mAh/g to 146.2 mAh/g at 0.5 C and from 147.5 mAh/g to 115.2 mAh/g at 3 C after 100 cycles in the range of 3.3–4.3 V. The apparent activation energy and the frequency factor of the decomposition of CoCO₃ are 69.83 kJ/mol and 1.369×10⁶, respectively, indicating that the ultrafine in-process product of Co₃O₄ can be quickly prepared at a low temperature.     

Mechanisms of ultralow and anisotropic thermal expansion in cordierite Mg2Al4Si5O18: Insight from phonon behaviors

Materials with negative or ultralow thermal expansion are of crucial importance for technological applications since they make it possible to tailor the coefficient of thermal expansion (CTE) of composite to a specific positive, negative or even zero value. In this work, first‐principle calculations were performed to investigate the thermal expansion behavior in cordierite Mg₂Al₄Si₅O₁₈, which is a representative silicate widely used in the ceramic industry and of promising application due to its ultralow CTE and good thermal shock resistance. According to the quasi‐harmonic approximation and the Grüneisen theory, temperature dependences of linear CTEs along a, b, and c directions were predicted. The transverse acoustic modes and low‐energy optic modes are identified to take the most of the responsibility for the negative CTE, especially at low temperatures while the high‐energy optic modes contribute positively to the thermal expansion, leading to increasing CTE at higher temperatures. The ultralow linear CTEs result from the weighted average of all the modal contributions with negative or positive Grüneisen parameters. In addition, the anisotropy of thermal expansion originates from its layered crystal structure containing rigid tetrahedron rings in a‐b plane staking along c direction. This work provides an insight into the mechanism of ultralow and anisotropic thermal expansion in Mg₂Al₄Si₅O₁₈ and further enriches the scope of material design for use in applications needing to control thermal expansion.     

Topochemical polymerisation of a diacetylene: Studies of lattice parameters and thermal expansion coefficients

The solid-state polymerisation of the disubstituted diacetylene, 2,4-hexadiynylene bis(p-toluene sulphonate). has been studied by x-ray diffraction in the temperature range 223 to 295 K. The variation in lattice parameters is shown to be similar to that reported in previous less extensive studies. This data is used to determine the behaviour of the thermal expansion coefficients as a function of polymer content. The relevance of these results to the question of polymer chain lengths at low conversion is discussed.     

Effects of Fe doping on structure,negative thermal expansion,and magnetic properties of antiperovskite Mn3GaN compounds

We synthesized antiperovskite Mn₃Ga_1−xFe_xN (0 ≤ x ≤ 0.30) compounds and investigated their negative thermal expansion (NTE) behavior, structure, and magnetic properties. A high-resolution transmission electron microscopy analysis and a selected-area electron diffraction (SAED) pattern indicate that the samples have high crystallinity with a single-phase cubic structure. Tunable NTE behavior appears below room temperature, and the NTE operation temperature range (△T) is broadened while increasing the Fe doping. Furthermore, introducing Fe in Mn₃Ga_1−xFe_xN can efficiently adjust the NTE coefficient from −232.57 × 10⁻⁶/K (x = 0) to −12.57 × 10⁻⁶/K (x = 0.20), and the corresponding △T can be broadened from △T = 22 K to 51 K. Besides, the total entropy change (ΔS_total) at the phase transitions continuously decreases from 9.2 to 4.7 J/(kg K) while increasing the Fe content from x = 0.05 to 0.10. With increasing Fe into Ga sites, the magnetic ordering varies from antiferromagnetic (AFM) to ferromagnetic (FM), the AFM to paramagnetic (PM) phase transition temperature decreases, whereas the FM to PM transition temperature increases when increasing the Fe content. The present study indicates that magnetic element doping can efficiently tune the NTE and the correlated physical features of the antiperovskite compounds.     

热电池用过渡金属二硫化物及其复合材料的研究进展

过渡金属二硫化物具有较高的理论比容量、稳定的电化学性能及成熟的制备工艺,是锂系热电池中应用最广的正极材料之一,但其同时也存在电极电位低、大功率放电能力弱等问题,致使其进一步的发展受到限制。目前,对于过渡金属二硫化物正极材料的优化及改性是锂系热电池领域的核心课题。本文综述了FeS₂、CoS₂与NiS₂等过渡金属二硫化物在放电机理、制备工艺及电化学性能方面的研究现状,介绍了双金属二硫化物及过渡金属二硫化物/碳素类复合材料的主要研究进展。同时,通过对现有研究的归纳与总结,指出了掣肘过渡金属二硫化物正极材料发展的关键问题,简述了针对过渡金属二硫化物的主要改性手段,并对其之后的研究提出了一些建议与想法。     

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.     

High pressure deformation mechanism of Li-ABW: Synchrotron XRPD study and ab initio molecular dynamics simulations

The response to compression of the synthetic zeolite Li-ABW (LiAlSiO₄ · H₂O, Z = 4, s.g. Pna2₁) was explored by synchrotron X-ray powder diffraction experiments, using silicone oil as non-penetrating pressure transmitting medium, and Car Parrinello Molecular Dynamics simulations. In the range P_amb – 8.9 GPa, a nearly isotropic compression for the axial parameters and a cell volume decrease of approximately 12% are observed. A discontinuity in the cell parameters vs P behaviour can be detected between 5 and 6 GPa. As a consequence, the bulk modulus was calculated separately in the P_amb – 4.9 GPa and 5.6–8.9 GPa pressure ranges. The corresponding values (72(2) GPa and 80(2) GPa, respectively) are among the highest found up to now for zeolites studied with non-penetrating P-transmitting media. Molecular Dynamics simulations were performed at volumes corresponding to P_amb, 1.5, 5.6, and 7.6 GPa, respectively. At 1.5 GPa the channel system is already elliptically deformed, and the zig-zag trend of the 4-ring tetrahedral chains is enhanced. Moreover, the water molecule chain running along the channel becomes interrupted and the water molecules are more strongly connected to the framework oxygen atoms. The four-fold coordination of Li cation is maintained up to the highest pressure and only a slight bond distance decrease is observed above 1.5 GPa. In the P_amb – 5.6 GPa range, all T–O–T angles decrease with pressure, and hence the Li-ABW structure can be defined as collapsible. Otherwise, at higher compression, average T–O–T angles increase slightly. Overall, the deformation of the Li-ABW upon compression resembles that achieved by anhydrous Li-ABW in the high temperature regimes.     

High-pressure structural stability,equation of state,and thermal expansion behavior of cubic HfO2

The structural stability, equation of state, and thermal expansion behavior of nanocrystalline cubic HfO₂, an ultra-high-temperature ceramic, have been investigated using X-ray diffraction at extreme conditions of pressures and temperatures. High-pressure studies show that the cubic structure is stable up to 26.2 GPa, while the high-temperature studies show the stability of the cubic structure up to 600°C. The Rietveld structure refinement of the high-pressure data reveals the progressive transition of secondary monoclinic phase to the cubic phase at higher pressures. The phase progression is accompanied by incompressibility along the b axis and a large compressibility along the c axis of the monoclinic structure. The second-order Birch-Murnaghan equation of state fit to the unit cell volume data yielded a bulk modulus of 242(16) GPa for the cubic structure. A linear thermal expansion value of α_a(c) = 8.80(15) × 10⁻⁶°C⁻¹ and a volume thermal expansion value of α_v = 26.5(4) × 10⁻⁶°C⁻¹ have been determined from the in situ high-temperature X-ray diffraction studies. The results are discussed by comparing with the high-pressure and high-temperature behavior of isostructural ZrO₂. To the best of our knowledge, this is the first experimental report on the structural stability of cubic HfO₂ at high pressures.     

Structural origin of negative thermal expansion of cordierite honeycomb ceramics and crystal phase evolution with sintering temperature

The structural origin of the negative coefficient of thermal expansion (CTE) along the c-axis in cordierite is investigated using high temperature X-ray diffraction. The evolution of the lattice parameters, bond length, covalent character, and electron density distributions are analyzed with increasing temperature. The increase of covalent character of the tetrahedral bonds in the six-membered hexagonal ring is considered as the possible origin for the negative expansion. In addition, the bridging oxygen can act as a buffer absorbing thermal energy and prevents the increase in M1-O-M2 bond. The electron density distribution indicates that the linking oxygen strongly vibrates transversely across two coordinate M1-O-M2 linkages. The CTE and pore size and distribution change drastically at near 1300 °C due to the substantial increase in cordierite phase proportion and the formation of a liquid phase. Raw materials are consumed completely at 1450 °C and the CTE decreases to 1.3 ppm K^?1.     

Phase transition and negative thermal expansion properties of Sc2−xCrxMo3O12

The crystal structure, phase transition and thermal expansion behaviors of solid solutions Sc_2−xCr_xMo₃O₁₂ (0≤x≤2) were investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). At room temperature, samples with x≤0.7 and x≥0.8 crystallize in orthorhombic and monoclinic structures, respectively. DSC result indicates that the phase transition of Sc_0.5Cr_1.5Mo₃O₁₂ from monoclinic to orthorhombic structure occurs at 203.66 °C. The linear thermal expansion coefficient of orthorhombic phases varies from −2.334×10⁻⁶ °C⁻¹ to 0.993×10⁻⁶ °C⁻¹ when x increases from 0.0 to 1.5. The near-zero linear thermal expansion coefficients of −0.512×10⁻⁶ °C⁻¹ and −0.466×10⁻⁶ °C⁻¹ are observed for compounds with x=0.5 and 0.7, respectively.     

Examination of the influence of cooperative segmental dynamics on the glass transition and coefficient of thermal expansion in thin films probed using poly(n-alkyl methacrylate)s

The thermal behavior of thin films of a homologous series of poly(n-alkyl methacrylate)s supported on silicon substrates was probed using spectroscopic ellipsometry. Deviations from bulk behavior for the glass transition temperature (T_g) and coefficient of thermal expansion (CTE) were observed for films thinner than approximately 60 nm, consistent with most observations for confinement effects in polymer films. However, the extent of the decrease of CTE and the deviation in T_g are significantly influenced by the alkyl chain length. As the alkyl chain length is increased from methyl to n-octyl, the deviation from bulk behavior is significantly suppressed. This behavior is similar to that observed by Torkelson and coworkers (Physical Review Letters 2004; 92: 095702) for polystyrene films as small molecule diluents were added; this behavior was attributed to the decrease in size of the cooperative segmental dynamics, ξ_i(CRR), with addition of solvent. ξ_i(CRR) decreases as the alkyl chain length is increased; this is consistent with the hypothesis for the relationship between ξ_i(CRR) and confinement effects in thin polymer films. However, a two order of magnitude difference between the thickness of nanoconfinement onset and ξ_i(CRR) for poly(n-octyl methacrylate) results in uncertainty for ξ_i(CRR) as the origin of the nanoconfinement effect.     

Tuning the electronic and thermal transport behaviors of metal-dispersed Ti2O3 composites derived by metal–insulator transition

Thermal management requires an understanding of the relations among the thermal energy transfer, electronic properties, and structures of thermoconductive materials. Here, we enhanced the metal–insulator transition (MIT)-induced effect on the thermal conductivities of microstructure-controlled Ti₂O₃ composites containing W as a thermal conductive filler at approximately 450 K. To change the electronic and thermal transport properties, we varied the particle radii of the conductive phases in the raw material. The change in the calculated electronic thermal conductivity relative to the electrical conductivity of the W_x(Ti₂O₃)_1?x composite was enhanced by compounding the material. When x was reduced from 50 vol% to 20 vol% and the W particle diameter was reduced from 150 μm to 5 μm, the variation in the estimated electronic thermal conductivity of the W_x(Ti₂O₃)_1?x composite was increased by a factor of 2.01. The total thermal conductivity was also changed by the MIT. At x = 50 vol% and a W particle diameter of 5 μm, the maximum thermal conductivity change was 6.34 times larger than that of pure Ti₂O₃. The detailed relation between the MIT-induced changes in thermal transport and the microstructure were elucidated in classical effective medium approximations.