Average Linear Thermal Expansion Coefficient Research Articles

Microstructure and Properties of Aluminum Alloy/Diamond Composite Materials Prepared by Laser Cladding.

In this article, AlSi10Mg aluminum alloy was used as the substrate to prepare aluminum alloy/diamond composite materials with laser cladding technology. The effects of the composition and laser power on the microstructure and thermal properties of the composite materials were studied. The results show that the prefabrication of tungsten carbide layer on the diamond surface enhances the wettability of diamond with aluminum alloy and reduces the laser reflection, which ensures the implementability of laser cladding technology for the preparation of aluminum alloy/diamond composites. The laser power and components determine the temperature of the molten pool and thus the state of the organization of the composite material to be formed by cladding. With the increase in the diamond content, the density, specific heat, mechanical properties, and average linear thermal expansion coefficient of the composite material gradually decrease, while the thermal conductivity first increases and then decreases. The thermal conductivity of the aluminum alloy/diamond composite material prepared by laser cladding is 200.68 W/mK, and the linear thermal expansion coefficient is 1.904 × 10-5/K, which are superior to those of the matrix AlSi10Mg aluminum alloy.

Thermal and chemical expansion of layered oxygen-deficient double perovskites

Layered oxygen-deficient double perovskites (ODP) based on the rare-earth elements (REE), barium and 3d-metals (Fe, Co, Cu etc.) are characterized by high values of electrical conductivity and high electrochemical activity in oxygen reduction reaction, and are considered as prospective cathode materials for intermediate-temperature solid oxide fuel cells (SOFC) on the base of proton- and oxygen-ion conducting solid electrolytes (SE). Effective cathode materials should be thermomechanically compatible with materials of SE, which tаkes place when the values of their thermal expansion coefficients (TEC) are close to each other. Due to this the study of thermal expansion of ODP as well as the isotation of different contributions in it (thermal, chemical, spin etc.), is of considerable interest. In this work using dilatometric method the thermal expansion of NdBa1–xSrxFeCo0,5Cu0,5O6−δ (0.0 ≤ х ≤ 1.0) (NBSFCC) ODP was studied using dilatometric method. It was established that the values of average linear thermal expansion coefficient (LTEC) (α) of the samples sharply increased from (15.1–16.2) · 10–6 K–1 at Т < 630–920 K to (18.9–23.5) 10–6 K–1 at Т > 630–920 K due to the evolution of weaklybonded oxygen from the samples. Values of α in the low-temperature region increase with increasing of values of their oxygen nonstoichiometry index (δ), and in the high-temperature one increase with the x increasing due to the increment of chemical contribution in the samples expansion. Based of the results of dilatometry, thermogravimetry, and iodometry, the thermal and chemical contributions in the expansion оn NBSFCC were isolated, and the effect of crystal structure, cationic and anionic composition of NBSFCC ODP on the values of their thermal and linear chemical expansion coefficient (LCEC, αδ ) was investigated. It was found, that LCEC values of the samples sharply increased from (8.6–11.8) · 10–3 at (х < 0.5) to (12.6–15.8) · 10–3 at (х > 0.5) when transition from ordered tetragonal (х < 0.5) to disordered cubic (х > 0.5) phase took place. It was shown, that dependences of LTEC and LCEC of NBSFCC phases on their crystal structure and chemical compositions obtained in this work are in good accordance with the analogous dependences determined earlier for the ODP of other types.

Древесно-композитные плиты с низким коэффициентом линейного теплового расширения

A number of industries require materials with a low coefficient of linear thermal expansion (CLTE), in particular, in the production of satellite spherical antennas. The latter are formed from composites containing carbon fibers and synthetic resins. The composition is cured by heating up to 180 °C. This leads to a thermal expansion of the mold and a change in the geometric characteristics of the product. Therefore, specific requirements are imposed on the materials for making molds. The high cost of special materials used for molds determines the need to search for other materials with a low CLTE. Wood is a possible solution to this problem. Its CLTE along the fibers is less than that of the vast majority of materials, and is approximately 3 ‧ 10-6 K–1, which is comparable to special materials. However, the expansion of wood across the fibers is much higher than the longitudinal one, which excludes the use of solid wood. Anisotropy can be reduced by creating a composite in which the fibers are uniformly oriented in all structural directions, bringing the value of wood expansion across the fibers closer to the value of expansion along the fibers. The traditional approach to producing wood composites, based on the use of synthetic adhesives, fails to achieve a noticeable reduction in thermal expansion due to the high CLTE of adhesives The use of boards made of hydrodynamically activated wood particles without binders is promising. Three series of experiments have been carried out: with varying the density of the boards, preliminary thermal modification of the original wood and the use of alkali during hydrodynamic processing. The thermal expansion study has been carried out using the NETZSCH DIL-402 C induction dilatometer in dynamic mode with a heating rate of 2 K/min. It has been established that thermal expansion increases with increasing density.The average CLTE at a density of 950 kg/m3 is 12 ‧10–6 K–1 and at a density of 1,100 kg/m3 it is 17‧10–6 K–1. At a comparable density, the thermal expansion of boards without binders is significantly lower than that of fiberboards (MDF). Preliminary thermal modification of wood does not significantly affect the CLTE of the boards. The use of alkali in the hydrodynamic treatment also has no effect.

Thermophysical properties and oxidation behaviour of the U0.8Zr0.2N solid solution

Thermophysical properties and oxidation behaviour of the composite pellet UN–20 vol%ZrN were investigated experimentally and compared with the behaviour of the pure UN pellet. A compound of a single phase, a solid solution of the average composition U0.8Zr0.2N, was obtained by Spark Plasma Sintering (SPS) of the powders UN and ZrN. Crystallographic and microstructural characterisation of the composite was performed using Scanning Electron Microscopy (SEM), standardised Energy Dispersive Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD). Nano hardness and Young’s modulus were also measured by the nanoindentation method. High-Temperature X-ray diffraction (XRD) was applied to obtain the lattice expansion as a function of temperature (room temperature to 673 K). Thermogravimetric Analysis (TGA) was applied to evaluate oxidation behaviour in air. Results demonstrate that the fabrication method results in a matrix of solid solution with homogeneous composition averaged to U0.8Zr0.2N. The mechanical properties of such solution are uniform, with variation only due to the crystallographic orientation of the grains of the solution phase, similar to pure UN. The obtained value for the average linear thermal expansion coefficient is α¯ = 7.94 × 10-6/K, which compares well to UN (α¯ = 7.95 × 10-6/K) for the same temperature range. The degradation behaviour of the composite pellet UN-20 vol%ZrN in air shows a lower oxidation onset temperature, compared to pure UN, with the final product of oxidation being mainly U3O8. Smaller crystallites in the product of corrosion of the composite pellet indicate that the mechanism of degradation of the solid solution phase U0.8Zr0.2N is accompanied by the formation of two distinct oxides and their interaction.

Observation of low thermal expansion behavior and weak thermal anisotropy in M3A2C phases

M3A2X phases, named 321 phases, are an atypical series of MAX phases featuring in the MA-triangular-prism bilayers, with the A = As/P, exhibiting excellent elastic properties. This work systematically studies the thermal expansion properties of 321 phases. We found their average linear thermal expansion coefficients (TECs), αL = 5-6 μK–1, are the lowest among the reported values of MAX phases. The lowest average TEC was found in Nb3As2C (αa = 4.46(4) μK–1, αc = 5.09(4) μK–1, αL = 5.09(4) μK–1). The average TEC and anisotropy factor (αc/αa) of Nb3As2C and Nb3P2C were lower than the ones of the corresponding 211 phases. The best isotropy performance was found in Nb3P2C (αc/αa = 1.11). Moreover, our first-principles calculations demonstrate that the weaker chemical bonding between Nb-As/P than Nb-C induces thermal expansion in M3A2X phases. Furthermore, a relatively weaker anharmonic effect in 321 phases than in the 211 phases was revealed by the as-calculated average Grüneisen parameters, which account for the lower TECs in 321 phases. The low TECs and enhanced thermal isotropy make 321 phases outstanding among MAX phases, which could be sound candidates for varying-temperature structural-functional components.

Low temperature synthesis and thermal expansion study of nanocrystalline CaTiO3

We have successfully synthesized nanocrystalline calcium titanate (CaTiO3) at low temperature by wet chemical method. The prepared CaTiO3 was characterized by simultaneous Thermogravimetry-differential thermal analysis. The CaTiO3 nanoparticles at different annealing temperatures confirms the formation of the single-phase CaTiO3 at 700 °C for 1 h. The influence of annealing temperatures on the microstructures are investigated by SEM and TEM.The thermal expansion of sintered CaTiO3 in the range of 30 °C to 950 °C exhibits average linear thermal expansion coefficient (α) of 12.94 × 10−6 K−1. The nanocrystalline CaTiO3 powder pelletized and sintered at 1250 °C for 5 h has achieved density > 95 %.

A novel composite oxygen electrode: PrBaCo2O5+δ combined with negative thermal expansion oxide applied to reversible solid oxide cells

The thermal expansion coefficient (TEC) of Co-based layered perovskite electrodes is about twice than that of common electrolytes, and this thermal mismatch between electrode and electrolyte leads to the delamination and cracking of electrode. To solve this problem thoroughly, a strategy of introducing negative thermal expansion (NTE) material is proposed. The average linear thermal expansion coefficient of PrBaCo2O5+δ (PBC) decreases significantly from 22.3 × 10−6 K−1 to 12.2 × 10−6 K−1 when compounds with 50 wt% NdMnO3-δ (NM). The results of multi physical field coupling calculation show that the introduction of NTE oxide can reduce the residual stress of oxygen electrodes and electrolytes, which decreases the trend of electrodes damaged by thermal stress. The composite electrode (PBC-NM) shows excellent electrocatalytic activities and reversible cycle performance. The peak power densities (PPDs) of the cell with PBC decreases from 1.4 to 0.48 W cm−2 (65.7% decrease) after 20 thermal cycles, while the one of PBC-NM-based cell decreases from 1.55 to 1.25 W cm−2 (19.4% decrease). Electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and distribution of relaxation time (DRT) analysis show that the improvement of thermal cycle stability of SOFC can be attributed to the ideal thermal matching between electrolyte and oxygen electrode.

Potential accident tolerant fuel candidate: Investigation of physical properties of the ternary phase U2CrN3

In the present study, physical properties of the ternary phase U2CrN3 are evaluated experimentally and by modeling methods. High density pellets containing the ternary phase were prepared by spark plasma sintering (SPS). The microstructural and crystallographic analyses of the composite pellets were performed using scanning electron microscopy (SEM), standardised energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). Evaluation of the mechanical properties was performed by nanoindentation test. The impact of temperature on lattice properties was evaluated using high temperature X-ray diffraction (XRD) coupled with modeling. Progressive change in the lattice parameters was obtained from room temperature (RT) to 673 K, and the result was used to calculate average linear thermal expansion coefficients, as well as an input for the density functional theory (DFT) modeling to reassess the degradation of the mechanical properties. The ab-initio calculation provides an initial assessment of electronic configuration of this ternary phase in a direct comparison with one of UN phase. For this goal, modeling was also employed to evaluate point defect formation energies and electronic charge distribution in the ternary phase. Results indicate that the U2CrN3 phase has similar mechanical properties to UN (Young's, bulk, shear moduli, hardness). No preferential crystallographic orientation was observed in the composite pellet. However, charge electron density distribution highlights the significant directionality of chemical bonds, which is in agreement with the anisotropy and non-linear behaviour of the obtained thermal expansion (α¯(aa) = 9.12 × 10−6/K, α¯(ab) = 5.81 × 10−6/K and α¯(ac) = 6.08 × 10−6/K). As a consequence, uranium was found to be more strongly bound in the ternary structure which may delay diffusion and vacancy formation, promising an acceptable performance as nuclear fuel.

Synthesis and characterization of negative thermal expansion of the Zr2(WO4)(PO4)2 system

In this study, Ti- and Mo-substituted Zr2(WO[Formula: see text](PO[Formula: see text] were synthesized using a conventional solid-state reaction technique. Coefficients of thermal expansions for samples were calculated by the results from the in situ high-temperature X-ray diffraction method. Doping with Ti[Formula: see text] reduces the voids occupied by the thermal vibration ellipsoid perpendicular to the bond axis. On the other hand, by doping Mo[Formula: see text], which has a smaller binding energy with oxygen atoms, thermal vibration in the direction of the bond axis is promoted. It is considered that the average linear thermal expansion coefficient became zero because the elliptical thermal vibration perpendicular to the coupling axis was suppressed by the synergistic effect of the co-doping of Ti and Mo.

Improved performance of IT-SOFC by negative thermal expansion Sm0.85Zn0.15MnO3 addition in Ba0.5Sr0.5Fe0.8Cu0.1Ti0.1O3−δ cathode

To improve performance of intermediate temperature solid oxide fuel cells (IT-SOFCs), the negative thermal expansion (NTE) material Sm0.85Zn0.15MnO3 (SZM) is introduced in Ba0.5Sr0.5Fe0.8Cu0.1Ti0.1O3−δ (BSFCT) cathode. XRD results indicate that BSFCT, SZM and Ce0.8Sm0.2O2−δ (SDC) oxides have good chemical compatibility up to 1173 K. The average linear thermal expansion coefficient of BSFCT–xSZM (x = 0, 10, 20 and 30 wt.%) decreases markedly from 29.2 × 10−6 K−1 for x = 0 wt.% to 15.6 × 10−6 K−1 for x = 30 wt.%. The electrochemical performance of single cells with configuration of NiO–BZCY|SDC|BSFCT–xSZM is comparatively investigated in the 773–973 K. The best performance is observed for x = 20 wt.%, which should be caused by the balance between thermal matching of cathode/electrolyte layers and oxygen reduction reaction activity of composite cathodes. The corresponding peak power density in the 773–973 K is 136–918 mW cm−2, which is 249%–64% higher than that (39–559 mW cm−2) with single BSFCT cathode. Due to the existence of electron blocking layer at anode/electrolyte interface, the open circuit voltage of all cells is higher than 1.0 V. In short, the introduction of NTE oxide in conventional cathode materials may provide an effective strategy to enhance the performance of IT-SOFCs with electron blocking layer.

Tailoring thermal properties of multi-component rare earth monosilicates

This work explores the possibility of tailoring the thermal conductivity and thermal expansion of rare earth monosilicates through the introduction of multiple rare earth cations in solid solution. Six rare earth monosilicates are studied: Sc2SiO5, Y2SiO5, Nd2SiO5, Dy2SiO5, Er2SiO5, and Yb2SiO5. Four equimolar binary cation mixtures and a five-cation equimolar mixture were characterized. Thermal expansion was measured up to 1200 °C with X-Ray Diffraction (XRD) and bulk thermal conductivity was measured by Hot Disk technique. The linear coefficient of thermal expansion (CTE) of mixed-cation systems followed a rule of mixtures, with average linear CTEs between 6 - 9 × 10−6 /°C. Scandium monosilicate showed a lower linear CTE value as well as a notably lower degree of CTE anisotropy than other rare earth monosilicates. Thermal conductivity was found to decrease below rule of mixtures values through increasing heterogeneity in rare earth cation mass and ionic radii, as expected for the thermal conductivity of solid-solutions. The five-cation equimolar RE2SiO5 (RE=Sc, Y, Dy, Er, and Yb) shows a thermal conductivity of 1.06 W/mK at room temperature, demonstrating that multi-component rare earth silicates are strong candidates for novel dual-purpose thermal and environmental barrier coatings.

Thermoelectric properties, efficiency and thermal expansion of ZrNiSn half-Heusler by first-principles calculations

In this work, we try to understand the experimental thermoelectric (TE) properties of a ZrNiSn sample with DFT and semiclassical transport calculations using SCAN functional. SCAN and mBJ provide the same band gap Eg of ∼0.54 eV. This Eg is found to be inadequate to explain the experimental data. The better explanation of experimental Seebeck coefficient S is done by considering Eg of 0.18 eV which suggests the non-stoichiometry and/or disorder in the sample. In the calculation of S and other TE properties temperature dependence on chemical potential is included. In order to look for the possible enhanced TE properties obtainable in ZrNiSn with Eg of ∼0.54 eV, power factor and optimal carrier concentrations are calculated. The optimal electron and hole concentrations required to attain highest power factors are ∼7.6 × 1019 cm−3 and ∼1.5 × 1021 cm−3, respectively. The maximum figure of merit ZT calculated at 1200 K for n-type and p-type ZrNiSn are ∼0.5 and ∼0.6, respectively. The % efficiency obtained for n-type ZrNiSn is ∼4.2% while for p-type ZrNiSn is ∼5.1%. The ZT are expected to be further enhanced to ∼1.1 (n-type) and ∼1.2 (p-type) at 1200 K by doping with heavy elements for thermal conductivity reduction. The phonon properties are also studied by calculating dispersion, total and partial density of states. The calculated Debye temperature of 382 K is in good agreement with experimental value of 398 K. The thermal expansion behaviour in ZrNiSn is studied under quasi-harmonic approximation. The average linear thermal expansion coefficient αave(T) of ∼7.8 × 10−6 K−1 calculated in our work is quite close to the experimental values. The calculated linear thermal expansion coefficient will be useful in designing the thermoelectric generators for high temperature applications.

Tailoring Thermal Properties of Ebcs in High Entropy Rare Earth Monosilicates

This work explores the possibility of tailoring the thermal conductivity and thermal expansion of rare earth monosilicates through the introduction of multiple rare earth cations in solid solution. Six rare earth monosilicates are studied: Sc2SiO5, Y2SiO5, Nd2SiO5, Dy2SiO5, Er2SiO5, and Yb2SiO5. Four equimolar binary cation mixtures and a high entropy five-cation equimolar mixture were characterized. Thermal expansion was measured up to 1200 ˚C with X-Ray Diffraction (XRD) and bulk thermal conductivity was measured by Hot Disk technique. The linear coefficient of thermal expansion (CTE) of mixed-cation systems followed a rule of mixtures, with average linear CTE between 6 - 9x10-6 /˚C. Scandium monosilicate showed a lower linear CTE value as well as a notably lower degree of CTE anisotropy than other rare earth monosilicates. Thermal conductivity was found to decrease below rule of mixtures values through increasing heterogeneity in rare earth cation mass and ionic radii, as expected for the thermal conductivity of solid-solutions. The high entropy mixture RE2SiO5 (RE=Sc, Y, Dy, Er, and Yb) shows a thermal conductivity of 1.06 W/mK at room temperature, demonstrating that high entropy rare earth silicates are strong candidates for novel dual-purpose thermal and environmental barrier coatings.

Crystal structure, oxygen nonstoichiometry and thermal expansion of ordered Y2Ba3Fe3.1Co1.9O13+δ

Single phase Y2Ba3Fe3.1Co1.9O13+δ was prepared at 1373 K in air. According to X-ray diffraction (XRD) it possesses the tetragonal structure (sp.gr. P4/mmm); the unit cell parameters are: a = 3.895(1)Å; c = 19.372(1)Å. Electron diffraction has shown the presence of 5-fold superstructure corresponding to the «ap × ap × 5ap» supercell. The oxygen content in Y2Ba3Fe3.1Co1.9O13+δ in air changes from 13.21 at room temperature down to 12.88 at 1390 K and average linear thermal expansion coefficient is equal to (15.4 ± 0.1) × 10−6 K−1 within the range of 298–1273 K in air.

New WC-Cu composites for the divertor in fusion reactors

The requirements for the divertor components of future fusion reactors are challenging and therefore a stimulus for the development of new materials. In this paper, WC-Cu composites are studied for use as thermal barrier between the plasma facing tungsten tiles and the copper-based heat sink of the divertor. Composite materials with 50% vol. WC were prepared by hot pressing and characterized in terms of microstructure, density, expansion coefficient, elastic modulus, Young's modulus and thermal diffusivity. The produced materials consisted of WC particles homogeneously dispersed in a Cu matrix with densifications between 88% and 98%. The sample with WC particles coated with Cu evidenced the highest densification. The thermal diffusivity was significantly lower than that of pure copper or tungsten. The sample with higher densification exhibits a low value of Young's modulus (however, it is higher compared to pure copper), and an average linear thermal expansion coefficient of 13.6 × 10−6 °C-1 in a temperature range between 100 °C and 550 °C. To estimate the behaviour of this composite in actual conditions, a monoblock of the divertor in extreme conditions was modelled. The results predict that while the use of WC-Cu interlayer leads to an increase of 190 °C on the temperature of the upper part of the monoblock when compared to a pure Cu interlayer, the composite will improve and reduce significantly the cold-state stress between this interlayer and the tungsten.

Investigations of nano-crystalline Sr0.5Ba0.5Nb2O6 and bulk ceramics synthesized by a polymerization method using PEG400

Nano-crystalline Sr0.5Ba0.5Nb2O6 was synthesized by a one-pot method using PEG400 and citric acid. Calcination of the (Sr,Ba,Nb)-gel at 600 °C leads to Sr0.5Ba0.5Nb2O6 with a crystallite size of 24(2) nm and a specific surface area of 38.5(10) m2 g−1. Sintering up to 1325 °C leads to ceramics with globular or irregular-shaped grains and average grain sizes between 1.3 and 2.4 μm, whereas higher temperatures lead to a rod-like microstructure. The indirect allowed optical band gap varies between 3.70(5) and 3.29(5) eV. Dielectric measurements show a diffuse phase transition and weak relaxor properties. The maximum of the permittivity occurs between 116 and 147 °C. The frequency dependence of the impedance can be well described by one or two RC-circuits depending on sintering temperature. The melting temperature is determined as 1506(7) °C with ΔHf = 140(20) kJ mol−1. The average linear thermal expansion coefficient is found to be 10.5(5)⋅10−6 K−1.

Structure, Thermal Stability, and Spectroscopic Properties of Triclinic Double Sulfate AgEu(SO4)2 with Isolated SO4 Groups.

Silver-europium double sulfate AgEu(SO4)2 was obtained by solid-phase reaction between Ag2SO4 and Eu2(SO4)3. The crystal structure of AgEu(SO4)2 was determined by Monte Carlo method with simulated annealing, and after that, it was refined by the Rietveld method from X-ray powder diffraction data. The compound crystallizes in the triclinic symmetry, space group P1̅ ( a = 0.632929(4), b = 0.690705(4), c = 0.705467(4) nm, α = 98.9614(4), β = 84.5501(4), γ = 88.8201(4)°, V = 0.303069(3) nm3). Two types of sulfate tetrahedra were found in the structure, which significantly affects the spectroscopic properties in the IR-range. In the temperature range of 143-703 K, the average linear thermal expansion coefficients of cell parameters a, b, and c are very similar, (1.11-1.67) × 10-5 K-1 in magnitude, and therefore, AgEu(SO4)2 expands almost isotropically. Upon heating in argon flow, AgEu(SO4)2 is stable up to 1053 K. The luminescence spectra in the region of ultranarrow 5D0-7F0 transition contain a single narrow and symmetric line at 579.5 nm that is evidence of good crystalline quality of AgEu(SO4)2 and uniform local environment of Eu3+ ions in the structure. Distribution of luminescence bands is determined by the environment of Eu3+ ions in the structure. Influence of Ag+ ions on the electron density distribution at Eu sites is detected.

Lindemann-like rule between average thermal expansion coefficient and glass transition temperature for metallic glasses

The correlations between the average linear thermal expansion coefficient < α > and glass transition temperature Tg and between GVm (G is shear modulus and Vm is molar volume) and Tg for a variety of metallic glasses (MGs) were investigated. A Lindemann-like equation, <α > ×Tg = 0.75 × 10−2, is observed, indicating that the glass transition of MGs follows Lindemann-like rule. The relationship provides a new perspective to understand the mechanism of glass transition and a simple method to predict Tg for a given MG. Additionally, Tg is found to vary linearly with GVm, implying that an inherent relevance between glass transition and plastic deformation of MGs.

Adjustable Thermal Expansion Properties in Zr2MoP2O12/ZrO2 Ceramic Composites.

Zr2MoP2O12/ZrO2 composites were successfully synthesized by the solid state method in attempt to fabricate the near-zero thermal expansion ceramics. The phase composition, micromorphology and thermal expansion behavior of the Zr2MoP2O12/ZrO2 composites with different mass ratios were investigated using X-ray diffraction, scanning electron microscopy and thermal mechanical analysis. Results indicate that Zr2MoP2O12/ZrO2 composites can be prepared by pre-sintering at 500°C for 3 h and then sintering at 1050°C for 6 h. The resulting Zr2MoP2O12/ZrO2 composites consisted of orthorhombic Zr2MoP2O12 and monoclinic ZrO2. With increasing content of Zr2MoP2O12, the Zr2MoP2O12/ZrO2 ceramics became more compact and the coefficient of thermal expansion decreased gradually. Zr2MoP2O12/ZrO2 composites show an adjustable coefficient of thermal expansion (CTE) from 5.57 × 10−6 K−1 to −5.73 × 10−6 K−1 by changing the mass ratio of Zr2MoP2O12 and ZrO2. The Zr2MoP2O12/ZrO2 composite with a mass ratio of 2:1 showed near zero thermal expansion, and the average linear thermal expansion coefficient is measured to be 0.0065 × 10−6 K−1 in the temperature range from 25 to 700°C.

Synthesis and characterization of the atomic laminate Mn2AlB2

Herein, we synthesize dense, predominantly single-phase polycrystalline samples of the Mn2AlB2 ternary compound, using reactive hot-pressing of manganese, aluminum, and boron powder mixtures under vacuum. With a Vickers hardness of 8.7 GPa, Mn2AlB2 is relatively soft for a transition metal boride and lacked dominant cracks at the corners of the indentations. With Young’s and shear moduli of 243 GPa and 102 GPa at 300 K, respectively, it is reasonably stiff. The Poisson’s ratio is calculated to be 0.19. With compressive strengths of 1.24 ± 0.1 GPa, the samples were quite strong considering the grain size (1–15 μm). The electrical resistivity at 300 K was ∼5 μΩm and decreased linearly upon cooling. At 0.0036 K−1, the temperature coefficient of resistivity was relatively high compared to MoAlB. The average linear thermal expansion coefficient was also found to be relatively high at 18.6 × 10-6 K−1 from 298 to 1173 K. Mn2AlB2 was not thermally stable above ∼1379 K. While Mn2AlB2 was not machinable with conventional tooling, intriguingly, high-speed carbide tools bits readily penetrate the surface – with no cracking or chipping for a few millimeters – before stopping.