Average Thermal Expansion Coefficient Research Articles

PrSr3Fe3O10−δ as cobalt-free cathode for intermediate-temperature solid oxide fuel cell

In this work, we investigate cobalt-free Ruddlesden Popper oxide with the nominal composition of PrSr3Fe3O10−δ (PSF) as potential cathode for intermediate temperature solid oxide fuel cells based on Ce0.8Sm0.2O1.9 (SDC) electrolyte. It is found that PSF is chemically compatible with the SDC for temperatures up to 1000 °C. The average thermal expansion coefficient of PSF in air is 16.5 × 10−6 K−1 in a temperature range of 30–1000 °C, and its electrical conductivity reaches the maximum value of 98 S cm−1 at 500 °C. The area specific resistance of PSF is 0.075 Ω cm2 at 800 °C. Peak power density of 405 mW cm−2 is achieved with PSF at 800 °C.

Mechanical and thermal properties of light weight boron‐mullite Al5BO9

AbstractAl5BO9 is a promising thermal sealing material for hypersonic vehicles due to its low density, theoretically predicted low shear modulus, and low thermal conductivity. However, experimental investigations on the mechanical and thermal properties of bulk Al5BO9 have not been carried out. Herein, we report the mechanical and thermal properties of bulk Al5BO9 prepared by spark plasma sintering of solid‐state reaction synthesized Al5BO9 powders. The bulk (B), shear (G), and Young's (E) moduli are 148 GPa, 85 GPa, and 214 GPa, respectively, which are close to the theoretical values. The Pugh's ratio G/B is 0.574, indicating its intrinsic damage tolerance, which is also revealed by Hertzian contact test. The Vickers hardness (Hv) is 10.8 GPa, being lower than mullite. The flexural strength, compressive strength, and fracture toughness are, respectively, 277 ± 35 MPa, 814 ± 75 MPa, and 2.4 ± 0.3 MPa·m1/2, which are close to those of mullite. Al5BO9 has anisotropic coefficient of thermal expansion (CTE) in three crystallographic directions, ie αa = (4.40 ± 0.21) × 10−6 K−1, αb = (7.11 ± 0.18) × 10−6 K−1, αc = (6.70 ± 0.29) × 10−6 K−1 from Debye temperature to 1473 K, which are underpinned by its structural feature, ie lower αa is resulted from the edge‐shared AlO6 octahedron chains along the [100] direction. The average CTE is (6.05 ± 0.06) × 10−6 K−1. The thermal conductivity declines with temperature as κ = 1336.39/T + 1.97, consisting with predicted trend from Slack's model. The low thermal conductivity and low density guarantee Al5BO9 a promising candidate as ceramic wafer in the seal structure for hypersonic vehicles.

Ionic conductivity and thermal expansion of anion-deficient Sr11Mo4O23 perovskite

Transport properties of perovskite-type Sr11Mo4O23 and composite Sr11Mo4O23 - 1 wt% Al2O3 were studied at 400–1300 K in the oxygen partial pressure range from 0.21 down to 10−19 atm. The electromotive force and faradaic efficiency measurements, in combination with the energy-dispersive spectroscopy of the fractured electrochemical cells, unambiguously showed prevailing role of the oxygen ionic conductivity under oxidizing conditions. At temperatures above 600 K, protonic and cationic transport can be neglected. The oxygen ion transference numbers vary in the range of 0.95–1.00 at 973–1223 K. At temperatures lower than 550 K, the total conductivity of Sr11Mo4O23 - 1 wt% Al2O3 composite measured by impedance spectroscopy tends to increase in wet atmospheres, thus indicating that hydration and protonic transport become significant. Reducing oxygen partial pressure below 10−10–10−9 atm leads to a significant increase in the n-type electronic conduction. The average thermal expansion coefficients in oxidizing atmospheres are (14.3–15.0) × 10−6 K−1 at 340–740 K and (18.3–19.2) × 10−6 K−1 at 870–1370 K.

Controllable negative thermal expansion in NaZn13-type La(Fe, Co, Al)13 compounds

Control of negative thermal expansion (NTE) is of great importance for various applications of NTE materials. Here, we report an effective way to control both the coefficient of thermal expansion (CTE) and NTE temperature-window in NaZn13-type La(Fe, Co, Al)13 compounds by Al and Co substitutions. Experiments show that the average CTE decreases with the increase in Al content. Besides, the NTE temperature-window shifts toward higher temperature due to Co doping. Further studies of magnetic characterizations reveal that the CTE is strongly correlated with the square of the spontaneous magnetization Ms2(T). Moreover, the NTE temperature-window is influenced by the density of 3d electrons at the Fermi level and the FeI–FeII magnetic exchange interactions. This effective way demonstrated in this work to achieve controllable NTE indicates the potentials in practical applications for NTE materials.

Scandium Molybdate Nanofibers with Negative Thermal Expansion for Fabricating Composites with Controllable Coefficients of Thermal Expansion

Single-crystal Sc2Mo3O12 nanofibers, an one-dimensional negative thermal expansion (NTE) material, have been successfully synthesized by electrospinning. The crystal structure, morphology, and NTE property of Sc2Mo3O12 nanofibers were characterized using typical X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), and variable-temperature XRD. Results indicate that as-deposited Sc2Mo3O12 nanofibers are amorphous and display a smooth surface and uniform diameter. Single-crystal Sc2Mo3O12 nanofibers are fabricated at 500 °C for 3 h and grown along the (111) orientation with an orthorhombic structure. The average diameter of single-crystal Sc2Mo3O12 nanofibers is ∼100 nm. Sc2Mo3O12 nanofibers exhibit anisotropic NTE with an average volumetric coefficient of thermal expansion (CTE) of −6.53 × 10–6 °C–1 from 25 °C to 700 °C. The average CTEs along the a-, b-, and c-axes are −6.62 × 10–6, 5.33 × 10–6, and −5.21 × 10–6 °C–1, respectively.

The thermal and mechanical properties of hafnium orthosilicate: Experiments and first-principles calculations

Hafnium orthosilicate (HfSiO4: hafnon) has been proposed as an environmental barrier coating (EBC) material to protect silicon and silicon-based ceramic materials at high temperatures and as a candidate dielectric material in microelectronic devices. It can naturally form at the interface between silicon dioxide (SiO2) and hafnia (HfO2). When used as an EBC its coefficient of thermal expansion (CTE) should match that of the protecting layer (e.g. silicon and SiC composites) to reduce the stored elastic strain energy, and thus the risk of failure of these systems. In this work, the physical, mechanical, thermodynamic and thermal transport properties of hafnon have been investigated using a combination of density functional theory (DFT) calculations and experimental assessments. The average linear coefficient of thermal expansion (CTE) calculated using the quasi-harmonic approximation increase from 3.06 × 10−6K − 1 to 6.36 × 10−6K − 1, as the temperature increases from 300 to 1500 K, in agreement with both X-ray diffraction lattice parameter and dilatometry measurements. The predicted thermal conductivity from Boltzmann transport theory is approximately 16.1 W/m.K at 300 K. The thermal conductivity of our samples using both hot disk and laser flash measurements gave a value of 13.3 W/m.K. This slightly lower value is expected and is indicative of residual disorder in the experimental samples, which is absent in the theoretical analysis. First-principles calculations and nanoindentation techniques are used to assess the ambient temperature elastic constants and bulk modulus respectively. The elastic properties obtained by both approaches agreed to within 5%, validating the computational approach and its future use for the study of the thermomechanical properties of other oxides or silicates.

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.

Effect of partial substitution of Ce for La on the structural, magnetic and abnormal thermal expansion properties of La1-Ce Fe11.2Al1.8 alloys

Abstract NaZn13-type La(Fe, M)13-based (M = Si, Al) intermetallic compounds find wide applications, ranging from microelectronics to space technology, because of their significant abnormal thermal expansion (ATE) associated with their huge magnetovolume effect. In this work, element La was partially substituted in LaFe11.2Al1.8 by element Ce to optimize the ATE characteristics of these alloys. The obtained average thermal expansion coefficient (CTE) of La0.8Ce0.2Fe11.2Al1.8 reaches as large as −21.7 × 10−6 K−1 in the temperature range of 100–200 K, which is nearly 25% larger than that of LaFe11.2Al1.8 (−17.31 × 10−6 K−1). Magnetic measurements confirmed that the improved negative thermal expansion (NTE) property is attributed to the enhanced magnetization originating from the magnetic coupling between Ce and Fe atoms. Additionally, smaller negative thermal expansion was observed in La0.4Ce0.6Fe11.2Al1.8 with an average CTE of −1.6 × 10−6 K−1 in a broad operating temperature window from 10 to 170 K. The enhanced NTE values of La(Fe, Al)13-based alloys with partial substitution of Ce for La demonstrated in this work show the potential of their practical applications.

Effect of high-content Yttria on the thermal expansion behaviour and ionic conductivity of a stabilised cubic Hafnia

The needs for space propulsion thruster induce the development of new designs and material compositions able to withstand 3000 K of flame combustion temperature. Cubic-stabilised hafnia appears as one of the most promising candidates to protect refractory materials in such conditions. Here, the influence of dopant content on the thermal expansion (473−1823 K) and ionic conductivity (600−1150 K) in highly doped-hafnia (12−33 mol% Y2O3) with disordered cubic systems is reported. The composition and the homogeneity of the samples were carefully checked using crystallographic, chemical and spectroscopy analyses. Finally, the study of thermal and oxygen conductivity properties highlighted their dependence on the amount of dopant. The average thermal expansion coefficient was lowered from 11.3 to 10.9 10−6/K and the ionic conductivity decreased by two decades with 33 mol% of Y2O3 by using the optimised substitution ratio. Interactions and local ordering of oxygen vacancies can explain this behaviour.

Simultaneous measurement of coefficient of thermal expansion and biaxial modulus of enamel thick films deposited on glass substrates by curvature technique

AbstractThe measurement of the thermoelastic properties of enamel thick films deposited onto soda‐lime silicate glass is challenging. The film properties can be modified by the interdiffusion between the glass substrate and the enamel and by the crystallization that occur during the sintering. The average biaxial modulus and coefficient of thermal expansion of several enamel thick films deposited onto 700 µm glass substrates have been simultaneously measured using the curvature method. The value of the coefficient of thermal expansion measured with a dilatometer on enamel bulk samples is significantly higher, associated with the absence of diffusion and a different enamel structure. The interdiffusion of elements between the enamel film and the glass substrate has been demonstrated with Time‐of‐Flight Secondary Ion Mass Spectrometry (TOF‐SIMS). The amount of porosity ratio presents in the enamel film, evaluated via Scanning electron microscopy(SEM), has a great influence on the biaxial modulus. The amount of compressive stress in the enamel, calculated from the film thermoelastic properties, is strongly correlated with the mechanical performance of enameled glasses, investigated by Ring On Ring methods. Therefore, a high Young's modulus for the enamel and a mismatch of the coefficient of thermal expansion between the enamel film and substrate, the film having the lowest value, has been found to increase significantly the mechanical performance of the stack.

Large anisotropic negative thermal expansion in Cu-TDPAT metal-organic framework: A combined in situ X-ray diffraction and DRIFTS study

Cu-TDPAT (H6TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine), a stable nanoporous metal-organic framework with rht topology, has sparked broad interest as an adsorbent for several chemical separation processes. In this work, in situ synchrotron diffraction experiments followed by sequential LeBail refinements reveal that Cu-TDPAT shows unusually large anisotropic negative thermal expansion (NTE). The PASCal crystallography tool, used to analyze the magnitude of the NTE, reveals an average volumetric thermal expansion coefficient αv = −20.3 MK−1. This value is significantly higher than the one reported for Cu-BTC (also known as HKUST-1), which contains the same Cu-paddlewheel building unit, αv ≈ −12 MK−1. In situ synchrotron single crystal X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were employed to shed light on the NTE mechanism. Using these two methods, we were able to elucidate the three main structural motions that are responsible for the NTE effect. The more pronounced NTE behavior of Cu-TDPAT is attributed to the lower symmetry combined with the more complex ligand structure when compared to Cu-BTC. The knowledge obtained in this work is important for understanding the behavior of the adsorbent under transient variable temperature conditions in fixed adsorption beds.

Electrochemical performance of Sn-doped Bi0.5Sr0.5FeO3- perovskite as cathode electrocatalyst for solid oxide fuel cells

Abstract The Sn-doped Bi0.5Sr0.5FeO3-δ (BSF)-based perovskite oxide is evaluated as novel cathode electrocatalyst for intermediate-temperature solid oxide fuel cells (IT-SOFCs). In particular, the effects of 10 mol% Sn substitution on phase evolution, thermal expansion behavior and electrochemical performance of Bi0.5Sr0.5Fe0.9Sn0.1O3-δ (BSFSn) material are systematically investigated. BSFSn crystallizes in cubic perovskite structure with space group Pm-3m. Sn doping is found to decrease the average thermal expansion coefficient (TEC) from 14.7 × 10−6 K−1 (BSF) to 12.9 × 10−6 K−1 (BSFSn) within a temperature range of 50–800 °C, due to the enlarged metal-oxygen (Sn-O) bond energy in BSFSn. The X-ray photoelectron spectroscopy (XPS) result proves that Sn doping promotes the oxygen adsorption ability on BSFSn surface. Consequently, the ORR activity of BSFSn is improved as expected. The polarization resistance (Rp) value of BSFSn cathode is 0.09 Ω cm2 at 700 °C in air, which is lower than BSF. The cathode overpotential is 35.6 mV at a current density of 140.8 mA cm−2 at 700 °C in air. The peak power density of the anode-supported cell reaches 960 mW cm−2 at 700 °C. Furthermore, the relationship between oxygen partial pressure and Rp demonstrates that oxygen surface adsorption-desorption is a major rate-limiting step for oxygen reduction reaction (ORR) process on BSFSn cathode. These attractive electrochemical properties suggest that BSFSn oxide is a promising potential cathode electrocatalyst for SOFCs.

Internal stress analysis of epoxy adhesively‐boned joints based on their thermomechanical properties at cryogenic temperature

AbstractInternal stress analysis is essential to structural design of materials applied in cryogenic engineering. In this contribution, thermomechanical properties including dynamic thermomechanical properties and thermal expansion behavior of four epoxy resins, namely the polyurethane modified epoxy resin (PUE), diglycidyl ether of bisphenol A (DGEBA), tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) and triglycidyl‐p‐aminophenol (TGPAP) were studied by dynamic thermomechanical analysis. Internal stress of the epoxy layer in the bonded joint was calculated based on the thermomechanical properties. Meanwhile, the structure‐cryogenic property relationship of epoxy resins were investigated. Results demonstrate that internal stress in the four epoxies bonded joints is 6 ~ 21 MPa at −150°C, and is positively correlated with the average thermal expansion coefficient (CTE) of epoxy resins. TGDDM and TGPAP showed higher retention of lap shear strength both at −196°C and after temperature cycling due to their lower CTE. Morphology of the fractured surface of bonded joints demonstrated that internal stress is responsible for the severe interface failure at −196°C. It reveals that selection of epoxy resins with low CTE is beneficial for designing high‐performance epoxy adhesive systems served at cryogenic temperature.

Ba0.95La0.05Fe0.8Zn0.2O3-δ cobalt-free perovskite as a triple-conducting cathode for proton-conducting solid oxide fuel cells

A triple-conducting Ba0.95La0.05Fe0.8Zn0.2O3−δ (BLFZ) cobalt-free perovskite was evaluated as cathode for proton-conducting solid oxide fuel cells based on BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) electrolyte. BLFZ had a cubic perovskite structure and good chemical compatibility with BZCYYb electrolyte at temperatures below 1100 °C. The average thermal expansion coefficient of BLFZ is 20.4 × 10−6 K−1 at 30 °C-1000 °C. The polarization resistance (Rp) of BLFZ decreased from 2.072 Ω cm2 in air to 1.334 Ω cm2 in wet air (3% H2O) at 600 °C due to the introduction of water. The single-cell power density with BLFZ–30 wt%BZCYYb composite cathode reached 329 mW cm2 at 750 °C, and the corresponding Rp is 0.083 Ω cm2. Based on the impedance and distribution of relaxation time analyses, proton diffusion and incorporation to the electrolyte lattice (Had+(Ni)→H+(surface,electrolyte) and H+(surface,electrolyte)→H+(bulk,electrolyte)) were the rate-limiting steps above 650 °C, whereas the oxygen incorporated into the lattice (O2−(BLFZ)→O2−(bulk,electrolyte)) and proton bulk diffusion to the triple-phase boundary (H+(bulk,electrolyte)→H+(TPB)) were the rate-limiting steps below 650 °C. The single cell with BLFZ–30 wt% BZCYYb composite cathode showed good stability at 700 °C during a 100-h test.

The Synthesis and Thermal Expansion Behavior of Sodium and Calcium Zirconium Copper Phosphates

The crystal-chemical approach has been applied to design materials with regulated thermal expansion. To that end, model simulations have been performed for compositions of phosphates that yield solid solutions of the following type Na1 + 2xZr2 –xCux(PO4)3 and Ca0.5 +xZr2 –xCux(PO4)3, 0.1 ≤ x ≤ 0.5 with the expected structure of NaZr2(PO4)3 (NZP). The new phosphates have been prepared by solid-state reactions and characterized by X‑ray diffraction, IR spectroscopy, and scanning electron microscopy. The compounds have been shown to crystallize in the NZP structure, with a particle size from 0.1 to 1 μm. The thermal expansion of the compounds has been studied by high-temperature X-ray diffraction in the temperature range from 25 to 700°C. Linear, average, and volume coefficients of thermal expansion and anisotropy of thermal expansion have been calculated and analyzed in relation to composition of Na, Zr, Cu and Ca, Zr, Cu phosphates in the studied sets.

BaCe0.7–xZr0.2Y0.1FexO3–δ derived from proton-conducting electrolytes: A way of designing chemically compatible cathodes for solid oxide fuel cells

The present study describes the rational engineering, preparation and characterisation of new mixed ionic-electronic conductors (MIECs) having great potential for application in solid oxide fuel cells (SOFCs) based on proton-conducting electrolytes. The developed MIECs are derived from promising Ba(Ce,Zr)O 3 -materials doped with iron as a transition element: BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ (x = 0–0.7, Δx = 0.1). The comprehensive analysis of the functional properties (crystal structure, densification, microstructure, defect structure, thermal expansion behaviour, electrical conductivity) indicate that a moderate iron content is beneficial in order to achieve a certain compromise. In detail, the gradual Fe-doping results in an enhancement of transport properties (including, ionic-electronic conductivity level) and deterioration of mechanical characteristics (an increase of average thermal expansion coefficient values). The composition with x = 0.6, identified as more optimal, was used as a cathode for an intermediate-temperature SOFC; this cathode displays a satisfactory polarisation resistance level, 0.21 Ω cm 2 at 700 °C, without the use of any additional electroactivation technique. The obtained results indicate that BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ MIECs having one of the highest chemical compatibility with state-of-the-art proton-conducting electrolytes can be considered as advanced electrodes for designing new solid oxide electrochemical devices with prolonged and stable operation mode. • BaCe 0.7–x Zr 0.2 Y 0.1 Fe x O 3–δ (BCZYFx) materials were prepared for the first time. • The BCZYFx materials are single-phase across the entire x range (0 = x ≤ 0.7). • Fe-doping leads to an increase in both ionic and electronic conductivities (at x ≥ 0.4). • At the same time, TECs values increase and chemical strain becomes more pronounced. • BCZYF0.6 with an optimal combination of properties was utilised as a SOFC cathode.

Influence of tin substitution on negative thermal expansion of K2Zr2-xSnxP2SiO12 (x = 0 - 2) phosphosilicates ceramics

In this research work, compounds of the chemical formula K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1, 1.5, 2) were synthesized by solution method and characterized by powder X-ray diffraction and spectroscopic techniques. Powder XRD analysis revealed that the phase formation temperature vary with the substitution of Sn4+ for Zr4+ at the octahedral site of langbeinite structure. The stretching and bending vibrational modes of PO43− and SiO44− tetrahedra were identified in the region of 407 cm−1 - 1094 cm−1. Thermogravimetric analysis proved that the compounds K2Zr2P2SiO12 and K2Sn2P2SiO12 were thermally stable up to 1000 °C and 650 °C, respectively. Interestingly, negative thermal expansion coefficient was observed for the solid solutions K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1, 1.5, 2). The average thermal expansion coefficients of K2Zr2P2SiO12, K2Zr1.5Sn0.5P2SiO12, K2ZrSnP2SiO12, K2Zr0.5Sn1.5P2SiO12 and K2Sn2P2SiO12 in the temperature range 30 °C–600 °C were found to be −7.01 × 10−6/°C, −4.96 × 10−6/°C, −1.08 × 10−5/°C, −1.53 × 10−5/°C and −1.27 × 10−5/°C, respectively. Coefficient of thermal expansion was increased by the substitution of tin for zirconium. The increase was obvious up to 250 °C and stabilized after 300 °C. The ionic radii, bond strength, structural distortion, density and microstructures were considered to explain the variation in thermal expansion.

Phase transition temperature and negative thermal expansion of Sc-substituted In2(MoO4)3 ceramics

A series of Sc-substituted In2Mo3O12 ceramics were synthesized by the chemical co-precipitation method. The results reveal that In3+ can be substituted by Sc3+ and form a single phase with high purity for all In2−xScxMo3O12 (x = 0, 0.3, 0.6, 0.9, 1.2 and 1.5) samples. The crystal structure of In2−xScxMo3O12 changes from monoclinic to orthorhombic symmetry with increasing Sc3+-content, confirmed by X-ray diffraction and Raman spectroscopy (Raman). With increasing concentration of A-site Sc3+ cations, the microstructure of In2−xScxMo3O12 becomes denser and the shape and size distribution of grains is more regular and uniform. The monoclinic-to-orthorhombic phase transition temperature of In2Mo3O12 is successfully decreased from 343 °C to room temperature via the substitution of In3+ by Sc3+. When x = 1.5, the occurrence of the monoclinic-to-orthorhombic phase transition for In0.5Sc1.5Mo3O12 solid solution is at around 7 °C. It has an average linear coefficient of thermal expansion of − 5.08 × 10−6 °C−1 in 25–600 °C. The phase transition results obtained by theoretical calculation using the framework of spin-polarized DFT accord well with the experimental evidences.

Effect of CeO2 addition on crystallization and thermophysical properties of Li2O-ZnO-SiO2 glass-ceramics

The effect of CeO2 addition on crystallization and thermo-physical properties of lithium zinc silicate (LZS) glasses containingLi2O-ZnO-SiO2-Al2O3-Na2O-P2O5 was investigated. The changes of CeO2 contents (2-8 wt.%) had an obvious influence on thetransition temperatures (Tg) and crystallization temperatures (Tc) of LZS glass-ceramics, and they increased with CeO2 contentincreasing. According to XRD analysis, CeO2 promoted the formation of cristobalite and β-spodumene crystals, and β-spodumene increased obviously. As the CeO2 content increasing, the microstructure and microhardness (being 6.88 Gpa at 880oC) of glass-ceramics had great changes. The average thermal expansion coefficient (20 - 450 oC) showed first increasing thendecreasing, having a wide range. The maximum of thermal expansion coefficient was obtained when the glass-ceramicscontained 4 wt.% CeO2, being 175×10−7 K−1 (at 700 oC) and 178×10−7 K−1 (at 880 oC) respectively. Excellent thermo-physicalproperties indicate the glass has greater potential application, such as being used as sealing glass.