Average Thermal Expansion Coefficient Research Articles

Crystal growth of Sr3BeB6O13 and its thermal and optical properties

Bulk single crystals of Sr3BeB6O13 with dimensions up to 50 × 30 × 5 mm3 were grown for the first time by a top-seeded solution growth method using H3BO3-LiF-SrF2 as flux. The average thermal expansion coefficients along the a-, b- and c-axis from 50 °C to 500 °C were determined as αa = 9.18 × 10−6 K−1, αb = 14.63 × 10−6 K−1, αc = 8.56 × 10−6 K−1, respectively. The specific heat was measured to be 0.771–0.844 J/(g·K) over the temperature range of 50–500 °C. In addition, the UV cutoff wavelength of Sr3BeB6O13 is located at 190 nm. Its refractive indices were accurately measured by a minimal deviation method, based on which the Sellmeier equations were derived.

Plant Cellulose Nanofiber-Derived Structural Material with High-Density Reversible Interaction Networks for Plastic Substitute.

Ubiquitous petrochemical-based plastics pose a potential threat to ecosystems. In response, bioderived and degradable polymeric materials are being developed, but their mechanical and thermal properties cannot compete with those of existing petrochemical-based plastics, especially those used as structural materials. Herein, we report a biodegradable plant cellulose nanofiber (CNF)-derived polymeric structural material with high-density reversible interaction networks between nanofibers, exhibiting mechanical and thermal properties better than those of existing petrochemical-based plastics. This all-green material has substantially improved flexural strength (∼300 MPa) and modulus (∼16 GPa) compared with those of existing petrochemical-based plastics. Its average thermal expansion coefficient is only 7 × 10-6 K-1, which is more than 10 times lower than those of petrochemical-based plastics, indicating its dimension is almost unchanged when heated, and thus, it has a thermal dimensional stability that is better than those of plastics. As a fully bioderived and degradable material, the all-green material offers a more sustainable high-performance alternative to petrochemical-based plastics.

Magnetic-field-induced structural phase transition and giant magnetoresistance in La0.85Ce0.15Fe12B6

Magnetoelastic coupling, structural, magnetic, electronic transport, and magnetotransport properties of ${\mathrm{La}}_{0.85}{\mathrm{Ce}}_{0.15}{\mathrm{Fe}}_{12}{\mathrm{B}}_{6}$ have been studied by a combination of macroscopic [magnetization, electrical resistivity, and magnetoresistance (MR)] and microscopic temperature- and magnetic-field-dependent x-ray powder diffraction measurements. The itinerant-electron system ${\mathrm{La}}_{0.85}{\mathrm{Ce}}_{0.15}{\mathrm{Fe}}_{12}{\mathrm{B}}_{6}$ exhibits an antiferromagnetic (AFM) ground state and multiple magnetic transitions, AFM-ferromagnetic (FM) and FM-paramagnetic (PM), triggered by changes in both temperature and magnetic fields. At low temperatures, the field-induced first-order AFM-FM metamagnetic phase transition is discontinuous, manifesting itself by extremely sharp steps in magnetization as well as in MR and is accompanied by large magnetic hysteresis. A remarkably large negative MR of \ensuremath{-}73% was discovered. In addition, the time evolution of the electrical resistivity displays a colossal spontaneous jump when both the applied magnetic field and temperature are constant. Diffraction data reveal a magnetic-field-induced structural phase transition associated with the AFM-FM and PM-FM transformations. The lattice distortion is driven by magnetoelastic coupling and converts the crystal structure from rhombohedral ($R\overline{3}m$) to monoclinic $(C2/m)$. The AFM and PM states are related to the rhombohedral structure, whereas the FM order develops in the monoclinic symmetry. A huge volume magnetostriction of \ensuremath{\sim}0.9% accompanies this symmetry-lowering lattice distortion. Meanwhile, a highly anisotropic thermal expansion involving giant negative thermal expansion with an average volumetric thermal expansion coefficient ${\ensuremath{\alpha}}_{V}=\ensuremath{-}195\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ was observed. The consistency seen in these different experimental data constitutes direct evidence of the strong correlations between charge, magnetic, and crystallographic degrees of freedom in this material.

Synthesis, structural and thermal expansion investigation of La, Ce and Eu substituted Bi4(SiO4)3

A series of selected rare earth ions substituted bismuth silicates of the chemical formula Bi 4-x RE x (SiO 4 ) 3 (RE = La, Ce and Eu: X = 0.1, 0.2, 0.3) was synthesized by the solution method. Rietveld refinement study revealed that the compounds Bi 4 (SiO 4 ) 3 , Bi 3.9 La 0.1 (SiO 4 ) 3 , Bi 3.8 La 0.2 (SiO 4 ) 3 , Bi 3.7 La 0.3 (SiO 4 ) 3 , Bi 3.9 Ce 0.1 (SiO 4 ) 3 and Bi 3.9 Eu 0.1 (SiO 4 ) 3 were crystallized in cubic structure with I - 43d space group. Scanning electron microscopic images indicated that the larger and rod shaped particles were transformed into smaller and agglomerated ones when the rare earth ions were substituted for Bi ion in the octahedral site. UV–visible diffuse reflectance spectra displayed a shift in absorption edge upon rare earth ion substitution due to the overlapping of s-p transition band with Ln 3+ -O 2- charge transfer band. Bulk thermal expansion of the pure phases was tested using push rod dilatometer. The average coefficients of thermal expansion for Bi 4 (SiO 4 ) 3 , Bi 3.9 La 0.1 (SiO 4 ) 3 , Bi 3.9 Ce 0.1 (SiO 4 ) 3 and Bi 3.9 Eu 0.1 (SiO 4 ) 3 were found to be 5.19 x 10 −6 / ° C, 5.59 x 10 −6 / ° C, 7.10 x 10 −6 / ° C and 7.94 x 10 −6 / ° C, respectively. The effect of rare earth ionic substitution in thermal expansion behavior was investigated. • New rare earth substituted eulytite type ceramics were prepared by solution method. • Rietveld refinement study proved the formation of cubic phases with I - 43d space group. • The effect of rare earth ionic substitution was observed from SEM and UV-DRS. • Average thermal expansion coefficients the compounds were found to be in the range of 5.19–7.94 x 10 −6 /°C. • Heating and cooling cycles of thermal expansion showed different amounts of hysteresis.

Thermal expansion of bismuth magnesium tantalate and niobate pyrochlores

The thermal behavior of pyrochlores composing of Bi1·5Mg0.75M1.5O6.75 (M = Nb, Ta) (sp. gr. Fd-3m:2) was studied using the high-temperature X-ray powder diffraction in a wide temperature range of 30–1200 °C. At a temperature above 1080 °C both compounds thermally dissociate forming one of the reaction products MgMO6 (M = Nb, Ta) whose reflexes are traced on X-ray diffraction patterns after cooling the sample down to room temperature. In the case of Bi1·5Mg0·75Nb1·5O6.75 orthoniobate α-BiNbO4 forms at about 800–1020 °C as admixture. The thermal expansion analysis of Bi1·5Mg0.75M1.5O6.75 (M = Nb, Ta) showed that the compounds studied belong to slightly or moderately expanding materials. Thermal expansion for both compounds is isotropic. With a rise in temperature the unit cell parameter a and the thermal expansion coefficient (TEC) are increased uniformly and slightly for M = Ta (Nb): from 10.52822 (10.55325) Å (30 °C) up to 10.59181 (10.62801) Å (1050 °C) and from 3.8 (30 °C) up to 7.4 (8.9) × 10−6 °С−1 at 800 °C respectively. The average TEC values in the range of 30–800 °C range are 5.6 (6.4) × 10−6 °C−1 for M = Ta (Nb) respectively. Bi1.5Mg0.75Nb1.5O6.75 is characterized with the highest thermal expansion that may be related to the longer bond-length of Nb(Bi)–O in the polyhedra.

Langbeinite phosphosilicates K2-xCsxZr2P2SiO12 (x = 0, 0.5, 1.0, 1.5, 2.0) for cesium encapsulation; synthesis, chemical durability and thermal expansion study

The volatization of cesium at high temperatures makes its immobilization challenging to the nuclear scientists. Present work reports the feasibility of cesium incorporation into an orthorhombic langbeinite phosphosilicate. The structural flexibility, leachability and thermal expansion of K2-xCsxZr2P2SiO12 (x = 0, 0.5, 1.0, 1.5, 2.0) have been investigated. Powder X-ray results authenticates the accommodation of cesium into a single phasic orthorhombic langbeinite structure up to 29.17 wt %. Morphological study reveals the particle agglomeration and poor crystallinity, and vibrational spectral analysis shows peak broadening and peak shift upon increasing the cesium concentration. The static leach test has been performed on the pellet sample and the normalized leaching of Cs is found to be in the order of 101 g/m2. The average coefficient of thermal expansion for K0.5Cs1.5Zr2P2SiO12 is registered as 7.45 × 10−6/K between 303 and 873 K. Cesium insertion into K2Zr2P2SiO12 displays a large deviation in thermal expansion due to the size effect as observed by several researchers for other phosphate and phosphosilicate members.

Impact of Praseodymia Additions and Firing Conditions on Structural and Electrical Transport Properties of 5 mol.% Yttria Partially Stabilized Zirconia (5YSZ)

Ceramics samples with the nominal composition [(ZrO2)0.95(Y2O3)0.05]1-x[PrOy]x and praseodymia contents of x = 0.05–0.15 were prepared by the direct firing of compacted 5YSZ + PrOy mixtures at 1450–1550 °C for 1–9 h and characterized for prospective applicability in reversible solid oxide cells. XRD and SEM/EDS analysis revealed that the dissolution of praseodymium oxide in 5YSZ occurs via the formation of pyrochlore-type Pr2Zr2O7 intermediate. Increasing PrOy additions results in a larger fraction of low-conducting pyrochlore phase and larger porosity, which limit the total electrical conductivity to 2.0–4.6 S/m at 900 °C and 0.28–0.68 S/m at 700 °C in air. A longer time and higher temperature of firing promotes the phase and microstructural homogenization of the ceramics but with comparatively low effect on density and conductivity. High-temperature processing leads to the prevailing 3+ oxidation state of praseodymium cations in fluorite and pyrochlore structures. The fraction of Pr4+ at 600–1000 °C in air is ≤2% and is nearly independent of temperature. 5YSZ ceramics with praseodymia additions remain predominantly oxygen ionic conductors, with p-type electronic contribution increasing with Pr content but not exceeding 2% for x = 0.15 at 700–900 °C. The average thermal expansion coefficients of prepared ceramics are in the range of 10.4–10.7 ppm/K.

Effects of Melt Ultrasonic Treatment and Forming Processes on Thermo- Physical Properties of SiC<sub>p</sub>/Mg and (SiC<sub>p</sub>+Mg<sub>2</sub>Si)/Mg Composites

The 10 vol% SiCp/Mg composites were prepared by external addition and stirring-casting method, and the hybrid reinforced (10 vol% SiCp+10 vol% Mg2Si)/Mg composites were prepared by combining in-situ method. The effects of melt ultrasonic treatment (UT) and forming processes on the thermophysical properties of the two composites were studied. The results show that UT can effectively disperse SiC particles in molten magnesium and reduce the casting porosity, while squeeze casting can significantly reduce the porosity of the composites, which can also significantly improve the thermal conductivity. The thermal conductivity (λ) of 10 vol.% SiCp/Mg composites squeeze casted after UT is 135.3 W/(mK) and the average coefficient of thermal expansion (CTE) is 19.95×10-6 K-1 at 293-373 K. Compared with gravity casting, the λ is increased by 17% and the CTE is reduced by 0.8%. The λ of (SiCp+Mg2Si)/Mg composite squeeze casted after UT is 132.4 W/(mK), and the CTE is 18.95×10-6 K-1, which is 27% lower than the CTE of pure magnesium.

Preparation and Thermal Properties of BN and LPSO Hybrid Reinforced Magnesium Matrix Composite

Hexagonal boron nitride (h-BN) is a ceramic material with high thermal conductivity (TC) and low coefficient of thermal expansion (CTE), which can improve multiple thermal properties of metal-matrix composites as a reinforcing particle, but its wettability with metal melt is very poor. In order to enhance the wettability between the h-BN and magnesium alloy melt, the electroless plating was used to coat a thin layer of pure nickel on h-BN particles, which was proved to be effective and efficient in this study. The results showed that by adding Y element to magnesium alloy melt to consume Ni element melted from the nickel-plating layer, the long period stacking ordered (LPSO) structure composed of Mg-Ni-Y was successfully formed, and the magnesium matrix composite reinforced by hybrid h-BN and LPSO structure was obtained. After ultrasonic treatment (UT), the TC of the magnesium composite containing 3 vol% h-BN and 14.16 vol% LPSO is 99.92 W/(m·K), which is a 8.3% enhancement compare to the composite without UT. The average CTE (293-373 K) of the composite is 18.36×10-6 K-1, which is reduced by 29.4% compared with pure magnesium.

Study on Ce and Y co-doped BaFeO3-δ cubic perovskite as free-cobalt cathode for proton-conducting solid oxide fuel cells

The use of triple-conducting (electron, proton, oxide ion) cathodes is an effective strategy for significantly decreasing cathode polarization of proton-conducting SOFCs. In this study, a new triple-conducting BaFe0.8Ce0.1Y0.1O3-δ (BFCY) perovskite cathode is prepared by Pechini sol-gel process and its properties are evaluated comprehensively. High-temperature XRD measurement demonstrates that the codoping of Ce and Y can stabilize the cubic perovskite of BFCY in investigated temperature range from room temperature to 900 °C. BFCY material exhibits a moderate average thermal expansion coefficient of 22.08 × 10−6 K−1 smaller than cobalt-based cathode and good chemical compatibility with BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte after the calcining treatment at 1000 °C. XPS analysis indicates the existence of Ce3+/4+ and Fe3+/4+ ions and abundant oxygen vacancies in BFCY powder surface. Thermal gravimetric analysis reveals that a larger number of oxygen deficiencies -are generated at elevated temperatures, which favors the catalytic activity on oxygen reduction. The maximum value of BFCY electrical conductivity remains at 1.55 S cm−1 at 600 °C in humidified air. BCFY (BaCe0.8Fe0.1Y0.1O3-δ) material is introduced in order to construct BFCY-BCFY composite cathode with the good cathode/electrolyte interface adhesion. For the single cell with BFCY-BCFY composite cathode, the polarization resistance as low as 0.05 Ω cm2 and peak power density as high as 750 mW cm−2 are reached at 700 °C, respectively, demonstrating the great potential of BFCY oxides as proton-conducting SOFC cathode.

Graphene-like carbon nanosheet/copper composite with combined performance designed by pyrolyzing trimesic acid@copper formate

Abstract Graphene or graphene-like carbon nanosheet (GNS) with excellent properties presents great potential to improve substantially the combined properties of copper matrix composites. However, it is still a great challenge to develop new methods for the preparation of GNS-reinforced copper composites. In this work, high-strength, high-conductivity and low-thermal expansion GNS/Cu composites were prepared by pyrolyzing trimesic acid@copper formate and spark plasma sintering. Both the volume fraction and the order degree of carbon in GNS/Cu composites were improved by the introduction of trimesic acid. The highest tensile and compressive yield strength of GNS/Cu composites are 542 MPa and 637 MPa, respectively. After hot-rolling process, the plastic deformation and the electrical conductivity of the composites are improved effectively and reach 9% and 86.2% IACS, respectively; the average coefficient of thermal expansion (CTE) of the composite is as low as 12.4 × 10−6 °C−1, which is only 72.9% of pure Cu material. This work provides an effective solution for the design of the GNS/Cu composites with excellent combined performance.

Effects of Bonding Treatment and Ball Milling on W-20 wt.% Cu Composite Powder for Injection Molding.

W-20 wt.% Cu pseudo-alloys were produced via powder injection molding (PIM) with powders prepared thermochemically. Bonding treatment and ball milling (BTBM) were used, and the effects of BTBM on the characteristics of the powders, rheological properties of the feedstock, shrinkage and properties of the sintered samples were studied. The morphology of the powder changed from extremely agglomerated small particles to pebble-shaped smooth large particles which were composed of several small particles combined tightly. The tap density increased from 3.25 g/cm3 to 7.22 g/cm3, and the specific surface area decreased from 0.86 m2/g to 0.45 m2/g. The critical powder loading of the feedstock increased from 45 vol.% to 56 vol.% due to the change in powder characteristics, thereby improving densification and dimension precision. For the PIM samples sintered at 1290 °C for 120 min in a hydrogen gas, the oversizing factor decreased from 1.297 to 1.216, and the dimension fluctuation ratio decreased from ±0.61% to ±0.33%. At the same time, the relative density increased from 97.8% to 98.6%, the thermal conductivity increased from 218 W/(m·K) to 233 W/(m·K), and the average coefficients of thermal expansion were roughly similar, within the range of 8.43–8.52 × 10−6/K.

Cobalt–free perovskite cathode BaFe0.9Nb0.1O3–δ for intermediate–temperature solid oxide fuel cell

Cobalt–free BaFe0.9Nb0.1O3–δ (BFNb) was investigated as a cathode material for intermediate–temperature solid oxide fuel cell (IT–SOFC). XRD refinements favour the co–existence of at least cubic and tetragonal phases in the BFNb sintered at 1000 or 1100 °C, in which the content of the cubic phase decreased with increasing sintering temperature. Because of the presence of BaFe2O4 impurity in the 1100 °C prepared sample, the temperature of 1000 °C was preferred for the final sample preparation. At IT region (600–800 °C), the electrical conductivity of the BFNb sample was 2.5–1.8 S cm–1, and the average thermal expansion coefficient (TEC) was 18.3 × 10–6 K–1. The polarization resistance of the BFNb cathode on Gd0.1Ce0.9O1.95 (GDC) electrolyte achieved 0.102 Ω cm2 at 700 °C. For a single cell with BFNb cathode and 300–μm–thick GDC electrolyte, a peak power density of 397 mW cm–2 was attained at 700 °C, and a 30 h long–term testing demonstrates the good stability of the BFNb cathode under a real SOFC operating condition.

Thermal and microwave dielectric properties of Li–Si-based ceramics

This paper investigates thermal conduction, thermal expansion and microwave dielectric properties of LixSi(0.50x~0.65x)O(1.5x~1.8x) (LS-based) ceramics. All samples were synthesized via the traditional solid-state reaction route. The mole ratio of Si4+/Li+ ranges from 0.50 to 0.65. According to the results, the composite of Si4+/Li+ = 0.55 showed high thermal conductivity of 8.325 W/(mK) and an average coefficient of thermal expansion of 8.401 × 10−6/K (at the temperature between 100 °C to 150 °C). In order to enhance the thermal properties, 4 wt% Al2O3 is added to the LS-based ceramics and the most excellent thermal properties were obtained on the sample with the mole ratio of Si4+/Li+ = 0.55, exhibiting the properties of the highest thermal conductivity of 11.836 W/(mK), an average coefficient of thermal expansion of 10.748 × 10−6/K (at the temperature between 100 °C to 150 °C), the lower dielectric constant of 6.32, excellent flexural strength of 194 MPa, and the optimum Q × f of 4565 GHz. In the present study, a new type of LS-based ceramics suitable for the transition layer of circuit board was developed. The doping of the Al2O3 into the LS-based ceramics can significantly improve its thermal conductivity, adjust the coefficient of thermal expansion and promote the start-temperature of crystallization to a lower direction.

Experimental Study on Thermal Expansion Behavior of Concrete under Three-Dimensional Stress

Concrete is widely used in underground engineering and bears three-dimensional stress transmitted by overlying load. When a fire occurs, the thermal expansion of concrete structure under such stress state is different from that under stress-free state. For this purpose, a self-developed real-time high-temperature true triaxial test system was applied to investigate the thermal expansion behavior of concrete under three-dimensional stress state. The thermal expansion strain of concrete under the three-dimensional stress undergoes strain increasing and strain stabilizing stages. At 600°C, the maximum thermal expansion strain of concrete under the three-dimensional stress is 0.75%. The average coefficient of thermal expansion of concrete under three-dimensional stress condition was then calculated, and its value reaches the minimum of 8.68 × 10−6/°C at 200°C and the maximum of 13.41 × 10−6/°C at 500°C. Comparing the coefficient of thermal expansion of concrete under stress-free condition given by Eurocode, it is found that the three-dimensional stress has an obvious restraint on the thermal expansion of concrete. The research results can provide theoretical basis for the stability analysis of underground engineering concrete structures under high-temperature environment.

Development of cobalt-free oxide (Sm0.5Sr0.5Fe0.8Cr0.2O3-δ) cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs)

A cobalt-free perovskite oxide Sm0.5Sr0.5Fe0.8Cr0.2O3-δ (SSFC) has been exploited as a novel cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The cathode model was synthesized with the addition of the chromium element in the B side of the composite metallic oxide system, which was then formed by the solid-state reaction method. The model system was further characterized in detail for getting the properties behavior. The solid-state reaction of the SSFC system was observed through thermal gravimetric analysis. Meanwhile, the structural properties were investigated by x-ray diffraction, and the weight loss was examined by the thermal gravimetric analysis as well. Furthermore, the thermal expansion coefficient was determined by the thermal-mechanical analysis, and the conductivity properties were tested by the thermal conductivity analysis. The result showed that the SSFC cathode demonstrated the crystalline structure based on the design with a perovskite phase. The oxygen content created on the model structure was obtained to be 2.98 after the calcination process. The average thermal expansion coefficient was achieved up to 5.0×10-6 K-1 as the heating given up to 800 °С. Moreover, the conductivity value reached from 2 S∙cm-1 at 400 °С and it increased to be a maximum of 7.5 S∙cm-1 at 700 °С. In addition, the presence of Cr6+ cation valence coordinated with the oxygen anion could lead to generating a large concentration of oxygen vacancies on the cathode surface, facilitating the transport of the O2− anion in the cathode system. Based on these results, the SSFC cathode has good properties as a composite system promising for IT-SOFCs application in the future

Effects of rare earth oxides on microstructures and thermo-physical properties of hafnia ceramics

Rare earth oxides doped hafnia ceramics, with a formula of Hf0.76LnxY0.24-xO1.88 (Ln = Gd, Yb, Gd + Yb or La + Yb), were prepared by solid state sintering at 1500 °C. The effects of the rare earth oxides on the microstructures, sintering resistance, and thermo-physical properties of the doped hafnia ceramics were investigated. Results show that the Gd-Y, Yb-Y or Gd-Yb-Y co-doped hafnia ceramics remain the same defect fluorite (F) structure, while the La-Yb-Y co-doped hafnia revealing coexistence of pyrochlore (P) and fluorite structures. Yb-Y co-doped samples exhibited much better sintering resistance compared with Gd-Y and Gd-Yb-Y co-doped samples. The coexistence of P and F phases is beneficial to improved sintering capability. The thermal conductivities of the Gd-Y, Yb-Y and Gd-Yb-Y doped samples are relatively lower (1.4-1.7 W m−1 K−1 at 1200 °C), but for the La-Yb-Y co-doped samples, the thermal conductivity increases dramatically with temperature due to increased thermal radiation at high-temperature. The average thermal expansion coefficients (TECs) of the Gd-Y, Yb-Y and Gd-Yb-Y co-doped samples are as high as ∼10.3 × 10−6 K−1 in temperature range between 200−1200 °C.

Report of the Double-Molybdate Phase Cs2Ba(MoO4)2 with a Palmierite Structure and Its Thermodynamic Characterization.

The existence of a novel double-molybdate phase with a palmierite-type structure, Cs2Ba(MoO4)2, is revealed in this work, and its structural properties at room temperature have been characterized in detail using X-ray and neutron diffraction measurements. In addition, its thermal stability and thermal expansion are investigated in the temperature range 298–673 K using high-temperature X-ray diffraction, leading to the volumetric thermal expansion coefficient αV ≈ 43.0 × 10–6 K–1. The compound’s standard enthalpy of formation at 298.15 K has been obtained using solution calorimetry, which yielded ΔfHm°(Cs2Ba(MoO4)2, cr, 298.15 K) = −3066.6 ± 3.1 kJ· mol–1, and its standard entropy at 298.15 K has been derived from low-temperature (2.1–294.3 K) thermal-relaxation calorimetry as Sm°(Cs2Ba(MoO4)2, cr, 298.15 K) = 381.2 ± 11.8 J K–1 mol–1.

Langbeinite Phosphates KPbM2(PO4)3 (M = Cr, Fe): Synthesis, Structure, Thermal Expansion, and Magnetic Properties Investigation.

New langbeinite-type phosphates KPbCr2(PO4)3 and KPbFe2(PO4)3 are synthesized by solution method and characterized by powder X-ray diffraction, infrared spectra, thermogravimetric and differential thermal analysis, scanning electron microscope, and energy dispersive X-ray analysis. Rietveld refinement reveals that both of the compounds crystallize in the cubic system with P213 space group, and the calculated lattice parameters for Cr and Fe phases are 9.7332(2) and 9.8325(7) Å, respectively. The electron micrographs confirm the crystalline nature of the samples from their surface morphologies. Infrared spectra display the characteristic features of P-O and M-O vibrational bands for both of the phases. Thermal analysis of KPbCr2(PO4)3 and KPbFe2(PO4)3 indicates that they are thermally stable up to 1273 K. The axial thermal expansion is studied by high-temperature X-ray diffraction between 298 and 1073 K. The average thermal expansion coefficients of KPbCr2(PO4)3 and KPbFe2(PO4)3 are identified as 8.9 × 10-6 and 10.8 × 10-6 K-1, respectively. Magnetic study reveals both of the compounds follow Curie-Weiss behavior in the higher-temperature region, and antiferromagnetic interactions are dominant.

Effect of SiO2/Al2O3 ratio on the structure and electrical properties of MgO–Al2O3–SiO2 glass-ceramics doped with TiO2

Glass-ceramics of the MgO–Al2O3–SiO2 (MAS) ternary system were successfully prepared through a melting method with borax, quartz sand, and chemical reagents as the main raw materials. The effects of SiO2/Al2O3 ratios on the structure and properties of glass-ceramics were systematically investigated by differential thermal analysis (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), dielectric properties and electrical resistivity measurements. The results show that the average coefficient of thermal expansion (CTE) (30–800 °C) of all the samples increased with increasing of the SiO2/Al2O3 ratio, but the density of the glass-ceramics and the grain refinement decreased at the same time. The crystalline phase of all the samples was a prepared sapphirine phase when the SiO2/Al2O3 ratio was equal or greater than 1.78 and a second phase of enstatite precipitation. The electrical performance was the best when the SiO2/Al2O3 ratio was equal to 1.27, and its dielectric constant, dielectric loss, and electrical resistivity (room temperature) were 8.78 (1 MHz), 3.55 × 10−3 (1 MHz), and 10.57 × 10 11 Ω m, respectively.