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1.
《Ceramics International》2020,46(10):16068-16073
In this study, nonstoichiometric hafnium carbonitrides (HfCxNy) were fabricated via short-term (5 min) high-energy ball milling of Hf and C powders, followed by combustion of mechanically induced Hf/C composite particles in a nitrogen atmosphere (0.8 MPa). The obtained HfC0.5N0.35 powder exhibited a rock-salt crystal structure with a lattice parameter of 0.4606 nm. The melting point of this synthesized ceramic material was experimentally shown to be higher than that of binary hafnium carbide (HfC). The nonstoichiometric hafnium carbonitride was then consolidated under a constant pressure of 50 MPa at a temperature of 2000 °C and a dwelling time of 10 min, through spark plasma sintering. The obtained bulk ceramic material had a theoretical material density of 98%, Vickers hardness of 21.3 GPa, and fracture toughness of 4.7 MPa m1/2.  相似文献   

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《Ceramics International》2022,48(7):9407-9412
Ca1-xBaxMgSi2O6(x = 0–0.4) ceramics were prepared through a traditional solid-state reaction sintering route with various sintering temperatures. The effects of substituting Ba2+ for Ca2+, the relative density, phase composition, crystal morphology, and microwave dielectric properties of Ca1-xBaxMgSi2O6 (x = 0–0.4) ceramics were thoroughly studied. X-ray diffraction patterns indicate a single phase was formed in the samples when x ≤ 0.2, and the second phase BaMg2Si2O7 appeared at x = 0.4. As the amount of Ba2+ substitution increases, the Q×f value first increases and then decreases due to the combined effects of FWHM of peak v11 and atomic packing density, and the εr value was increased continuously which was closely corrected with the relative density and molecular polarization. The τf value improved slightly with the substituting Ba2+ for Ca2+. Typically, the Ca0.88Ba0.12MgSi2O6 ceramic can be well sintered at 1275 °C for 4 h with a maximum relative density of 99.3%, and possesses optimal microwave dielectric properties: εr=7.49, Q×f=64310 GHz, τf=-44.02 ppm/°C.  相似文献   

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Dielectric tunable devices with improved overall tunability properties are in urgent demand for tunable applications. Hence, a series of Pb-free dielectric tunable ceramics based on (Ba1?xCax) (Zr0·18Ti0.82)O3 (abbreviated as BCZTx, x = 0.05–0.21, corresponding to BCZT05 to BCZT21) were carefully prepared using the traditional solid-state route in this work. The crystal structure, surface morphology, dielectric properties, and tunable performance of different BCZTx ceramics at room temperature (RT) were systematically studied. The temperature-dependent dielectric tunable performance was further investigated. The phase evolutions were co-confirmed by XRD and dεrdT-T curves. Interesting, high tunability (86.09%), together with a relatively low dielectric loss (~0.19% @7.42 kV/cm) were obtained in BCZT09 ceramics at 1 kHz, resulting in a giant figure-of-merit (FOM) of 448, which implied these ceramics are promising matrix for dielectric tunable applications that operated at RT. From the Tunability?T and FOM?T curves, it can be found that Ca2+ incorporation can improve the temperature stability of dielectric tunable performance to a certain extent. In addition, the FOM?T curve of BCZT09 showed advantages over other compositions in the temperature range of ?20 °C–85 °C, and its maximum FOM (~886) was reached at 40 °C. These observations suggest the BCZT09 ceramic as a promising matrix for application in dielectric tunable devices operating at RT. This work may guide the design of novel high-performance tunable ceramic materials.  相似文献   

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《Ceramics International》2019,45(11):14160-14166
The CaMg1-xMnxSi2O6(x = 0–0.08)ceramics were reported here for the first time. The relationships among structural characteristics, vibrational modes and dielectric properties for the ceramics were researched based on complex chemical bond theory and Raman vibrational spectroscopy. The formation of a single phase with clinopyroxene structure when x = 0 to 0.08 was detected by X-ray diffraction. The monotonous increase of εr is ascribed to the average bond covalency, polarizability and Raman shift. The Q×f value is influenced by total lattice energy and full width at half maximum of Raman spectra which are both connected with the intrinsic loss. The variation of τf is related to thermal expansion coefficient and M1-site bond valence. Furthermore, the CaMg0.98Mn0·02Si2O6 ceramic sintered at 1300 °C possessed optimal microwave dielectric properties of εr = 8.01, Q×f = 83469 GHz and τf = −45.27 ppm/°C.  相似文献   

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Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (εr= 12.18, Q×f?=?170,130?GHz, τf?=??53.1?ppm/°C, x?=?0.2).  相似文献   

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Ba1.5Sr1.5Co2-xZnxFe22O41(x = 0,0.4,0.8,1.2,1.6,2.0) hexaferrites substituted by Zn were prepared via conventional solid-state reaction. The influences of Zn substitution content on phase formation, microstructure, and magnetic properties, especially high-frequency magnetic properties, were systematically investigated. Results indicate that, when sintering temperature is 1200 °C, pure ferrite phase of Co2Z is formed, and Zn2+ is successfully incorporated into the lattice. Appropriate amount of Zn substitution can improve the densification and saturation magnetization (Ms) of Z-type ferrite, thereby effectively promoting permeability. However, due to limitations of Snoek's law, cut-off frequency is found to be reduced with Zn substitution. For x = 0.4, the sample exhibits both high permeability (up to 22.49) and high cut-off frequency (~900 MHz), with Snoek constant (μi?1)×fr reaching 19.337 GHz. Furthermore, magnetic loss for the sample with x = 0.4 is found to be low. It is anticipated that this material will have extensive application prospects for miniaturization and high frequency antenna applications.  相似文献   

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《Ceramics International》2021,47(18):25229-25235
We report the single crystal growth and characterization of the quasi-one-dimensional superconductor Li0.9Mo6O17 via temperature-gradient flux method. The grown single crystals show a clear ab plane identified by the x-ray diffraction (XRD) pattern. Temperature dependent resistivities reveal a metallic to semiconducting crossover at TM = 24 K followed by a superconducting transition at Tc = 2.2 K for ρa and ρc. In addition, the upper critical fields demonstrate a large anisotropy with Hc2b>Hc2a>Hc2c both at ρa and ρc. Particularly, an upper critical field Hc2b of about 16.2 T at zero temperature limit was deduced from the field dependence of resistivity measurements, which is notably larger than the estimated Pauli paramagnetic limit 3.1 T and supports the existence of the spin-triplet superconducting pairing and unconventional superconductivity in Li0.9Mo6O17. The XRD, resistivities and upper critical field measurements all imply a high quality of the as-grown Li0.9Mo6O17 samples. Furthermore, the interlayer and in-plane magnetoresistivity (MR) up to 60 T reveal the possible phase transition driven by the density-wave gap suppression and Zeeman split effect in the high field state.  相似文献   

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《Ceramics International》2022,48(17):24439-24453
Lead-free multiferroic 3–0 type particulate composites with a composition (1?x)(Ba0.85Ca0.15Zr0.1Ti0.9O3) – x(Ni0.7Zn0.3Fe2O4) [(1?x)BCZT – xNZFO with 0 ≤ x ≤ 100 at%] were prepared using solid state reaction method. Structural and microstructural analysis using XRD, FESEM and Raman techniques confirmed the phase formation of the ferroelectric (BCZT) and magnetostrictive (NZFO) phases without any detectable presence of impurity phases. Rietveld refinement of the XRD data revealed a tetragonal (P4mm) and a cubic structure (Fd3m) for the BCZT and NZFO phases, respectively. Elemental compositions of the constituent phases were assessed by EDS and XPS analyses. Electrical, magnetic, and magnetoelectric (ME) measurements were performed. The composites exhibit typical well-saturated magnetic hysteresis (M?H) loops at room temperature, having very low coercive field (HC) values, indicating their soft ferromagnetic behavior. Various parameters extracted from the M?H curves including HC, magneto-crystalline anisotropy, squareness, and magnetization were found to depend on x. Frequency dependence of capacitance and admittance exhibited a resonance behavior corresponding to the radial mode of the electromechanical resonance (EMR). ME coefficients were studied in both longitudinal (αE33) and transverse (αE31) modes. The highest coupling coefficients, αE31 ~14.5 mV/Oe.cm and αE33 ~13 mV/Oe.cm were obtained for composite with 50 at% NZF at off-resonance frequency of 1 kHz. At the EMR frequency of 314 kHz, the αE31 value in 0.5BCZT-0.5NZFO composite enhanced enormously to ~5.5 V/Oe.cm. The studies conclude that x = 0.5 is an optimum atomic fraction of NZFO in the particulate composite for maximum ME coupling.  相似文献   

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《Ceramics International》2017,43(11):8517-8524
Transition metal nitrides are being widely applied, as durable sensors, semiconductor and superconductor devices, their electrical conductivity and wear resistance having a significant influence on these applications. However, there are few reports about how to improve above properties. In this paper, tantalum was incorporated into hafnium nitride films through Hf1-xTaxNy [x=Ta/(Hf+Ta), y=N/(Hf+Ta)] solid solution. The electrical conductivity and wear resistance of the films were significantly improved, due to the increase of the electron concentration (tantalum has one more valence electron than hafnium) and the increase in H/E and H3/E2 ratios caused by the effect of solid solution hardening, respectively. The highest electrical conductivity of Hf1-xTaxNy films is 8.3×105 S m−1, which is 1.7 times and 5.2 times of that of hafnium nitride and tantalum nitride films, respectively. In addition, the lowest wear rate of films is 1.2×10−6 mm3/N m, which is only 10% and 48% of that of hafnium nitride and tantalum nitride films, respectively. These results indicate that alloying with another transition metal is an effective method to improve electrical conductivity and wear resistance of transition metal nitrides.  相似文献   

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