Structure,bond characteristics and Raman spectra of CaMg1-xMnxSi2O6 microwave dielectric ceramics

The CaMg_1-xMn_xSi₂O₆(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 ${\epsilon }_r$ is ascribed to the average bond covalency, polarizability and Raman shift. The $Q\times f$ 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 ${\tau }_f$ is related to thermal expansion coefficient and M1-site bond valence. Furthermore, the CaMg_0.98Mn_0·02Si₂O₆ ceramic sintered at 1300 °C possessed optimal microwave dielectric properties of ${\epsilon }_r$ = 8.01, $Q\times f$ = 83469 GHz and ${\tau }_f$ = −45.27 ppm/°C.     

Structural dependence of microwave dielectric properties of spinel structured Mg2(Ti1-xSnx)O4 solid solutions: Crystal structure refinement,Raman spectra study and complex chemical bond theory

Mg₂(Ti_1-xSn_x)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(Ti_1-xSn_x)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(Ti_1-xSn_x)O₄ compounds were obtained (${\epsilon }_r$= 12.18, $Q\times f$?=?170,130?GHz, ${\tau }_f$?=??53.1?ppm/°C, x?=?0.2).     

Extremely-ductile alkali-activated slag-based composite with a tensile strain capacity up to 22%

Highly-ductile alkali-activated slag-based composites (HD-AASC) are fiber-reinforced cement-free materials possessing pseudo strain-hardening behavior and multiple-cracking phenomena. In this research, the feasibility of developing extremely-ductile alkali-activated slag-based composite (ED-AASC) with a tensile strain capacity over 20% is presented. Specimens with a moderate amount of sand and crumb rubber particles were made by applying new mixing and curing procedures. Then the density, compressive strength, and tension tests were performed. Test results showed that the ED-AASC (R5-S8-M1 mixture) had a tensile strain capacity of 22.3%, compressive strength of 53.6 MPa, and average crack width of 212 μm. By adopting two performance indexes ($f_c{\epsilon }_{ts}$ and $f_{ts}{\epsilon }_{ts}$), the performance of ED-AASC was compared with those of previous high-ductile composites; the tensile strain capacity of the composite was also compared with the minimum extensibility of steel bars for concrete reinforcement, as specified in ASTM and ISO. In addition, the sustainability of ED-AASC was evaluated.     

Effect of annealing on structure and properties of Ta–O–N films prepared by high power impulse magnetron sputtering

High power impulse magnetron sputtering of a Ta target in various $\mathrm{Ar}+{\mathrm{O}}_2+{\mathrm{N}}_2$ gas mixtures was utilized to prepare amorphous tantalum oxynitride (Ta–O–N) films with a finely controlled elemental composition in a wide range. We investigate the effect of film annealing at $900°\mathrm{C}$ in vacuum on structure and properties of the films. We show that the finely tuned elemental composition in combination with the annealing enables the preparation of crystalline Ta–O–N films exhibiting a single TaON phase with a monoclinic lattice structure, refractive index of $2.65$ and extinction coefficient of $2.0\times {10}^2$ (both at the wavelength of $550\mathrm{nm}$), optical band gap width of $2.45\mathrm{eV}$ (suitable for visible light absorption up to $505\mathrm{nm}$), low electrical resistivity of $0.4\text{Ω}\mathrm{cm}$ (indicating enhanced charge transport in the material as compared to the as-deposited counterpart), and appropriate alignment of the band gap with respect to the redox potentials for water splitting. These films are therefore promising candidates for application as visible-light-driven photocatalysts for water splitting.     

Optical,thermal and electrical characterization of PEO/CMC incorporated with ZnO/TiO2 NPs for advanced flexible optoelectronic technologies

The optical, thermal, and electrical properties of a blend of polyethylene oxide (PEO) and carboxymethyl cellulose (CMC) are examined in the current work in relation to the effects of zinc oxide (ZnO) and titanium dioxide (TiO₂) nanoparticles. To create hybrid ZnO/TiO₂ NPs nanocomposites with a PEO/CMC matrix, the solution casting method was utilized. The XRD study results demonstrate that the nanocomposite films' crystallinity decreases with increasing ZnO/TiO₂ NP concentrations. FT-IR spectra reveal the interaction between metal oxide NPs and the PEO/CMC composite. UV/Vis analytical spectroscopy was used to calculate the optical properties, such as the energy gap (Eg), refractive index (n), and the number of carbon atoms (M). The inclusion of 7 wt%ZnO/TiO₂ NPs decreased the polymer matrix's allowed direct energy gap from 3.68 to 2.81 eV. The AC conductivity results show that the ${\sigma }_{dc}$ of the nanocomposite samples decreases with increasing ZnO/TiO₂ NPs concentrations. The ${\sigma }_{dc}$ of the final sample (PEO/CMC@7 wt% ZnO/TiO₂) was 5.18 × 10⁻⁷Scm⁻¹. According to exponential factor (S) results, the dominates conduction mechanism is correlated barrier hopping (CBH) with non-Debye relaxation processes. Space charge polarization was demonstrated by large ε′ values in the low-frequency dielectric properties, whereas an increase in energy loss may be related with a larger εʹ' value in the composite samples. These results prove that these nanocomposites can be used in a variety of energy-related devices, such as flexible capacitors, and energy storage systems.     

Enhancing pyroelectric properties in (Pb1–1.5xLax)(Zr0.86Ti0.14)O3 ceramics through composition modulated phase transition

Currently, there is an urgent need of extraordinary comprehensive pyroelectric materials for the wide application in detectors and energy harvesters. In this study, the (Pb_1–1.5xLa_x)(Zr_0.86Ti_0.14)O₃ (abbreviated as PLZT, x?=?0.02, 0.03, 0.04 and 0.05) ceramics located in ferroelectric-antiferroelectric (FE-AFE) phase boundary were designed and synthesized by using conventional solid-state reaction method. The microstructures, phase structures, dielectric, ferroelectric, thermal depolarization and pyroelectric properties of the PLZT ceramics with different La content were investigated thoroughly. The XRD results show that the PLZT ceramics change from FE phase to AFE phase with increasing La content. The significant improvement of pyroelectric coefficient $p$ and figures of merit (FOMs) are achieved in the PLZT ceramics with the increase in La content because of the increased metastable ferroelectric phase under the application of electric field. The (Pb_0.955La_0.03)(Zr_0.86Ti_0.14)O₃ (x?=?0.03) ceramic exhibits not only high $p$ of $5.2\times {10}^{?8}\mathrm{C}/{\mathrm{cm}}^2\mathrm{K}$ and high depolarization temperature (T_d) of 179?℃ but also excellent FOMs with $F_i=2.2\times {10}^{?10}\mathrm{m}/\mathrm{V}$, $F_v=5.0\times {10}^{?2}{\mathrm{m}}^2/\mathrm{C}$, and $F_d=3.47\times {10}^{?5}{\mathit{Pa}}^{?1/2}$. In addition, the highest $p$ of $6.8\times {10}^{?8}\mathrm{C}/{\mathrm{cm}}^2\mathrm{K}$ is achieved in (Pb_0.94La_0.04)(Zr_0.86Ti_0.14)O₃ (x?=?0.04) ceramic. These results demonstrate that the PLZT ceramics of x?=?0.03 and 0.04 are promising candidates for pyroelectric applications.     

Dielectric abnormality and high-permittivity microwave dielectric properties of SrO-TiO2-CeO2 solid solution

The SrO-TiO₂-CeO₂ (Sr_1?1.5×Ce_xTiO₃, SCTO, 0?≤?x?≤?0.2, sintered in N₂) solid solution exhibited the existence of dielectric abnormality/anomaly (for polished samples) and high-permittivity microwave dielectric properties (for unpolished samples). X-ray diffraction (XRD) and Rietveld refinement, along with high-resolution transmission electron microscopy (HRTEM), indicated the evidence of cubic like structure. The SEM-EDX maps demonstrated the formation of a complete solid solution, which further support the XRD results. X-ray photoelectron spectroscopy (XPS) analysis showed mixture of ion valence states upon lattice defects formation. The activation of the TO2/TiO4 polar bands usually described a relaxor-type-dielectric anomaly. The ε′-T curve, together with the polar nature measurements exhibited hysteresis loops, indicating that ceria ions induced weak relaxor behavior. The observed Q×f values were primarily dependent on the lattice defects and Ti³⁺ cations. The temperature coefficient of resonant frequency (${\tau }_f$) shifted gradually from more positive (+1321?ppm/°C) to less positive (+539?ppm/°C) values with a rise of Ce content (x). The unpolished sample with x?=?0.2 exhibited a high permittivity microwave dielectric properties with ε_r =?182, ${\tau }_f$?=?+539?ppm/°C, and Q×f =?668?GHz.     

Vibrational properties and infrared dielectric features of Gd2CoMnO6 and Y2CoMnO6 double perovskites

Gd₂CoMnO₆ and Y₂CoMnO₆ double perovskite ceramics were obtained from the polymeric precursors method and investigated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman and Fourier Transform Infrared (FTIR) spectroscopies. Our results show that these samples present similar structural and vibrational characteristics that are fully compatible with a monoclinic structure belonging to the P2₁/n space group, with ordered Co²⁺ and Mn⁴⁺ cations. Infrared-reflectivity spectroscopy was employed to investigate the polar phonon features and to determine the intrinsic dielectric response of the materials. In particular, the extrapolated dielectric constants at the lower frequency infrared limit showed to be independent on the particle size, and were determined as ${\epsilon \prime }_{\mathit{intr}}\approx 17.8$ and 16.0, for Gd₂CoMnO₆ and Y₂CoMnO₆, respectively. Otherwise, it is shown that for smaller RE radius the FTIR bands become more evidenced, due to a higher octahedral rotation and lower $<$Co-O-Mn$>$ angle into the distorted monoclinic structure.     

Effect of Gd doping on structural,optical properties,photoluminescence and electrical characteristics of CdS nanoparticles for optoelectronics

Synthesis of pure and 0.1 to 5?wt.% Gd-doped CdS nanoparticles (NPs) was achieved through a modified domestic microwave-assisted route in a short timespan at 700?W power. The formation of hexagonal CdS NPs was verified via X-ray diffraction analysis, and no structural variation was observed except for lattice variation. The size of the crystallites (D), dislocation concentration, and lattice strain were calculated, and the D was in the range of 3–6?nm. Fourier transform-Raman analysis confirmed the presence of 1LO, 2LO, and 3LO modes at 294.76, 590, and 890?cm^?1, respectively, in all the synthesized nanostructures, with minute variations in their positions due to doping; however, no new mode was observed. The position of the vibration modes was red shifted compared to that of the bulk material, indicating a confinement effect. Scanning electron microscopy (SEM) mapping/energy-dispersive X-ray spectroscopy revealed homogeneous doping of Gd and the presence of all the constituents in the final products. The morphology of the synthesized materials was tested via field-emission SEM, which revealed spherical NPs with small dimensions. Additionally, high-resolution transmission electron microscopy was performed to visualize the shape and size of the prepared 0.1% Gd:CdS NPs. The energy gap was calculated using the Kubelka–Munk theory and found to be in the range of 2.31–2.41?eV. The photoluminescence emission spectra exhibited two green emission peaks at 516?±?2?nm and 555?±?2?nm and showed the reduction of defects with Gd doping in terms of intensity quenching. The dielectric constant (${\epsilon }^{\text{'}}$), loss, and alternating-current electrical properties were studied in the high-frequency range. The values of ${\epsilon }^{\text{'}}$ were in the range of 17–27. An enhancement of these values was observed for CdS when it was doped with Gd. The electrical conductivity exhibited frequency power law behavior.     

Microwave dielectric properties of Ca1-xBaxMgSi2O6 ceramics

Ca_1-xBa_xMgSi₂O₆(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 Ca_1-xBa_xMgSi₂O₆ (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 ${\epsilon }_r$ value was increased continuously which was closely corrected with the relative density and molecular polarization. The ${\tau }_f$ value improved slightly with the substituting Ba²⁺ for Ca²⁺. Typically, the Ca_0.88Ba_0.12MgSi₂O₆ 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: ${\epsilon }_r=7.49$, $Q\times f=64310$ GHz, ${\tau }_f=-44.02$ ppm/°C.     

Synthesis and physical properties of the theoretically predicted spin-triplet superconductor Li0.9Mo6O17

We report the single crystal growth and characterization of the quasi-one-dimensional superconductor Li_0.9Mo₆O₁₇ 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 T_M = 24 K followed by a superconducting transition at T_c = 2.2 K for ${\rho }_a$ and ${\rho }_c$. In addition, the upper critical fields demonstrate a large anisotropy with $H_{c2}^b>H_{c2}^a>H_{c2}^c$ both at ${\rho }_a$ and ${\rho }_c$. Particularly, an upper critical field $H_{c2}^b$ 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 Li_0.9Mo₆O₁₇. The XRD, resistivities and upper critical field measurements all imply a high quality of the as-grown Li_0.9Mo₆O₁₇ 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.     

Fracture mechanics of microcrystalline/nanocrystalline composited multilayer chemical vapor deposition self-standing diamond films

Though microwave plasma chemical vapor deposition (MPCVD) diamond films exhibit extraordinary strength, the toughness improvement is still a huge challenge. The catastrophic fracture of the diamond films is undesirable in many applications, especially for the application of fabricating cutting tools. In the present study, adopting the pre-notched and unnotched cantilever bending tests, fracture behaviors of monolayer microcrystalline diamond (m-M), monolayer nanocrystalline diamond (m-N), and microcrystalline/nanocrystalline composited multilayer diamond films were observed and compared. Typical fracture mechanics, including Young's modulus (E), fracture strength (${\sigma }_F$), and fracture toughness (K_IC) of different diamond films were investigated. Effects of diamond crystal structure, intrinsic stress, and tensile-side roughness were systematically analyzed. Grain size and graphite phase content dominated the E of self-standing diamond films. Tensive-side surface roughness and intergranular bonding strength affected the ${\sigma }_F$. When the growth side in tension, E of the multilayer film (modulation period Λ = 3 h) was 16.0% lower than m-M and 26.6% higher than m-N, ${\sigma }_F$ of multilayer film was 16.8% higher than m-M and 8.3% lower than m-N. At fixed Λ, doubling the total deposition period, E, ${\sigma }_F$, and K_IC of the multilayer film increased 72.3%, 22.3%, and 2.7%, respectively. MCD/NCD composited multilayer architecture presented significant strengthening and toughening effects on self-standing diamond films.     

Physical,optical and gamma radiation shielding competence of newly boro-tellurite based glasses: TeO2–B2O3–ZnO–Li2O3–Bi2O3

Herein, a traditional melt quenching method was utilized to synthesize glasses with a nominal chemical composition (80-x)TeO₂-xB₂O₃–5ZnO–5Li₂O₃–10Bi₂O₃: 30≤ x ≤ 80 mol%). The produced sample was coded as TBBZL30 to TBBZL80. X-ray diffraction (XRD) has been employed to test the amorphous nature of the synthesized samples. In the range of 200–500 nm wavelength, UV–Vis spectra for the glasses have been performed. Optical energy gaps ($E_{gap}$) have been determined based on the absorption measurements. With the help of ($E_{gap}$), refractive index (n), molar polarizability (α^M), metallization criterion (M^Cri.), molar refractivity (R^M), static dielectric constant (ε^Sta.), optical dielectric constant (ε^Opt.), reflection loss (R^L) and optical transmission (T^Opt.) have been calculated. For the fabricated boro-tellurite glasses, Phy-X/PSD was used to report some shielding factors for several energies between 15 keV and 15 MeV. The maximum attenuation for all samples took place at 15 keV and the mass attenuation coefficient varied between 52.309 and 57.084 cm²/g. The linear attenuation coefficient (LAC) results demonstrated that TBBZL80 has the highest attenuation than the rest of samples which is due to high content of TeO₂ (containing 80 mol% of TeO₂) whereas TBBZL30 has the lowest attenuation. The LAC for the fabricated samples varied between 230.160 and 351.064 cm-¹ at 15 keV. The minimum effective atomic number (EAN) occurred between 0.8 and 4 MeV and varied between 15.16 and 17.35 for TBBZL30 and 25.10–28.33 for TBBZL80. The addition of TeO₂ was found to enhance the EAN and improved shielding properties for the tested TBBZL glass systems.