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.     

Comparison of theoretical and experimental microhardness of tetrahedral binary Zn1-xErxO semiconductor polycrystalline nanoparticles

${\mathrm{Zn}}_{1?\mathrm{x}}{\mathrm{Er}}_{\mathrm{x}}\mathrm{O}$ polycrystalline nanoparticles with various compositions $(x=0.01,0.02,0.03,0.04,0.05,$ and $0.10)$were prepared using sol–gel techniques, for which zinc acetate dihydrate and erbium 2–4 pentanedionate are used as precursors. Nanoparticles were pressed under a pressure of $4$?tons for $5$?min into disk-shaped compacts with 2?mm thicknesses and 10?mm diameters. The pressed samples were annealed at 400?°C for $30$?min. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vickers microhardness analyses of the produced Er-doped $\mathrm{ZnO}$ bulk nanomaterials were performed. Specifically, in this study we focused on the analysis of their mechanical properties. Undoped and Er-doped bulk samples were investigated according to Meyer's law; the proportional sample resistance (PSR), elastic/plastic deformation (EPD), and indentation-induced cracking (IIC) models; and the Hays–Kendal (HK) approach. As a result, the IIC model was more suitable to determine the micromechanical properties and the reverse indentation size effect ($\mathrm{R}\mathrm{ISE}$) behavior of Er-doped $\mathrm{ZnO}$ semiconductors.     

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.     

Proton mobility in Ruddlesden–Popper phase H2La2Ti3O10 studied by 1H NMR

To study protons localization in H_1.83K_0.17La₂Ti₃O₁₀·0.17H₂O and their motional characteristics, complementary Nuclear Magnetic Resonance (NMR) techniques have been applied. ¹H Magic Angle Spinning NMR evidences the presence of different proton containing species. By analyzing the temperature dependence of the ¹H MAS NMR spectrum we attribute the observed lines to interlayer H⁺ in regular sites (isolated and in water rich environment), water protons and protons from various defects. The temperature behaviors of the spectral lines intensities and widths point out that intercalated water molecules are involved in translational motion that is confirmed by spin lattice relaxation rate ($R_1$) and spin-lattice relaxation rate in rotating frame ($R_{1\rho }$) measurements. It has been shown that for a correct determination of the proton motional parameters the Kohlrausch-Williams-Watts correlation function must be used. Its application results in the following parameters of proton motion in the interlayer space of H_1.83K_0.17La₂Ti₃O₁₀·0.17H₂O: $E_{\mathrm{a}}$?=?0.194(2) eV, $\mathrm{\beta }$?=?0.28(1), ${\tau }_0=6.2(1)\times {10}^{?10}$?s.     

Enhanced resistance in Bi(Fe1-xScx)O3-0.3BaTiO3 lead-free piezoelectric ceramics: Facile analysis and reduction of oxygen vacancy

We reported a facile analysis and reduction of oxygen vacancy (${\mathrm{V}}_{\mathrm{O}}^{??}$) in 0.7Bi(Fe_1-xSc_x)O₃-0.3BaTiO₃ (0≤x≤0.08) ceramics. The leakage current mechanism was investigated intensively. Our results indicated that oxygen vacancies are the main cause for the high conductivity in BF-BT ceramics, and their concentration was quantitatively estimated from the Bi³⁺ content and the average oxidation state of iron. The ${\mathrm{V}}_{\mathrm{O}}^{??}$ concentration was effectively suppressed and the insulation resistance was enhanced by almost two orders of magnitude after doping 2%mol Sc³⁺. The enhanced insulation resistance contributed to excellent piezoelectric properties with d₃₃ = 165 pC/N, T_C = 505 °C, and k_p = 26%. The proposed analysis method used to quantify the ${\mathrm{V}}_{\mathrm{O}}^{??}$ concentration provides valuable indications to reduce the leakage current density and improve the piezoelectric properties of BF-BT based ceramic.     

Structure,magnetic and transmission characteristics of the Co substituted Mg ferrites synthesized via a standard ceramic route

Co-Mg ferrites, ${\mathrm{Co}}_{\mathrm{x}}{\mathrm{Mg}}_{1?\mathrm{y}}{\mathrm{Fe}}_{2?\mathrm{z}}{\mathrm{O}}_4$ (x?=?0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, 0?<?y?<?0.34 and 0?<?z?<?0.67), were synthesized via a standard ceramic route, and the structural, morphological, magnetic properties and transmission parameter of the samples were studied. The thermal behavior of the ground powder was characterized using a differential thermal analysis technique (DTA). The XRD patterns proved the formation of single phase Mg-ferrite in the samples with "x" contents varying from 0.0 to 0.8. The sample with x?=?1.0 showed two phases: a spinel Mg-ferrite and a secondary (Co,Mg)O phase. The lattice parameter and crystallite size of the samples increased remarkably by increasing the x content. The SEM images revealed that Co substitution in Mg ferrite at x?=?0.2 causes the particle growth, but their growth was not significant until x?=?0.8. For x?=?1.0, a remarkable particle growth was again observed. A maximum bulk density of 4.94?g/cm³ was obtained for x?=?0.8. Magnetic properties of the sintered samples showed an increase in coercive force up to 113?Oe by increasing Co substitution up to x?=?1.0. Saturation magnetization reached a maximum value of ~45.40?emu/g at x?=?0.8. Studying the microwave transmission behavior of the samples, using a vector network analyzer (VNA), indicated that by increasing Co, the transmission loss was reduced from $~$??15?dB for x?=?0.0 to less than ??10?dB for x?=?0.8 in the frequency range of 8–12?GHz.     

Photocatalysis performance enhancement of Ag2O/Al-doped ZnO heterojunction by introducing ZnO nanorod array

Fabric-based nano semiconductor photocatalysts have attracted much attention in recent years. In this study, polyester fibers were modified by Ag₂O/ZnO nanorod (NR)/Al-ZnO p-type/high resistivity/n-type (P-HR-N) heterojunction arrays. Al-doped ZnO (Al-ZnO) seed layer was reactively sputtered on polyester fibers. Al doping was used to change the work function (WF) of the ZnO film. The ZnO NR arrays were hydrothermally grown on the Al-ZnO seed layer and modified with Ag₂O film. The work functions (WFs) of Ag₂O and Al-ZnO layers were measured, resulting in $5.53$ and $4.81\mathrm{e}\mathrm{V}$, respectively. The WF difference between the two layers was $0.72\mathrm{e}\mathrm{V}$. The electron-hole separation of the P-HR-N heterojunction array was characterized by surface photovoltage (SPV) spectra. The photocatalytic activities of the prepared samples were investigated by removing Rhodamine B (RB) under UV irradiation. The P-HR-N heterojunction sample displayed a better photocatalytic performance than the Ag₂O/Al-doped ZnO PN heterojunction sample and ZnO NR/Al-ZnO array-coated sample. The enhanced photocatalytic performance of the P-HR-N heterojunction based sample was mainly attributed to the high and widened built-in electric field (BEF) in the multilayer film.     

Correlation of the crystal features,magnetic parameters,and electronic structure of Bi-substituted BaFe12-xBixO19 hexaferrites: Theoretical background

Herein, using first-principles density functional theory (DFT) calculations, we have investigated the effects of Bi substitution on the structural, electronic, and magnetic properties of barium hexaferrite (BaFe_12-xBi_xO₁₉, x = 0; 0.5; 1.5 and 2). As a result of the calculation, it was determined that the most stable structure exists if the spin of the Fe atom on the 2a, 2b, and 12k positions of the barium hexaferrite compound is taken in the upward direction. The calculated lattice constant $\left(\raisebox{1ex}{$\mathrm{c}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{a}$}\right.=3.9\right)$ and magnetic moment $\left(4.24{\mu }_{\mathrm{B}}\right)$ of iron ions are in reasonable agreement with other experimental works. Moreover, the presence of bismuth reduces the electronic band gap. Energy gain and magnetic anisotropy energy calculations for FIM, FM, and NM states were performed for the most stable states. It has been established that the most stable structural state is characteristic of х = 0.5. It has been calculated that substitution by the large Bi³⁺ ion dramatically changed the electronic structure and sharply reduced the band gap. This paper is the first step towards establishing the nature of the distribution of ions in M-type hexaferrites under conditions of substitution by ions with a large ionic radius.     

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.