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.     

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.     

Investigation on the structural,multiferroic and magnetoelectric properties of BaTi1-xNixO3 ceramics

In this paper, we report the influence of Ni doping on the structural, electrical, magnetic and magnetoelectric properties of BaTiO₃ (BTO) ceramics. X-ray diffraction (XRD) analysis indicates a phase transition from tetragonal to hexagonal at x?=?2.5?mol%. Further, XRD data has been refined using Rietveld method to extract the phase formation, lattice parameters, and the phase fraction of BaTi_1-xNi_xO₃ $\left(\mathrm{BTNO}\right)(0\le x\le 10\mathrm{mol}\%)$ ceramics. The ferroelectric polarization decreases with Ni doping concentration. The relative permittivity of BTNO compositions decreases while the corresponding dielectric loss increases with Ni doping concentration. Room temperature magnetic hysteresis (M-H) loop of all BTNO samples exhibit ferromagnetic nature with a saturated loop except for x?=?2.5?mol% Ni doping concentration. At x?=?2.5?mol% Ni doping concentration, a small amount of diamagnetism is observed at higher fields along with ferromagnetism. The origin of ferromagnetism is due to the F- center exchange interaction via oxygen vacancies. The highest remnant magnetization (M_r) is 11.76 memu/g for x?=?10?mol%. The Magnetodielectric coefficient (MD) and magnetoelectric coefficient (ME) gradually increases with increasing Ni doping concentration, and are 1.72% and 4.51 $\mathrm{mV}{\mathrm{cm}}^{?1}{\mathrm{Oe}}^{?1}$ respectively for x?=?10?mol%.     

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.     

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.     

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.     

Microstructure development in (Co,Ta)-doped SnO2-based ceramics with promising varistor and dielectric properties

Following the $\mathit{3}Sn{\mathit{(}IV\mathit{)}}_{Sn\mathit{(}IV\mathit{)}}^{\times }\leftrightharpoons Co{\mathit{(}II\mathit{)}}_{Sn\mathit{(}IV\mathit{)}}^{\mathrm{″}}+2Ta{\mathit{\left(}V\mathit{\right)}}_{Sn\mathit{(}IV\mathit{)}}^{\cdot }$ charge compensation mechanism we optimized densification and electrical properties of Ta₂O₅-doped SnO₂–CoO ceramics. We show that incorporation of acceptor dopant Co²⁺ in SnO₂ is promoted after the addition of donor dopant like Ta⁵⁺, whereas any surplus of Co would form secondary Co₂SnO₄ phase. A balanced addition of both dopants is needed to promote densification, and any surplus of donor dopants that remain present at the grain boundaries retard the grain growth and deteriorate electrical properties. Varistor and dielectric properties are then strongly influenced by donor doping. Optimum varistor properties (α = 40, U_T = 272 V/mm, I_L = 1.2 μA) were measured for the sample with 1 mol% Ta₂O₅ and the best dielectric properties (ε = 6525; tan(δ) = 0.057@1kHz) were measured for the sample with 0.10 mol% Ta₂O₅ with the largest SnO₂ grain sizes.     

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.     

Structural phase transition,impedance spectroscopy and narrow optical band Gap in 1-xKNbO3-xBaSc12Nb12O3

In the progress of exploring lead-free ferroelectric perovskites, a new solid solution of $\left(1-x\right)\mathrm{}\mathrm{K}\mathrm{N}\mathrm{b}{\mathrm{O}}_3-\mathrm{}x\mathrm{}\mathrm{B}\mathrm{a}\left({\mathrm{S}\mathrm{c}}_{\frac{1}{2}}\mathrm{}{\mathrm{N}\mathrm{b}}_{\frac{1}{2}}\right)O_3$ is synthesized using solid state method. The effect of Ba and Sc codoping on structural phase transition, dielectric, ferroelectric, electrical, and optical properties is systematically studied. A narrow band gap of 1.98eV is observed at x?=?0.05. On further increase in x, the optical band gap increases due to increased strain. The crystal symmetry changes from orthorhombic at x?=?0.00 to tetragonal phase at x?≤?0.15, remains in pseudocubic phase for 0.15?<?x?<?0.35, and finally transforms to the cubic symmetry at x?≥?0.35. A new Raman active mode evolves at 180?${\mathrm{c}\mathrm{m}}^{-1}$ at x?=?0.15, which could be the TO or LO phonon of ${\mathrm{A}}_1$ symmetry. The electrical microstructure of the prepared electroceramics at room temperature has been investigated using impedance spectroscopy. This newly synthesized ferroelectric perovskite material has promising potential applications for photocatalysis and photovoltaics, especially under the visible light spectrum.     

Correlation between structural and optical properties of Dy3+ doped BaGd2O4 phosphors intended for solid-state lighting applications

Highly crystalline and single phase BaGd${}_{2-x}$Dy${}_x$O${}_4$ (0.00 $\le$x $\le$ 0.16) phosphors, with an average crystallite size around 126 nm, have been synthesised using solid-state reaction technique. The structural and optical properties of these phosphors have been studied in detail to establish an unambiguous correlation between these properties. High-angle annular dark field (HAADF) images have confirmed that the constituent elements are homogeneously distributed in the particles, and their elemental composition has been established using X-ray photoelectron spectroscopy (XPS). The tuning of optical band gap with x has been achieved, which is a rare achievement in these phosphors. Also, the optimum concentration of Dy${}^{3+}$ ions has been found to be 0.8 mol%, which is the lowest among the Dy${}^{3+}$ doped BaGd${}_2$O${}_4$ phosphors reported so far. This concentration quenching effect has been discussed on the basis of a combination of decay curve analysis, calculation of average critical distance between the Dy${}^{3+}$ ions and integrated intensities of photoluminescence (PL) emission bands. The average crystallite size and optical band gap has also been found to decrease after x = 0.016, from which their correlation with concentration quenching effect has been investigated. The asymmetry ratio between the integrated intensities of yellow and blue PL emission bands has been observed to be greater than 2 throughout x, which confirmed the preferential lattice site for Dy${}^{3+}$ ions in these phosphors with present synthesis conditions. The variation of asymmetry ratio and Gd${}^{3+}$-dominated IR-active lattice vibrations with x, and Vegard’s law pertaining to the volume of a unit cell confirms that the local bonding environment in the lattice of these phosphors gets modified at x = 0.016. The photometric parameters for these phosphors reveal their suitability for fabrication of warm light orange LEDs on appropriate UV chips.     

Transparent sol-gel glass ceramics containing β-NaYF4:Yb3+/Er3+ nanocrystals: Structure,upconversion luminescent properties and optical thermometry behavior

Transparent bulk glass ceramics (GCs) containing $\beta ?\mathit{NaY}{\mathrm{F}}_4:{\mathit{Yb}}^{3+}/{\mathit{Er}}^{3+}$ upconversion nanocrystals were successfully prepared via a new sol-gel route for the first time. The structure, composition and morphology of the as-fabricated glass ceramics are characterized by X-ray diffraction ($\mathit{XRD}$), scanning electron microscopy ($\mathit{SEM}$) and transmission electron microscopy ($\mathit{TEM}$), which confirm the segregation of β-NaYF₄ nanocrystals in silica glass matrix with the maintenance of their crystalline phase and microstructure. More significantly, intense upconversion (UC) emissions can be realized for ${\mathit{Yb}}^{3+}/{\mathit{Er}}^{3+}$ co-doped glass ceramics by profiting from low-phonon-energy environment of erbium ions in β-NaYF₄ nanophase. Furthermore, temperature-dependent UC emission performance of the present GC is systematacially investigated to explore their potential application in optical thermometry. Obviously, owing to intense UC emissions of $\beta ?\mathit{NaY}{\mathrm{F}}_4:{\mathit{Yb}}^{3+}/{\mathit{Er}}^{3+}$ nanocrystals and high transparency, superior chemical/mechanical stability of oxide glassy matrix, the as-fabricated GCs exhibit good temperature sensing performance and good thermostability for precise temperature detecting. It is expected that the preliminary research can give a reference for designing new transparent bulk GCs and may exploit a valid method for developing high-performance optical temperature sensors.     

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.