Novel single-host Al<Subscript>1−x</Subscript>Si<Subscript>x</Subscript>C<Subscript>x</Subscript>N<Subscript>1−x</Subscript>: Mn<Superscript>2+</Superscript> white phosphors for field emission displays

A white-emitting novel Al_1?x Si _x C _x N_1?x : Mn²⁺ carbidonitride phosphor was synthesized by introducing SiC into AlN: Mn²⁺at the temperature as low as 1500?°C. The influence of Mn²⁺ and SiC doping concentration on the structure, morphology and luminescent properties was systematically investigated by XRD, EDS, solid state NMR, FESEM, and PL. The relatively low calcination temperature endows AlN: Mn²⁺ with different luminescent properties. Under 254 nm UV excitation, it not only exhibits a characteristic red emission from Mn²⁺ but also covers a broad violet-blue-green emission from defects. The CIE coordinates (0.2999, 0.2510) precisely locate in the white region. With the introduction of SiC, an increasing of the red emission from Mn²⁺ is observed, while no variation occurs for the defect emission. The maximum red luminescence is attained for the composition of x?=?0.05 that has an improved thermal stability by 20%. Finally, a low-voltage FED device was fabricated by using Al_0.95Si_0.05C_0.05N_0.95: 0.7% Mn²⁺ carbidonitride phosphor. Under low-voltage excitation, it exhibits a high brightness, low saturation, and good color stability, which makes Al_1?xSi_xC_xN_1?x: Mn²⁺ carbidonitride phosphor have a great potential for full color FEDs.     

Study on the mechanism of NH<Subscript>3</Subscript>-selective catalytic reduction over CuCe<Subscript>x</Subscript>Zr<Subscript>1–x</Subscript>/TiO<Subscript>2</Subscript>

Copper-cerium-zirconium catalysts loaded on TiO₂ prepared by a wet impregnation method were investigated for NH₃-selective catalytic reduction (SCR) of NO_x. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH3 is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe_0.25Zr_0.75/TiO₂ at high temperature, while Brønsted acid sites are more important than Lewis acid sites at low temperature. For the NH₃+NO+O₂ co-adsorption, NH3 species occupy most of activity sites on CuCe_0.25Zr_0.75/TiO₂ catalyst, and mainly exist in the forms of NH₄ ⁺ (at low temperature) and NH₃ coordinated (at high temperature), playing a crucial role in the NH₃-SCR process. Two different reaction routes, the L-H mechanism at low temperature (< 200°C) and the E-R mechanism at high temperature (> 200°C), are presented for the SCR reaction over CuCe_0.25Zr_0.75/TiO₂ catalyst.     

Novel temperature stable Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>V<Subscript>2</Subscript>O<Subscript>6</Subscript> microwave dielectric ceramics with ultra-low sintering temperature

New temperature stability Ba_1?xSr_xV₂O₆ (0.35?≤?x?≤?0.55) microwave dielectric ceramics prepared by the conventional solid-state route were investigated. X-ray diffraction confirmed that all the specimens formed a solid solution single phase with orthorhombic structure. The microwave dielectric properties strongly depended on the compositions, densification and microstructure of the specimens. Furthermore, partial Sr ions substitution for Ba ions in Ba_1?xSr_xV₂O₆ lattices not only successfully improved the temperature stability of BaV₂O₆-based ceramic but also promoted the sinterability of SrV₂O₆-based one. Out of these compositions, Ba_0.5Sr_0.5V₂O₆ sintered at 625?°C exhibited a near-zero τ_f together with a low permittivity ε_r?~?11.5 and a quality factor Q?×?f?~?14 100 GHz, which also showed good chemical compatibility with Al electrodes.     

Laser and electromagnetic loss properties of Perovskite SmNi<Subscript>x</Subscript>Fe<Subscript>1−x</Subscript>O<Subscript>3</Subscript>

SmNi_xFe_1?xO₃ (0?≤?x?≤?0.5) with perovskite-type structure has been successfully prepared by conventional solid-state reaction as a microwave and laser multi-functional material. The optimized synthesis temperature and the effects of Ni doping on the reflectivity, electromagnetic loss properties were investigated in details. XRD results shown that synthesis temperature did not change the perovskite structure of SmFeO₃. The reflectivity at 1.06 μm was about 0.33% at 1200–1300?°C. Doping Ni did not cause the change of perovskite structure. The incorporation of Ni in SmFeO₃ contributed to the decrease of reflectivity at a wider wavelength, SmNi_0.3Fe_0.7O₃ possessed the lowest reflectivity at 1.06 μm. Moreover, electromagnetic property was very sensitive to Ni content. The real and imaginary parts of complex permeability were enhanced remarkably at a certain frequency. The changes in magnetic performance provided possibility of choosing specific frequency of magnetic loss. The difference in electric and magnetic losses caused by Ni concentration could result in microwave absorption at different frequency. In a word, SmNi_xFe_1?xO₃ could be a promising candidate for a multi-functional material with compatible camouflage capability for radar and laser waveband.     

Characterization and electrical conductivity of La<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>CrO<Subscript>3</Subscript> NTC ceramics

The La_1?xSr_xCrO₃ (x?=?0–0.1) negative temperature coefficient (NTC) ceramics have been prepared by the traditional solid state reaction method. X-ray diffraction (XRD) analysis has revealed that the as-sintered ceramics crystallize in a single perovskite structure. Scanning Electron Microscope (SEM) images show that the doped Sr²⁺ contributes to in the decrease in porosity. X-ray photoelectron spectroscopy (XPS) analysis indicates the existence of Cr³⁺ and Cr⁶⁺ ions on lattice sites, which result in hopping conduction. The presence of the Cr⁶⁺ is one of the key factors that affect the electrical conductivity of La_1?xSr_xCrO₃. Resistance–temperature characteristics were studied in the range of ?80 to 10?°C for the ceramic samples, the electrical characterizations show that the electrical resistivity and material constant B decrease with the increase of the strontium content.     

Thermal expansion of TlIn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ce<Subscript>x</Subscript>Se<Subscript>2</Subscript> crystals

The linear thermal expansion coefficient of TlIn_1?x Ce_xSe₂ (0 ≤ x ≤ 0.04) crystals has been measured at temperatures from 300 to 600 K.     

Effect of annealing on exchange bias in Mg<Subscript>0.2</Subscript>Fe<Subscript>x</Subscript>Cr<Subscript>1.8−x</Subscript>O<Subscript>3</Subscript> nano oxides

Magnesium-iron chromium oxides (Mg_0.2Cr_1.8?x Fe _x O₃ with x varying from 0.3 to 0.9) produced by hydrothermal process in a stirred pressure reactor from pure metal chlorides have been annealed at 700 °C. Single phase corundum structure and nanophase structure of the as-synthesized samples were confirmed by X-ray diffraction (XRD). Instead of the correlation between H _EB and D _XRD observed at T _A = 600 °C, we find significant changes. The H _EB increases with decreasing particle size reaches a maximum at ~43 nm (x = 0.5) then decreases.     

Characterization of In<Subscript>1 − x</Subscript>Cd<Subscript>x</Subscript>S,In<Subscript>2</Subscript>S<Subscript>3</Subscript> and CdS thin films grown by SILAR method

Successive Ionic Layer Adsorption and Reaction (SILAR) technique was used to deposit In_1???xCd_xS, In₂S₃ and CdS thin films on glass substrate at room temperature. The crystal structure and crystal size of the thin films were characterized by X-ray diffraction (XRD) method. Scanning Electron Microscopy (SEM) was used to determine morphology and composition of the films. Optical and electrical properties of these films have been investigated as a function of temperature. The photoluminescence measurements were carried out at room temperature and absorption measurements were carried out in the temperature range 10–320 K with a step of 10 K. The band gap energies for CdS, In_0.8Cd_0.2S, In_0.6Cd_0.4S, In_0.4Cd_0.6S, In_0.2Cd_0.8S and In₂S₃ thin films were found as 2.22 eV, 2.56 eV, 2.52 eV, 2.46 eV, 2.38 eV, and 2.72 eV, respectively. The refractive indices (n), optical static and high frequency dielectric constants (\({\in }_{0}\), \({\in }_{{\infty}}\)) values have been calculated by using the energy bandgap values. The electrical resistivity of CdS, Cd_0.5In_0.5S and In₂S₃ thin films have been determined using a ‘dc’ two probe method, in the temperature range of 300–450 K. The electrical resistivity values have been calculated at 300 K.     

Microstructure and electrical properties of (Na<Subscript>1.015−x</Subscript>K<Subscript>x</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

In order to obtain the morphotropic phase boundary (MPB) and good piezoelectric properties, lead-free (Na_1.015−xK_x)NbO₃ (x = 0.32–0.35) piezoceramics were synthesized by conventional solid state sintering. The x-ray diffraction results show that the lattice parameters of the monoclinic primitive cell peak at x = 0.34. The scanning electron microscopy and energy dispersive spectroscopy reveal that the excess sodium may be an important reason for the abnormal growth of the grains larger than 20 μm. All the samples exhibit double-like hysteresis loops and it may also be attributed to the excess Na⁺. Although the salient microstructure was found in the studied range, the piezoelectric and ferroelectric properties changed slightly with increasing x from 0.32 to 0.35. The values of piezoelectric coefficient d ₃₃ obtained in this study are as high as about 75 pC/N which is close to that of normally prepared (Na_0.5K_0.5)NbO₃ ceramics with MPB structure.     

Magnetism in BiFe<Subscript>1−x</Subscript>Ni<Subscript>x</Subscript>O<Subscript>3</Subscript>: studied through electron spin resonance spectroscopy

The effect of Ni doping in BiFe_1?xNi_xO₃ (BFNO) multiferroics are studied by X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), hysteresis loop (M–H), temperature dependent magnetization (FC-ZFC) measurements and electron spin resonance (ESR) techniques. The XRD and FTIR studies indicate that the BFNO compounds remain in rhombohedral (R3c) phase without appearance of any structural transformation due to Ni doping. The XPS studies show the oxidation states of Fe ions as 3⁺, whereas Bi is found to be in a mixed valence state of 2⁺ and 3⁺ in BFNO. The Ni ion doping enhances the saturation magnetization from 0.179 emu/g (x?=?0.025) to 2.38 emu/g (x?=?0.20), which is higher than the reported values found in literature. The FC-ZFC magnetization studies suggest the presence of a magnetic phase transition from a weak ferromagnetic to a spin glass state at low temperature. The ESR studies confirm the ferromagnetic state of BFNO samples.     

Microstructure and properties of the Ba<Subscript>0.75−x</Subscript>Ca<Subscript>x</Subscript>La<Subscript>0.25</Subscript>Fe<Subscript>11.6</Subscript>Co<Subscript>0.25</Subscript>Ti<Subscript>0.15</Subscript>O<Subscript>19</Subscript> hexaferrites

In the case of Ti⁴⁺ remain unchanged, the Ca²⁺ substituted Ba_0.75?xCa_xLa_0.25Fe_11.6Co_0.25Ti_0.15O₁₉ (0?≤?x?≤?0.05) were prepared by conventional solid-state reaction method at temperature of 1280 °C. A ball-to-power weight ratio of 10:1. Their crystal structure and magnetic properties were mainly investigated. The results show that the single magnetoplumbite phase structure transformed into the multiphase structure. Meanwhile, the small amount of α-Fe₂O₃ phase existed in M-type phase. The micrographs were observed by a field emission scanning electron microscopy (SEM). Vibrating sample magnetometer (VSM) was used to analyze the magnetic properties. The saturation magnetization (M _s ) first increases then decreases when x from 0 to 0.03. But, when x from 0.03 to 0.05, the saturation magnetization (M _s ) first increases then decreases too. The maximum value is at x?=?0.04 (M _s ?=?70.73 emu/g). The value of coercivity (H _c ) first increases then decreases when x from 0 to 0.04. But, the value increased when x from 0.04 to 0.05. The maximum value is at x?=?0.02 (H _c ?=?1691 Oe).     

Electrical properties of B site substituted (K<Subscript>0.48</Subscript>Na<Subscript>0.52</Subscript>)(W<Subscript>2/3</Subscript>Bi<Subscript>1/3</Subscript>)<Subscript>x</Subscript>Nb<Subscript>1−x</Subscript>O<Subscript>3</Subscript> piezoceramics

Lead-free (K_0.48Na_0.52)(W_2/3Bi_1/3)_xNb_1−xO₃ (KNN-WBi) piezoceramics with x ranging from 0.004 to 0.010 were synthesized by conventional ceramic processing. The sintered KNN-WBi ceramics showed perovskite structure without detectable secondary phase containing W and Bi. With increasing x, the orthorhombic-tetragonal phase transition temperature (T _O-T) decreased from 200 to 184 °C whereas, the tetragonal-cubic phase transition temperature (T _C) decreased slightly. With the doping of (W_2/3Bi_1/3), the piezoelectric properties were greatly improved and the piezoelectric constants d ₃₃, k _p, Q _m exhibited maximum values of 136 pC/N, 43.3% and 175, respectively at x = 0.008. The KNN-WBi ceramics also exhibited good ferroelectric properties with remnant polarizations P _r higher than 25 μC/cm² and coercive fields E _c lower than 1,000 V/mm. The results strongly suggest that the B site doping of constructed quinquevalent element is an effective method for the investigation of potassium sodium niobate system.     

La<Subscript>1−x</Subscript>Ag<Subscript>x</Subscript>FeO<Subscript>3</Subscript>/halloysites nanocomposite with enhanced visible light photocatalytic performance

La_1?xAg_xFeO₃/halloysites nanotubes (HNTs) nanocomposite was synthesized by sol–gel method. It was characterized by X-ray diffraction, transmission electron microscope, Fourier transform infrared spectroscopy and UV–visible diffused reflectance spectroscopy measurements. The photo-activity of the La_1?xAg_xFeO₃/HNTs nanocomposite was evaluated via degradation of methylene blue (MB) under visible-light irradiation. The results showed that the HNTs with unique pore structure favored the adsorption of organic molecules. Adequate Ag⁺ doping improved the absorption ability for visible light. The La_0.95Ag_0.05FeO₃/HNTs demonstrated the best photocatalytic performance, which achieved as high as 99 % for MB degradation exposed 2 h irradiation. However,further increasing of Ag⁺ doping gradually reduced the photocatalytic activity. The nanocomposite catalyst showed outstanding recyclability after eight cycles which still remained up to 90 %.     

Microstrucutre and thermoelectric properties of rapidly prepared Sn<Subscript>1−x</Subscript>Mn<Subscript>x</Subscript>Te alloys

Sn_1?xMn_xTe (x?=?0, 0.09, 0.15, 0.20) bulk materials were prepared by melt spinning combined with spark plasma sintering process. Nanoscale grains were obtained, and the solid solubility of Mn was much enhanced by the ultrafast-cooling synthesis technique. The maximum of Seebeck coefficient and power factor are 242 µVK^?1 and 19.97 µW cm^?1K^?2 at 873 K with the doping concentration of 15 at% Mn. A large amount of grain boundaries and doped atoms improve the scattering of heat-carrying phonons in a wide range of frequencies, and the scattering mechanisms are also explained by theoretical calculation. As a result, the minimum of lattice thermal conductivity is 0.66 µVK^?1 at 873 K, the corresponding figure of merit is 1.26 for Sn_0.85Mn_0.15Te sample. This value is improved by 35% comparing with previously reported result. Our work indicates that melt spinning process is effective to develop SnTe related thermoelectric materials with excellent thermoelectric properties, which has the widespread commercial value and the prospects for development.     

Magnetic Properties of CuTi<Subscript>2−2<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>4</Subscript> Materials

The magnetic properties of semi-conductor CuTi_2−2x Cr_2x S₄ systems have been studied. The nearest neighbour J ₁(x) and the next-neighbour super-exchange J ₂(x) interactions are evaluated by using the mean field theory for this spinel CuTi_2−2x Cr_2x S₄ system. The magnetic energy, the intraplanar and the interplanar interactions are deduced. The high-temperature series expansion (HTSE) combined with the Padé approximants method (PA) is applied to this spinel system to determinate the magnetic phase diagrams, i.e. T _C versus dilution x. The critical exponents associated with the magnetic susceptibility (γ) and with the correlation length (ν) are deduced in order phase.     

Investigation on the Current Transport Characteristics of SrTiO<Subscript>3</Subscript>/YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−x</Subscript> Heterostructure

By the combined use of the sol-gel and pulsed laser deposition methods, the SrTiO₃/YBa₂Cu₃O_7?x (STO/YBCO) heterostructure was prepared on a LaAlO₃ substrate. XRD results and φ scanning test showed that the prepared STO/YBCO heterostructure had good biaxial texture. Moreover, a Pt electrode was sputtered on the STO/YBCO heterostructure to investigate the current density-voltage (J ? V) characteristic curves of STO/YBCO in the 50–300 K temperature range. The results showed that the STO/YBCO heterostructure had good rectifying characteristics. With an applied positive bias voltage smaller than 3.7 V, the current density of the STO/YBCO heterostructure decreased with the decrease of temperature; for higher voltages, on the contrary, the current density increased with the decrease of temperature. When the YBCO experienced superconducting transition, the turn-on voltage (V _t) changed suddenly due to the sudden opening of the superconducting energy gap of YBCO. The V _t variation obtained from the experiment was essentially consistent with the known value of the YBCO superconducting energy gap.     

Effects on dielectric and magnetic properties of Cr-doped Bi<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>Fe<Subscript>1−x</Subscript>Cr<Subscript>x</Subscript>O<Subscript>3</Subscript> ceramic

In this paper, Cr-doped Bi_0.9Ba_0.1Fe_1?xCr_xO₃ (x = 0.00, 0.05, 0.10, 0.15, 0.20) ceramic materials were prepared by traditional state solid synthesized method, and the effects of Cr³⁺ ion on magnetic and dielectric properties were investigated. All samples showed BiFeO₃ phase formation were successful synthesized. The SEM images showed the shape of samples changed from regular to irregular shape. With increasing of Cr²⁺ ions, Saturation magnetization (M _s) increased from 5.24 to 8.6 emu/g, and then decreased to 7.31 emu/g, and coercivity (H _c) increased from 110.66 to 256.49 Oe. All the samples showed high dielectric constants at low frequency and the values of dielectric constants decreased slightly with frequency increasing. Delectric loss (tanδ) values kept a steady in a wide range frequency of 10–600 MHz. They ranged in tanδ from 0.01 to 0.07, which was a low dielectric loss in Bi_0.9Ba_0.1Fe_1?xCr_xO₃ ceramics.     

Influence of Dy-doping on ferroelectric and dielectric properties in Bi<Subscript>1.05−x</Subscript>Dy<Subscript>x</Subscript>FeO<Subscript>3</Subscript> ceramics

Bi_1.05−xDy_xFeO₃ (BDFO) (x = 0−0.2) ceramics were synthesized by solid-state reaction method. The influence of Dy dopant on crystal structural, dielectric and ferroelectric properties was investigated. The lattice parameter and the Curie temperature of BDFO were degraded continuously with increasing contents of Dy³⁺ cations. Leakage current density, ferroelectric polarization and dielectric loss were improved by appropriate Dy doping. When x = 0.1, BDFO showed the best electric properties. At applied electric field of 53 kV/cm, the remnant polarization (2P _r ) was 12.2 μC/cm².These improvements in electric properties in BDFO ceramics could have resulted from the relatively low oxygen vacancy concentration and structural distortion.     

Y<Subscript>3−x</Subscript>Gd<Subscript>x</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript>: controlled synthesis,characterization and investigation of its magnetic properties

Gadolinium substituted yttrium iron garnet (Gd: YIG: Y_3?xGd_xFe₅O₁₂ where x?=?0, 0.25, 0.5, 0.75, 1, 1.25, 1.5) nanopowders were synthesized by microwave hydrothermal method. Phase structure of synthesized powders was examined using fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) which revealed a cubic garnet structure. Spherical-like morphology of synthesized powders was confirmed by field emission scanning electron microscopy (FESEM) studies. The synthesized powders were sintered at 1100?°C for 60 min using microwave furnace and characterized by using XRD and FESEM. Magnetic properties such as saturation magnetization and Curie temperature were measured using vibration sample magnetometer (VSM) and differential scanning calorimetry (DSC) studies respectively. Temperature stability of magnetization was measured using pulse magnetometer and complex permeability was measured over a frequency range of 100 kHz–1.8 GHz. The obtained results showed that the saturation magnetization as well as permeability decrease while curie temperature and temperature stability increase with Gd concentration. It is concluded that substitution of Gd makes the YIG better microwave magnetic material, which may be used in high power non-reciprocal microwave devices in the microwave region.     

Synthesis of Cu<Subscript>2</Subscript>ZnSn(S<Subscript>x</Subscript>Se<Subscript>1−x</Subscript>)<Subscript>4</Subscript> thin films directly on transparent conductive glass substrates by solvothermal method

In this paper, the single-step solvothermal method was proposed to grow directly Cu₂ZnSn (S_xSe_1?x)₄ (CZTSSe) thin films on FTO substrates. The composition ‘x’ was varied by changing the molar ratios of thiourea to selenourea in the precursor solutions. The effects of the molar ratios of thiourea to selenourea on the structure, morphology and optical properties of CZTSSe thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electronic microscopy, energy dispersive spectrometry and UV–Vis spectrophotometry. The results indicated that CZTSSe thin films are composed of a large number of uniform sphere-like particles, and the diameter of particles varies from 600 to 280 nm when the molar ratios is changed from 1 to 0. The major XRD diffraction peaks shift towards lower diffraction angles, the Raman peak position of A1 mode of CZTSSe thin films moves consecutively towards the lower frequency due to the S replacement by Se. CZTS and CZTSe thin films are single kesterite structure, however, CZTSSe thin films are mixture structure of kesterite and wurtzite. By varying the molar ratios of thiourea to selenourea in the precursor solution, the atom ratios of S/Se in CZTSSe NCs thin films can be well controlled over the whole range, resulting in tunable optical band gap from 1.54 to 1.38 eV.