Synthesis and optical properties of novel mixed-metal cation CsPb1−xTixBr3-based perovskite glasses for W-LED

In this report, a mixed-metal cation-based halide perovskite (HP) CsPb_1−xTi_xBr₃ quantum dots (QDs) were first embedded in the B–Si–Zn glasses using a traditional approach of melt quenching and heat treating. A battery of test results such as photoluminescence, X-ray diffraction, and time-resolved attenuation prove that Ti ions do not destroy the properties of CsPbBr₃, and they are successfully doped into CsPbBr₃. At the same time, the doping of Ti ions also reduces the toxicity of lead. By altering the ratio of Pb/Ti, we determined the optimum ratio of CsPb_0.7Ti_0.3Br₃ QDs through experimental data. Due to the excellent optical properties and stability of CsPb_0.7Ti_0.3Br₃ QDs glass, it was designed to construct the white-light emitting diode device with tunable color coordinate, color rendering index, correlated color temperature, and a high luminous efficiency compared with CsPbBr₃ QDs glass, which may be a promising candidate for the field of lighting and displays.     

Effect of gallium addition on physical and structural properties of Ge–S chalcogenide glasses

GeS_2.5 chalcogenide glass was selected for studying effects of Ga addition on physical and structural properties. Glassy and partially crystallized samples of (100−x)GeS_2.5−xGa (5 mol% ≤ x ≤ 40 mol%) were prepared, and their thermal and optical properties were characterized. With increasing Ga content (x), values of T_g and optical band gap of glasses initially increased and then decreased, showing a maximal value at x = 25 mol%, that is, with stoichiometric composition of 85.7GeS₂·14.3Ga₂S₃. These changes were discussed and correlated to evolution of network structure, which was investigated by Raman spectra recorded in glassy matrices of (100−x)GeS_2.5−xGa (5 mol% ≤ x ≤ 40 mol%). This work contributes to understanding of composition–structure–property relationship of chalcogenide glasses.     

Microhardness and optical property of chalcogenide glasses and glass-ceramics of the Sn–Sb–Se ternary system

The microhardness of chalcogenide glasses (ChGs) of the Sn–Sb–Se (SSS) ternary system was investigated, and the correlation of microhardness with the mean coordination number of the SSS ChGs was determined. To prepare infrared-transparent SSS glass-ceramics (GCs), two SSS ChGs (A, Sn_6.23Sb_14.11Se_79.66; B, Sn_9.8Sb_17.22Se_72.98; by molar composition) were selected and thermally treated at 433 and 448 K, respectively. The improved microhardness (with values that increased by 11.5% and 7.3% for SSS ChG A and B, respectively) of the resulting SSS GCs is attributed to the formation of Sb₂Se₃ nanocrystals.     

Nanocrystallization of α-CsPbI3 perovskite nanocrystals in GeS2-Sb2S3 based chalcogenide glass

Black α-phase CsPbI₃ of cubic perovskite structure receives intense attentions recently for its unique combination of high photoluminescence quantum yield, suitable bandgap, and long lifetime. However, α-CsPbI₃ presents poor chemical and thermodynamic stability under atmosphere condition. Here, we report a strategy for confining the α-CsPbI₃ perovskite into chalcogenide glassy matrix through controllable glass nanocrystallization. In the chalcogenide glass with an elaborately designed composition of 80GeS₂·16Sb₂S₃·4CsPbI₃, spherical α-CsPbI₃ nanocrystals were formed and observed clearly, which present good red photoluminescence centered at 701 nm. With the increasing heat-treated temperature, the size of α-CsPbI₃ nanospheres increases, while the crystal quantity decreases. It is found that the nanocrystallization of α-CsPbI₃ nanospheres in chalcogenide glass is controlled by Ostwald-ripening process.     

Composition dependence of specific heat in Se80 − x Te20Sn x chalcogenide glasses

Differential Scanning Calorimetry (DSC) is performed at different heating rates under non-isothermal conditions to study the specific heat studies of glassy Se_{80 ? x} Te₂₀Sn _x (0 ≤ x ≤ 10) alloys. An extremely large increase in the specific heat values has been observed at the glass transition temperature. It has also been found that the values of C _p below glass transition temperature (C _pg ) and after glass transition (C _pe ) are highly composition dependent. This indicates that the Sn additive used in the present study influences the structure of the glassy Se₈₀Te₂₀ alloy. The results show that C _p values reveal local extrema in Se-Te-Sn glassy system at x = 4 and x = 8. The composition dependence of both parameters (C _pe and C _pg ) has been explained in terms of the glassy structure of Se-Te-Sn system.     

Influence of Fe3+-doping on optical properties of CeO2−y nanopowders

Ce_1?xFe_xO_2?y (0≤x≤0.05) nanopowders were synthesized using hydrothermal method at low calcination temperature and low doping regime. Structural and morphological characterization has been carried out by the X-ray diffraction method and non-contact atomic force microscopy. Vibrational properties were investigated by Raman spectroscopy. It was observed that the content of oxygen vacancies increased significantly with Fe doping up to 3 mol%. For higher dopant concentration, phase separation was detected. The optical properties of pure and Fe³⁺-doped CeO_2?y samples were investigated by spectroscopic ellipsometry. Several analytical models were applied to analyze the optical absorption onset of ceria defective structure. It was found that, Cody–Lorentz model most suitably described the sub-band gap region of CeO_2?y nanopowders and consequently gave more accurate band gap values, which are closer to the direct band gap transitions than to the indirect ones. The increased content of localized defect states in the ceria gap and corresponding shift of the optical absorption edge towards visible range in Fe-doped samples can significantly improve the optical activity of nanocrystalline ceria.     

Microstructural and optical properties of SnO2–ZnSnO3 ceramics

This work deals with some physical investigation on SnO₂–ZnSnO₃ ceramics grown on glass substrates at different temperatures (450 °C and 500 °C). Structural and optical properties were investigated using X-Ray diffraction (XRD), Raman, infrared (IR) absorption (FTIR), UV–visible spectroscopy and Photoluminescence (PL) techniques. XRD results revealed the existence of a mixture of SnO₂/ZnSnO₃ phases at different annealing temperatures. Structural analysis showed that both phases are polycrystalline. On the other hand, the optical constants (refractive index, extinction coefficient and the dielectric constants) have been obtained by the transmittance and the reflectance data. The optical band gap energy changed from 3.85 eV to 3.68 eV as substrate temperature increased from 450 °C to 500 °C. Raman, FTIR modes and PL reinforced this finding regarding the existence of biphasic (SnO₂ and ZnSnO₃) which is detected also by X-Ray diffraction analysis. Finally, the Lattice Compatibility Theory was evoked for explaining the unexpected incorporation of zinc ions in a rhombohedral structure within SnO₃ trigonal lattice, rather than the occupation of SnO₂ available free loci. All the results have been discussed in terms of annealing temperature.     

Structural and magnetic properties of Yb1−xSrxMnO3

The structural and magnetic properties of YbMnO₃ and Yb_0.82Sr_0.18MnO₃ multiferroics were studied by neutron powder diffraction (NPD), magnetometry and electron spin resonance (ESR) technics in a wide temperature range. Neutron diffraction measurements showed that the substitution of ytterbium ions with strontium ions in hexagonal h - YbMnO₃ (space group P6₃cm) leads to the destabilization of the crystal structure of the last compound and appearance of the mixture of three phases with different structure: hexagonal phase h - Yb_0.95Sr_0.05MnO₃ (space group P6₃cm), orthorhombic phase o - Yb_0.69Sr_0.31MnO₃ (space group Pbnm), hexagonal phase SrMnO₃ (space group P6₃cm). This fact was proved by the ESR measurements in which a several signals due to the phases of different structure were observed. NPD measurements showed that the magnetic structure of h - Yb_0.95Sr_0.05MnO₃ phase is similar to the magnetic structure of the pure h - YbMnO₃ and demonstrate the presence of the antiferromagnetic ordering in the samples. ESR and magnetization measurements of h - YbMnO₃ sample proved the presence of the antiferromagnetic correlations and also they showed the appearance of the ferromagnetically correlated nanoregions.     

Catalytic properties of SrSn1−xSbxO3 in methanol oxidation

Ceramic model catalyst materials of general formula SrSn_1–x Sb _x O₃ are synthesised by solid state reaction. X-ray diffraction shows the materials to be single phase over the composition range 0 x0.085, with a second phase, identified as SrSb₂O₅, being produced at higher antimony doping levels. XPS, Auger electron spectroscopy and valence band photoemission show strong segregation of Sb to the surface of the material even within the single phase regime. The catalytic properties of the materials are examined using methanol oxidation as a test reaction. The activity and selectivity to formaldehyde production shown by these materials is found to be strongly correlated with the attainment of the bulk solubility limit of Sb in the SrSnO₃ perovskite host.     

Structural,optical, and thermodynamic properties of an LiCa2Mg2As3xV3−3xO12 solid-solution garnet

A series of LiCa₂Mg₂As_3xV_3−3xO₁₂ garnet powders (x = 0, 0.25, 0.50, 0.667, 0.75, and 1) were synthesized using solid-state reaction from mixed precursor powders. A complete solid-solution series was found between the endmembers. Energy-dispersive spectroscopy confirmed the homogeneity of the synthesized garnets. The compositions reversibly melted between 1000 and 1160°C and had low sintering temperatures between 650 and 900°C. Thermal diffusivity, heat capacity, thermal conductivity, density, lattice parameter, thermal expansion, index of refraction, and dispersion were measured from room temperature to 800°C.     

Growth and optical properties of ZnO–In2O3 heterostructure nanowires

ZnO–In₂O₃ heterostructure nanowires were grown on a Si (111) substrate using the thermal evaporation method. Scanning electron microscopy results showed that the ZnO nanowires had spherical caps. The X-ray diffraction (XRD) pattern and energy-dispersive X-ray (EDX) spectrum indicated that these caps were In₂O₃. An analysis of the early growth process revealed that indium oxide might have played a self-catalytic role. Therefore, it was plausible that the vapor–liquid–solid mechanism (VLS) was responsible for the growth of the ZnO–In₂O₃ heterostructure nanowires. The optical properties of the products were characterized using a photoluminescence (PL) technique. The PL results for the ZnO–In₂O₃ heterostructure nanowires showed a strong peak in the ultraviolet region as a result of the near band emission and a negligible peak for the visible emissions that occurred as a result of the defects. Based on these PL results, it was found that the In₂O₃ nanostructures not only introduced the caps at the tips of the ZnO nanowires but also partially passivated the nanowire surfaces, leading to an improved near band edge emission and the suppression of the defect luminescence.     

Structural and electric properties of polycrystalline Bi1−xErxFeO3 ceramics

Polycrystalline Bi_1?xEr_xFeO₃ ceramics were synthesized by the solid state reaction method followed by rapid liquid phase sintering. The effects of Er substitution on the structure, morphology and electrical properties of the BiFeO₃ multiferroic ceramics were investigated. X-ray diffraction and Raman studies reveal that the structure of BiFeO₃ is changed from rhombohedral to orthorhombic in the Er concentration range of 0.10–0.15, and the impurity phases decrease both due to Er substitution. The X-ray photoelectron spectroscopy shows that Fe²⁺ could be suppressed by Er substitution. The SEM investigations suggest that the Er substitution could significantly reduce the grain sizes and increase the density of the samples. The leakage current is found to be decreased with increasing Er concentration. The dielectric and ferroelectric measurements show that dielectric constant, dielectric loss and ferroelectric properties are strongly dependent on the Er concentration. Er substitution can significantly improve the dielectric constant and remnant polarization, and decrease the dielectric loss by reducing the leakage current.     

Control of oxygen deficiency in Ca1−x La x MnO3−δ and its cathodic properties in alkaline solution

Ceramic samples of composition Ca_0.9La_0.1MnO_3– having various oxygen contents were prepared by a quenching method under nitrogen atmosphere. As the 3 – value decreased from 2.97 to 2.79, the sample conductivity decreased from 10² to 10^–1 S cm^–1. The porous ceramic samples showed good properties as cathode materials in alkaline solution without using conductive material such as graphite, but the discharge capacity decreased with decreasing sample conductivity. The discharge termination is explained by a simple model considering dissipation of the conductive path (high conductivity core) present in the porous sintered ceramic.     

Thermoelectric properties and figure of merit of perovskite-type Sr1−xLaxSnO3 ceramics

The thermoelectric properties of perovskite-type Sr_1−xLa_xSnO₃ ceramics with x=0.01–0.05 were evaluated from the Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ measured at high temperatures. The La-doped ceramics were n-type semiconductors exhibiting thermally activated electrical conduction behaviors in the temperature range of 473–1073 K. Eelectron carriers were introduced into the conduction band from doped La atoms up to x=0.03, which was the solubility limit of La at Sr site. The temperature dependence of the κ values for the ceramics was unaffected by both the La content and the microstructures. Estimations of the electronic thermal conductivities by the Wiedemann-Franz law revealed that the phonon thermal conductivities were dominant for all ceramics. The dimensionless figure of merit ZT increased with increasing temperature for all ceramics and reached 0.02–0.05 at 1073 K. In contrast to cubic Ba_1−xLa_xSnO₃ ceramics, bending of the Sn–O–Sn bonds due to octahedral tilting distortion in Sr_1−xLa_xSnO₃ lowered the electron mobility, decreasing the power factor S²σ and ZT values, although it effectively reduced the phonon mean free path, decreasing the κ values.     

Cd-composition induced effects on structure,optical and electrical properties of sputtered Zn1−xCdxO films

Zn_1−xCd_xO films with different Cd contents (0≤x≤1) were successfully deposited on quartz substrates by the direct current reactive magnetron sputtering and post-annealing techniques. It was found that structures, band gaps and electrical properties of the films can be tuned by changing Cd contents x. The Zn_1−xCd_xO film consists of wurtzite phase with highly (002)-preferred orientation at x from 0 to 0.2, mixture of wurtzite and cubic phases at x=0.5, and cubic phase with highly (200)-preferred orientation at x≥0.8. The band gap decreases from 3.25 eV at x=0 to 2.75 eV at x=0.2 for the wurtzite Zn_1−xCd_xO, and decreases from 2.52 eV at x=0.8 to 2.42 eV at x=1, which has a little change for cubic Zn_1−xCd_xO. In addition, Hall measurement results indicate that the influence of Cd content on the conduction behavior of Zn_1−xCd_xO films is significant. The chemical compositions and the bonding states of Zn_1−xCd_xO films were examined by X-ray photoelectron spectroscopy analysis.     

Nonlinear optical properties of (1−x) CaFe2O4–xBaTiO3 composites

In this paper, we report nonlinear optical properties of a composite nanostructure with the general formula (1−x) CaFe₂O₄–(x) BaTiO₃ (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) prepared by sol–gel and conventional solid-state reaction methods. Structural properties and chemical compositions of the samples were characterized using XRD and HRTEM. Basic optical constants, band gap energy and linear absorption coefficient were calculated through optical absorbance measurements. The nonlinear optical properties were investigated using the single-beam open aperture Z-scan technique. The obtained nonlinearity fits to Two-photon absorption process and all samples display high nonlinear absorption effect. The incorporation of BaTiO₃ into CaFe₂O₄ systems show a significant improvement in the nonlinear optical properties. These composite that exhibit efficient optical limiting can have potential applications in photonic devices.     

Elucidating the influences of Tantalum (V) oxide in Bi2O3–TeO2–ZnO ternary glasses: An experimental characterization study on optical and nuclear radiation transmission properties of high-density glasses

We report the optical and experimental gamma-ray and neutron attenuation properties of tantalum pentoxide reinforced Bi₂O₃–TeO₂–ZnO ternary glasses with a nominal composition of 10Bi₂O₃–70TeO₂-(20-x)ZnO-xTa₂O₅ (where x = 0,2,4, and 6 mol%). Measurements of transmittance and absorbance spectra for all of the synthesized samples are performed with Analytik Jena Specord 210 plus device between the range of 190–1100 nm. Moreover, ¹³³Ba and ²⁴¹Am/Be sources are utilized for experimental gamma-ray and neutron attenuation studies of BTZT glasses. According to results, the absorption edge is consistently moved from 380 nm to 390 nm as a result of ZnO/Ta₂O₅ translocation. In addition to decrease in optical band gap values of glass series, the fact that doping the structure containing Ta₂O₅ is lead to an increase in Urbach energies. The obtained irregularity through an increasing Ta₂O₅ additive is also changed the overall nuclear radiation attenuation properties of the BTZT glasses. The gamma-ray attenuation properties are obviously enhanced within the energy range of ¹³³Ba radioisotope. The attenuation properties against fast neutron emitted from ²⁴¹Am/Be were significantly enhanced through increasing Ta₂O₅ contribution. It can be concluded that BTZT6 glass sample may be regarded as a beneficial glass composition for multifunctional applications. It can be also concluded that ZnO/Ta2O5 translocation in Bi₂O₃–TeO₂–ZnO ternary glasses may be regarded as a monotonic tool where the neutron attenuation properties should be strengthened in addition to gamma attenuation properties.     

Changes in ordered structure and dielectric properties with the A-site and B-site cation ratios of complex perovskites (Sr1−xBax)(Sr0·33+yTa0·67−y)O3−δ

Complex perovskites with large-sized B′-site cations, (Sr_1−xBa_x)(Sr_0·33+yTa_0·67-y)O_3−δ (0 ≦ x ≦ 1, 0 ≦ y≦ 0·17), were fabricated to examine the transformation behavior between the (1:1) and (1:2) order types and dielectric property change with A-site cation substitution. The (1:2) type order was found to appear in a limited Ba-rich composition range. Structural strain induced by size difference between the A-site and large-sized B′-site cations might be responsible for the occurrence of the (1:1) type order in perovskite compounds substituted with more than 50% Sr²⁺ on the A-site sublattice. Low ε_r and positive temperature coefficient of ε_r observed for the (1:2) ordered samples were explained by the restricted ion movement in the (1:2) type order array.     

Thermal properties and elastic constants of ζ-Ta4C3−x

Thermal and elastic properties were measured for ceramics that contained as much as 96 wt% zeta phase tantalum carbide (ζ-Ta₄C_3−x). The ceramics were produced from tantalum hydride that was milled to reduce particle size and then blended with carbon. Powders were reaction hot-pressed at 1800°C for 2 hours under a flowing He environment, which resulted in ζ-Ta₄C_3−x that was about 99% dense. The main secondary phases present in the reacted ceramic were TaC and Ta₂O₅. ζ-Ta₄C_3−x had a thermal conductivity of 9.6 W/m·K and an electrical resistivity of 160 ± 4.2 μΩ-cm, which are lower and higher than those of TaC, respectively. The Young's modulus was 379 ± 5 GPa and the hardness was 5.1 ± 0.7 GPa, which are also both lower than TaC. This study is the first to report the thermal properties and elastic moduli of high-purity ζ-Ta₄C_3−x.