Aqueous germanate solution,alternative sol–gel precursor for preparation of Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> diluted magnetic semiconductors

The solids content and gelation time of aqueous germanate solution were examined in this work. Samples of 5, 10 and 20 mol% Mn doped Ge were prepared by using the aqueous germanate solution as a liquid Ge precursor. No second phase such as Mn₅Ge₃ was detected in the 5 and 10 mol% Mn doped samples, implying that Mn ions were uniformly diluted into the Ge host matrix. The 5 and 10 mol% Mn-doped Ge samples exhibit room-temperature ferromagnetic behaviors that are likely originated from the RKKY (Ruderman–Kittel–Kasuya–Yosida)-like interaction between the localized Mn ions in the Ge matrix. Therefore, the aqueous germanate solution can be an alternative sol–gel precursor for preparation of the Mn _x Ge_1−x diluted magnetic semiconductors (DMSs).     

Synthesis, structural and photocatalytic studies of Mn-doped CdS nanoparticles

Mn-doped CdS nanoparticles (Cd_1?x Mn _x S; where x = 0.00–0.10) were synthesized by a chemical precipitation method. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope (TEM), and UV–Vis spectrometer. The XRD and TEM measurements show that the size of crystallites is in the range of 10–40 nm. Optical measurements indicated a red shift in the absorption band edge upon Mn doping. The direct allowed band gaps of undoped and Mn-doped CdS nanoparticles measured by UV–Vis spectrometer were 2.3 and 2.4 eV at 400 °C, respectively. Photocatalytic activities of CdS and Mn-doped CdS were evaluated by irradiating the solution to ultraviolet light and taking methyl orange (MO) as organic dye. It was found that 5 mol% Mn-doped CdS bleaches MO much faster than undoped CdS upon its exposure to the ultraviolet light. The experiment demonstrated that the photo-degradation efficiency of 5 mol% Mn-doped CdS was significantly higher than that of undoped CdS.     

Facile ion-exchange synthesis of Gd-doped K2Ta2O6 photocatalysts with enhanced visible light activity

One of the well-known ways of increasing the visible light absorption capability of semiconducting materials is cation doping. This study aims to use Gd doping to tailor the bandgap energy of K₂Ta₂O₆ (KTO) for photocatalytic degradation of organic pollutants under visible light irradiation. Accordingly, the parent KTO and Gd-doped KTO with different Gd concentrations (K_2-3xGd_xTa₂O₆; x = 0.025, 0.05, 0.075 and 0.1 mol%) were synthesized by hydrothermal and facile ion-exchange methods, respectively. The powder XRD, FT-IR, SEM-EDS, TEM-SAED, N₂ adsorption-desorption, XPS, UV–Vis DRS, PL and ESR techniques were used to investigate the effect of Gd dopant concentration on the structural and photocatalytic properties of KTO. The photocatalytic activity of these samples was investigated for the photocatalytic degradation of methylene blue (MB) dye in an aqueous solution at room temperature under visible light irradiation. The experimental results show that all Gd-doped KTO samples exhibit enhanced photocatalytic activity compared with parent KTO toward MB degradation. In particular, Gd-KTO obtained by doping of 0.075 mol% shows the highest photocatalytic activity among the Gd-doped samples and the degradation efficiency of MB was 79% after 180 min of visible light irradiation, which is approximately 1.5 times as high as that by parent KTO (53%). In addition, trapping experiments and electron spin resonance (ESR) analysis demonstrated that the hydroxyl radicals (^?OH) have played a crucial role in the photocatalytic degradation of MB. The reusability and stability of Gd doped-KTO with a Gd content of 0.075 mol% against MB degradation were examined for five cycles. Based on the present study results, a visible light induced photocatalytic mechanism has been proposed for Gd0075-KTO sample.     

The magnetic polaron modulated luminescence bands of organic-inorganic hybrid ferroelectric anti-perovskite (C3H9N)3Cd2Cl7 doped with Mn2+

Recently, the excellent optical properties of organic-inorganic hybrid metal halides have attracted much attention in the optoelectronic field. However, their complicated preparation processes seriously influence their properties and applications. In this work, we developed a series of organic-inorganic hybrid metal halides (C₃H₉N)₃Cd₂Cl₇:x%Mn²⁺ with an antiperovskite structure with ferroelectrics in an early report, giving tunable emissions contemporarily with different manganese (Mn)²⁺ concentrations via a simple mechanochemical method. Meanwhile, their single crystals were also grown by a slow thermal evaporation method. The as-grown products with Mn dopants exhibited diluted magnetic semiconductor behavior and varied emission profiles by different excitation wavelengths, which could be modified by the heat treatment. All the emission bands come from the different magnetic polarons with enhanced electron-phonon coupling or self-trapped exciton formation. Ferromagnetic coupling Mn–Mn pairs or clusters in the doped lattice favor the magnetic polaron and red emission at room temperature and even give much stronger emission above room temperature. The excitonic magnetic polaron and local excitonic magnetic polaron were detected at about 309 nm and 398 nm, respectively, with Mn doping. Without Mn²⁺ dopant, the weak emission band at about 398 nm can also be detected from an intrinsically bound exciton or confined exciton from the amine incorporated metal chlorides. This Mn-doped anti-perovskite Cd halides may find applications in the solid display and lighting, as well as the magneto-optical devices.     

XAFS characterization of La1−xSrxMnO3±δ catalysts prepared by Pechini’s method

XAFS experiments at the Mn and Sr K-edges were carried out in order to investigate the short-range arrangement of Mn and Sr sites on La_1−xSr_xMnO_3±δ highly doped perovskites (x = 0, 0.2, 0.4 and 0.6). The Mn K-edge EXAFS spectra show a static Jahn–Teller distortion of the MnO₆ for x = 0 and 0.2, which is drastically reduced as x increases. The distortion of perovskite, characterized by the Mn–O–Mn tilt angle, progressively decreases with increasing Sr contents. Sr K-edge results indicated a decrease on the Sr–Mn coordination number upon Sr doping. Based on this and TPD results, a charge compensating mechanism is proposed suggesting a partial Mn oxidation and formation of Mn defect vacancies due to the introduction of Sr.     

Structure distortion and magnetism in double perovskites Ca2−xLaxFeReO6 (0≤x≤0.8)

The crystal structure and magnetism of Ca_2−xLa_xFeReO₆ (0≤x≤0.8) double perovskites have been investigated. The samples with low doping (x≤0.4) are found to crystallize with the monoclinic P2₁/n superstructure, while those in the high doping ones (x≥0.6) have orthorhombic Pbnm superstructure. With the increase of an La doping, the anti-site defects increases, giving rise to highly disordered samples at the Fe and Re positions. At the low doping region (x≤0.4), the compounds undergo a simultaneous structural and magnetic transition accompanying a slight increase of the Curie temperature. The increase of Curie temperature is discussed in terms of the structural change with doping.     

Lu掺杂AlN的电子结构和光学性质的第一性原理研究

为了探索 AlN在光电器件中的潜在应用,采用第一性原理计算了不同 Lu掺杂浓度(以原子分数 x表示)的 AlN(Al_1-xLu_xN)的电子结构和光学性质。研究结果表明,Al_1-xLu_xN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al_1-xLu_xN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al_1-xLu_xN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al_1-xLu_xN的光电导率在低能区随能量的增加而急剧增加。     

Anode performance of Mn-doped ceria–ScSZ for solid oxide fuel cell

The 70 wt.% Mn-doped CeO₂ (MDC)-30 wt.% Scandia-stabilized zirconia (ScSZ) composites are evaluated as anode materials for solid oxide fuel cells (SOFCs) in terms of chemical compatibility, thermal expansion coefficient, electrical conductivity, and fuel cell performance in H₂ and CH₄. The conductivity of MDC10 (10 mol.% Mn-doping), MDC20, and CeO₂ are 4.12, 2.70, and 1.94 S cm⁻¹ in H₂ at 900 °C. With 10 mol.% Mn-doping, the fuel cells performances improve from 166 to 318 mW cm⁻² in H₂ at 900 °C. The cell with MDC10–ScSZ anode exhibits a better performance than the one with MDC20–ScSZ in CH₄, the maximum power density increases from 179 to 262 mW cm⁻². Electrochemical impedance spectra indicate that the Mn doping into CeO₂ can reduce the ohmic and polarization resistance, thus leading to a higher performance. The results demonstrate the potential ability of MDC10–ScSZ composite to be used as SOFCs anode.     

Lu掺杂AlN的电子结构和光学性质的第一性原理研究

为了探索AlN在光电器件中的潜在应用,采用第一性原理计算了不同Lu掺杂浓度(以原子分数x表示)的AlN(Al_1-xLu_xN)的电子结构和光学性质。研究结果表明,Al_1-xLu_xN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al_1-xLu_xN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al_1-xLu_xN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al_1-xLu_xN的光电导率在低能区随能量的增加而急剧增加。     

Effects of dopant concentration and aging on the electrical properties of Y-doped ceria electrolytes

High purity cerium oxide and yttrium oxide were used to form ceria-based solid solution (Ce_1−xY_xO_2−δ, 0.05x0.4) via a conventional mixed-oxide method. All the samples used were aged at 1000 °C in air for 8 days. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ionic conductivity (i.e., grain interior (GI) grain boundary (GB) and total conductivities) in this system were systematically studied as a function of dopant content over the temperature range of 250–850 °C in air using an impedance spectroscopy. The lattice parameter decreased with increasing the Y content, but it did not obey Vegard's law. The Y doping had no significant effect on densification behavior and final sintered density, but leading to a significant decrease in grain size as compared to the undoped ceria. The composition x0.1 had a maximum GI conductivity, while a maximum total conductivity was observed at x0.15. A significant high-temperature aging effect was also found for the samples with higher Y doping levels. 10% and 15% decreases in the GI and GB conductivities, respectively, were detected in the aged Ce_0.7Y_0.3O_2−δ ceramic.     

Microstructure,dielectric and piezoelectric properties of (Pb1−xSrx)Nb1.96Ti0.05O6 ceramics

(Pb_1−xSr_x)Nb_1.96Ti_0.05O₆ with 2 wt% excess PbO (x = 0, 0.02, 0.04, 0.06, 0.08) piezoelectric ceramics with high Curie temperature were fabricated via the conventional solid state reaction method. Effects of Sr²⁺ amount on crystallite structure, microstructure, dielectric and piezoelectric properties were studied. The substitution of Sr²⁺ ions for Pb²⁺ ions is effective to lower sintering temperatures. X-ray diffraction patterns indicate that all ceramics form the single orthorhombic ferroelectric phase. The doping of Sr²⁺ ions facilitates improving densification of the ceramics. Grain size and lattice parameters of the ceramics vary with the change of the Sr²⁺ contents. Both Curie temperature and maximum dielectric constant change with increasing the Sr²⁺ amounts. The dielectric constant data were also studied using the Curie–Weiss law and modified Curie–Weiss law. The ceramic with x = 0.04 possesses excellent piezoelectric and dielectric properties, presenting a high potential to be used in high-temperature applications as piezoelectric transducers.     

Influence of different precursors and Mn doping concentrations on the structural,optical properties and photocatalytic activity of single-crystal manganese-doped ZnO

Mn-doped ZnO single-crystal micronuts were synthesized via hydrothermal method in an hexamethylenetetramine aqueous solution. These micronuts are of wurtzite crystal structure. The effects of Mn doping amount and precursor concentration on the structural, optical properties and photocatalytic activity have been investigated. The synthesized Mn-doped ZnO was characterized by X-ray powder diffraction, field emission scanning electron microscopy (FESEM), UV–Vis absorption and photoluminescence spectroscopy. The structural analyses based on X-ray diffraction revealed the absence of Mn-related secondary phases. According to FESEM results, the length of ZnO micronuts was in the range of 5–8 μm. The band gap energy increased on increasing Mn doping concentration. The photocatalytic activity was studied by degradation of methyl orange aqueous solution, which showed that the Mn-doped ZnO micronuts prepared in precursor concentration of 0.1 M and 4% Mn doping had the highest photocatalytic activity. The effects of crystal defect and band gap energy on photocatalytic activity of Mn-doped ZnO samples were studied in different precursors and Mn doping amounts.     

The calculated magnetic and optical properties of (Mn,N) Co-doped ZnS

Based on the density functional pseudo-potential method, the density of states, the magnetic and the optical properties of the Mn-doped and (Mn,N) co-doped ZnS are calculated. The calculation results indicate that (Mn,N) co-doping can realize more effective p-type doping than Mn-doped does. Both Mn-doping and (Mn,N) co-doping exhibit spin polarization states, which can realize 100% spin polarization of the carrier injection by transfer of effective masses. Compared with that of pure ZnS, the optical absorption edges of both Mn-doped and (Mn,N) co-doped ZnS make red shifts. The peak value of the reflection coefficient increases and the main reflection peaks move to the lower energy after doping. Meanwhile, the location of peaks move toward the direction of lower energy which corresponds to the sharp decline of reflection spectrum.     

Tuning magnetic,electronic, and optical properties of Mn-doped NiCr2O4 via microwave method

The main aim of the paper to the synthesis of Mn (x)-doped NiCr₂O₄ nanoparticles by varying Mn content (x = 0.00%, 0.01%, 0.02%, and 0.03%) by microwave method for correlating the effect of NiCr₂O₄ on structural, optical, and magnetic properties of the materials. Understanding the optical, magnetic, and structural properties of huge reservoir factors has essential applications in various aspects of materials science. Our study is to relate the reduction of grain size of Mn content in NiCr₂O₄ host material. The XRD results revealed that there was an apparent decrease in the characteristic peaks of Mn in the MnNiCr₂O₄ nanostructure. Particularly, the peak position of (2 2 0) and (3 1 1) planes was decreased. This decrease in peak position is attributed to the creation of defects or disorders due to the Mn ions in the chromite lattice structure. This inter-site Mn cation migration is responsible for the breaking of long-range cation order and the introduction of defects at both the T-site and O-sublattices site simultaneously.     

Ferroelectric and dielectric properties of bismuth-layered structural Sr2Bi4−xLnxTi5O18 (Ln=La, Nd, Sm and Dy) ceramics

La, Nd, Sm, and Dy-doped Sr₂Bi₄Ti₅O₁₈ (SBTi) ceramic samples have been prepared by the solid-state reaction method. The X-ray diffraction reveals that all of the ceramic samples are single phase compounds. Their remnant polarization (2P_r) increases at first, and then decreases with the increase of doping content. When doping content is 0.01, Sm and Dy-doped SBTi samples exhibit the maximum 2P_r of 18.2 and 20.1 μC/cm², respectively. While La and Nd-doped SBTi samples display the maximum 2P_r value of 18.4 and 19.1 μC/cm² with doping content of 0.05 and 0.10, respectively. The ferroelectric properties of Sr₂Bi_4−xLn_xTi₅O₁₈ are found to be dominated by the competition of the decrease of oxygen vacancy concentration and the relief of structural distortion.     

Dielectric relaxation,AC conductivity behavior and its relation to microstructure in mechanochemically synthesized Mn-doped CeO2 nanocrystals

A simple mechanical alloying process has been implemented to obtain cerium oxide nanocrystallites monodoped with transition metal element (Mn). The microstructural, compositional and crystallographic information are investigated by employing Rietveld refinement using X-ray diffraction (XRD) data, energy dispersive X-ray (EDX) pattern and analyzing high resolution transmission electron microscopy (HRTEM) images. The results reveal that the sample exhibits a single phase cubic fluorite-type Ce_0.95Mn_0.05O_2-δ structure. Rietveld analysis shows the coexistence of Ce³⁺ and Ce⁴⁺ ions in the sample. HRTEM image reveals the sheer plastic deformation on lattice planes. The frequency and temperature dependent electrical behavior of the undoped, Mn-doped and sintered samples are analyzed by impedance spectroscopy, dielectric relaxation and ac conductivity studies. The correlated barrier hopping (CBH) model has well explained the ac conduction mechanism. The release of electrons during the reduction of Ce⁴⁺ and/or Mn⁴⁺ ions to Ce³⁺ and/or Mn³⁺/Mn²⁺ ions by the exclusion of excess oxygen in the lattice are responsible for the electronic conductivity of the samples. The activation energy of the sintered sample is estimated both from relaxation and hopping processes and the estimated values ascertain that the charge carrier hopping process in the samples is accompanied by the dielectric relaxation.     

Citrate-gel synthesis and characterization of yttrium-doped multiferroic BiFeO<Subscript>3</Subscript>

Perovskite Bi_1−x Y _x FeO₃ (0.0 ≤ x ≤ 0.1) oxides were prepared by a citrate-gel method. The crystal structure examined by X-ray powder diffraction indicates that the samples were single-phase and crystallize in a rhombohedral (space group, R-3c no. 161) structure. The structural phase transition from rhombohedral to orthorhombic phase was observed at x = 0.10. Increase in magnetization was observed as a result of Y doping. The optical band-gap of (Bi, Y)FeO₃ materials were determined. The observed increase in magnetization and low band-gap of (Bi, Y)FeO₃ ceramics position them for potential magenotoelectric and photocatalytic applications, respectively.     

Untersuchungen an Beliten und Dicalciumsilicaten. II. Phasen-, Wertigkeits- und Reaktivitätsänderungen von Mn-dotiertem Ca2SiO4 bei thermischer Behandlung

Investigations on Belites and Dicalcium Silicates. II. On the Changes of Phases, Valency, and Reactivity during Heat Treatment of Mn-doped Ca₂SiO₄ Annealing of blue Mn-doped single crystals of Ca₂SiO₄ at T > 1450°C causes decolorization. The Mn profile in the crystals, formed during the process of crystal growth, vanishes. The experimental results suggest a causal connection between

• — the change of valency of the doping component (Mn)
• — its mobility between tetrahedral positions, and
• — the reactivity of the Ca₂SiO₄

and the phase transformation α′ _H → α of dicalcium silicate (Hedvall effect).     

Preparation and electrical properties of Nd and Mn co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

Ferroelectric thin films of Nd and Mn co-doped bismuth titanate, Bi_3.15Nd_0.85Ti_3−x Mn _x O₁₂ (BNTM) (x = 0–0.1), were fabricated on Pt/TiO₂/SiO₂/Si(100) substrates by a sol–gel technique. The BNTM films had a polycrystalline perovskite structure and uniform and dense surface morphologies. A lattice distortion was observed in the BNTM films due to Mn ion doping. The ferroelectric measurement of the films indicated that the values of coercive field (E _c ) decreased gradually with the increase of the Mn content (x), however, the remanent polarization (P _r ) increase firstly and then decrease with the increase of x. The sample with x = 0.05 had optimum electrical properties and a maximum 2P _r value. The 2P _r and 2E _c values of the film at a maximum applied electric field of 400 kV/cm were 38.3 μC/cm² and 180 kV/cm, respectively. Moreover, this BNTM capacitors did not show fatigue behaviors after 1.0 × 10¹⁰ switching cycles at a frequency of 1 MHz, suggesting a fatigue-free character. The main reason for the increase of the 2P _r and the decrease of the 2E _c might be attributed to the lattice distortion in BNTM films due to Mn ion doping.     

Enhanced photoluminescence properties of Gd (x-1) Sr x O: CdO nanocores and their study of optical,structural, and morphological characteristics

Synthesis of Gd doped Sr_x O: CdO (x = 1.4, 1.6, 1.8) nanostructures (NS) was achieved through the coprecipitation method by using CTAB (cetyl trimethyl ammonium bromide) with the purpose to investigate the effect of Gd doping on the optical, structural, morphological, and photoluminescence properties at room temperature. Mixed phase of tetragonal crystal structure verified via X-ray diffraction technique, no structural variation was observed except lattice distortion. Size of the crystallites (D), morphology studied by SEM (scanning electron microscopy) analysis, nanoparticles (NPs) crystalized roughly flake-like morphology with homogeneous particle distribution centered at ~ 78 nm, ~56 nm, ~65 nm, ~88 nm for pure and Gd _(x-1) doped Sr _xO: CdO nanostructure, respectively. Fourier transform infrared spectroscopic investigation (FTIR) revealed the presence of Gd–O–Gd, Cd–O, Sr–O, and OH peaks appeared at ~1321 cm ^?1, ~1550 cm ^?1, ~1400 cm ^?1–3300 cm ^?1 with small variation in vibration modes due to Gd doping. Optical absorptivity observed in the range of 325 nm–359 nm (redshifted) with absorption edges at 346 nm, 364 nm, and 380 nm for Gd _(x-1) doped Sr _xO: CdO nanostructure, respectively. This redshift on the bandgap was discussed in terms of new band levels below conduction band. The energy gap was calculated using Kubelka-Munk theory and was found to be in the range of 3.22 eV–2.61 eV. X-ray photoelectron spectroscopy (XPS) performed to determine chemical composition and binding energies of Gd 3d _3/2, Sr 3d _3/2, and Cd 3d _3/2, O1s, and C1s observed at 150.8 eV, 141.6 eV, 411.0 eV, 530.4 eV, and 285.6 eV indicating Gd⁺³ ion replaces Sr⁺² in all concentrations. Our results showed that Gd-doped Sr _xO: CdO nanoparticles exhibited enhanced photoluminescence (PL) properties in contrast to the pure Gd₂O₃ with Gd⁺³ randomly incorporated into crystal structure, probably in tetrahedral sites. The composition of Gd _0.6 doped Sr _x O: CdO NS exhibited photoluminescent emission spectra, peaks centered at 433 ± 3 nm, 449 ± 3 nm, and 469 ± 2 nm (λ _excitation = 318 nm) and for Gd _0.8 doped Sr _x O: CdO nanostructure showed broad emission peak at 412 ± 2 nm to 433 ± 2 nm (λ _excitation = 380 nm), which indicates a reduction in defects with an increase in Gd doping. The transitions can be ascertained with shielding of 4f shells of Gd ⁺³ ions by 6s, 5d shells by the interaction of other Gd ⁺³ ions.