Non-doped Samples Research Articles

The Photocatalytic Activity of TiO2 Nanotube Doped Zn for Methylene Blue Degradation

TiO2 nanotube (TiO2-NT) is one of the promising materials for photocatalytic water remediation. TiO2-NT doped Zn (Zn/TiO2-NT) is synthesized from P25 Degussa via one step hydrothermal method. From XRD and UV-DRS analysis, it showed that Zn as a doping material led to decrease band gap energy and decrease the crystallite size. The best results obtained was Zn/TiO2-NT with a crystallite size of 7.14 nm, and band gap energy value of 3.18 eV. Photocatalytic activity of Zn/TiO2-NT was also tested for photocatalytic activity of textile dye (methylene blue) degradation. During the photocatalytic activity for methylene blue degradation, the Zn/TiO2-NT shows higher activity compared to non-doped sample. The non-doped sample shows degradation activity of 87.72%, meanwhile the Zn/TiO2-NT shows degradation activity of 95.88%.

Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran on Alkali Doped Ru/C Catalysts. Electron Properties of Ruthenium Species as Descriptor of Catalytic Activity.

Selective aerobic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran has been achieved on alkali doped Ru/C catalyst. Optimization of Ru metal nanoparticles, as well as the nature and amount of the alkali dopant have been performed. The results showed that doping the Ru/C catalyst with controlled amount of potassium increases the catalytic activity, 2.5 fold with respect to the non-doped sample. Spectroscopic studies showed that these differences in activity can be attributed to a different oxidation reaction mechanism associated to the presence of electron rich Ru species in the promoted sample that facilitate the dissociation of O2, while prevents the oxidation of the metal. The Ru/C-K doped catalyst resulted very stable against leaching and metal sintering, being possible the reuse over several consecutive runs. Moreover, the catalyst could be successfully applied to the oxidation of different alcohols.

Introducing nano-scale MgO particles into RHQT Nb3Al superconducting wires to significantly improve the critical current density

This research introduced nano-scale particles into the RHQT Nb3Al superconducting wires, which was confirmed by TEM that nanoparticles with size of 5–25 nm distributed in the wires and might act as the extra flux pinning centers. The precursor wires were fabricated by powder in tube process with nano-sized MgO (n-MgO) doped in the raw powder. Uniform microstructure and chemical composition were obtained in the superconducting wires. Besides nanoparticles, high density stacking faults with spacing of 5–20 nm were observed in the Nb3Al superconducting wire, which acted as the dominant flux pinning centers. It had great importance that nanoparticles were introduced into the RHQT Nb3Al wires and combined with the high density stacking faults to significantly improve the critical current density (Jc) of the wires. The magnetic Jc results of 1 wt% n-MgO doped Nb3Al wire were about twice of the non-doped sample, corresponding to Jc values of 3.18 × 105 A/cm2, 2.38 × 105 A/cm2 and 1.72 × 105 A/cm2 at 4.2 K and 8 T, 10 T and 12 T.

The influence of Sc3+ doping on the crystal structure and electrical conductivity of Sr(Ti0.2Zr0.2Y0.2Sn0.2Hf0.2)O3-σ high-entropy perovskite oxides

High entropy materials offer optimal conditions for regulating and modifying new material properties due to their vast composition space. Through traditional solid phase sintering, this article successfully synthesized a series of Sr(Ti0.2Zr0.2Y0.2Sn0.2Hf0.2Sc0.2x)O3-σ high entropy perovskite oxides with varying Sc3+ doping concentrations and comprehensively investigated the microstructure morphology, crystal structure, and electrical conductivity of Sc-doped HEPs as well as their influence on oxygen transfer rate. The results demonstrate the successful incorporation of Sc3+ into the high entropy lattice, resulting in a transformation of the crystal to a positively cubic structure with enhanced reciprocity. While the lattice vibration of BO6 octahedron is weakened by the introduction of Sc3+, it has no impact on the phase stability of the crystal structure. Moreover, The results of the electrochemical impedance spectroscopy test demonstrate that at a temperature of 750 °C, with a doping amount of Sc3+ at 0.14, the conductivity (σ) of Sc3+ is measured to be 5.74 × 10−3 S/cm, exhibiting an increase of 61.7% compared to non-doped samples. Correspondingly, the activation energy (Ea) is reduced from 0.51 eV to 0.39 eV as well. This doping strategy effectively expands the potential applications of high entropy perovskite oxides in solid oxide fuel cells (SOFCs). These findings serve as a driving force for further investigation into high entropy ceramics of the strontium series that exhibit optimal properties.

Unexpected Potential Dependent HER Behaviors of Cationic Phosphorus Doped WO3 Nanosheets

TMOs are generally considered as catalytically inert for hydrogen evolution reaction (HER).[1] This unique property has promoted a wide variety of applications of TMOs, such as aqueous-based lithium ionic batteries, electrochromic smart windows, electrocatalysts and/or catalyst supports. However, hydrogen evolution as an undesired side reaction is commonly observed when they are used in aqueous-based supercapacitors and battery applications.[2] The unexpected HER mechanism for intrinsic TMOs has not been studied until very recently by McKone and Mpourmpakis groups.[3] With careful theoretical calculations, they clearly demonstrated that intrinsic WO3 is not HER active. Bulk hydrogen (H) intercalation into WO3 is a prerequisite for its catalytic activity toward HER. Applying electrochemical potential to WO3 primarily sets the bulk H stoichiometry of thus formed hydrogen bronzes HxWO3. The level of intercalation (x), precisely to say, the density of the intercalated hydrogen in the WO3, in turn determines the formation of W-H*, the bonding strength of W-H*, and their consumption to H2 (HER). Significant HER is only seen at potentials negative enough when x > 0.5. Beyond this intercalation level, HER is no longer dictated by potential-dependent activation energies, instead, is controlled by the density of the hydrogen intercalation on the surface of WO3 catalysts. In line with this extensive theoretical study, Augustyn group very recently experimentally demonstrated the dependence of HER activity of WO3 materials on their electrochemical insertion characteristics.[4] By including crystal water between the WO3 sheets, proton intercalation is greatly facilitated likely with a Grotthuss mechanism. Accordingly, the HER kinetics is largely improved with a large positive shift of the HER on-set potential. On the other hand, by inclusion of molecular pillars in the WO3 lattice to physically block proton intercalation, the HER activity of WO3 was largely inhibited. Recently, we developed a facile approach to cationically dope WO3 nanosheets with red phosphorus. The proton interaction and the associated HER behavior as a function of electrochemical potentials were carefully studied with multiple electrochemical techniques. Interestingly, we found that proton interaction is largely suppressed even without including molecular pillars in the P-doped WO3 lattice. At lower intercalation levels before the so-called “potential independent regime”, the HER kinetics is largely decreased, as expected, compared to the non-doped WO3 control sample. While in the “potential independent regime”, the HER kinetics is largely enhanced. Furthermore, including alkaline metal ions into the electrolyte, the HER kinetics is further suppressed as demonstrated by largely negatively shifted onset potentials and the increased Tafel slopes. Interestingly, in the “potential independent regime”, the HER kinetics is further drastically enhanced. Extensive structural characterization and theoretical calculations are undergoing to reveal the mechanism behind these interesting tunable potential dependent - proton interaction and HER behavior, which will be reported in this work. Understanding how heteroatomic doping could modulate proton interaction and HER behaviors of TMOs at atomic levels would provide practical guidance for designing more efficient and selective electrochemical catalysts for various catalytic reduction reactions, such as carbon dioxide reductions and nitrogen/nitrate reductions to valuable compounds.[1] Zhang, S.; Zhang, X.; Rui, Y.; Wang, R.; Li, X., Recent advances in non-precious metal electrocatalysts for pH-universal hydrogen evolution reaction. Green Energy & Environment 2021, 6 (4), 458-478.[2] Wang, R.; Mitchell, J. B.; Gao, Q.; Tsai, W.-Y.; Boyd, S.; Pharr, M.; Balke, N.; Augustyn, V., Operando Atomic Force Microscopy Reveals Mechanics of Structural Water Driven Battery-to-Pseudocapacitor Transition. ACS Nano 2018, 12 (6), 6032-6039.[3] Miu, E. V.; McKone, J. R.; Mpourmpakis, G., The Sensitivity of Metal Oxide Electrocatalysis to Bulk Hydrogen Intercalation: Hydrogen Evolution on Tungsten Oxide. Journal of the American Chemical Society 2022, 144 (14), 6420-6433.[4] Spencer, M. A.; Fortunato, J.; Augustyn, V., Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides. The Journal of Chemical Physics 2022, 156 (6), 064704. Figure 1

Significantly enhanced superconductivity in monolayer FeSe films on SrTiO3(001) via metallic δ-doping.

Superconductivity transition temperature (Tc) marks the inception of a macroscopic quantum phase-coherent paired state in fermionic systems. For 2D superconductivity, the paired electrons condense into a coherent superfluid state at Tc, which is usually lower than the pairing temperature, between which intrinsic physics including Berezinskii-Kosterlitz-Thouless transition and pseudogap state are hotly debated. In the case of monolayer FeSe superconducting films on SrTiO3(001), although the pairing temperature (Tp) is revealed to be 65-83K by using spectroscopy characterization, the measured zero-resistance temperature ([Formula: see text]) is limited to 20K. Here, we report significantly enhanced superconductivity in monolayer FeSe films by δ-doping of Eu or Al on SrTiO3(001) surface, in which [Formula: see text] is enhanced by 12K with a narrowed transition width ΔTc ∼ 8K, compared with non-doped samples. Using scanning tunneling microscopy/spectroscopy measurements, we demonstrate lowered work function of the δ-doped SrTiO3(001) surface and enlarged superconducting gaps in the monolayer FeSe with improved morphology/electronic homogeneity. Our work provides a practical route to enhance 2D superconductivity by using interface engineering.

Structural and magnetic properties of Dy doped SrFe12O19 ferrites

Hexagonal Sr1−xDyxFe12O19 (x = 0.0–0.1) have been prepared by high-energy ball milling technique. The effect of Dy doping on the structural and magnetic properties is studied. Crystal structure, morphology and magnetic properties are investigated. Single polycrystalline phase of SrFe12O19 is obtained and proved by X-ray diffraction (XRD) analysis. All Sr1−xDyxFe12O19 samples displayed single polycrystalline phase whatever the amount of Dy is. Magnetic properties, as a function of magnetic field and of temperature, were examined before and after Dy doping. Significant improvement of saturation magnetization (Ms) and intrinsic coercivity (Hc) at room temperature were achieved as a result of the Dy substitution. High coercivity were observed for all samples, suggesting the materials are good candidates for high frequency applications. Remnant magnetization (Mr) is obtained from the hysteresis loop and found at 13.5 emu/g for the non-doped sample. The value showed significant increase, reaching 34.2 emu/g, with increasing the dopant (Dy) amount. Magnetic interactions were explored via temperature dependent zero field cooling (ZFC) and field cooling (FC) magnetization measurements. FC magnetization increased slowly with temperature reduction for the samples x = 0, 0.02 and 0.04, indicating the weakly coupled magnetic system. But for highly doped samples (x = 0.06 and 0.08) the FC magnetization decreased with decreasing of temperature, indicating the strong coupling interactions. The ZFC and FC magnetization data indicates that the blocking temperature (TB) is well above the room temperature.

Significant improvement of injection efficiency in deep-UV LD structures by light Mg doping in p-core layer

Improvement of carrier injection efficiency is essential to achieve lower threshold and shorter wavelength in deep-ultraviolet laser diodes. We have confirmed that the introduction of electron blocking layer and Mg doping layer into the core layer significantly improves the injection efficiency. In this study, we show that optimizing the Mg doping level in the core layer improves the external quantum efficiency by a factor of about 10 compared to the non-doped sample. The dependence of the external quantum efficiency on Mg flow rate can be interpreted in terms of a reduction of the dip at the p-side core/cladding interface in the conduction band. The dip is expected to be suppressed by ionized Mg activated by the Poole–Frenkel effect, resulting in improved carrier injection efficiency. A remarkable improvement in efficiency is also observed when the Mg doping region is limited to the vicinity of the core/cladding layer interface.

Amorphous non-doped and Se-, Cu-, and Zn-doped Sb2S3 nanoparticles prepared by a hot-injection method: bandgap tuning and possible observation of the quantum size effect

Amorphous, non-doped, and copper- and selenium-doped Sb2S3 nanoparticles were synthesized by a hot-injection method. Zinc-doped Sb2S3 nanoparticles were prepared for the first time using the same approach. Electron microscopy revealed that spherical nanoparticles of 1–4 nanometers aggregated into larger spherical clusters. Introducing dopants into the Sb2S3 structure neither influenced the samples’ spherical morphology nor their sizes. The presence of the dopants (Cu, Se, or Zn) was confirmed by energy dispersive X-ray (EDX) and, in the case of Zn, also by inductively coupled plasma-mass spectrometry (ICP-MS). The X-ray powder diffraction (XRPD) patterns of the non-doped and doped samples imply an amorphous structure. Crystalline Zn-doped Sb2S3 revealed defined peaks from only the Sb2S3 phase, indicating successful doping. Diffuse reflectance spectroscopy (DRS) revealed high optical bandgap energies (2.03–2.12 eV) compared to the values (1.6–1.7 eV) for large non-doped and doped particles obtained at 240 °C, which might be attributed to a quantum size effect. X-ray photoelectron spectroscopy (XPS) revealed a phase without any impurities for the undoped and characteristic peaks for copper, selenium, and zinc Auger for the doped samples. XPS valence band confirm for the Zn-doped particles a shift towards lower binding energy compared to the non-doped samples, indicating successful doping. Photoluminescence (PL) measurements show that embedding Zn into the Sb2S3 host lattice suppresses the wide luminescence band related to intrinsic vacancy defects. Narrow peaks at 1.7–2.4 eV were found to be associated with singlet excitons. The energy dependence of the light emission on the synthesized nanoparticles’ size suggests quantum confinement.

Suppression of discontinuous precipitation and strength improvement by Sc doping in Cu-6 wt%Ag alloys

• Sc doping significantly suppressed discontinuous Ag precipitates in Cu-Ag alloys. • Sc-doping led to a 55 MPa increase in strength, with only a slight decrease in conductivity. • Sc segregation at grain boundaries inhibited the nucleation of discontinuous precipitates • The UTS of Sc-doped samples was 1080 MPa, 205 MPa higher than that of non-doped samples. In low-Ag Cu matrix alloys, the presence of coarse discontinuous precipitates may limit strength. We demonstrated that discontinuous precipitation was suppressed, and continuous precipitation was enhanced by the doping of Cu-6 wt%Ag with Sc. A high-volume fraction of continuous precipitates, which nucleated on {111} planes, led to a 55 MPa increase in strength, with only a slight decrease in electrical conductivity. The addition of Sc inhibited the nucleation of discontinuous precipitates by causing the Sc and the Ag to co-segregate onto grain boundaries, thus forming a thin intermetallic compound layer between grains. After deformation, both discontinuous and continuous precipitates were drawn into Ag fibers. The combination of deformation strain and doping caused an increase in density and a decrease in the diameter of Ag fibers, resulting in about 205 MPa increase in doped samples when the deformation strain reached 4.9. The thinner, denser Ag fibers in the doped samples also caused higher electron scattering at interfaces, leading to electrical conductivity that was 11% IACS lower than in non-doped samples. For reference, 100% IACS (International Annealed Copper Standard) is equivalent to 1.7241 μΩ cm.

Fabrication of Mo-doped TiO2 nanotube arrays photocatalysts: The effect of Mo dopant addition time to an aqueous electrolyte on the structure and photocatalytic activity

Molybdenum-doped TiO2 nanotubes (TNTs) samples were synthesized in two routes by a single-step anodization method for a sustainable photocatalytic process. This study aimed to evaluate the effectiveness of dopant adding time on the photocatalytic activity of TiO2 nanotubes. In the first route, molybdenum dopant with three initial concentrations of 0.02, 0.06, and 0.1 M was added to the electrolyte at the beginning of the anodizing process, while in the second route, molybdenum precursors were added to the electrolyte after 30 min from the beginning of anodization (after the formation of nanotubes). The structural characteristics of Mo-doped TNTs in both routes were compared with non-doped nanotubes using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. The optical properties and efficiency of electron-hole pairs separation and charge transfer kinetics were evaluated by diffuse reflectance spectroscopy (DRS) and electrochemical impedance spectroscopy (EIS) methods. Moreover, methylene blue (MB) degradation under visible light was performed to investigate the photocatalytic activity. The results indicate that the second route of synthesis causes the formation of well-aligned TNTs while increasing the Mo concentration will destroy the tube structure in some places on the surface and cause the loss of structural order, in the first path. By Mo doping into TiO2 nanotubes, the optical properties are improved and the absorption edge of TiO2 nanotubes was extended to the visible region. The Mo-doped samples in the second route with concentrations of 0.1 M exhibited the highest visible light absorption and charge transfer rate among all the Mo-doped samples. Also, Mo-doped samples had better photocatalytic activity than non-doped samples in MB degradation and the highest photocatalytic efficiency was related to the Mo-doped sample synthesized in the second route with a Mo concentration of 0.1 M.

Dy-modified barium calcium titanate sintered in a reducing atmosphere: Crystal structure, microstructure, and electrical characteristics

The microstructure, crystal structure, and electrical properties of calcium-doped BaTiO3 (BCT) sintered at 1180 °C for 1 h in a reducing atmosphere were investigated in this study. A detailed mechanism for improving the reliability of Dy-modified BCT sintered in a reducing atmosphere has been proposed. Ca in BCT mostly substituted for Ba and occupied A-site, according to the Rietveld analysis. The Dy3+-added sample revealed a core-shell structure with lamellar domain walls in the core region, as seen in TEM images. Curie temperature and dielectric constant increased as calcium concentration increased. Dy3+ doped samples had a higher Curie temperature and dielectric constant than non-doped samples. The Dy-doping and substitution of Ca2+ for Ba2+ can significantly increase the grain conductivity activation energy for Dy-doped BCT sintered under reduction atmosphere. It suggests that Dy3+ and Ca2+ doping can effectively suppress the formation of oxygen vacancies and inhibit their movement, potentially improving the HALT of BME-MLCC.

Modulating trap levels via co-doping Ca2 + /Si4+ in LiTaO3:Pr3+ to improve both the intensity and threshold of mechanoluminescence

We report a novel mechanoluminescent phosphor Li1−xCaxSixTa1−xO3:0.01Pr3+ (x = 0–0.04). The crystal structure, photoluminescence (PL), optical diffuse reflectance spectra, afterglow (AG), fluorescence decay curves, and mechanoluminescence (ML) properties were investigated. To clarify the defect types and the mechanoluminescence mechanisms, an X-ray photoelectron spectroscopy (XPS) and thermoluminescence curve (TL) were measured. The dopants Ca2+ and Si4+ ions occupied the Li+ and Ta5+ sites, respectively. An optimal sample Li0.98Ca0.02Si0.02Ta0.98O3:Pr3+ was obtained with great enhancement in mechanoluminescence intensity, higher than that of non-doped sample LiTaO3:Pr3+ by 262%. And the compression threshold, over which the ML intensity could not maintain the linear increase, has also been greatly improved. Furthermore, the stable output of Tribo-L was achieved, which was visible to the naked eye. A probable mechanism was proposed to illustrate the mechanoluminescent process in Li1-xCaxSixTa1-xO3:0.01Pr3 + (x = 0–0.04). The study indicates that adjusting trap distribution by substituting host ions may be a novel way to develop high-quality mechanoluminescence.

Influence of the size of Au nanoparticles on the photoinduced birefringence and diffraction efficiency of polarization holographic gratings in thin films of azopolymer nanocomposites

This study is aimed to determine the influence of the size of gold (Au) nanoparticles (NP) doped in azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]) on the photoinduced birefringence of the nanocomposite thin films as well as on the diffraction efficiency of polarization holographic gratings recorded in them. For this reason, we used spherical Au NP with five different dimensions – 10, 20, 30, 40 and 50 nm. Concentrations of the NP in the nanocomposites varied from 0 a.u. (non-doped samples) to 16 a.u. where 1 a.u. corresponds to 0.015 wt %. Birefringence was induced with He–Cd laser (λ = 442 nm) and measured at 635 nm using DPSS laser. We observe an enhancement of photoinduced birefringence, which is most pronounced for the Au NP with size 20 nm. The polarization holographic gratings were inscribed with two orthogonal circular polarizations (left- and right-handed). AFM measurements were performed to determine the properties of the resulting surface relief gratings. Our results indicate that both the diffraction efficiencies and surface relief modulation of the gratings inscribed in the nanocomposite thin films are higher compared to those in the non-doped samples.

Structural, morphological, optical, and electronic properties of amorphous non-doped and I and Sn doped Sb2S3 nanoparticles

Amorphous non-doped, iodine- and tin-doped Sb2S3 nanoparticles were prepared via the hot-injection method. HRTEM of amorphous undoped and doped samples revealed the formation of spherical nanoparticles of 20–50 nm diameter aggregated into clusters in the size of 100–200 nm. EDX analysis indicated the presence of desired elements in all observed samples. The bandgaps of non-doped and doped samples were determined from the reflectance spectra, and variations of the bandgaps, even small ones, are insufficient indications of doping. These uncertainties are further clarified by investigating crystalline undoped and doped samples in addition to the amorphous ones. XRPD results of the amorphous samples confirmed the amorphous structure, while Le Bail refinements of the crystalline samples show well-defined peaks from only the Sb2S3 phase, indicating a successful doping process. XPS measurements revealed that the phase of the undoped sample is free of impurities and that 3 d peaks of iodine and tin in the doped samples are present. The XPS valence bands shifted towards higher (I) or lower (Sn) binding energies compared to the undoped samples for both amorphous and crystalline samples, which is an additional support that incorporation of dopant ions in the Sb2S3 lattice took place.

Chromium-doped cryptomelane: Mn-O debilitation and reactive enhancement in formaldehyde abatement

Nano-rod chromium-doped cryptomelane was prepared by co-precipitation and characterized by XRD, EDX elemental maps, SEM, ICP-MS and N2 adsorption. Temperature-programmed desorption of oxygen (O2-TPD) revealed a significant down-shift of oxygen desorption temperature regarding atomic oxygen bounded Mn3+ sites from ~40 to ~488 °C corresponded to 0–4.9 wt% of chromium loading. This result was consistent with the elevation of Mn-average-oxidation-state (Mn-AOS) from 3.6 to 3.8 for non-doped and Cr-doped cryptomelane samples. The catalytic performance of Cr-doped cryptomelane on formaldehyde oxidation was correlated with the chromium loading because of the change in Mn-AOS values and debilitation of Mn-O in Mn-O-Cr bridges.

XPS study of iodine and tin doped Sb2S3 nanostructures affected by non-uniform charging

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements are used for investigating incorporation of iodine and tin into the stibnite (Sb2S3) lattice, as well as for determining surface composition and structure, respectively. The XRD analysis revealed the visible presence of a single phase, that of pure orthorhombic Sb2S3 structure. XPS survey spectra confirmed the presence of expected elements (Sb, S, Sn and I) at the surface of corresponding samples. Since the bonding identification was hindered by non-uniform charging of samples during acquiring the photoelectron spectra, a novel approach for the analysis of high resolution spectra was proposed and successfully implemented. XPS results showed that surface composition of the non-doped sample coincides with that of the bulk, while doping strongly affects surface of the samples. Sn-doped sample appears to be prone to surface oxidation. The presence of Sb2S3, Sb2O3, SnS2 and Sn(0) phases at the surface was revealed. Strong segregation of antimony was observed in the I-doped Sb2S3 sample. Iodine is also present at the surface in the form of the SbI3 phase, while the detected sulphur signal most probably corresponds to S atoms from unaltered deeper layers.

Growth and Characterizations of Iron-based Superconductor (Ba1-x Rb x ) Fe2As2 Single Crystals

Novel nematic states as well as remarkable superconducting properties were reported in iron-based superconductors. We synthesized high-quality single crystals of (Ba1-x Rb x )Fe2As2 close to the optimal composition of x ≈ 0.4, and have characterized normal state and superconducting properties for pristine and proton irradiated samples. The highest Tc was found to be ∼36.6 K for pristine samples. A maximum critical current density of 12 MA/cm2 was achieved in a proton irradiated sample, which is comparable to that in irradiated (Ba0.6K0.4) Fe2As2. Twin boundaries were observed optically in both non-doped and under-doped samples. We also attempted local magnetic field measurements induced by transport current in a sample with twin boundaries for future exploration of nematic states in different regions of doping.

Defect chemistry in perovskite ferroelectrics—History, present status, and future prospects—

Perovskite ferroelectrics such as BaTiO3 and PbTiO3 provide various functions arising from spontaneous polarization. Here, the history, present status, and future prospects of the defect chemistry for BaTiO3 are described. Even for non-doped samples, unintentional impurities including Fe govern the defect chemistry and its related properties. By solving multiple nonlinear equations employing the thermodynamic data set reported, majority/minority defect-concentration diagrams are available not only in a high-temperature equilibrium state but also in a low-temperature quenched one. As an example, the defect diagrams of Ba(Ti,Ca)O3 and Ba(Ti,Mn)O3 are shown, and the roles of fixed valence (Ca) and variable-valence (Mn) acceptors are explained. I also introduce an example of the defect control in BaTiO3 single crystals; an activation of visible-light photovoltaic effect, where two redox potentials derived from Fe2+ and Fe3+ act as scaffolds for generating electron–hole pairs.

Fabrication and Electromagnetic wave absorption Properties of Co-Cu-substituted Ni-Zn Spinel Ferrite-epoxy Composites

Spinel ferrites (Ni0.5Zn0.5)1-<i>x-y</i>Co<i>x</i>Cu<i>y</i>Fe2O4, (<i>x</i> = 0 and <i>y</i> = 0, <i>x</i> = 0.2 and <i>y</i> = 0, <i>x</i> = 0.1 and <i>y</i> = 0.1, <i>x</i> = 0 and <i>y</i> = 0.2) were prepared by sol-gel method and post-annealed at 1100 <sup>o</sup>C. The grain growth of the sample is very sensitive to the Cu substitution <i>y</i>. The average grain size of the non-doped sample (<i>x</i> = 0, <i>y</i> = 0) was ~400 nm and it increased to ~3 μm at the sample with <i>x</i> = 0 and <i>y</i> = 0.2. The real and imaginary parts of permittivities (<i>ε', ε"</i>) and permeabilities (<i>μ', μ"</i>) were measured on the spinel ferrite powder-epoxy (10 wt%) composite samples by a network vector analyzer in the frequency range of 0.1 ≤ <i>f</i> ≤ 15 GHz. The <i>μ'</i> and <i>μ"</i> depend on Co substitution <i>x</i> and the <i>ε'</i> is sensitive to Cu doping <i>y</i>. Reflection loss (RL), which implies electromagnetic (EM) wave absorption properties, were analyzed based on the complex permeability, permittivity spectra. In the RL map plotted as functions of sample thickness (<i>d</i>) and frequency (<i>f</i>), the intensive EM absorbing area (RL < -30 dB) shifted to a high frequency region with increasing Co substitution. This can be attributed to a permeability spectra shift, due to the increase in ferromagnetic resonance frequency produced by the Co substitution. The samples with <i>x</i> = 0.1 and <i>y</i> = 0.1, <i>x</i> = 0.2 and <i>y</i> = 0 also exhibited a very broad-ranged EM wave absorbing performance with a <i>d</i> < 3 mm, indicated by RL < -10 dB being satisfied in the frequency range 7~14 GHz.